Heterobridged dinuclear, tetranuclear, dinuclear-based 1-D, and heptanuclear-based 1-D complexes of copper(II) derived from a dinucleating ligand: Syntheses, structures, magnetochemistry, spectroscopy, and catecholase activity

ARTICLE

pubs.acs.org/IC

Heterobridged Dinuclear, Tetranuclear, Dinuclear-Based 1-D, and

Heptanuclear-Based 1-D Complexes of Copper(II) Derived from

a Dinucleating Ligand: Syntheses, Structures, Magnetochemistry,

Spectroscopy, and Catecholase Activity

Samit Majumder,^†Sohini Sarkar,^†Sujit Sasmal,^†E. Carolina Sa~nudo,*^,‡and Sasankasekhar Mohanta*^,†

^†Department of Chemistry, University of Calcutta, 92 A. P. C. Road, Kolkata 700 009, India

^‡Department de Química Inorgꢀanica i Institut de Nanociꢀencia i Nanotecnologia, Universitat de Barcelona, Diagonal 647,

08028 Barcelona, Spain

S Supporting Information

b

ABSTRACT: The work in this paper presents syntheses, char-

acterization, crystal structures, variable-temperature/ﬁeld mag-

netic properties, catecholase activity, and electrospray ion-

ization mass spectroscopic (ESI-MS positive) study of ﬁve

copper(II) complexes of composition [Cu^IIL(μ_1,1-NO₃)-

2

(H₂O)(NO₃)](NO₃) (1), [{Cu^IIL(μ-OH)(H₂O)}(μ-ClO₄)]_n-

2

(ClO₄)_n(2), [{Cu^IIL(NCS)₂}(μ_1,3-NCS)]_n(3), [{Cu^IIL(μ_1,1-

2

N₃)(ClO₄)}₂(μ_1,3-N₃)₂] (4), and [{Cu^IIL(μ-OH)}{Cu^IIL-

2

(μ_1,1-N₃)}{Cu^II(μ_1,1-N₃)₄(dmf)}{Cu^II₂(μ_1,1-N₃)₂(N₃)₄}]_n

ndmf (5), derived from a new compartmental ligand 2,6-bis[N-(2-

3

pyridylethyl)formidoyl]-4-ethylphenol, which is the 1:2 condensa-

tion product of 4-ethyl-2,6-diformylphenol and 2-(2-ami-

noethyl)pyridine. The title compounds are either of the following

nuclearities/topologies: dinuclear (1), dinuclear-based one-dimensional (2 and 3), tetranuclear (4), and heptanuclear-based one-

dimensional (5). The bridging moieties in 1ꢀ5 are as follows: μ-phenoxo-μ_1,1-nitrate (1), μ-phenoxo-μ-hydroxo and μ-perchlorate

(2), μ-phenoxo and μ_1,3-thiocyanate (3), μ-phenoxo-μ_1,1-azide and μ_1,3-azide (4), μ-phenoxo-μ-hydroxo, μ-phenoxo-μ_1,1-azide, and μ_1,1-

azide (5). All the ﬁve compounds exhibit overall antiferromagnetic interaction. The J values in 1ꢀ4 have been determined (ꢀ135 cm^ꢀ1for

1, ꢀ298 cm^ꢀ1for 2, ꢀ105 cm^ꢀ1for 3, ꢀ119.5 cm^ꢀ1for 4). The pairwise interactions in 5have been evaluated qualitatively to result in S_T=

3/2 spin ground state, which has been veriﬁed by magnetization experiment. Utilizing 3,5-di-tert-butyl catechol (3,5-DTBCH₂) as the

substrate, catecholase activity of all the ﬁve complexes have been checked. While 1and 3are inactive, complexes 2, 4, and5show catecholase

activity with turn over numbers 39 h^ꢀ1(for 2), 40 h^ꢀ1(for 4), and 48 h^ꢀ1(for 5) in dmf and 167 h^ꢀ1(for 2) and 215 h^ꢀ1(for 4) in

acetonitrile. Conductance of the dmf solution of the complexes has been measured, revealing that bridging moieties and nuclearity have been

almost retained in solution. Electrospray ionization mass (ESI-MS positive) spectra of complexes 1, 2, and 4 have been recorded in

acetonitrile solutions and the positive ions have been well characterized. ESI-MS positive spectrum of complex 2 in presence of 3,5-

DTBCH₂have also been recorded and, interestingly, a positive ion [Cu^IIL(μ-3,5-DTBC^2ꢀ)(3,5-DTBCH^ꢀ)Na^I]⁺has been identiﬁed.

2

’ INTRODUCTION

magnetism because of a number of coordination modes of this

potentially bridging ligand as well as because of its ability to mediate

ferro- or antiferromagnetic interactions among metal centers. How-

ever, in spite of the considerable amount of information available, it is

quite diﬃcult to control/predict composition and topology of a new

metallo-azide compound because, for a particular metal ion, the ﬁnal

product is primarily dependent on the organic ligand(s) and also on

the reaction conditions. Clearly, new types of composition and

topology may be achieved on utilizing new organic ligands.

Some of the important aspects in coordination chemistry research

are rational design of organic blocking ligands and utilization of

organic/inorganic bridging ligands to develop metalꢀorganic mol-

ecules, including dinuclear systems, oligo- and polynuclear clusters,

and 1-D, 2-D, and 3-D self-assemblies, having interesting properties

relevant to the frontier areas such as molecular magnetism,^1ꢀ10

supramolecular chemistry/crystal engineering,^3a,11,12and modeling

the active sites of metallo-enzymes.^13ꢀ21

To develop varieties of topologies, pseudohalides like azide^1a,3aꢀ3d

and thiocyanate^3eare known to behave excellently as bridging ligands.

Metallo-azide species, in particular, have been always of great interest

in supramolecular chemistry/crystal engineering and molecular

Received: February 28, 2011

Published: July 21, 2011

r

2011 American Chemical Society

7540

dx.doi.org/10.1021/ic200409d Inorg. Chem. 2011, 50, 7540–7554

|

Inorganic Chemistry

ARTICLE

Catechol oxidase is an enzyme with the type-3 active site that

catalyzes the oxidation of a wide range of o-diphenols (catechols)

to the corresponding o-quinones coupled with 2e/2H⁺reduction

of O₂to H₂O, in a process known as catecholase activity.^13ꢀ22The

crystal structure of the met form of the enzyme was determined in

1998 revealing that the active center consists of a hydroxo-

bridged dicopper(II) center in which each copper(II) center is

coordinated to three histidine nitrogens and adopts a trigonal

pyramidal environment with one nitrogen in the apical site.^13fThe

structure determination of catecholase oxidase has encouraged an

extensive investigation on model compounds to understand the

structureꢀproperty relationship.^{5b,13aꢀ13c,14bꢀ14f,15ꢀ21}As the

structure contains dicopper(II) moiety, several dicopper(II)

complexes derived from nitrogen-containing dinucleating

ligands have been mainly employed for this purpose. Several

monocopper(II) complexes are also known to exhibit the

activity. Recently, catecholase activity of complexes of other

metal ions, Mn for example, has also been observed.¹⁸Moreover,

few structureꢀproperty correlations that were determined are

not suﬃciently wide but only applicable for a set of few

compounds.^{5b,9d,13,14,19,20}All in all, the problem of modeling

the catecholase activity remains open, and therefore, catecholase

activity of new systems should be explored to get better insight

and more straightforward structureꢀproperty correlations.

On transforming both the dialdehyde moieties of 4-substituted-

2,6-diformylphenol to imine or amine functionality, a number of

dinucleating acyclic ligands having monophenoxo bridging ability

have been reported previously.^{5b,9d,13aꢀ13c,14aꢀ14d,21ꢀ25}In terms

of the set of donor atoms to accommodate two metal ions, the

combination of the two sites of these ligands is usually NOꢀNO,

N₂OꢀN₂O, N₃OꢀN₃O, or N₂O₂ꢀN₂O₂. As the donor centers

of both of the two sites cannot satisfy the required coordination

number of the metal ions, these ligands are excellent systems to

stabilize heterobridged metal complexes having bridging moieties

like μ-phenoxo-μ-X, μ-phenoxo-bis(μ-X), μ-phenoxo-μ-X-μ-Y, etc.

(X/Y = chloro, bromo, hydroxo, methoxy, azide, cyanate, per-

chlorate, carboxylate, pyrazolate, etc.).^{5b,9d,13aꢀ13c,14aꢀ14d,21ꢀ25}

Regarding copper(II) complexes derived from such ligands,

several double- or triple-bridged dicopper(II) compounds have

been reported.^{5b,9d,13aꢀ13c,14aꢀ14d,21ꢀ23}Utilizing dicarboxylates

and dipyridines having 4,4⁰-bipyridine functionality as the second

bridging ligand, a few tetracopper(II) systems are also known.²⁴

A few polymeric copper(II) compounds have also been reported

where the heterobridged dicopper(II) cores are interlinked by

bridging ligands (azide, alkoxo, etc.).²⁵Catecholase oxidase

activity of some of these dicopper(II) systems have been

investigated,^{5b,9d,13aꢀ13c,14aꢀ14d,21,22}while magnetic studies have

been carried out for some of these di-, tetra- and polynuclear

systems.^{5b,9d,21,23ꢀ25}To explore the copper(II) compounds

derived from similar but new dinucleating acyclic ligands, we have

synthesized 2,6-bis[N-(2-pyridylethyl)formidoyl]-4-ethylphenol

(HL; Chart 1) and utilized it to prepare ﬁve copper(II) com-

pounds [Cu^IIL(μ_1,1-NO₃)(H₂O)(NO₃)](NO₃) (1), [{Cu^IIL-

Chart 1. Chemical Structure of HL

’ EXPERIMENTAL SECTION

Materials and Physical Measurements. All the reagents and

solvents were purchased from commercial sources and used as received.

2,6-Diformyl-4-ethylphenol was prepared according to the procedure

reported for the synthesis of 2,6-diformyl-4-methylphenol.²⁶Elemental

(C, H, and N) analyses were performed on a Perkin-Elmer 2400 II

analyzer. IR spectra were recorded in the region 400ꢀ4000 cm^ꢀ1on a

Bruker-Optics Alpha-T spectrophotometer with samples as KBr disks.

Magnetic susceptibility measurements were carried out on polycrystal-

line samples with a DSM5 QuantumDesign magnetometer working in the

range of 2ꢀ300 K under magnetic field of 1 T. Diamagnetic corrections

were estimated from Pascal Table. Electronic spectroscopic measure-

ments and catecholase activity were performed with a Hitachi U-3501

spectrophotometer. The electrospray ionization mass (ESI-MS positive)

spectra were recorded on a Micromass Qtof YA 263 mass spectrometer.

Molar conductivity (Λ_M) of 1 mM solution in dmf was measured at

25 °C with a Systronics conductivity bridge.

Syntheses 2,6-Bis[N-(2-pyridylethyl)formidoyl]-4-ethyl-

phenol (HL) Solution in Methanol. 2,6-Diformyl-4-ethylphenol

(1.780 g, 10 mmol) and 2-(2-aminoethyl)pyridine (2.443 g, 20 mmol)

were dissolved in 50 mL methanol, and the mixture was refluxed for 2 h.

After cooling and filtration to remove the suspended particles, the

volume of the solution was adjusted to 100 mL. This “solution of HL”

was considered to contain 10 mmol of the ligand HL and was used for

subsequent reactions without further purification.

[Cu^IIL(μ_1,1-NO₃)(H₂O)(NO₃)](NO₃) (1). Ten milliliters of the

2

“solution of HL” containing 1 mmol HL was taken and diluted to 30 mL

with methanol. To this solution were dropwise added successively a

methanol (10 mL) solution of triethylamine (0.101 g, 1 mmol) and an

acetonitrile solution (15 mL) of copper(II) nitrate trihydrate (0.482 g,

2 mmol), and the resulting deep green solution was refluxed for 2 h. Then

the mixture was filtered, and the filtrate was kept at room temperature

for slow evaporation. After 2ꢀ3 days, a deep green crystalline compound

containing diffraction quality single crystals was deposited, which was

collected by filtration, washed with cold methanol, and air-dried. Yield:

0.57 g (80%). Anal. Calcd for (%) C₂₄H₂₇N₇O₁₁Cu₂: C, 40.23; H, 3.80;

N, 13.68. Found: C, 40.19; H, 3.82; N, 13.72. IR (KBr pellet, cm^ꢀ1):

ν(H₂O), 3417(b); ν(CdN), 1645(s); ν(NO₃), 1385 (vs), 1279(s).

UVꢀvis (DMF) λmax/nm (ε in M^ꢀ1cm^ꢀ1): 267 (34287), 374 (8680),

648 (145).

[{Cu^IIL(μ-OH)(H₂O)}(μ-ClO₄)]_n(ClO₄)_n(2). To a 10 mL “solu-

2

tion of HL” containing 1 mmol HL were dropwise added successively

under stirring a methanol (10 mL) solution of triethylamine (0.101 g,

1 mmol) and a methanol (10 mL) solution of copper(II) perchlorate

hexahydrate (0.744 g, 2 mmol). Immediately, a green compound started

to deposit. After stirring for 2 h, the green solid was collected by filtration

and washed with methanol. Recrystallization from an acetonitrileꢀtoluene

(1:2) mixture produced a green crystalline compound containing

diffraction quality single crystals. Yield: 0.56 g (75%). Anal. Calcd for

(%) C₂₄H₂₈N₄O₁₁Cl₂Cu₂: C, 38.62; H, 3.78; N, 7.51. Found: C, 38.57;

H, 3.75; N, 7.50. IR (KBr pellet, cm^ꢀ1): ν(H₂O), 3510(b); ν(CdN),

2

(μ-OH)(H₂O)}(μ-ClO₄)]_n(ClO₄)_n(2), [{Cu^IIL(NCS)₂}-

2

(μ_1,3-NCS)]_n(3), [{Cu^IIL(μ_1,1-N₃)(ClO₄)}₂(μ_1,3-N₃)₂] (4),

and [{Cu^IIL(μ-OH)}{Cu^I²^IL(μ_1,1-N₃)}{Cu^II(μ_1,1-N₃)₄(dmf)}-

2

{Cu^II(μ_1,1-N₃)₂(N₃)₄}]_nndmf (5). Herein, we report synthe-

2

3

ses, characterization by FT-IR and molar conductance data,

crystal structures, magnetic properties, catecholase activity, and

electrospray ionization mass spectroscopic (ESI-MS positive)

studies of these ﬁve compounds.

7541

dx.doi.org/10.1021/ic200409d |Inorg. Chem. 2011, 50, 7540–7554

Inorganic Chemistry

ARTICLE

Table 1. Crystallographic Data for 1ꢀ5

1

2

3

4

5

empirical formula

formula weight

crystal system

space group

a (Å)

C

₂₄H₂₇N₇O₁₁Cu₂

C₂₄H₂₂N₄O₁₁Cl₂Cu₂

740.44

C₂₇H₂₅N₇OS₃Cu₂

686.80

C₄₈H₅₀N₂₀O₁₀Cl₂Cu₄

1392.14

C₅₄H₆₄N₄₃O₅Cu₇

1840.26

716.61

triclinic

orthorhombic

Pbca

monoclinic

Cc

triclinic

P1

10.169(5)

11.127(5)

13.182(6)

94.846(12)

104.436(11)

105.468(11)

1373.8(11)

2

17.3516(7)

14.5574(6)

22.5361(9)

90.00

12.4131(4)

26.1746(8)

8.7937(3)

90.00

8.9895(2)

12.0401(3)

13.2996(3)

73.8450(10)

86.4900(10)

74.2360(10)

1330.47(5)

1

11.5844(10)

11.9880(10)

14.8922(13)

106.7910(10)

104.2630(10)

107.7670(10)

1754.0(3)

1

b (Å)

c (Å)

R (°)

β (°)

γ (°)

V (Å³)

90.00

91.7770(10)

90.00

5692.5(4)

8

2855.77(16)

4

Z

D (calculated, g cm^ꢀ3

)

1.732

1.728

1.597

1.738

1.742

λ (Mo K_R), Å

0.71073

1.623

0.71073

μ (mm^ꢀ1

T (K)

)

1.748

1.744

1.757

2.162

293(2)

100(2)

293(2)

100(2)

F(000)

732

2992

1400

708

932

2θ range for data collection (°)

index ranges

3.24ꢀ52.58

ꢀ12 e h e 12

ꢀ13 e k e 13

ꢀ16 e l e 16

17262

3.62ꢀ50.76

ꢀ20 e h e 20

ꢀ17 e k e 17

ꢀ27 e l e 27

64647

3.12ꢀ61.08

ꢀ17 e h e 17

ꢀ33 e k e 35

ꢀ12 e l e 11

21254

3.18ꢀ56.60

ꢀ11 e h e 11

ꢀ16 e k e 16

ꢀ17 e l e 17

19187

3.08ꢀ50.66

ꢀ13 e h e 13

ꢀ14 e k e 14

ꢀ17 e l e 17

12925

no. measured reﬂections

no. independent reﬂections

R_int

5485

5226

7262

6316

9863

0.0583

0.0748

0.0338

0.0264

0.0425

no. reﬁned parameters

no. observed reﬂections, I g 2σ (I)

goodness-of-ﬁt on F², S

505

428

449

479

936

4031

4007

6170

5365

7655

0.907

1.113

1.002

1.088

1.038

R₁, wR₂^b[I g 2σ (I)]

0.0438, 0.1235

0.0677, 0.1399

0.0635, 0.1274

0.0856, 0.1380

0.0307, 0.0494

0.0435, 0.0526

0.412, ꢀ0.451

0.0304, 0.0581

0.0386, 0.0605

0.558, ꢀ0.489

0.0627, 0.1361

0.0870, 0.1514

1.514, ꢀ1.388

a

R₁, wR₂^b[all data]

max, min electron density (eÅ^ꢀ3

)

0.675, ꢀ0.654

0.843, ꢀ1.114

^aR₁= [∑ F_o| ꢀ |F_c/∑|F_o|]. ^bwR₂= [∑w(F_oꢀ F_c²)²/∑wF_o]

.

2

4 1/2

1642(s); ν(ClO₄), 1111(vs), 624(w). UVꢀvis (DMF) λmax/nm (ε in

a brown compound started to deposit. Reflux was continued for 2 h, and

then the mixture was filtered to give rise a brown solid and a deep green

filtrate. The brown solid was recrystallized on diffusing diethyl ether into

a dmf solution in long tubes to produce brown crystalline compound 5

containing diffraction quality single crystals. On the other hand, the deep

green filtrate was evaporated on a rotary evaporator to give rise a deep

green solid, which was collectedafter washing with methanolꢀwater(1:2)

mixture. This deep green mass was recrystallized from an acetonitrileꢀ

toluene (1:2) mixture to produce a deep green crystalline compound 4

containing diffraction quality crystals. Data of 4: Yield: 0.35 g (25%).

Anal. Calcd for (%) C₄₈H₅₀N₂₀O₁₀Cl₂Cu₄: C, 41.41; H, 3.62; N, 20.12.

Found: C, 41.39; H, 3.59; N, 20.15. IR (KBr pellet, cm^ꢀ1): ν(N₃),

2082(s), 2041(s); ν(CdN), 1644(s); ν(ClO₄), 1091(s), 622(w).

UVꢀvis (DMF) λmax/nm (ε in M^ꢀ1cm^ꢀ1): 267 (33567), 384

(15600), 713 (390). Data of 5: Yield: 0.65 g (35%). Anal. Calcd for

(%) C₅₄H₆₅N₄₃O₅Cu₇: C, 35.23; H, 3.56; N, 32.71. Found: C, 35.25; H,

3.64; N, 32.65. IR (KBr pellet, cm^ꢀ1): ν(N₃), 2069(s), 2034(s);

ν(CdN), 1643(s). UVꢀvis (DMF) λmax/nm (ε in M^ꢀ1cm^ꢀ1): 267

(33960), 380 (17800), 707 (634).

M

^ꢀ1cm^ꢀ1): 267 (33980), 384 (7360), 635 (130).

[{Cu^IIL(NCS)₂}(μ_1,3-NCS)]_n(3). To a stirred 10 mL “solution of

2

HL” containing 1 mmol HL were dropwise added successively a methanol

(10 mL) solution of triethylamine (0.101 g, 1 mmol) and a methanol

(10 mL) solution of copper(II) perchlorate hexahydrate (0.744 g,

2 mmol). The resulting green solution was refluxed for 0.5 h, and then

to the refluxed solution was added an aqueous (5 mL) solution of

ammonium thiocyanate (0.304 g, 4 mmol). Immediately, a brown solid

started to deposit. After refluxing for additional 2 h, the deposited solid

was collected by filtration and washed with methanol. Recrystallization

on diffusion diethyl ether into a N,N-dimethylformamide (dmf) solution

in long tubes produced a brown crystalline compound containing diffrac-

tion quality single crystals. Yield: 0.48 g (70%). Anal. Calcd for (%)

C₂₇H₂₅N₇OS₃Cu₂: C, 47.22; H, 3.67; N, 14.27. Found: C, 47.25; H,

3.64; N, 14.28. IR (KBr pellet, cm^ꢀ1): ν(SCN), 2082(vs); ν(CdN),

1638(s). UVꢀvis (DMF) λmax/nm (ε in M^ꢀ1cm^ꢀ1): 266 (34305),

368 (6280), 660 (154).

[{Cu^IIL(μ_1,1-N₃)(ClO₄)}₂(μ_1,3-N₃)₂] (4), and [{Cu^IIL(μ-

2

OH)}{Cu^II₂L(μ_1,1-N₃)}{Cu^II(μ_1,1-N₃)₄(dmf)}{Cu^II₂(μ_1,1-N₃)₂-

Crystal Structure Determination of 1ꢀ5. The crystallographic

data for 1ꢀ5 are summarized in Table 1. Diffraction data were collected

on a Bruker-APEX II SMART CCD diffractometer at 293 K for 1, 3, and

4 and at 100 K for 2 and 5 using graphite-monochromated Mo KR

radiation (λ = 0.71073 Å). For data processing and absorption correc-

tion the packages SAINT^27aand SADABS^27bwere used. The structures

(N₃)₄}]_nndmf (5). To a mixture of a 10 mL “solution of HL”

3

containing 1 mmol HL, a methanol (10 mL) solution of triethylamine

(0.101 g, 1 mmol), and a methanol (10 mL) solution of copper(II)

perchlorate hexahydrate (0.744 g, 2 mmol), an aqueous solution (5 mL)

of sodium azide (0.260 g, 4 mmol) was added under reflux. Immediately,

7542

dx.doi.org/10.1021/ic200409d |Inorg. Chem. 2011, 50, 7540–7554

Inorganic Chemistry

ARTICLE

were solved by direct and Fourier methods and refined by full-matrix least-

squares based on F²using SHELXTL^27cand SHELXL-97^27dpackages.

During the development of the structures of 2 and 5, it became

apparent that few atoms were each disordered over two sites. These

disordered atoms are C18, N4, O6, O7, O10, and O11 for 2 and N34 and

N35 for 5. This was allowed for reﬁning freely, and the ﬁnal linked

occupancy parameters for these disordered atoms are 0.74 and 0.26 for

C18; 0.63 and 0.37 for N4; 0.71 and 0.29 for O6; 0.61 and 0.39 for O7;

0.86, and 0.14 for O10; 0.93 and 0.07 for O11; and 0.60 and 0.40 for N34

and N35.

All the hydrogen atoms in 1 and 4 were located, while all the hydrogen

atoms in 5 were inserted at calculated positions with isotropic thermal

parameters. In 2, it was not possible to either locate or insert six hydrogen

atoms: two linked with the water oxygen atom, one linked with the

hydroxo oxygen atom, two linked with C18, and one of two linked with

C19. All other hydrogen atoms in 2 were inserted at calculated positions

with isotropic thermal parameters. In 3, two hydrogen atoms (H7A and

H7B) linked with C7 and one hydrogen atom (H22) linked with C22

were inserted at calculated positions with isotropic thermal parameters.

All other hydrogen atoms in 3 were located.

Because of the nonpositive deﬁnite problem, few nonhydrogen atoms

in the structures of 2 and 5 had to be reﬁned isotropically. These atoms are

O10A, O11A, and C18A for 2 and C15, C26, C34, C35, C38, C41, C44,

N9, N21, N25, N27, N40, N34A, and N35A for 5. All other nonhydrogen

atoms in 2 and 5 and all the nonhydrogen atoms in 1, 3, and 4 were

reﬁned anisotropically, while all the hydrogen atoms in 1ꢀ5 were

reﬁned isotropically. The ﬁnal reﬁnements converged at the R₁values

(I > 2σ(I)) 0.0438, 0.0635, 0.0307, 0.0304, and 0.0627 for 1, 2, 3, 4, and

5, respectively.

Figure 1. Crystal structure of complex [Cu^II₂L(μ_1,1-NO₃)(H₂O)-

(NO₃)](NO₃) (1). Counter nitrate anion and all the hydrogen atoms

are omitted for clarity.

4 behave as 2:1 electrolytes, while3and 5behaveas1:1electrolytes

in solution.²⁸It is probable that in solution some of the long apical

bonds (vide infra) are ruptured, and the vacant positions are

occupied by solvent molecules (S). For example, the apical

’ RESULTS AND DISCUSSION

monodentate nitrate ion is probably eliminated from [Cu^IIL-

2

Syntheses, FT-IR Spectra, and Proposed Composition in

Solution. In the reaction of HL with copper(II) nitrate and

copper(II) perchlorate in the presence of the base, Et₃N, the

exogeneous position is occupied by a nitrate and a hydroxo anions

(μ_1,1-NO₃)(H₂O)(NO₃)](NO₃) (1) to produce the 2:1 elec-

trolyte [Cu^II₂L(μ_1,1-NO₃)(H₂O)(S)](NO₃)₂. Similarly, the

coordinated perchlorate ion is probably eliminated from

[{Cu^IIL(μ-OH)(H₂O)}(μ-ClO₄)]_n(ClO₄)_n(2) to produce 2:1

2

to result in the formation of compounds [Cu^IIL(μ_1,1-NO₃)-

electrolyte [{Cu^IIL(μ-OH)(H₂O)(S)₂](ClO₄)₂. In the case of

2

compound [{Cu^II²L(μ_1,1-N₃)(ClO₄)}₂(μ_1,3-N₃)₂] (4), which is

(H₂O)(NO₃)](NO₃) (1) and [{Cu^II₂L(μ-OH)(H₂O)}(μ-

ClO₄)]_n(ClO₄)_n(2), respectively. When HL in the presence

of Et₃N is treated with copper(II) perchlorate and sodium

2

neutral according to solid state composition, two axial perchlo-

rate ions are most probably eliminated to produce the 2:1

azide, two compounds [{Cu^IIL(μ_1,1-N₃)(ClO₄)}₂(μ_1,3-N₃)₂] (4)

electrolyte [{Cu^IIL(μ_1,1-N₃)(S)}₂(μ_1,3-N₃)₂](ClO₄)₂, which

2

and [{Cu^IIL(μ-OH)}{Cu^IIL(μ_1,1-N₃)}{Cu^II(μ_1,1-N₃)₄(dmf)}

is a better probable than another 2:1 electrolyte [{Cu^IIL(μ_1,1-

2

{Cu^II(μ_1,1-N₃)₂(N₃)₄}]_nndmf (5) are produced. It may be

2

N₃)(S)_n](ClO₄/N₃)₂. The 1:1 electrolyte species in the case of

3

[{Cu^IIL(NCS)₂}(μ_1,3-NCS)]_n(3) is most probably [{Cu^IIL-

noted that it was not possible to isolate HL in solid state; evaporation

of solvent from even at high vacuum results in an orange oil, which

contains mostly HL contaminated with some minor impurity(ies) as

evidenced from its ¹H NMR spectrum.

2

(NCS)₂}(S)₂](NCS), in which the bridging, which is also apical,

thiocyanate moiety of the parent molecule is eliminated. As

discussed below, [{Cu^IIL(μ-OH)}{Cu^IIL(μ_1,1-N₃)}{Cu^II(μ_1,1-

2

N₃)₄(dmf)}{Cu^II(μ_1,1-N₃)₂(N₃)₄}]_nndmf (5) can be consid-

The characteristic CdN stretching in compounds 1ꢀ5 appear

as a strong band at about 1640 cm^ꢀ1. Presence of nitrates in

compound 1 is evident by the observation of two strong bands at

1385 and 1279 cm^ꢀ1. The characteristic perchlorate vibrations

are observed at 1111 and 624 cm^ꢀ1for 2 and at 1091 and

622 cm^ꢀ1for 4. Two strong bands at 2082 and 2041 cm^ꢀ1for 4

and at 2069 and 2034 cm^ꢀ1for 5 are indicative of the presence of

azide and more than one type of azide in both these molecules.

The strong peak at 2082 cm^ꢀ1in the spectrum of 3 appears due

to thiocyanate stretching. The presence of water molecules in

compounds 1 and 2 is evident by the appearance of broad bands

centered at 3417 cm^ꢀ1for 1 and at 3510 cm^ꢀ1for 2.

2

3

ered as a self-assembly of a pentanuclear unit and a dinuclear unit,

which are interlinked by semicoordination. It is logical that the

semicoordination is ruptured in solution to produce a composition

[{Cu^IIL(μ-OH)}{Cu^IIL(μ_1,1-N₃)(S)}{Cu^II(μ_1,1-N₃)₄}(S)_n]²⁺-

2

[{Cu^II2(μ_1,1-N₃)₂(N₃)₄}(S)_n]^2ꢀ, which is a 1:1 electrolyte.

2

Description of Structures of [Cu^IIL(μ_1,1-NO₃)(H₂O)(NO₃)]-

2

(NO₃) (1), [{Cu^IIL(μ-OH)(H₂O)}(μ-ClO₄)]_n(ClO₄)_n(2), [{Cu^II₂L-

2

(NCS)₂}(μ_1,3-NCS)]_n(3), [{Cu^II₂L(μ_1,1-N₃)(ClO₄)}₂(μ_1,3-N₃)₂]

(4), and [{Cu^IIL(μ-OH)}{Cu^IIL(μ_1,1-N₃)}{Cu^II(μ_1,1-N₃)₄(dmf)}

2

{Cu^II(μ_1,1-N₃)₂(N₃)₄}]_nndmf (5). All these five complexes

2

3

contain L^ꢀ, which has two N₂O compartments. Each of these

compartments has one pyridine nitrogen and one imine nitrogen

atoms and a common phenoxo oxygen atom. In all the five

complexes, L^ꢀacts as a dinucleating ligand by incorporating one

copper(II) ion in each N₂O compartment. Clearly, phenoxo

To understand the composition in solution, molar conduc-

tance of the 10^ꢀ3(M) dmf solution of complexes 1ꢀ5 were

measured. The conductance (Ω^ꢀ1cm²M^ꢀ1) values at 298 K for

1ꢀ5 are 185, 150, 92, 180, and 73, indicating that 1, 2, and

7543

dx.doi.org/10.1021/ic200409d |Inorg. Chem. 2011, 50, 7540–7554

Inorganic Chemistry

ARTICLE

oxygen atom in these complexes provides an endogeneous bridge

for two copper(II) centers and L^ꢀsatisfies three coordination

positions of each of the two metal ions.

Information. The structure reveals that compound 2 is a dicopper-

(II)-based one-dimensional polymer. In the dinuclear core, the

metal centers are doubly bridged by an endogeneous phenoxo

atom of L^ꢀand an exogeneous hydroxo oxygen atom. One metal

center, Cu2, is pentacoordinated; a water oxygen atom (O3)

occupies the ﬁfth position. On the other hand, Cu1 is hexacoordi-

nated due to the coordination of two perchlorate oxygen atoms,

O5B and O7C, of two diﬀerent perchlorate anions. Another

oxygen atom (O7B and O5C) of each of these two perchlorate

anions coordinates to two diﬀerent copper(II) centers (Cu1H

and Cu1D), which are symmetry related to Cu1, of two diﬀerent

dinuclear units to generate a dicopper(II)-based one-dimen-

sional polymeric structure in 2 (Figure S1 of the Supporting

Information).

The crystal structure of [Cu^IIL(μ_1,1-NO₃)(H₂O)(NO₃)]-

2

(NO₃) (1) is shown in Figure 1. The structure reveals that it is

a heterobridged μ-phenoxo-μ_1,1-nitrate dicopper(II) compound

in which the metal centers are doubly bridged by the phenoxo

oxygen atom of L^ꢀand one oxygen atom of a bridging nitrate ion.

Both the metal centers are pentacoordinated; the ﬁfth coordina-

tion positions of Cu1 and Cu2 are occupied by one oxygen atom

of a monodentate nitrate anion and a water molecule, respec-

tively. Interestingly, compound 1 is the only example of a

heterobridged μ-phenoxo-μ-nitrate dicopper(II) system.

The structure of [{Cu^IIL(μ-OH)(H₂O)}(μ-ClO₄)]_n(ClO₄)_n

2

(2) is shown in Figure 2 and Figure S1 of the Supporting

As shown in Figure 3, [{Cu^IIL(NCS)₂}(μ_1,3-NCS)]_n(3) is a

2

monophenoxo-bridged dicopper(II)-based one-dimensional

polymer. In the dinuclear unit, two metal centers are singly

bridged by the phenoxo oxygen of L^ꢀ. Each of the two metal

centers is coordinated to a terminal N-coordinated NCS^ꢀanion.

The ﬁfth coordination position of Cu2 is occupied by the nitrogen

atom of another NCS^ꢀanion, the sulfur atomofwhichcoordinates

to a copper(II) center, Cu1B, of a neighboring dicopper(II) unit.

Clearly, as shown in Figure 3, one monophenoxo-bridged

dicopper(II) unit is interlinked with two neighboring symmetry

related dinuclear units due to the bridging NCS^ꢀligand to result

in the generation of a one-dimensional polymeric structure in

compound 3. It is evident also that both the metal centers are

pentacoordinated with a N₃OS and a N₄O coordination environ-

ments for Cu1 and Cu2, respectively.

As shown in Figure 4, [{Cu^IIL(μ_1,1-N₃)(ClO₄)}₂(μ_1,3-N₃)₂]

2

(4) is a tetracopper(II) compound. This tetracopper(II) system

may be consideredtoconsist oftwo symmetryrelated dicopper(II)

units, of composition [Cu^IIL(μ_1,1-N₃)(ClO₄)]⁺, interlinked by

2

two end-to-endbridgingazide anions. Inthe dicopper(II) unit, the

two metal centers are doubly bridged by a phenoxo oxygen atom

of L^ꢀand a nitrogen atom of an end-on azide anion. One end-to-

end azide anion bridges two metal centers, Cu1 and Cu2A, of two

dinuclear units. Obviously, a symmetry related end-to-end azide

anion bridges the second metal centers, Cu2 and Cu1A, of the

same two dinuclear units. Clearly, two heterobridged μ-phenoxo-

μ_1,1-N₃dicopper(II) units are interlinked by two end-to-end

Figure 2. Crystal structure of complex [{Cu^II₂L(μ-OH)(H₂O)}(μ-

ClO₄)]_n(ClO₄)_n(2). All the hydrogen atoms are omitted for clarity.

Symmetry code: B, 0.5 ꢀ x, y ꢀ 0.5, 1 + z; C, x, y ꢀ 1, 1 + z.

Figure 3. Perspective view of complex [{Cu^II₂L(NCS)₂}(μ_1,3-NCS)]_n3 showing the dicopper(II)-based one-dimensional structure. Symmetry code:

A, x, y, 1 + z; B, x, y, z ꢀ 1.

7544

dx.doi.org/10.1021/ic200409d |Inorg. Chem. 2011, 50, 7540–7554

Inorganic Chemistry

ARTICLE

Figure 4. Crystal structure of complex [{Cu^IIL(μ_1,1-N₃)(ClO₄)}₂(μ_1,3

-

2

N₃)₂] (4). All the hydrogen atoms are omitted for clarity. Symmetry code:

A, 1 ꢀ x, 1 ꢀ y, ꢀz.

Figure 5. Perspectiveviewof the structure ofheptacopper(II)-basedone-

azide bridges to generate the tetracopper(II) moiety having three

types of bridges, μ-phenoxo, μ_1,1-N₃, and μ_1,3-N₃. Cu2 is addi-

tionally coordinated to a perchlorate oxygen atom (O3). Clearly,

Cu2 is hexacoordinated, while Cu1 is pentacoordinated. Interest-

ingly, the tetranuclear cluster 4, resulting because of the inter-

linking of two μ-phenoxo-μ_1,1-azide dinuclear units by end-to-end

azide bridges, is a new type of structure in the family containing

numerous azide compounds of any metal ion.

dimensional polymeric self-assembly [{Cu^IIL(μ-OH)}{Cu^IIL(μ_1,1

-

2

N₃)}{Cu^II(μ_1,1-N₃)₄(dmf)}{Cu^II(μ_1,1-N₃)₂(N₃)₄}]_nndmf (5). Azide

2

3

atoms N34 and N35 are disordered; hence, for clarity, only one compo-

nent for each is shown. Symmetry codes: B, x, y ꢀ 1, z; C, x ꢀ 1, y ꢀ 1,

z ꢀ 1; D, 1 + x, 1 + y, 1 + z.

coordinate bonds are responsible to generate a pentacopper(II)

unit containing Cu1, Cu2, Cu3, Cu4 and Cu5, as well as a

dicopper(II) unit containing Cu6 and Cu7, these pentanuclear

and dinuclear units are self-assembled to result in a heptacopper-

(II) aggregate because of Cu4ꢀN33 and Cu6ꢀO3 interactions.

As already mentioned, in addition to the two end-on azide bridges,

Cu7 is coordinated to two other azide anions. The coordinating

nitrogen atom, N39, of one such azide anion interacts with a

copper(II) center, Cu1D, of a symmetry related neighboring

heptacopper(II) unit. Clearly, one heptacopper(II) aggregate is

interlinked with two neighboring such aggregates because of two

such end-on azide bridges (Cu7 is bridged with Cu1D, and Cu1

is bridged with Cu7C) to generate a heptacopper(II)-based one-

dimensional polymer, which propagates along the crystallo-

graphic b axis. Interestingly, the heptanuclear assembly as well

as the heptanuclear-based one-dimensional aggregate in 5 is a

new type of structure in the family containing numerous azide

compounds of any metal ion.

The displacement of the metal center and average deviation of

the constituent atoms from the corresponding least-squares basal

plane and the ranges of the transoid angles, cisoid angles, bond

lengths involving the basal atoms, bond lengths involving the

apical atoms along with the coordination geometry, apical

moiety(ies), apical atom(s), and τ values for the metal centers

in 1ꢀ5 are compared in Table S1 of the Supporting Information,

while the selected bond lengths and angles in the coordination

Crystal structure of [{Cu^IIL(μ-OH)}{Cu^IIL(μ_1,1-N₃)}-

2

{Cu^II(μ_1,1-N₃)₄(dmf)}{Cu^II(μ_1,1-N₃)₂(N₃)₄}]_nndmf (5) is

2

3

shown in Figure 5. The structure reveals that compound 5 is a

heptacopper(II)-based one-dimensional polymer. This com-

pound contains two L^ꢀ, each of which incorporates two metal

ions; Cu1 and Cu2 occupy two compartments of one L^ꢀ, while

Cu4 and Cu5 occupy two compartments of another L^ꢀ. In

addition to the bridging phenoxo oxygen atom of L^ꢀ, Cu1 and

Cu2 are bridged by an exogeneous hydroxo oxygen atom, while

Cu4 and Cu5 are bridged by a nitrogen atom of an end-on azide

anion. Each of the four metal ions of the Cu1 Cu2 and

3 3 3

Cu4 Cu5 units are bridged with another copper(II) ion,

3 3 3

Cu3, by each of four end-on azide anions. Clearly, ﬁve copper(II)

ions, Cu1, Cu2, Cu3, Cu4, and Cu5, are the members of a

pentacopper(II) unit, generated because of coordinate bondings.

The remaining two copper(II) ions, Cu6 and Cu7, are bridged by

two end-on azide ligands. Each of these two copper(II) centers

are also coordinated to two other azide anions. The coordinating

nitrogen atom, N33, of one such azide anion, coordinated to Cu6,

interacts weakly with Cu4. Clearly, although the Cu4 N33

3 3 3

interaction is weak, it may be considered that Cu4 and Cu6

are bridged by an end-on azide anion. The bridging phenoxo

oxygen atom, O3, of the Cu4 Cu5 unit interacts weakly with

3 3 3

Cu6, and hence Cu4 and Cu5 may be considered as bridged with

Cu6 because of the O3 Cu6 semicoordination. Clearly, while

3 3 3

7545

dx.doi.org/10.1021/ic200409d |Inorg. Chem. 2011, 50, 7540–7554

Inorganic Chemistry

ARTICLE

environment of the metal ions in 1ꢀ5 are listed in Tables S2ꢀS6

of the Supporting Information, respectively. The coordination

geometry of the pentacoordinated metal ions, Cu1 and Cu2 in

both 1 and 3, Cu2 in 2, Cu1 in 4, and Cu2, Cu3, Cu5, and Cu6 in 5,

are square pyramidal. On the other hand, the coordination

geometry of the hexacoordinated metal centers, Cu1 in 2, Cu2

in 4, and Cu1 and Cu4 in 5, is distorted octahedral. The only

tetracoordinated metal ion, Cu7 in 5, adopts a distorted square

planar coordination geometry. Varying extent of distortion of the

coordination environments is evidenced by the τ values

(0.043ꢀ0.35), average deviation (0.003ꢀ0.30 Å) of the consti-

tuent atoms, and displacement (0.008ꢀ0.27 Å) of the metal ions

from the corresponding least-squares basal plane. As listed in

Table S1 of the Supporting Information, the ranges of the cisoid

and transoid angles, along with the ranges of the bond lengths are

also indicative of varying extent of distortion. As usual for

copper(II), the bond distance(s) involving the apical atom(s)

is/are signiﬁcantly longer than the bond distances involving the

basal atoms for all the metal centers in 1ꢀ5.

metal centers in the dinuclear unit. Clearly, in comparison to the

strong or very strong interaction within the dinuclear unit, the

very weak interaction through the axialꢀaxial bridging perchlo-

rate, thiocyanate and azide moieties can be logically neglected,

and therefore, the magnetic data of compounds 2, 3, and 4 were

modeled as isolated dicopper(II) systems, using the same spin

Hamiltonian as that of compound 1. In the susceptibility versus

T plot of 3, one can observe an increase atthe lowest temperatures,

after a maximum is reached, which indicates the presence of a small

amount of paramagnetic impurity (F). Fitting of the experimental

data with the theoretical expression results in J = ꢀ135 cm^ꢀ1and

g = 2.19 for 1, J = ꢀ298 cm^ꢀ1and g = 2.14 for 2, J = ꢀ105 cm^ꢀ1

,

g = 2.24, and F = 5% for 3, and J = ꢀ119.5 cm^ꢀ1and g = 2.07 for 4.

In addition to some relevant structural informations, the

J values of 1ꢀ4 are listed in Table 2. The magnetic orbital for

all the copper(II) centers in 1ꢀ4 is dx²ꢀ y². In 2, both the

bridging oxygen atoms, phenoxo and hydroxo, occupy basal

positions (equatorialꢀequatorial) of both of the metal centers

with bridge angles, 100.81(17)° and 105.25(17)°, respectively,

greater than the crossover angle (97.5°).^1a,8Moreover, the brid-

ging moiety is nearly planar as evidenced by the torsion angle

(7.7°) in the [Cu₂O₂] unit and the dihedral angle (δ = 13.7°)

between the two basal planes. All these structural parameters^1a,8,9

indicate propagation of very strong antiferromagnetic interac-

tion, as observed (J = ꢀ298 cm^ꢀ1) in 2. In 1, while the bridging

phenoxo oxygen atom occupies basal positions (equatorialꢀ

equatorial) for both the metal ions with the bridge angle of

107.19(13)°, the bridging nitrate oxygen atom occupies the basal

position for one metal ion and the axial position for the second

(axialꢀequatorial) with the bridge angle of 95.50(11)°. Clearly,

the nitrate route can only mediate weak interaction and that may

be ferromagnetic, eventually reducing the overall strength of

antiferromagnetic coupling that is expected through the phenoxo

pathway. The extent of antiferromagnetic interaction is further

reduced due to twisting of the bridging moiety, as evidenced by

the torsion angle (23°) in the [Cu₂O₂] unit and the dihedral

angle (δ = 40.4°) between the two basal planes. Eventually, the

For all the pairs of metal ions interlinked by bridging ligands

in 1ꢀ5, the bridging moiety, bridging fashion (equatorialꢀ

equatorial, axialꢀaxial, or equatorialꢀaxial), the metal metal

3 3 3

distance, bridge angle(s), and dihedral angle (δ) between the two

basal planes are summarized in Table 2. These aspects are

described below along with the description of magnetic properties.

Magnetic Properties of 1ꢀ4. The cryomagnetic behavior

of [Cu^IIL(μ_1,1-NO₃)(H₂O)(NO₃)](NO₃) (1), [{Cu^IIL(μꢀ

2

OH)(H₂O)}(μ-ClO₄)]_n(ClO₄)_n(2), [{Cu^IIL(NCS)₂}(μ_1,3

-

2

NCS)]_n(3), and [{Cu^IIL(μ_1,1-N₃)(ClO₄)}₂(μ_1,3-N₃)₂] (4) are

2

shown as χT versus T plots in Figure 6, Figures S2 and S3 of the

Supporting Information, and Figure 7, respectively. The χT

values at 300 K for 1ꢀ4 are 0.57, 0.15, 0.62, and 1.00 cm³

K mol^ꢀ1, respectively, which are smaller than the expected values

of 0.75 cm³K mol^ꢀ1for two copper(II) ions (for 1ꢀ3) and

1.5 cm³K mol^ꢀ1for four copper(II) ions (for 4) with g = 2.0 and

S = 1/2. As the χT value of complex 2 is only 0.15 cm³K mol^ꢀ1at

300 K, susceptibility data of this compound were collected for

higher temperatures up to 370 K. However, the χT value at 370 K

is also significantly smaller, 0.26 cm³K mol^ꢀ1. As temperature

decreases from 370 K for 2 and from 300 K for 1, 3, and 4, the χT

product decreases steadily until the samples become diamagnetic

below 100 K for complex 1, 200 K for 2, and 50 K for compounds

3 and 4. The susceptibility data indicate very strong antiferro-

magnetic interaction in 2 and strong antiferromagnetic interac-

tion in 1, 3, and 4.

magnitude of antiferromagnetic coupling constant of

1

(ꢀ135 cm^ꢀ1) is much smaller than that of 2 (ꢀ298 cm^ꢀ1). The

phenoxo oxygen bridges two metal ions in 3 in equator-

ialꢀequatorial fashion. As the CuꢀOꢀCu bridge angle in 3 is

110° greater than those (95.5 and 107.2° in 1; 100.8 and 105.2°

in 2) in 1 and 2, one would expect stronger antiferromagnetic

interaction in the former. However, as the bridging moiety in 3

is more twisted than those in 1 and 2 (δ = 40.4, 13.7, and 52.9° in

1, 2 and 3, respectively), antiferromagnetic interaction in 3

(J = ꢀ105 cm^ꢀ1) becomes weaker than those in 1 and 2.^1a,8ꢀ10

The magnetic interaction through the heterobridged μ-phenoxo-

μ_1,1-azide moiety^4,5,9f(both bridges are equatorialꢀequatorial) is a

combined eﬀect of the superexchange through the two individual

bridges, phenoxo and end-on azide. As the phenoxo bridge angle

(102°) is greater than 97.5°, antiferromagnetic interaction is

expected. On the other hand, as the end-on azide bridge angle

(101°) is less than 108°, the azide route should propagate

ferromagnetic interaction.⁶Superexchange through the phenoxo

route dominates over that through the end-on azide route

As compound 1 is an isolated dicopper(II) system, the magnetic

^

data of 1 were modeled with the spin Hamiltonian H = ꢀ2J

^

[S₁S₂]. In compounds 2, 3, and 4, the magnetic exchange

3

between the μ-phenoxo-μ-hydroxo dicopper(II) (in 2), μ-phe-

noxo dicopper(II) (in 3), and μ-phenoxo-μ_1,1-azide dicopper(II)

(in 4) units should be very weak because of the occupation of the

bridging perchlorate oxygen atoms (in 2), end-to-end thiocya-

nate nitrogen and sulfur atoms (in 3), and end-to-end azide

nitrogen atoms (in 4) in the axial positions (axialꢀaxial) as well

as because of long copper(II)ꢀperchlorate (2.683(5) and 2.536

(9) Å), copper(II)ꢀμ_1,3-thiocyanate (2.190(2) and 2.7936(8) Å),

and copper(II)ꢀμ_1,3-azide (2.2370(19) and 2.5786(17) Å)

bond distances (Tables 2, S1, and S3ꢀS5 of the Supporting

Information). On the other hand, as is discussed below,

μ-phenoxo-μ-hydroxo, μ-phenoxo, and μ-phenoxo-μ_1,1-azide

moieties in 2, 3, and 4, respectively, oﬀer a very good pathway

of strong or very strong antiferromagnetic coupling between the

resulting in J = ꢀ119.5 cm^ꢀ1

.

It is relevant to mention the magnetic exchange interaction in

the previously reported related compounds. In a few μ-phenoxo-

μ-hydroxo dicopper(II) complexes, characterized by both single

crystal structures and magnetic studies, both the bridges are

equatorialꢀequatorial (as in 2) with bridge angles greater than

7546

dx.doi.org/10.1021/ic200409d |Inorg. Chem. 2011, 50, 7540–7554

Inorganic Chemistry

ARTICLE

Table 2. J Values/Expected Magnetic Interaction along with Some of Structural Information that may Inﬂuence Magnetic

Properties

bridged metal

pair

metal metal

J (cm^ꢀ1)/ expected

3 3 3

compound

bridging moiety

bridging fashion

bridge angle (deg)

mistance (Å) δ (deg)

interaction

1

Cu1 Cu2

μ-phenoxo

phenoxo: eq(Cu1)-eq(Cu2)

Cu1ꢀO1ꢀCu2 = 107.19(13)

3.1969(14)

40.4

ꢀ135

ꢀ298

3 3 3

μ_1,1-NO₃

μ-phenoxo

μ-hydroxo

μ-ClO₄

μ_1,1-NO₃: ax(Cu1)-eq(Cu2)

Cu1ꢀO2ꢀCu2 = 95.50(11)

Cu1ꢀO1ꢀCu2 = 100.81(17)

2

Cu1 Cu2

phenoxo: eq(Cu1)-eq(Cu2)

3.0519(9)

13.7

3 3 3

hydroxo: eq(Cu1)-eq(Cu2) Cu1ꢀO2ꢀCu2 = 105.25(17)

μ-ClO₄: ax(Cu1)-ax(Cu1D)

Cu1 Cu1D

7.2791(3)

3.2553(4)

6.0234(5)

3.0970(3)

7.9

negligible

ꢀ105

3 3 3

3

4

Cu1 Cu2

μ-phenoxo

μ_1,3-SCN

μ-phenoxo

μ_1,1-azide

μ_1,3-azide

μ-phenoxo

μ-hydroxo

μ-phenoxo

μ_1,1-azide

phenoxo: eq(Cu1)-eq(Cu2)

μ_1,3-SCN: ax(Cu1)-ax(Cu2A)

phenoxo: eq(Cu1)-eq(Cu2)

Cu1ꢀO1ꢀCu2 = 110.13(8)

52.9

23.1

3 3 3

Cu1 Cu2A

negligible

ꢀ119.5

3 3 3

Cu1 Cu2

Cu1ꢀO1ꢀCu2 = 102.36(6)

3 3 3

μ_1,1-azide: eq(Cu1)-eq(Cu2) Cu1ꢀN5ꢀCu2 = 101.39(8)

μ_1,1-azide: ax(Cu1)-ax(Cu2A)

Cu1 Cu2A

6.0148(4)

23.1

5.0

negligible

3 3 3

5

Cu1 Cu2

phenoxo: eq(Cu1)-eq(Cu2)

hydroxo: eq(Cu1)-eq(Cu2)

phenoxo: eq(Cu4)-eq(Cu5)

Cu1ꢀO1ꢀCu2 = 98.3(3)

Cu1ꢀO2ꢀCu2 = 103.5(3)

Cu4ꢀO3ꢀCu5 = 98.8(3)

3.0398(19)

antiferromagnetic

3 3 3

Cu4 Cu5

3.0522(18)

3.1294

6.1

antiferromagnetic

ferromagnetic

3 3 3

μ_1,1-azide: eq(Cu4)-eq(Cu5) Cu4ꢀN21ꢀCu5 = 103.6(4)

μ_1,1-azide: eq(Cu6)-eq(Cu7)

Cu6ꢀN24ꢀCu7 = 104.3(5)

μ_1,1-azide: eq(Cu6)-eq(Cu7) Cu6ꢀN27ꢀCu7 = 102.9(5)

Cu6 Cu7

3 3 3

Cu1 Cu3

μ_1,1-azide: ax(Cu1)-eq(Cu3)

μ_1,1-azide: ax(Cu2)-eq(Cu3)

μ_1,1-azide: eq(Cu3)-ax(Cu4)

μ_1,1-azide: eq(Cu3)-ax(Cu5)

Cu1ꢀN8ꢀCu3 = 124.3(4)

Cu2ꢀN5ꢀCu3 = 127.2(4)

Cu3ꢀN14ꢀCu4 = 127.8(5)

Cu3ꢀN11ꢀCu5 = 129.1(5)

4.016(2)

3.946(2)

3.948(2)

3.880(2)

55.0

52.2

48.7

47.9

weak ferromagnetic

3 3 3

Cu2 Cu3

3 3 3

Cu3 Cu4

3 3 3

Cu3 Cu5

3 3 3

Cu1 Cu7C

μ_1,1-azide

μ_1,1-azide: ax(Cu1)-eq(Cu7C) Cu1ꢀN39CꢀCu7C = 99.3(4)

3.3803(18)

3.5062(17)

7.9

5.0

weak ferromagnetic

3 3 3

Cu4 Cu6

μ-phenoxo

phenoxo: eq(Cu4)-ax(Cu6)

μ_1,1-azide: ax(Cu4)-eq(Cu6)

phenoxo: eq(Cu5)-ax(Cu6)

Cu4ꢀO3ꢀCu6 = 94.1(3)

Cu4ꢀN33ꢀCu6 = 95.2(6)

Cu5ꢀO3ꢀCu6 = 94.8(3)

3 3 3

μ_1,1-azide

Cu5 Cu6

μ-phenoxo

3.5293(18)

7.6

weak ferromagnetic

3 3 3

the crossover angle (97.5°), and the J values in these compounds

range between ꢀ182 and ꢀ426 cm^ꢀ1.⁹Previously reported

monophenoxo-bridged dicopper(II) compounds having the equa-

torialꢀequatorial bridging fashion as in 3 are coupled by moderate

antiferromagnetic interaction with J values lying between ꢀ48

behavior could be rationalized on the basis of established

magnetostructural correlation.

Magnetic Properties of 5. DC magnetic susceptibility data

were collected for a crushed crystalline sample of [{Cu^IIL-

2

(μ-OH)}{Cu^IIL(μ_1,1-N₃)}{Cu^II(μ_1,1-N₃)₄(dmf)}{Cu^II(μ_1,1-

2

and ꢀ122 cm

.

^{ꢀ1 10}As in 4, the antiferromagnetic phenoxo route

N₃)₂(N₃)₄}]_nndmf (5) at an applied magnetic field of 1 T in the

3

dominates over the ferromagnetic azide route in all of the

previously reported μ-phenoxo-μ_1,1-azide compounds,^4,5,9f

resulting in weak^5c(e.g., J = ꢀ8.7 cm^ꢀ1), moderate^4d(e.g.,

J = ꢀ43.2 cm^ꢀ1), strong^5b(e.g., J = ꢀ119 cm^ꢀ1), and very

strong^4a(e.g., J = ꢀ204 cm^ꢀ1) antiferromagnetic interaction.

Although compound 1 has a new bridging moiety, its magnetic

2ꢀ300 K temperature range and 300 G in the 2ꢀ30 K

temperature range. No field dependence of the magnetic sus-

ceptibility response was observed. The data are shown in Figure 8

as a χT versus T plot. The χT value at 300 K is 2.4 cm³K mol^ꢀ1

,

below than the expected value of 2.6 cm³K mol^ꢀ1for seven

Cu(II) ions with g = 2.0 and S = 1/2. As temperature decreases,

7547

dx.doi.org/10.1021/ic200409d |Inorg. Chem. 2011, 50, 7540–7554

Inorganic Chemistry

ARTICLE

Figure 6. χT vs T plot of [Cu^II₂L(μ_1,1-NO₃)(H₂O)(NO₃)](NO₃) (1).

The solid line is the best ﬁtting to the experimental data.

Figure 8. χT vs T plot of [{Cu^IIL[{Cu^IIL(μ-OH)}{Cu^IIL(μ_1,1-N₃)}-

2

{Cu^II(μ_1,1-N₃)₄(dmf)}{Cu^II(μ_1,1-N₃)₂(N₃)₄}]_nndmf (5) at1 T from2

2

3

to 300 K and 300 G from 2 to 30 K.

Figure 7. χT vs T plot of [{Cu^II₂L(μ_1,1-N₃)(ClO₄)}₂(μ_1,3-N₃)₂] (4).

The solid line is the best ﬁtting to the experimental data.

Figure 9. Magnetization versus ﬁeld plot for [{Cu^IIL(μ-OH)}{Cu^IIL-

2

(μ_1,1-N₃)}{Cu^II(μ_1,1-N₃)₄(dmf)}{Cu^II(μ_1,1-N₃)₂(N₃)₄}]_nndmf (5) at

2

3

2 K. The solid line is the best Brillouin function for S = 3/2 and g = 2.1.

the χT product decreases until a plateau is reached at 80 K, with a

χT product value of 1.5 cm³K mol^ꢀ1. This indicates a combina-

tion of antiferromagnetic and ferromagnetic pairwise interactions

between the seven Cu(II) ions that lead to a nonzero ground

state. In fact, the plateau in the χT versus T plot suggests an

S_T= 3/2 for each [Cu₇] unit that form the coordination polymer

5. This is further confirmed by the magnetization versus field

measurement at 2 K; as shown in Figure 9, the magnetization

tends to saturation at a value of 3, indicating S_T= 3/2 spin ground

state. The solid line is the Brillouin function for g = 2.1 and

S_T= 3/2. The lack of agreement observed in the midfield range is

caused by the existence of low lying excited states because the

S = 3/2 is not an isolated state due to the fact that complex 5 is a

polymer of weakly coupled S = 3/2 units.

CuꢀOꢀCu angles of 103.5° and 98.3°, and therefore, Cu1 and

Cu2 should be coupled antiferromagnetically. The metal centers

in the Cu4 Cu5 pair are bridged by a μ-phenoxo-μ_1,1-azide

3 3 3

moiety, and both the bridges coordinate in equatorialꢀequatorial

fashion. The CuꢀOꢀCu and CuꢀNꢀCu angles are 98.8° and

103.6°; thus, weak antiferromagnetic coupling is expected. The

Cu6 Cu7 unit is bridged by two end-on azido ligands with

3 3 3

CuꢀNꢀCu angles of 102.9° and 104.3°, which as calculated by

Alvarez et al^3dshould lead to ferromagnetic coupling. The bridging

moieties in the Cu1 Cu7C, Cu4 Cu6, and Cu5 Cu6

3 3 3

are, respectively, μ_1,1-azide, μ-phenoxo-μ_1,1-azide, and μ-phe-

noxo. As all these bridges coordinate in axialꢀequatorial fashion,

weak ferromagnetic interaction is expected between the metal

ions in these three pairs. Finally, Cu3 is bridged to Cu1, Cu2,

Cu4, and Cu5 by four end-on azido ligands, all of which are

equatorialꢀaxial. The interaction between Cu3 and its four

neighbors will thus be very weak ferromagnetic, which is frustrated

due to the dominant antiferromagnetic coupling within the

Cu1 Cu2 and Cu4 Cu5 pairs. Thus, ﬁve Cu(II) ions in 5

Complex 5 is a coordination polymer formed by repeating

[Cu₇] units (Figures 5 and 10). Even though 5 is too complicated

to model the magnetic data, the pairwise interactions can be

qualitatively evaluated (Figure 10 and Table 2) thanks to the

extensive magnetostructural correlations and calculations per-

formed on dicopper(II) complexes with hydroxo,^1aphenoxo^1a,8

or end-on N₃^3d,6bridges, as those found in 5. The magnetic orbital

of all the copper(II) centers in 5 is dx²ꢀ y². The metal centers in

3 3 3

have their spins parallel to the magnetic ﬁeld, while the other two

the Cu1 Cu2 unit are bridged by a μ-phenoxo-μ-hydroxo

3 3 3

moiety where both the bridges are equatorialꢀequatorial with

align theirs an antiparallel fashion (Figure 10) resulting in the

7548

dx.doi.org/10.1021/ic200409d |Inorg. Chem. 2011, 50, 7540–7554

Inorganic Chemistry

ARTICLE

Figure 10. Core of the [Cu₇] repeating unit of Complex 5, with a

schematic representation of the spin alignments in the complex.

Table 3. UVꢀVis Spectral Bands in dmf along with Tentative

Assignment

compounds

λ_nm(ε, M^ꢀ1cm^ꢀ1

)

tentative assignment

π f π*

PhO^ꢀ/NO₃^ꢀf Cu(II)

1

267 (34287)

374 (8680)

648 (145)

Figure 11. Spectral proﬁle showing the increase of quinone band at

393 nm after the addition of 100 fold of 3,5-DTBCH₂to a solution

containing complex 2 (0.25 ꢁ 10^ꢀ4M) in MeCN. Spectra were

recorded after each 5 min.

d f d

2

3

4

5

267 (33980)

384(7360)

635 (130)

π f π*

PhO^ꢀ/OH^ꢀf Cu(II)

d f d

266 (34305)

368 (6280)

660 (154)

π f π*

PhO^ꢀ/NCS^ꢀf Cu(II)

reaction was followed by recording UVꢀvis spectra of the mixture

under aerobic condition at diﬀerent times up to 60 or 90 min.

Experiments with complexes 1, 2, and 4 were done in both MeCN

and dmf to check the role of solvent on the catalytic activity, while

the experiments with complexes 3 and 5 were done in dmf only

because these two complexes are practically insoluble in MeCN.

Spectral changes of complex 2 in MeCNare shownin Figure11.

After mixing 3,5-DTBCH₂with complex 2, the spectral changes at

an interval of 5 min are shown in this ﬁgure. Because of the

addition of 3,5-DTBCH₂, the LMCT band of the complex 2 at

384 nm becomes slightly red-shifted to 393 nm with gradual

increase of intensity, indicating more and more formation of the

quinone, 3,5-DTBQ. Clearly, complex 2 in acetonitrile shows

catecholase activity. Similar spectralchangestake place for complex

2 in dmf (Figure S4 of the Supporting Information), for complex 4

in MeCN (Figure S5 of the Supporting Information) and dmf

(Figure 12), and for complex 5 in dmf (Figure S6 of the

Supporting Information). On the other hand, generation of the

quinone band does not take place for complex 1 in both MeCN

and dmf and for complex 3 in dmf. Clearly, complexes 1 and 3 are

not catalysts of catecholase activity. On the other hand, com-

plexes 2 and 4 in both MeCN and dmf and complex 5 in dmf

show catecholase activity. At this juncture, it may be mentioned

that the maximum of the quinone band changes slightly as the

function of a particular complex as well as of the solvent: 393 nm

for 2 in MeCN, 393 nm for 2 in dmf, 397 nm for 4 in MeCN,

393 nm for 4 in dmf, and 395 nm for 5 in dmf.

d f d

267 (33567)

384 (15600)

713 (390)

π f π*

PhO^ꢀ/N₃^ꢀf Cu(II)

d f d

267 (33960)

380 (17800)

707 (634)

π f π*

PhO^ꢀ/OH^ꢀ/ N₃^ꢀf Cu(II)

d f d

observed experimental value of S_T= 3/2 for the repeating [Cu₇]

unit of 5.

Electronic Spectra and Catecholase Activity. All the com-

plexes 1ꢀ5 are practically insoluble in methanol but well soluble

in dmf. Again, while compounds 1, 2, and 4 are soluble in

acetonitrile, other two compounds (3and 5) are practically insoluble

in acetonitrile. Accordingly, electronic spectra (200ꢀ1200 nm) of

1, 2, and 4 were recorded in both MeCN and dmf, while those

of 3 and 5 were recorded in dmf only. The band positions and

ε values in dmf are listed in Table 3. In dmf, three characteristic

bands are observed in all the spectra: two strongly intense bands

at 266/267 nm (ε about 34000 M^ꢀ1cm^ꢀ1) and in the range of

368ꢀ384 nm (ε = 6280ꢀ17800 M^ꢀ1cm^ꢀ1) and a less intensity

band in the range of 635ꢀ713 nm (ε = 130ꢀ634 M^ꢀ1cm^ꢀ1).

The spectra of 1, 2, and 4 in MeCN are almost similar to those in

dmf, except that band intensity and position of band maximum

are slightly changed. The probable assignment of the bands is

summarized in Table 3.

3,5-Di-tert-butylcatechol (3,5-DTBCH₂) is usually used to study

the catecholase activity of copper(II) complexes because of the ease

of oxidation of 3,5-DTBCH₂to its corresponding quinone, 3,5-di-

tert-butylquinone (3,5-DTBQ), the later of which has a character-

istic transition at about 400 nm.^{5b,13aꢀ13c,14bꢀ14f,15ꢀ21}To check the

ability of complexes 1ꢀ5 to behave as catalysts for catecholase

activity, a 0.25 ꢁ 10^ꢀ4M solution of a complex is treated with a 100-

fold concentrated solution of 3,5-DTBCH₂, and the course of the

Kinetic studies of the catecholase activity of catalyst complexes

2, 4, and 5 have been performed to understand the extent of their

eﬃciency. For this purpose, a 0.25 ꢁ 10^ꢀ4M solution of a

complex was treated with the substrate solution having concen-

tration ranging between 10-fold and 100-fold than that of the

complex. The experiments were done at a constant temperature,

25 °C, under aerobic condition. For a particular complexꢀsub-

strate mixture, time scan at the maximum of the quinone band

was carried out for a period of 60ꢀ90 min. It may be noted here

7549

dx.doi.org/10.1021/ic200409d |Inorg. Chem. 2011, 50, 7540–7554

Inorganic Chemistry

ARTICLE

Figure 13. Initial rates versus substrate concentration for the 3,5-

DTBCH₂f 3,5-DTBQ oxidation reaction catalyzed by complex 2 in

acetonitrile. Inset shows LineweaverꢀBurk plot. Symbols and solid lines

represent the observed and simulated proﬁles, respectively.

Figure 12. Spectral proﬁle showing the increase of quinone band at

393 nm after the addition of 100 fold of 3,5-DTBCH₂to a solution

containing complex 4 (0.25 ꢁ 10^ꢀ4M) in dmf. Spectra were recorded after

each 5 min.

that the blank experiment without a catalyst does not show

formation of the quinone up to 12 h in MeCN and up to 3 h in

dmf. The rate constant for a particular complexꢀsubstrate mixture

was determined from the optical density versus time plot by the

initial rate method. The rate constant versus concentration of

substrate data were then analyzed on the basis of the Michaelisꢀ

Menten approach of enzymatic kinetics to get the Lineweaverꢀ

Burk plot as well as the values of the parameters V_max, K_M, and

K_cat. Observed and simulated rate constant versus [substrate]

plots and the LineweaverꢀBurk plot for complex 2 in MeCN and

complex 4 in dmf are shown in Figures 13 and 14, respectively,

while similar plots for complex 2 in dmf, for complex 4 in MeCN,

and complex 5 in dmf are shown in Figures S7, S8, and S9 of the

Supporting Information, respectively. The kinetic parameters for

all the cases are listed in Table 4. Compounds 2, 4, and 5 show

turnover numbers (K_cat) in between 39 and 215 h^ꢀ1, which lie in

the range of the K_catvalues of other model complexes, and

therefore, the compounds 2, 4, and 5 can be considered as

functional models of catechol oxidase.^{5b,13aꢀ13c,14bꢀ14f,15ꢀ21}

The better eﬃciency in MeCN in comparison to dmf probably

occurs because dmf is a better coordinating solvent.

Figure 14. Initial rates versus substrate concentration for the 3,5-

DTBCH₂f 3,5-DTBQ oxidation reaction catalyzed by complex 4 in

dmf. Inset shows LineweaverꢀBurk plot. Symbols and solid lines represent

the observed and simulated proﬁles, respectively.

complicated. For example, while a Cu Cu distance in the

3 3 3

range of 2.9ꢀ3.25 Å is proposed as the optimum for best

catalyst,^13b,14e,19a number of good catalysts are known in which

this distance lies at about 4 Å and even much larger such as 7.8

Å.^13bAgain, there is example of poor activity in spite of Cu Cu

3 3 3

distance, 2.85 Å, less than even 2.9 Å.^14bSimilar complications

are there regarding coordination geometry.^{9d,14aꢀ14c,14g,14h}In

the crystal structure of the met form of the enzyme, two

copper(II) centers are hydroxo-bridged, and each is a trigonal

pyramidal. In model systems, some authors observed and

proposed better activity if the coordination geometry is a trigonal

bipyramidal,^14cwhile some others observed better activity for

square pyramidal^14aor even square planar^14g,14h, cases. Regarding

the exogeneous bridging ligand, it has been proposed that activity

should be better for small exogeneous ligands, hydroxo for

example.^{5b,14e,14f,15b}In practice, although some hydroxo-bridged

complexes are known as eﬃcient catalysts, some other are also

known with very poor activity. Clearly, the ability of a complex to

show catecholase activity as well as the turn over number is a

composite eﬀect of several parameters. Nonetheless, some com-

ments may be noted regarding the activity of the title compounds.

The lack of activity for the μ-phenoxo-μ_1,1-nitrate dicopper(II)

compound 1 may be due to the fact that nitrate is a poor leaving

group and the catechol moiety cannot substitute it. In contrast,

the hydroxo group in 2, end-on azide in 4, and either or both of

the hydroxo and end-on azide in 5 are the leaving groups in

The native met form of catechol oxidase consists of a hydroxo-

bridged dicopper(II) center. On the other hand, all the model

copper(II) compounds showing catecholase activity are either

dicopper(II) or monocopper(II). Interestingly, only in the present

investigation, a cluster (4) or one-dimensional copper(II) com-

pounds (2 and 5), have been checked for the ﬁrst time to show

catecholase activity and also found as active catalyst.

It has been proposed previously that several factors may

inﬂuence the eﬃciency of a complex to catalyze catecholase

activity.^{5b,9d,13,14,19,20}These factors are Cu Cu distance, co-

3 3 3

ordination geometry around the metal center, nature of the

exogeneous bridging ligand, ﬂexibity of the primary ligand, etc.

However, a literature survey reveals that the problem is rather

7550

dx.doi.org/10.1021/ic200409d |Inorg. Chem. 2011, 50, 7540–7554

Inorganic Chemistry

ARTICLE

Table 4. Kinetic Parameters for the Complexes

complex

solvent

V_max(M min^ꢀ1

)

std. error

K_M(M)

std. error

K_cat(h^ꢀ1

)

2

dmf

1.628 ꢁ 10^ꢀ5

6.996 ꢁ 10^ꢀ5

1.662 ꢁ 10^ꢀ5

8.606 ꢁ 10^ꢀ5

2.007 ꢁ 10^ꢀ5

1.592 ꢁ 10^ꢀ6

2.791 ꢁ 10^ꢀ6

4.917 ꢁ 10^ꢀ7

4.682 ꢁ 10^ꢀ6

9.344 ꢁ 10^ꢀ7

0.000686

0.001096

0.000651

0.001304

0.000436

0.0002103

0.0001029

0.0000571

0.0001549

0.0000724

39.0

167.9

39.9

acetonitrile

dmf

4

5

acetonitrile

dmf

215.1

48.2

presence of catechol moiety to result in the catecholase activity of

these three complexes.

It is also relevant to mention the activity of previously published

systems having bridging moieties, closely similar to those in the

title compounds. Activity of a few dicopper(II) compounds having

μ-phenoxo-μ-hydroxo moiety has been checked; while some are

inactive, most are active with K_catvalues ranging between 5 and

5470 h^{ꢀ1 9d,13aꢀ13c,14}

Out of four monophenoxo-bridged

.

dicopper(II) compounds for which activity has been tested,

two are inactive, while two others are active with K_catvalues

37 and 900 h .

^{ꢀ1 21}On the other hand, very low catalytic activity

has been observed for a μ-phenoxo-μ-hydroxo-μ-perchlorate

dicopper(II) compound derived from 2,6-bis[N-(2-pyridylethyl)-

formidoyl]-4-methylphenol.²²The low activity in this case

probably arises because of the triple-bridging moiety, which

imposes a steric limitation of the catechol to coordinate to the

metal ion.

Electrospray Ionization Mass Spectral Study. The electro-

spray ionization mass spectroscopy (ESI-MS positive) spectra of

compounds 1, 2, and 4 were recorded in acetonitrile solutions.

Figure 15. Electrospray mass spectrum (ESI-MS positive) of

[{Cu^II₂L(μ-OH)(H₂O)}(μ-ClO₄)]_n(ClO )_n(2) in acetonitrile show-

4

ing observed and simulated isotopic distribution pattern.

The spectra of [Cu^IIL(μ_1,1-NO₃)(H₂O)(NO₃)](NO₃) (1),

2

[{Cu^IIL(μ-OH)(H₂O)}(μ-ClO₄)]_n(ClO₄)_n(2) and [{Cu^IIL-

2

the observation of positive ions [Cu^IIL(μ-OH)]²⁺and [Cu^IIL-

(μ_1,1-N₃)(ClO₄)}₂(μ_1,3-N₃)₂] (4) are shown in Figure S10 of

the Supporting Information, Figure 15, and Figure S11 of the

Supporting Information, respectively.

2

(μ-OH)(ClO₄)]⁺, both having a μ-phenoxo-μ-hydroxo dicopper-

(II) core, is quite normal. However, the appearance of a positiove

ion [Cu^IIL(μ-O)]⁺having a μ-phenoxo-μ-oxo dicopper(II) core

Compound 2 exhibits four peaks at m/z = 264 (100%, line to

line separation 0.5), 345 (13%, line to line separation 1.0), 529

(25%, line to line separation 1.0), and 628 (38%, line to line

separation 1.0). The peaks at m/z = 264 and 628 are well assignable

to the μ-phenoxo-μ-hydroxo dicopper(II) species, dicationic

[Cu^IIL(μ-OH)]²⁺(C₂₄H₂₆N₄O₂Cu₂) and monocationic [Cu^IIL-

2

is interesting. Again, signiﬁcant decomposition of the ligand

system takes place to stabilize a mononuclear positive ion

[Cu^IIL¹]⁺, which contains a ligand having one formyl group

condensed with the amine moiety but the second formyl group

remaining as such.

2

(μ-OH)(ClO₄)]⁺(C₂₄H₂₆N₄O₆ClCu₂), respectively, while the

peak at 529 can be assigned to the monocationic dinuclear μ-

[{Cu^IIL(μ_1,1-N₃)(ClO₄)}₂(μ_1,3-N₃)₂] (4) and [Cu^IIL(μ_1,1-

2

NO₃)(H₂O)(NO₃)](NO₃) (1) contain μ-phenoxo-μ_1,1-azide

and μ-phenoxo-μ_1,1-nitrate dicopper(II) cores, respectively.

However, no peak corresponding to a species having a μ-

phenoxo-μ_1,1-azide or μ-phenoxo-μ_1,1-nitrate bridging moiety

is observed in the ESI-MS positive spectra. On the other hand,

the spectra of 1 and 4 are similar to that of the μ-phenoxo-μ-

hydroxo dicopper(II) compound 2. Clearly, positive ions having

μ-phenoxo-μ_1,1-azide dicopper(II) and μ-phenoxo-μ_1,1-nitrate

dicopper(II) cores in this ligand system are practically very

unstable in comparison to the μ-phenoxo-μ-hydroxo dicopper-

(II) cores in the ESI-MS positive time scale, and therefore, a

positive ion having a μ-phenoxo-μ-hydroxo dicopper(II) core is

produced for all three compounds resulting in similar spectra.

To get an insight to the nature of possible complexꢀsubstrate

intermediate, ESI-MS positive spectra of a 1:100 mixture of

complex 2 and 3,5-DTBCH₂were recorded after 5 min of

mixing. This observed spectra along with simulated patterns

are presented in Figure 16. In this case, ﬁve peaks are observed at

phenoxo-μ-oxo moiety [Cu^IIL(μ-O)]⁺(C₂₄H₂₅N₄O₂Cu₂). On

2

the other hand, the observation of the peak at 345 indicates the

presence of the mononuclear monocationic species [Cu^IIL¹]⁺

(C₁₇H₁₇N₂O₂Cu); HL¹is the 1:1 condensation product of 2,6-

diformyl-4-ethylphenol and 2-(2-aminoethyl)pyridine. As shown

in Figure 15, the isotopic distribution of the observed and

simulated spectral patterns are in excellent agreement with each

other, indicating right assignment of the positive ions.

The ESI-MS positive spectrum of compound 4 (Figure S11 of

the Supporting Information) is similar to that of compound 2.

The spectrum of compound 1 (Figure S10 of the Supporting

Information) is also similar to that of complexes 2 and 4, except

that the peak at m/z 628 due to [Cu^IIL(μꢀOH)(ClO₄)]⁺is not

2

present because compound 1 does not contain a perchlorate

moiety.

Compound 2, [{Cu^IIL(μ-OH)(H₂O)}(μ-ClO₄)]_n(ClO₄)_n,

2

contains a μ-phenoxo-μ-hydroxo dicopper(II) core, and therefore,

7551

dx.doi.org/10.1021/ic200409d |Inorg. Chem. 2011, 50, 7540–7554

Inorganic Chemistry

ARTICLE

Existence of a 1:2 dicopper(II)ꢀsubstrate aggregate, with 3,5-

DTBCH₂as the substrate, has also been claimed from UVꢀvis

spectroscopic studies.^29dClearly, in all the established complexꢀ

substrate aggregates, the catechole moiety is linked in its didepro-

tonated dinegative form and binds the metal centers either as a

bridging ligand or as a chelating ligand. Therefore, the existence

of [Cu^IIL(μ-3,5-DTBC^2ꢀ)(3,5-DTBCH^ꢀ)Na^I]⁺having both

2

the di- and mononegative forms as well as having both the

bridging and monodentate modes of the catechol moiety can be

considered as an interesting observation.

Two catalytic mechanisms of the catecholase activity have

been proposed, one by Kreb’s group^13f,13gand another by Solomon’s

group.^13dIn both these two mechanisms, 1:1 adduct formation

between a dicopper(II) core and the substrate has been men-

tioned. However, the main diﬀerence between the two mechan-

istic proposals involves the binding mode of the substrate to the

dicopper(II) core; whereas a monodentate asymmetric coordi-

nation of the substrate was proposed by Krebs and co-workers, a

simultaneous coordination of the substrate to both copper

centers in the dinucleating bridging fashion is suggested by

Solomon et al. As mentioned above, a complexꢀsubstrate

Figure 16. Electrospray mass spectra (ESI-MS positive) of a 1:100

mixture of [{Cu^II₂L(μ-OH)(H₂O)}(μ-ClO₄)]_n(ClO₄)_n(2) and 3,

5-DTBCH₂in acetonitrile recorded after 5 min of mixing, showing

observed and simulated isotopic distribution pattern.

aggregate [Cu^IIL(μ-3,5-DTBC^2ꢀ)(3,5-DTBCH^ꢀ)Na^I]⁺hav-

2

ing both a bridging bidentate (as in Solomon’s mechanism)

and a monodentate (as in Kreb’s mechanism) catechol moiety

has been identiﬁed in ESI-MS positive spectrum. However, as

applicable to solid state structures, the ESI-MS positive stabilized

aggregates may not be considered as a real intermediate in the

course of catecholase activity because these aggregates are stabi-

lized in the time scale of the spectrum and as a positive ion.

Nontheless, the aggregate identiﬁed here deserves importance

because this is clear evidence of the coordination and bridging

ability of the substrate to the complexes, which is essentially

required for catecholase activity.

m/z = 243 (28%, line to line separation 1.0), 264 (100%, line to

line separation 0.5), 387 (31%, line to line separation 1.0), 629

(17%, line to line separation 1.0), and 977 (10%, line to line

separation 1.0). Among these, the peaks at 264 and 629 are same

as in the spectrum of complex 2. Of the remaining three peaks,

the signal at 243 is well assignable to the quinoneꢀsodium

aggregate [3,5-DTBQ-Na]⁺(C₁₄H₂₀O₂Na), while the peak at

387 arises because of the monoprotonated ligand [LH₂]⁺

(C₂₄H₂₇N₄O) in which probably both the imine nitrogen atoms

are protonated. The remaining peak at 977 is quite interesting

because the peak position and matching of the isototropic

distribution of the observed and simulated patterns (Figure 16)

clearly indicate that this peak arises because of the 1:2 complexꢀ

’ CONCLUSIONS

One aim of the present investigation has been to derive

complexes having a new type of composition and topology by

utilizing new organic blocking ligands in combination with sec-

ondary ligands, azide in particular. As anticipated, we have isolated

two azide-containing compounds, tetranuclear compound 4 and

heptanuclear-based 1-D compound 5, both having new types of

structures in the family containing numerous azide compounds

of any metal ion. Again, compound 1 is the sole example to have a

μ-phenoxo-μ_1,1-nitrate bridging moiety. Thus, new types of struc-

tures have been isolated on designing a new ligand. All ﬁve

complexes exhibit overall antiferromagnetic interaction. Com-

pound 5 may be considered as a nice example to simplify

qualitatively the quantitatively complicated situation on applying

the magnetoꢀstructural correlations. An important aspect of the

present investigation is the catecholase activity by three com-

plexes 2, 4, and 5. To the best of our knowledge, the tetranuclear

compound 4 and heptacopper(II)-based and dicopper(II)-based

one-dimensional compounds, 5 and 2, are the sole examples of

multicopper(II) systems employed to check the possibility of

catecholase activity and also to respond positively. Although ESI-

MS positive spectra may apparently indicate that a μ-phenoxo-μ-

hydroxo dicopper(II) core is responsible for catecholase activity

of the tetracopper(II) compound 4 and heptacopper(II) com-

pound 5, conductance measurements reveal that the active species

substrateꢀsodium aggregate [Cu^IIL(3,5-DTBC^2ꢀ)(3,5-DTB-

2

CH^ꢀ)Na^I]⁺(C₅₂H₆₆N₄O₅Cu₂Na). It has been already discussed

that, in addition to the endogeneous bridging phenoxo oxygen

atom of L^ꢀ, one exogeneous bridging group (nitrate in 1, hydroxo

in 2 and 5, and azide in 4 and 5) potentially bridges two

copper(II) centers, and therefore, it is more probable that the

3,5-DTBC^2ꢀand 3,5-DTBCH^ꢀmoieties in [Cu^IIL(3,5-DTB-

2

C^2ꢀ)(3,5-DTBCH^ꢀ)Na]⁺behave as an exogeneous bridging

ligand and a monodentate ligand, respectively. Thus the positive

ion can be better formulated as [Cu^IIL(μ-3,5-DTBC^2ꢀ)(3,

2

5-DTBCH^ꢀ)Na]⁺

It is relevant to brieﬂy mention at this stage the type of

complexꢀsubstrate aggregates reported previously. Using tetra-

chlorocatechol (TCCH₂) as the substrate, crystal structures of a

few 1:1 dicopper(II)-TCC^2ꢀsystems are known in which TCC^2ꢀ

acts as a bridging ligand through its two anionic oxygen atoms.^29a

With the same substrate^29band also with 3,4-dihydroxy-methyl-

benzoate,²²a few 1:2 dicopper(II)-TCC^2ꢀsystems have also

been characterized crystallographically; in these compounds,

each TCC^2ꢀacts as a chelating ligand for a copper(II) center.

Using inactive p-nitrocatechol, one example of a 1:2 dicopper-

(II)-substrate aggregate having dinegative chelating substrate

has been characterized by UVꢀvis spectroscopic studies.^29c

to initiate catecholase activity for 4 and 5 are most probably Cu^II

4

and Cu^IImoieties, respectively. The observation deserves

5

7552

dx.doi.org/10.1021/ic200409d |Inorg. Chem. 2011, 50, 7540–7554

Inorganic Chemistry

ARTICLE

importance because it opens the utilization of copper(II) clusters

andpolymers to mimic the biocatalysis. In ESI-MS positive spectra,

the identiﬁcation of the rarely observed μ-phenoxo-μ-oxo moiety

(9) (a) Sorrell, T. N.; Jameson, D. L.; O’Connor, C. J. Inorg. Chem.

1984, 23, 190–195. (b) O’Connor, C. J.; Firmin, D.; Pant, A. K.; Babu,

B. R.; Stevens, E. D. Inorg. Chem. 1986, 25, 2300–2307. (c) Lor€osch, J.;

Hasse, W. Inorg. Chim. Acta 1985, 108, 35–40. (d) Banerjee, A.; Sarkar,

S.; Chopra, D.; Colacio, E.; Rajak, K. K. Inorg. Chem. 2008, 47,

4023–4031. (e) Lor€osch, J.; Quotschalla, U.; Hasse, W. Inorg. Chim.

Acta 1987, 131, 229–236. (f) Mallah, T.; Boillot, M.-L.; Kahn, O.;

Gouteron, J.; Jeannin, S.; Jeannin, Y. Inorg. Chem. 1986, 25, 3058–3065.

(10) (a) Choudhury, C. R.; Dey, S. K.; Karmakar, R.; Wu, C.-D.; Lu,

C.-Z.; EJ Fallah, M. S.; Mitra, S. New. J. Chem. 2003, 27, 1360–1366.

(b) Bertoncello, K.; Fallon, G. D.; Hodgkin, J. H.; Murray, K. S. Inorg.

Chem. 1988, 27, 4750–4758.

(11) (a) Transition Metals in Supramolecular Chemistry. In Per-

spectives in Supramolecular Chemistry 5; Sauvage, J.-P., Ed.; Wiley:

London, 1999. (b) Zaworotko, M. J. J. Am. Chem. Soc. 2010, 132,

7821–7822. (c) Zhang, J. J.; Wojtas, L.; Larsen, R. W.; Eddaoudi, M.;

Zaworotko, M. J. J. Am. Chem. Soc. 2009, 131, 17040–17041.

(12) (a) Nayak, M.; Koner, R.; Lin, H.-H.; Fl€orke, U.; Wei, H.-H.;

Mohanta, S. Inorg. Chem. 2006, 45, 10764–10773. (b) Nayak, M.; Jana,

A.; Fleck, M.; Hazra, S.; Mohanta, S. CrystEngComm 2010, 12,

1416–1421.

and the complexꢀsubstrate aggregate [Cu^IIL(μ-3,5-DTBC^2ꢀ)-

2

(3,5-DTBCH^ꢀ)Na^I]⁺should be considered as other two inter-

esting outcomes of the present study.

’ ASSOCIATED CONTENT

S

Supporting Information. Crystallographic data of 1ꢀ5

b

in CIF format, Table S1ꢀS6 and Figures S1ꢀS11. These materials

are available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION

Corresponding Author

*E-mail: sm_cu_chem@yahoo.co.in (S.M.), carolina.sanudo@

qi.ub.es. (E.C.S).

(13) (a) Koval, I. A.; Gamez, P.; Belle, C.; Selmeczi, K.; Reedijk, J.

Chem. Soc. Rev. 2006, 35, 814–840. (b) Selmeczi, K.; Reglier, M.; Giorgi,

M.; Speier, G. Coord. Chem. Rev. 2003, 245, 191–201. (c) Than, R.;

Feldmann, A. A.; Krebs, B. Coord. Chem. Rev. 1999, 182, 211–241.

(d) Solomon, E. I.; Sundaram, U. M.; Machonkin, T. E. Chem. Rev. 1996,

96, 2563–2606. (e) Kitajima, N.; Moro-oka, Y. Chem. Rev. 1994,

94, 737–757. (f) Klabunde, T.; Eicken, C.; Sacchettini, J. C.; Krebs, B.

Nat. Struct. Biol. 1998, 5, 1084–1090. (g) Eicken, C.; Krebs, B.;

Sacchettini, J. C. Curr. Opin. Struct. Biol. 1999, 9, 677–683.

(14) (a) Reim, J.; Krebs, B. J. Chem. Soc., Dalton Trans.

1997, 3793–3804. (b) Rey, N. A.; Neves, A.; Bortoluzzi, A. J.; Pich,

C. T.; Terenzi, H. Inorg. Chem. 2007, 46, 348–350. (c) Belle, C.; Beguin,

C.; Gautier-Luneau, I.; Hamman, S.; Philouze, C.; Pierre, J. L.; Thomas,

F.; Torelli, S. Inorg. Chem. 2002, 41, 479–491. (d) Anekwea, J.;

Hammerschmidta, A.; Rompelb, A.; Krebs, B. Z. Anorg. Allg. Chem.

2006, 632, 1057–1066. (e) Ackermann, J.; Meyer, F.; Kaifer, E.;

Pritzkow, H. Chem.ꢀEur. J. 2002, 8, 247–258. (f) Mukherjee, J.;

Mukherjee, R. Inorg. Chim. Acta 2002, 337, 429–438. (g) Ghosh, D.;

Lal, T. K.; Ghosh, S.; Mukherjee, R. J. Chem. Soc. Chem. Commun.

1996, 13–14. (h) Ghosh, D.; Mukherjee, R. Inorg. Chem. 1998,

37, 6597–6605.

’ ACKNOWLEDGMENT

Financial support from the Government of India through the

Department of Science and Technology (SR/S1/IC-12/2008),

Council for Scientiﬁc and Industrial Research (fellowships to S.

Majumder), and University Grants Commission (fellowships to

S. Sarkar and S. Sasmal) is gratefully acknowledged. Crystal-

lography was performed at the DST-FIST, India-funded Single

Crystal Diﬀractometer Facility at the Department of Chemistry,

University of Calcutta. E.C.S. acknowledges the ﬁnancial support

from the Spanish Government, (Grant CTQ2006/03949BQU

and Juan de la Cierva fellowship).

’ REFERENCES

(1) (a) Kahn, O. Molecular Magnetism; VCH Publications: New

York, 1993. (b) Single-Molecule Magnets and Related Phenomena; Winpenny,

R., Ed.; Springer: New York, 2006. (c) Magnetism: Molecules to Materials II;

Miller, J. S., Drillon, M., Eds.; Willey-VCH: Weinheim, Germany, 2001.

(2) (a) Papatriantafyllopoulou, C.; Stamatatos, T. C.; Wernsdorfer,

W.; Teat, S. J.; Tasiopoulos, A. J.; Escuer, A.; Perlepes, S. P. Inorg. Chem.

2010, 49, 10486–10496. (b) Alborꢁes, P.; Rentschler, E. Angew. Chem.,

Int. Ed. 2009, 48, 9366–9370.

(3) Following references and the references therein: (a) Sasmal, S.;

Hazra, S.; Kundu, P.; Majumder, S.; Aliaga-Alcalde, N.; Ruiz, E.; Mohanta,

S. Inorg. Chem. 2010, 49, 9517–9526. (b) Koner, R.; Hazra, S.; Fleck, M.;

Jana, A.; Lucas, C. R.; Mohanta, S. Eur. J. Inorg. Chem. 2009, 4982–4988.

(c) Sun, H.-L.; Wang, Z.-M.; Gao, S. Chem. ꢀEur. J. 2009, 15, 1757–1764.

(d) Manca, G.; Cano, J.; Ruiz, E. Inorg. Chem. 2009, 48, 3139–3144.

(e) Serna, Z. E.; Cortꢁes, R.; Urtiaga, M. K.; Barandika, M. G.; Lezama, L.;

Arriortua, M. I.; Rojo., T. Eur. J. Inorg. Chem. 2001, 865–872.

(4) (a) Kahn, O.; Mallah, T. J. Chem. Soc., Dalton Trans.

1989, 1117–1126. (b) Cheng, P.; Liao, D.; Yan, S.; Jiang, Z.; Wang, G.;

Yao, X.; Wang, H. Inorg. Chim. Acta 1996, 248, 135–137. (c) Benzekri, A.;

Dubourdeaux, P.; Latour, J.-M.; Laugier, J.; Rey, P. Inorg. Chem. 1988,

27, 3710–3716.

(15) (a) Merkel, M.; Mcller, N.; Piacenza, M.; Grimme, S.; Rompel,

)

A.; Krebs, B. Chem.ꢀEur. J. 2005, 11, 1201–1209. (b) Fernandes, C.;

Neves, A.; Bortoluzzi, J.; Mangrich, A. S.; Rentschler, E.; Szpoganicz, B.;

Schwingel, E. Inorg. Chim. Acta 2001, 320, 12–21. (c) Neves, A.; Rossi,

L. M.; Bortoluzzi, A. J.; Mangrich, A. S.; Haase, W.; Werner, R. J. Braz.

Chem. Soc. 2001, 12, 747–754.

(16) Nanda, P. K.; Bertolasi, V.; Aromí, G.; Ray, D. Polyhedron 2009,

28, 987–993.

(17) Gupta, R.; Mukherjee, S.; Mukherjee, R. Polyhedron 2000,

19, 1429–1435.

(18) Majumder, A.; Goswami, S.; Batten, S. R.; El Fallah, M. S.;

Ribas, J.; Mitra, S. Inorg. Chim. Acta 2006, 359, 2375–2382.

(19) Kao, C.-H.; Wei, H.-H.; Liu, Y.-H; Lee, G.-H; Wang, Y.; Lee,

C.-J. J. Inorg. Biochem. 2001, 84, 171–178.

(20) Thirumavalavan, M.; Akilan, P.; Kandaswamy, M.; Chinnakali,

G.; Senthil Kumar, G.; Fun, H. K. Inorg. Chem. 2003, 42, 3308–3317.

(21) Smith, S. J.; Noble, C. J.; Palmer, R. C.; Hanson, G. R.; Schenk,

G.; Gahan, L. R.; Riley, M. J. Biol. Inorg. Chem. 2008, 13, 499–510.

(22) Manzur, J.; García, A. M.; Vega, A.; Iba~nez, A. Polyhedron 2007,

26, 115–122.

(5) (a) Mallah, T.; Kahn, O.; Gouteron, J.; Jeannin, S.; Jeannin, Y.;

O’Connor, C. J. Inorg. Chem. 1987, 26, 1375–1380. (b) Banerjee, A.;

Singh, R.; Colacio, E.; Rajak, K. K. Eur. J. Inorg. Chem. 2009, 277–284.

(c) Boillot, M.-L.; Kahn, O.; O’Connor, C. J.; Gouteron, J.; Jeannin, S.;

Jeannin, Y. J. Chem. Soc., Chem. Commun. 1985, 178–180.

(6) Tandon, S. S.; Thompson, L. K.; Manuel, M. E.; Bridson, J. N.

Inorg. Chem. 1994, 33, 5555–5570.

(7) Chou, Y.-C.; Huang, S.-F.; Koner, R.; Lee, G.-H.; Wang, Y.;

Mohanta, S.; Wei, H.-H. Inorg. Chem. 2004, 43, 2759–2761.

(8) Thompson, L. K.; Mandal, S. K.; Tandon, S. S.; Bridson, J. N.;

Park, M. K. Inorg. Chem. 1996, 35, 3117–3125.

(23) (a) Mallah, T.; Boillot, M.-L.; Khan, O.; Gouteron, J.; Jeannin,

S.; Jeannin, Y. Inorg. Chem. 1986, 25, 3058–3065. (b) O’Connor, C. J.;

Firmin, D.; Pant, A. K.; Babu, B. R.; Stevens, E. D. Inorg. Chem. 1986,

25, 2300–2307. (c) Gagne, R. R.; Kreh, R. P.; Dodge, J. A. J. Am. Chem.

Soc. 1979, 101, 6917–7822. (d) Khan, O.; Mallah, T.; Gouteron, J.;

Jeannin, S.; Jeannin, Y. J. Chem. Soc., Dalton Trans. 1989, 1117–1126.

7553

dx.doi.org/10.1021/ic200409d |Inorg. Chem. 2011, 50, 7540–7554

Inorganic Chemistry

ARTICLE

(24) (a) Visinescu, D.; Pascu, G. I.; Andruh, M.; Magull, J.; Roesky,

H. W. Inorg. Chim. Acta 2002, 340, 201–206. (b) Visinescu, D.; Madalan,

A. M.; Kravtsov, V.; Simonov, Y. A.; Schmidtmann, M.; M€uller, A.;

Andruh, M. Polyhedron 2003, 22, 1385–1389.

(25) (a) Tandon, S. S.; Bunge, S. D.; Motry, D.; Costa, J. S.; Aromí,

G.; Reedijk, J.; Thompson, L. K. Inorg. Chem. 2009, 48, 4873–4881.

(b) Tandon, S. S.; Bunge, S. D.; Patel, N.; Thompson, L. K. Inorg. Chem.

Commun. 2009, 12, 1077–1080.

(26) Ullman, F.; Brittner, K. Chem. Ber. 1909, 42, 2539–2548.

(27) (a) APEX-II, SAINT-Plus, and TWINABS; BrukerꢀNonius

AXS, Inc.: Madison, WI, 2004 (b) Sheldrick, G. M. SAINT, version

6.02 and SADABS, version 2.03; Bruker AXS, Inc.: Madison, WI, 2002.

(c) SHELXTL, version 6.10; Bruker AXS, Inc.: Madison, WI, 2002.

(d) Sheldrick, G. M. SHELXL-97, Crystal Structure Reﬁnement Program;

University of G€ottingen: Germany, 1997.

(28) Geary, W. J. Chem. Rev. 1971, 7, 81–122.

(29) (a) Karlin, K. D.; Gultneh, Y.; Nicholson, T.; Zubieta, J. Inorg.

Chem. 1985, 24, 3725–3727. (b) B€orzel, H.; Comba, P.; Pritzkow, H.

Chem. Commun. 2001, 97–98. (c) Plenge, T.; Dillinger, L.; Santagostini,

L.; Casella, L.; Tuczek, F. Z. Anorg. Allg. Chem. 2003, 629, 2258–2265.

(d) Torelli, S.; Belle, C.; Hamman, S.; Pierre, J.-L.; Saint-Aman, E. Inorg.

Chem. 2002, 41, 3983–3989.

7554

dx.doi.org/10.1021/ic200409d |Inorg. Chem. 2011, 50, 7540–7554

Article Doi

Heterobridged dinuclear, tetranuclear, dinuclear-based 1-D, and heptanuclear-based 1-D complexes of copper(II) derived from a dinucleating ligand: Syntheses, structures, magnetochemistry, spectroscopy, and catecholase activity

DOI: 10.1021/ic200409d

Source and publish data:

Authors:

Article abstract of DOI:10.1021/ic200409d

Full text of DOI:10.1021/ic200409d

Products guided by the article

R&D Labs maybe for 1315461-69-8

Relevant to this article

Hot Product