The effect of ligand architecture on the structure and properties of nickel and copper complexes of amide-based macrocycles

FULL PAPER

DOI: 10.1002/ejic.200900623

The Effect of Ligand Architecture on the Structure and Properties of Nickel

and Copper Complexes of Amide-Based Macrocycles^[‡]

Savita K. Sharma,^[a]Geeta Hundal,^[b]and Rajeev Gupta*^[a]

Keywords: Nickel / Copper / Macrocyclic ligands / Electrochemistry / Oxidation

The present work demonstrates the influence of electron-do-

nating and electron-withdrawing substituents on the struc-

tural, chemical and redox properties of nickel(II) and cop-

per(II) complexes in a set of 12-membered macrocyclic li-

gands. Four macrocyclic ligands, H₂L^H, H₂L^Cl, H₂L^Me, and

H₂L^OMe, in their doubly deprotonated form, have been used

to synthesize the Ni^IIand Cu^IIcomplexes. The crystallo-

graphic studies reveal that whereas the nickel ion is in an

N₄square-planar environment, the Cu^IIcomplexes have a

square-pyramidal geometry with an N₄basal plane and the

O_amideatom in the apical position. Furthermore, the Cu–

N_amidebonds are shorter than the Ni–N_amidebonds. The Ni^II

and Cu^IIcomplexes are capable of undergoing one- and two-

electron oxidations that are most likely metal- and ligand-

centered. The electrochemical results indicate that the

Ni^III/IIpotentials are more positive than the Cu^III/IIpotentials.

Electron-donating substituents on the ring shift the redox-

potential value towards less positive values and better stabi-

lize a higher oxidation state of the metal ion. The Ni^IIIand

Cu^IIIspecies were generated in solution both electrochemi-

cally as well as chemically and are shown to have rich spec-

troscopic features. The absorption and anisotropic EPR spec-

tra of the nickel complexes suggest that the Ni^IIIspecies is

in a square-planar geometry. The spectroscopic data for the

nickel(III) and copper(III) species bearing an OMe group on

the ligand suggest a metal complex with a semiquinone-type

ligand-based radical.

ion.^[11–13]In this category, the ligand system based on an o-

phenylenediamine skeleton containing additional nitrogen,

oxygen and sulfur donors has shown quite interesting re-

sults.^[11–13]Thus, the redox non-innocence of the o-phen-

ylenediamine fragment [NH(C₆H₄)NH] when coordinating

to a metal ion has been a major focus of study.^[11–13]Ex-

tended conjugation of the o-phenylenediamidate fragment

in a metal complex may alter its redox properties as it in-

volves both metal- and ligand-based orbitals. In this regard,

an investigation to assess the possible role of non-innocent

ligands derived from o-phenylenediamine in the stabiliza-

tion of the high-valent nickel complexes has been initiated

by us recently.^[14,15]Our goal is to understand the factors

that contribute towards the stability of metal ions in high

oxidation states where both the metal center and the ligand

can serve as electron reservoirs. The present study forms the

basis of our earlier work on the coordination chemistry and

redox investigation of nickel ions with amide-based macro-

cyclic ligands^[14]and their open-chain analogues^[15]

(Scheme 1). These macrocyclic ligands and their open-chain

analogues have been shown to stabilize +2 as well as +3

(transiently) oxidation states of the nickel ion in a square-

planar geometry. Herein, we extend our earlier work on

macrocyclic chemistry and present the synthesis of three

new 12-membered macrocyclic ligands containing electron-

withdrawing (Cl) and electron-donating groups (CH₃and

OCH₃). We then discuss the effect of such substituents on

the structure, properties and redox chemistry of nickel and

copper ions.

Introduction

The importance of redox-active transition metal ions in

metalloenzymes is an area of considerable research interest.

The coordination chemistry of nickel and copper in variable

oxidation states is particularly important in this context.^[1]

The structure, spectroscopy and redox investigation of high-

valent nickel and copper complexes has received much at-

tention from inorganic chemists as biomimetic models or

for potential use as catalytic oxidants.^[2]Interest in the re-

dox chemistry of nickel and copper complexes has been fur-

ther renewed due to the participation of such species in the

redox catalytic cycle of several metalloenzymes.^[3,4]Thus, a

good number of well-characterized high-valent nickel and

copper complexes with diverse ligand types and coordina-

tion geometries are available,^[5,6]including the square-

planar nickel(III) and copper(III) complexes of amidate-

containing ligands from the groups of Margerum,^[7,8]Col-

lins^[5,9]and Journaux.^[10]On the other hand, the participa-

tion of redox-active ligands adds a new dimension to the

coordination and redox chemistry of the transition metal

[‡] Part 2: Electronic Effects. Part 1: Ref.^[14]

[a] Department of Chemistry, University of Delhi,

Delhi 110007, India

Fax: +91-11-27666605

E-mail: rgupta@chemistry.du.ac.in

[b] Department of Chemistry, Guru Nanak Dev University

Amritsar, Punjab 143005, India

Supporting information for this article is available on the

WWW under http://dx.doi.org/10.1002/ejic.200900623.

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S. K. Sharma, G. Hundal, R. Gupta

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lowed by addition of the [M(H₂O)₆](ClO₄)₂salt. The usual

workup and recrystallization procedures afforded highly

crystalline materials in moderate recrystallized yields

(Scheme 2). All nickel complexes are deep yellow to orange

in colour, whereas the copper complexes are blue, except

for complex 7, which is dark green. The absence of a ν_N–H

stretching frequency in the FTIR spectra^[16]confirms the

deprotonated nature of the amide ligands. Furthermore, the

bathochromic shift in the ν_C=Ostretching frequency ob-

served for all complexes with respect to the free ligand fur-

ther confirms that the deprotonated N_amidegroup is in-

volved in coordination.^[14–16]Different shifts were noticed

in the position of the ν_C=Ostretches for the nickel (55 cm^–1)

and copper complexes (70 cm^–1) with respect to the free li-

gand. This difference indicates different degrees of delocal-

ization of the excess electron density on the deprotonated

N_amideatom into the NCO fragment for these complexes.

Solution conductivity data^[17]confirmed the non-electro-

lytic nature of all metal complexes, and elemental analysis

results authenticated the purity of the bulk samples. The

solution-state magnetic moment was determined for copper

complexes 4–7 by using Evans’ NMR method.^[18]The

room-temperature magnetic moments (µ_eff) in dmf were

found to be 1.70, 1.80, 1.65 and 1.68 µ_B, respectively. These

values are in the range for S = 1/2 in a magnetically dilute

condition. A weak interaction between two copper(II) ions

cannot, however, be ruled out if the solid-state 1D zig-zag

chain structure (see below) is retained in solution.

Scheme 1. Ni^IIcomplexes of macrocyclic and open-chain ligands

reported by our laboratory.

Results and Discussion

Ligand Design: Emphasis on Electronic Effects

The ligands H₂L^H, H₂L^Cl, H₂L^Meand H₂L^OMehave been

designed to subtly change the electronic character of the o-

phenylene ring directly attached to the amide groups. The

design element originated from our earlier study,^[14]where

we showed that out of four macrocyclic ligands used to syn-

thesize Ni^IIcomplexes A–D (Scheme 1), ligand H₂L^Hstabi-

lized the Ni^IIIstate to a great extent. We reasoned that the

proximity of the o-phenylenediamidate fragment to the

nickel(III) ion in the complex C with H₂L^Hhelped to delo-

calize the unpaired electron density onto the ligand’s π or-

bitals.^[14]This success with ligand H₂L^Hprompted us to

introduce electron-withdrawing (Cl) and -donating groups

(CH₃and OCH₃) onto the phenylene ring to gain a thor-

ough understanding of the electronic effects on the relative

stabilization of the M^2+/3+states. In addition, the present

work compares the chemistry of nickel with that of copper

to further delineate the effect of the ligand architecture on

the physical and redox properties of the metal center. The

ligands H₂L^H, H₂L^Cl, H₂L^Me, and H₂L^OMewere synthe-

sized in a manner similar to that of the previously reported

12-membered macrocyclic ligands.^[14]The process involves

two steps whereby the diamine is first converted into the

respective bis(chloroacetamide) and then macrocyclized

with a secondary amine to obtain the desired ligands. All

new ligands were thoroughly characterized by various spec-

troscopic techniques and gave satisfactory microanalysis re-

sults.

Scheme 2. Synthesis of Ni^IIand Cu^IIcomplexes.

Metal Complexes

Crystal Structure Studies

Ni^IIcomplexes 1–3 and Cu^IIcomplexes 4–7 were synthe-

Some representative nickel and copper complexes were

sized as follows: a dmf solution of the respective ligand was structurally characterized. The coordination geometry

first deprotonated with NaH under N₂, and then the metal around the nickel center is square-planar in complexes 1

salt [NiCl₂or Cu(OTf)₂] was added. Complexes 3 and 7 and 2, whereas it is square-pyramidal for copper complexes

could be synthesized in better yield by treating an MeOH 5 and 6. The metal ion is coordinated by two deprotonated

solution of the ligand H₂L^OMewith 2 equiv. of NaOH fol- N_amideatoms and two neutral N_amineatoms in the N₄basal

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Eur. J. Inorg. Chem. 2010, 621–636

Nickel and Copper Complexes of Amide-Based Macrocycles

plane in all cases, although the fifth coordination site in the keep the water molecule out of the coordination sphere of

copper complexes is occupied by an O_amidegroup from a the metal atom, where it is maintained by various H-bond-

neighboring molecule^[19]to form a 1D chain. The metal ion ing interactions.

is surrounded by four five-membered chelate rings in all

complexes.^[14]The bond angles formed by the lateral chelate

rings about the metal center are close to the ideal value of

90° for a perfect square-planar complex. For nickel (copper)

complexes, however, the bond angle involving two anionic

N_amideatoms has a slightly smaller value of about 88° (84°),

which is compensated by a slightly wider angle of 93° (ap-

prox. 90°) for the chelate ring involving the two N_amine

atoms.^[14]For copper complexes, the bond angles involving

the two N_amideand two N_amineatoms are around 4° nar-

rower than in the nickel complexes. An interesting feature

of all structures is the orientation of the CH₂CH₂fragments

of the amine part of the macrocyclic ligand, which adopts

an envelope conformation similar to that in our earlier

nickel complexes A–D (see Scheme 1).^[14]The lateral five-

membered chelate rings [C(O)CH₂fragment] in all com-

plexes also adopt an envelope conformation.^[14]Both carbon

atoms in these rings are present on the same side of the

Figure 1. Molecular structure of complex 1 (thermal ellipsoids are

drawn at the 50% probability level). Hydrogen atoms and water

molecule have been omitted for clarity.

N

_amide–Ni–N_amineplane, with a larger displacement of the

carbon atoms connected to the amine nitrogen atoms. The

methyl groups on the tertiary nitrogen centers are located

on one side of the plane in all cases. This is in line with our

earlier examples of Ni^IIcomplexes A–D,^[14]although it is in

contrast to a number of examples where the relative posi-

tion of the N–H or N–R groups results in the presence of

geometrical isomers.^[20]

Extensive H-bonding involving the water molecule, car-

bonyl oxygen atoms, chlorine atoms and various carbon

atoms (Table S1) forms a 3D H-bonded network. The water

molecule O1W donates hydrogen bonds to carbonyl oxygen

atoms O1 and O2 and accepts hydrogen bonds from methyl-

ene and methyl carbon atoms. The H-bonding interactions

O1W–H2W···O2, C13–H13B···O2 and C9–H9B···O1W give

rise to linear chains running parallel to the a axis, whereas

C2–H2···Cl1 H-bonding interactions extend the structure

diagonally in the ab plane to form planar sheets. These par-

allel sheets interact with each other through the above-men-

tioned Ni···Cl2 and π···π interactions and O1W–H1W···O1,

C11–H11A···O1, C8–H8B···O2 and C10–H10B···N4 H-

bonds to form an extended 3D network (Figure S2).

Structure of [Ni(L^Cl)] (1)

The molecular structure of complex 1 is shown in Fig-

ure 1. The average Ni–N_amidebond length in this complex

is 1.81 Å, and the average Ni–N_aminebond length is

1.90 Å.^[14]The difference of 0.1 Å between the two is due

to the different coordination types (anionic for the depro-

tonated amide nitrogen atoms and neutral for the amine

nitrogen donors).^[14]The phenyl ring, the two chlorine

atoms and all four nitrogen atoms lie in a plane, with a

Structure of [Ni(L^Me)] (2)

The crystal structure of complex 2 (Figure 2) shows that

maximum deviation from this plane of 0.06 Å for N4 and there are two crystallographically independent molecules,

C2. Both carbonyl carbon atoms (C7 and C12) and the ad- henceforth referred to as molecule 1 (with Ni1) and mole-

jacent methylene carbon atoms (C8 and C11) also form a cule 2 (with Ni2), in the unit cell. The Ni^IIion is coordi-

plane, which is almost parallel to the previously defined nated by two N_amideand two N_amineatoms in an N₄basal

plane (dihedral angle 8°) and lies below it. The Ni atom lies plane, with maximum deviations of 0.05 and 0.04 Å, respec-

0.15 and 0.74 Å above these two planes, respectively, thus tively. The Ni^IIion lies 0.12 and 0.14 Å above these planes

giving the molecule a butterfly-like conformation. The Ni^IIin molecule 1 and molecule 2, respectively. These square

ion is thus exposed on one side and shows a weak coordina- planes are also coplanar with their respective phenyl rings

tion [3.319(1) Å] to Cl2ⁱof a symmetry-related molecule (i in both molecules (dihedral angles of 5.6° and 2.7°, respec-

= –x, –y + 1, –z + 1) to form a dimer in the bc plane tively). The two molecules are, however, rotated with respect

(Figure S1) These Ni–Cl interactions are very weak, as can to each other, with an angle of 58° between the two square

be seen from the Ni^II–Cl bond lengths of 2.053 Å in planes. The average Ni–N_amidebond length is 1.80 Å, and

NiCl₂.^[21]The dimers are further strengthened by face-to- the average Ni–N_aminebond length is 1.90 Å in both molec-

face π···π interactions between the two phenyl rings, with ules.^[14]

a centre-to-centre distance of 3.715(2) Å. The phenyl ring,

The crystal structure shows the formation of a 3D net-

methyl, methylene and carbonyl carbon atoms together cre- work arising from weak C–H···O-type H-bonding interac-

ate a hydrophobic environment around the Ni^IIion and tions within and between molecules 1 and 2. In molecule 1,

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S. K. Sharma, G. Hundal, R. Gupta

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Figure 2. Molecular structure of complex 2 (thermal ellipsoids are

drawn at the 50% probability level) showing two crystallographi-

cally independent molecules. Hydrogen atoms have been omitted

for clarity.

the intermolecular C–H···O H-bonding interactions be-

tween methyl carbon atoms C13 and C14 and amide oxygen

atoms O2 and O1, respectively, form a double helical chain

running parallel to the b axis. Figure 3 shows one such

chain. On the other hand, C24–H24B···O4 and C26–

H26B···O4 H-bonding interactions within molecule 2 gen-

erate centrosymmetric dimers which are further joined to

each other through C32–H32A···N5 hydrogen bonds to

form zig-zag chains running parallel to the a axis (Figure 4).

These two chains are further connected to each other

Figure 3. Space-filling models showing the double helical chain in

molecule 1 of complex 2: front view along the a axis (left) and side

view (right). Only atoms which form part of the helical chain are

shown.

Structure of [Cu(L^Cl)] (5)

A perspective view of 5 is shown in Figure 5, and selected

through various other C–H···O H-bonding interactions bonding parameters are given in Table 1. Each copper atom

(Figure S3, Table S2) to constitute a 3D H-bonded net- is coordinated by the O_amideatom to form a one-dimen-

work.

sional polymeric chain with an intramolecular Cu···Cu dis-

Figure 4. Centrosymmetric dimers in complex 2 formed by C24–H24B···O4 and C26–H26B···O4 H-bonding interactions in molecule 2.

These dimers are further joined to each other through C32–H32A···N5 hydrogen bonds to form zig-zag chains running parallel to the a

axis.

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Nickel and Copper Complexes of Amide-Based Macrocycles

tance of 6.153(4) Å^[19](Figure 6a). The square-pyramidal than in analogous Ni^IIcomplexes. These comparative pa-

Cu^IIion is coordinated by two N_amideand two N_amineatoms rameters indicate that the copper ion protrudes further out

in the basal plane, with the apical position being filled by of the basal plane in this 12-membered complex than in

the amide O atom from a neighboring complex [Cu–O(2) analogous nickel complexes.

2.214(3) Å]. This distance is around 0.14 Å shorter than the

Cu–O_amidedistances in a closely related system containing

an open-chain, amide-based ligand.^[19]The distortion pa-

Structure of [Cu(L^Me)] (6)

rameter τ, which is 0 for a perfect square-planar and 1 for

a perfect trigonal-bipyramidal geometry,^[22]is 0.029, thus

The molecular structure of 6 shows that the asymmetric

indicating a slightly distorted square-pyramidal geometry.

unit contains two independent molecules. In contrast to the

The copper atom is displaced by 0.5089 Å from the N₄

structure of 5, each dinuclear unit repeats rather than the

mononuclear unit. One such dinuclear unit is shown in Fig-

basal plane towards the O_amideatom O(2). The Cu–O(2)

bond is slightly bent off the perpendicular to the CuN₄

ure 7. Each copper atom is coordinated by an O_amideatom

plane by 8.753°. The average Cu–N_amidebond length is

to generate a one-dimensional polymeric chain with an in-

1.912 Å, whereas the average Cu–N_aminebond length is

2.044 Å. The difference of 0.13 Å is due to the anionic coor-

dination of the deprotonated amide nitrogen atoms com-

pared to the neutral amine nitrogen donors. The average

tramolecular Cu···Cu distance of 5.610(9) Å (Figure 6b).^[19]

The coordination environment around each Cu^IIion is dis-

torted square-pyramidal, with an N₄basal plane and O_amide

axial donor. The corresponding distortion value τ is 0.140

Cu–N_amidedistance is around 0.1 Å longer than the average

[0.110 for the Cu(2) atom].^[22]The average Cu–N_amidedis-

Ni–N_amidedistance (in complexes 1 and 2), whereas the Cu–

tance is 1.92 Å and is 0.13 Å shorter than the average Cu–

N

_aminedistance is around 0.16 Å longer than the Ni–N_amine

N_aminebond (2.052 Å). The average Cu–N_amidedistance is

0.1 Å longer than the average Ni–N_amidedistance, whereas

the Cu–N_aminedistance is 0.16 Å longer than the Ni–N_amine

bond length. The average N_amide–Cu–N_amideangle is about

4° smaller than the average N_amide–Ni–N_amidebond angle,

whereas the N_amine–Cu–N_aminebond angle is about 2°

smaller than the N_amine–Ni–N_amineangle. This trend indi-

cates the larger displacement of the copper ion in 12-mem-

bered macrocyclic systems out of the N₄basal plane com-

pared to nickel complexes. The other bonding parameters

are similar to those for 5 and comparable with a similar

crystallographically characterized system.^[19]

bond lengths. The average N_amide–Cu–N_amideand N_amine

Cu–N_amineangles are around 4° and 2°, respectively, smaller

–

The amide oxygen atoms O1 and O3 coordinate to Cu^II

ions at the apical position to form spiral coordination poly-

mers running parallel to the b axis and diagonally across

the ac plane. One such spiral chain is shown in Figure S4.

Intermolecular hydrogen bonding involving solvent water

and methanol molecules and the coordination polymer re-

sults in a very interesting and intricate crystal structure

(Table S3). Water molecule O1W lies on the twofold axis of

rotation and joins a pair of the above-mentioned spiral

chains through hydrogen bonding via two symmetry-related

Figure 5. Molecular structure of complex 5 (thermal ellipsoids are

drawn at the 50% probability level). Hydrogen atoms have been

omitted for clarity.

Table 1. Selected bond lengths [Å] and angles [°] for [Ni(L^Cl)]·H₂O (1), [Ni(L^Me)] (2), [Cu(L^Cl)] (5) and [Cu(L^Me)]·2H₂O·CH₃OH (6).

[Ni(L^Cl)] (1)

[Ni(L^Me)] (2)^[a]

[Cu(L^Cl)] (5)

[Cu(L^Me)] (6)^[b]

M1–N1

M1–N2

M1–N3

M1–N4

1.814(2)

1.897(2)

1.904(2)

1.810(2)

–

88.7(1)

89.7(1)

169.8(1)

171.1(1)

87.5(1)

92.8(1)

1.793(8), 1.804(7)

1.913(7), 1.914(7)

1.904(8), 1.916(7)

1.824(7), 1.802(7)

–

89.9(3), 89.8(3)

89.2(3), 89.0(3)

174.5(3), 172.8(3)

168.7(3), 168.5(3)

87.1(3), 87.2(3)

93.0(3), 92.8(3)

1.911(4)

2.056(4)

2.214(3)

1.913(4)

2.214(3)

85.0(1)

1.926(6)

1.929(6)

2.057(5)

2.029(5)

2.172(6)

84.1(2)

Cu2–N5

Cu2–N6

Cu2–N7

Cu2–N8

1.929(6)^[c]

1.931(6)^[c]

2.048(6)^[c]

2.043(6)^[c]

2.170(5)^[c]

83.9(3)^[c]

85.4(3)^[c]

150.3(3)^[c]

148.6(3)^[c]

86.1(3)^[c]

88.8(2)^[c]

M1–O

Cu2–O1

N1–M1–N2

N3–M1–N4

N1–M1–N3

N2–M1–N4

N1–M1–N4

N2–M1–N3

N5–Cu2–N6

N5–Cu2–N8

N6–Cu2–N8

N5–Cu2–N7

N6–Cu2–N7

N8–Cu2–N7

85.3(2)

90.0(2)

151.0(1)

149.1(1)

83.8(2)

146.8(2)

154.7(2)

85.8(2)

89.8(1)

85.9(2)

[a] There are two independent molecules in the asymmetric unit cell. Bonding parameters are reported for both molecules. [b] The repeat

unit is an O-amide-bridged dimer. [c] Distances/angles are for the Cu2 atom.

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S. K. Sharma, G. Hundal, R. Gupta

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Figure 6. Perspective views of the 1D polymeric chain in complexes 5 (a) and 6 (b). All hydrogen atoms have been omitted for clarity.

such pair of chains has a hydrophilic interior that leads to

the formation of channels filled with water molecules run-

ning parallel to the b axis (Figure S5b). Furthermore, each

amide oxygen atom O2 accepts a hydrogen bond from the

methanol oxygen atom O5 (Figure S5a). The water trimers

are further stabilized in the channels by O2W···O2W and

some C–H···O H-bonding interactions. Various C–H···O-

and C–H···N-type H-bonding interactions between amide

oxygen atoms, nitrogen atoms and methyl, methylene and

phenylene carbon atoms are further responsible for holding

these pairs of chains together (Table S3) and result in a

packing structure along the b axis (Figure S6).

It should be noted that the Cu^IIcomplex of a closely

related macrocyclic ligand (L¹) has been reported,^[23,24]al-

though the metal ion has a square-pyramidal geometry with

an N₄basal plane and an apical water molecule. Extensive

Figure 7. Molecular structure of complex 6 (thermal ellipsoids are

drawn at the 50% probability level). Water molecules, methanol

hydrogen bonding between the Cu^IIcomplex and water

and hydrogen atoms have been omitted for clarity.

molecules most likely prevents coordination to the O_amide

group of the neighboring complex, as observed in our case.

The average Cu–N_amidebond length in this complex is

1.926 Å, whereas the average Cu–N_aminebond length is

2.026 Å. The Cu–O_waterbond length is 2.165 Å. The

square-planar copper(II) complex of the corresponding 13-

O2W water molecules. Each O2W water molecule acts as

an H-bond donor to the carbonyl oxygen atom O3 and to

the water molecule O1W as shown in Figure S5. The inter-

molecular H-bonding interaction O2W···O1W forms water membered ligand (L²)^[23,24]has Cu–N_amideand Cu–N_amine

trimers that hold two spiral chains together. Thus, each distances of 1.905 and 1.992 Å, respectively. Furthermore,

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Nickel and Copper Complexes of Amide-Based Macrocycles

the copper(II) complex containing an analogous open- sign to charge transfer from OCH₃to Cu^II. High-energy

chain ligand^[19](reported by us previously) also has a sim- features below 310 nm are tentatively assigned as intra-li-

ilar structure to those of complexes 5 and 6, including the gand transitions.

O

_amide-bridged 1D chain. The average Cu–N_amide, Cu–

N_amineand Cu – O_amidebond lengths in this complex are

1.935, 2.075, and 2.354 Å, respectively.^[19]

Spectral Studies

The absorption spectra of complexes 1–3 in CH₃CN are

displayed in Figure 8. The Ni^IIcomplexes are deep yellow

to orange in color, and their spectra display distinct features

for the four-coordinate square-planar Ni^IIion. Three transi-

tions from the four lower-lying fully occupied d orbitals to

the upper empty d orbital are expected for a diamagnetic

Ni^IIion with d⁸electronic configuration in a square-planar

environment.^[10a,10b]However, these lower four orbitals are

often so close together in energy that individual transitions

to the upper d orbital cannot be distinguished. This results

in a single transition in the absorption spectrum,^[10a,10b]as

noted for the present complexes. Complexes 1–3 have very

similar λ_maxvalues (442–450 nm), thus indicating a similar

environment created by the ligand around the Ni ion. It is

important to mention here that complexes A–D also dis-

played a narrow range of absorption maxima (436–

444 nm).^[14]The similarity observed between the absorption

features of the nickel complexes is also reflected in their

solid-state crystal structures (see above) and solution-state

NMR spectra (see below). The high-energy features ob-

served below 310 nm could tentatively be assigned as intra-

ligand transitions.

Figure 9. UV/Vis spectra of Cu^IIcomplexes in CH₃CN: 4 (------),

5 (––––––), 6 (······), and 7 (-·-·-·).

In order to analyze the binding affinity of some potential

ligands towards the metal ion, all complexes were titrated

with Cl^–, pyridine, or 4-(dimethylamino)pyridine. No

change in the absorbance maxima was observed for any of

the complexes, thus ruling out the binding of these ligands

to the metal center. The spectra for copper complexes 4–7

were also recorded in a better coordinating solvent, such as

dmf, although they displayed similar features to those in

CH₃CN. Strain in the ring system is indicated by the high

value of the extinction coefficient and the redshift of the

absorption maxima for copper complexes with respect to

nickel complexes. The Cu^IIcomplex of ligand H₂L^OMe(7:

λ_max= 593 nm; ε = 300 ^–1cm^–1) exhibits the greatest

strain, whereas the least strain is observed for complex 4.

The solid-state EPR spectra (Figure S7) of copper com-

plexes 4–7 at liquid-nitrogen temperature exhibit the typical

axial spectra with g_ʈϾ g_Ќ.^[25]The g_ʈand g_Ќvalues for com-

plexes 4–7 were found to be 2.18 and 2.08, 2.15 and 2.06,

2.19 and 2.07, and 2.13 and 2.08, respectively. The observa-

tion of axial EPR spectra suggests anisotropy^[26]around the

copper centre, which most likely arises from coordination of

the O_amideatom from a neighboring molecule, as observed

structurally (cf. crystal structures of 5 and 6). Ruiz et

al.^[10a,10b]have reported similar EPR spectra for a series of

Cu^IIcomplexes supported with oxamide-based tetradentate

ligands. The room-temperature EPR spectra also display

similar features, as shown in Figure S7.

Figure 8. UV/Vis spectra of Ni^IIcomplexes in CH₃CN: 1 (------), 2

(······), and 3 (-·-·-·). Complex C (––––––) is shown here for com-

parison.

To investigate the solution-state structures of the nickel

1

complexes, their H and ¹³C NMR spectra were recorded

in [D₆]dmso (Figures S8 and S9 and Tables 2 and S4). All

nickel complexes are diamagnetic with an S = 0 ground

Copper complexes 4–7 display a single band in the region state, as highlighted by their sharp NMR spectra, which

573–593 nm (Figure 9), with extinction coefficients (ε) in show only minor chemical-shift differences with respect to

the range of 100–300 ^–1cm^–1. This low-energy band is the the free ligands. A comparison of the spectrum of complex

typical d–d transition band of a Cu^IIion in a square-planar C^[14]with that of complexes 1–3 shows an up-field shift of

environment and actually consists of three individual d–d around 0.39 ppm for the protons labeled f in the order 1 Ǟ

2

transitions (i.e. B_1gǞ²A_1g, B_1gǞ²B_2g, and B_1gǞ²E_1gin C Ǟ 2 Ǟ 3.^[27]This reveals a higher electron density on

D_4hsymmetry).^[10a,10b]The only exception is complex 7, the benzene ring with more electron-donating groups in the

which shows a second band at 430 nm with an extinction order Cl Ͻ H Ͻ Me Ͻ OMe. Interestingly, twisting of the

coefficient of around 1000 ^–1cm^–1that we tentatively as- -CH₂CH₂- fragment of the N,NЈ-dimethylethylenediamine

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627

S. K. Sharma, G. Hundal, R. Gupta

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1

Table 2. H NMR spectroscopic data for Ni^IIcomplexes [Ni(L^Cl)] (1), [Ni(L^Me)] (2), [Ni(L^OMe)] (3), and [Ni(L^H)] (C).^[a]

[a] Spectra recorded in [D₆]dmso. [b] Geminal coupling constant in Hz. [c] Ref.^[14]

part results in a different chemical environment for the pro- of the present systems. The electrochemical data for com-

tons attached to these carbon centers. Thus, two sets of H

signals (labeled as a and c) are observed as multiplets at δ

= 2.85 and 3.99, 2.87 and 4.05, and 2.81 and 3.94 ppm for

complexes 1–3, respectively. Our earlier nickel complexes

A–D also display a similar NMR spectral feature for the

-CH₂CH₂- fragment.^[14]Another interesting aspect of the

spectra for complexes 1–3 is the observation of an AB-type

or germinal coupling between the protons attached to the

-C(O)CH₂- fragment. The pair of protons from the -C(O)-

CH₂- fragment (d and e) appear at δ = 3.27 and 4.27 ppm

for 1, 3.32 and 4.28 for 2, and 3.21 and 4.20 ppm for com-

plex 3. The geminal coupling constant, J(H^dH^e) for com-

plexes 1, 2 and 3 was found to be 16.16, 15.30 and 16.0 Hz,

respectively. Similar values were found for our earlier Ni^II

complexes A–D (15.12–16.2 Hz).^[14]It can therefore be con-

cluded that the conformational rigidity of the macrocycle

plexes 1–7 are summarized in Table 3, and the oxidation

processes are displayed in Figures 10 and 11. All complexes

display a reversible to quasi-reversible one-electron oxidat-

ive response with lower potentials for the complexes carry-

ing electron-donating groups (Table 3). Each complex un-

dergoes a one-electron oxidation in the potential range

0.49–0.80 V (vs. SCE). As anticipated, the E values for the

Cu^IIcomplexes (4–7) are less positive than those for the

nickel complexes (1–3), thereby suggesting that the 12-mem-

bered ring is more suited for stabilization of the Cu^IIIoxi-

dation state. A dramatic influence of the peripheral substit-

uents in complexes 1–7 was observed in the CV analysis.

Thus, it was noted that on going from 1 to 3 and from 4 to

7, a potential of 350 and 145 mV, respectively, separates the

two extreme systems [Cl (1 and 4) and OCH₃(3 and 7)],

thus explaining the electronic effect on the relative accessi-

bility of the Ni^IIIand Cu^IIIstates.

Complexes 1–7 display oxidation waves corresponding to

both metal- and ligand-based oxidations. Complex 1 dis-

plays oxidation waves at 0.80 and 1.24 V, which we tenta-

tively assign to the Ni^3+/2+response and ligand oxidation,

respectively. Complex 2 displays a reversible metal-based

oxidation at 0.64 V and a ligand-based irreversible oxi-

dation at 0.96 V (E_pa), whereas complex 3 shows two revers-

ible oxidative waves at 0.48 and 0.83 V for metal- and li-

gand-centered oxidation, respectively. The significant shift

in the E₁potentials of complexes 1–3 towards less positive

values in the order [1] Ͼ [2] Ͼ [3] clearly suggests that the

first oxidation is metal-centered and leads to an Ni^IIIspe-

cies.^[14]Similarly, all copper complexes undergo a one-elec-

tron oxidation in the potential range 0.54–0.68 V (vs. SCE).

1

results in complex H NMR spectra for complexes 1–3.^[28]

1

In contrast to the H NMR spectra, the ¹³C NMR spectra

of 1–3 are quite straightforward (Table S4 and Figure S9).

Moreover, a close similarity in the ¹³C NMR chemical

shifts of identical carbon centers was observed for all com-

plexes. The observation of diamagnetic NMR spectra for

these complexes corroborates the conclusion drawn from

the absorption spectral studies, namely that the present

nickel complexes do not interact with or bind additional

axial ligands [Cl^–, pyridine, 4-(dimethylamino)pyridine]

and/or better coordinating solvents and retain their square-

planar geometry.

Electrochemical Studies

Cyclic voltammetric (CV) and controlled potential elec- The first redox responses were found to be reversible and

trolysis studies were performed on all Ni^IIand Cu^IIcom- are tentatively assigned as the metal-centered oxidation.

plexes to investigate the extent of stabilization of the M^IIIThe individual values for 4–7 were found to be 0.56, 0.68,

state and the role of electronic substituents present on the 0.54, and 0.535 V, respectively. The shift in the E₁potentials

ligand. In addition, the CV results should also help in un- for complexes 4–7 ([5] Ͼ [4] Ͼ [6] ≈ [7]) suggests that the

derstanding the accessibility of the higher oxidation states first oxidation is metal-centered and generates a Cu^IIIspe-

628

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Eur. J. Inorg. Chem. 2010, 621–636

Nickel and Copper Complexes of Amide-Based Macrocycles

Table 3. Cyclic voltammetric data^[a]for nickel(II) and copper(II) complexes 1–7 and comparison with literature.

Complex

E₁[V] (∆E_p) [mV]; n^[b]

E₂or E_pa[V]; n^[b]

Ref.

[Ni(L^Cl)] (1)

0.80 (70); 1.00

0.64 (60); 1.00

0.48 (100); 0.90

0.56 (60); 1.00

0.68 (90); 1.00

0.54 (80); 1.00

0.535(90); 0.71

0.61 (90); 0.94

0.78 (100); 0.96

0.71 (70); 1.00

0.83 (73); 1.02

0.75

1.24; 1.91

0.96; 1.98

0.83; 1.92

1.30; 1.92

1.37; 1.96

–

1.88; 1.91

1.10; 1.98

1.13; 1.96

–

1.10

1.00

1.14

–

this work

[Ni(L^Me)] (2)

[Ni(L^OMe)] (3)

[Cu(L^H)] (4)

[Cu(L^Cl)] (5)

[Cu(L^Me)] (6)

[Cu(L^OMe)] (7)

this work

[14]

A

[14]

[15]

[29]

B

C

D

E

F

0.82

0.80

0.78

G

H

[M^II(dioxo[12]aneN₄)]^[c]

[M^II(dioxo[13]aneN₄)]^[c]

[M^II(dioxo[14]aneN₄)]^[c]

[M^II(dioxo[15]aneN₄)]^[c]

0.62^[d]; 0.42^[e]

0.90^[d]; 0.56^[e]

0.80^[d]; 0.64^[e]

0.62^[d]; 0.69^[e]

–

[a] Conditions: complex approx. 1 m CH₃CN solution, TBAP supporting electrolyte approx. 100 m solution, potential vs. SCE, Pt as

the working electrode, Pt wire as auxiliary electrode, scan rate = 100 mV/s. [b] Coulombic n [number of electron(s) taking part in the

oxidation process]. [c] In water with Na₂SO₄as supporting electrolyte and glassy carbon as working electrode. [d] M = Ni^II. [e] M =

Cu^II.

Figure 10. Cyclic voltammograms of Ni^IIand Cu^IIcomplexes in

CH₃CN at a platinum working electrode. Scan rate: 100 mVs^–1;

supporting electrolyte: 0.1  TBAP.

Figure 11. Comparative cyclic voltammograms of nickel and cop-

per complexes in CH₃CN: (A) complexes C and 4, (B) complexes

1 and 5, (C) complexes 2 and 6, (D) complexes 3 and 7.

cies.^[10,14]The second oxidation potentials are irreversible

and are most likely ligand-centered. The electron-donating

substituents on the ring play an important role by shifting

the redox potential to a less positive value.^[28]

of electron-donating groups such as OCH₃stabilizes the

The E₁potential (the first oxidation process) for all Ni^IIIand Cu^IIIstate by about 200 mV. It should also be

nickel complexes (including complex C) falls within the po- noted that the corresponding Ni^3+/2+redox potentials for

tential range 0.49–0.80 V, whereas the potential range for the nickel complexes with analogous open-chain ligands

the copper complexes is 0.54–0.68 V. A comparison of the (E–H) are 0.75, 0.82, 0.80, and 0.78 V, respectively. In ad-

Ni^3+/2+redox potential of complex C (0.71 V) with that of dition, the redox potential for the [Ni/Cu(dioxo[12]aneN₄)]

the analogous copper complex 4 (0.56 V) shows that the complexes are 0.62/0.42 V (vs. SCE in H₂O),^[29]whereas the

Cu^IIIstate is more easily accessible by 150 mV.^[29,30]Overall, potentials for the analogous 13-, 14-, and 15-membered

we observe that the Cu^IIIstate is more easily accessible by macrocyclic systems are 0.90/0.56, 0.80/0.64, and 0.62/

at least 60 to 150 mV than the Ni^IIIstate. The incorporation 0.69 V, respectively.^[29]

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629

S. K. Sharma, G. Hundal, R. Gupta

FULL PAPER

Electrochemical Oxidation and Characterization of the

Oxidized Species

+

Ni^IIISpecies [1^Oxto 3^Ox

]

The singly oxidized forms of complexes 1–3 were gener-

ated electrochemically in CH₃CN and characterized by ab-

sorption and EPR spectroscopy. Electrochemical oxidation

of a solution containing the respective Ni^IIcomplex gener-

ated a metastable green to greenish-brown species, which

was stable enough to record its absorption (Figure 12) and

EPR spectra (Figure 13). The absorption spectra of these

oxidized complexes have rich features and are dominated

by a string of charge-transfer bands with ε values in the

range 500–1550 ^–1cm^–1. The EPR studies clearly indicate

the generation of an Ni^IIIspecies.

Figure 12. UV/Vis spectra of electrochemically generated Ni^IIIspe-

cies in CH₃CN: [1^{Ox +}

]

(-·-·-·), [2^{Ox +}

]

(------), [3^{Ox +}

]

(––––––), and

[C^{Ox +}(······). Species [C^{Ox +}

] ] is shown here for comparison.

Figure 13. EPR spectra of electrochemically generated Ni^IIIspecies

in CH₃CN at 100 K. Species [C^{Ox +}

] is shown here for comparison.

The oxidized species for complex 1 ([1^Ox]⁺) was gener-

ated by oxidizing the solution at 1.0 V vs. SCE, which re- served similarity between these Ni^IIIspecies and our sys-

sulted in a dark-green solution. An intense peak with λ_maxtems suggests a similar electronic structure. These authors

= 870 nm (ε ≈ 1000 ^–1cm^–1) was observed along with two suggested ligand-to-metal charge transfer as the origin of

weak features at around 764 and 575 nm. Qualitatively, this such intense features in the visible region, and they attrib-

oxidized species was also the most stable. We believe that uted the low energy of these transitions to a small energy

the presence of an electron-withdrawing group (Cl) lowers gap between the ground and excited states where MOs have

the redox-active o-benezenediamidate orbitals in energy or mainly developed on the ligand compared to those mainly

deactivates the ring, which results in forceful ejection of located on the metal center.^[31c]

electrons from the metal orbital.^[9b]In addition, the close

The oxidized species for complex 3 ([3^Ox]⁺) was gener-

proximity of the o-benezenediamidate fragment to the Ni^IIIated by oxidizing the solution at 0.70 V vs. SCE, which gave

center helps to better delocalize the unpaired spin onto the a brown solution. This solution displays very broad features

ligand’s π orbitals.^[9b]This enhanced delocalization results in the range 800–1000 nm. The absorption spectral features

in the higher stability of the green species as well as the of [3^{Ox +}are quite different to those of [1^Ox]⁺, [2^Ox]⁺, and

]

occurrence of the intense and broad absorption features in [C^Ox]⁺, thereby suggesting a different nature of the oxidized

the visible region. species (cf. EPR spectrum).

Species [2^{Ox +}The oxidized species [1^{Ox +}

was generated by oxidizing at a potential

at 0.85 V vs. SCE, which gave a green solution with λ_maxCH₃CN solution display anisotropic signals in their X-band

851 and 595 nm. The absorption spectral features for EPR spectra. The EPR spectra of the singly oxidized com-

[C^Ox]⁺were observed at 855, 580, and 430 nm.^[14]The close plexes [1^Ox]⁺, [2^{Ox +}and [3^{Ox +}

in frozen CH₃CN solution

similarity of the spectral features for [C^Ox]⁺,^[14][1^Ox]⁺, and at 100 K are shown in Figure 13. The spectra of [1^Ox]⁺and

]

to [3^{Ox +}

] generated in

=

]

[2^Ox]⁺suggests a similar electronic chromophore. The Ni^III[2^{Ox +}

] consist of a rhombic signal characteristic of a four-

species containing a tetradentate tetraamide ligand reported coordinate square-planar Ni^IIIion (d⁷low-spin system)

by Journaux and Ruiz-Garcia^[31]displays λ_maxvalues at 863 with an S = 1/2 ground state.^[32,33]The individual g values

and 993 nm for the ligand with OCH₃substituents and for [1^{Ox +}

]

and [2^{Ox +}

]

are 2.28, 2.23, and 2.008 and 2.23,

1014 nm for the ligand with CH₃substituents.^[31c]The ob- 2.197, and 2.008, respectively. The large rhombicity and the

630

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Eur. J. Inorg. Chem. 2010, 621–636

Nickel and Copper Complexes of Amide-Based Macrocycles

high average g values [g_av= (g₁+ g₂+ g₃)/3] of 2.173 and Qualitatively, this oxidized species was found to be the most

2.145 for [1^{Ox +}and [2^Ox]⁺, respectively, unambiguously stable, as was also the case for the analogous nickel system.

]

indicate that the oxidation is located at the Ni center.^[27,31]The presence of electron-withdrawing groups (Cl) on the

For comparison, the g values for [C^{Ox +}

are 2.300, 2.225, ring most likely lowers the redox-active benzene orbital in

and 2.008 (g_av= 2.178).^[14]In a similar manner, the ob- energy, which means that removal of electrons from the

served g values for [E^{Ox +}and [F^{Ox +}were 2.278, 2.232, metal orbital is easier.^[14,28]In addition, the close proximity

and 2.009 and 2.300, 2.230, and 2.015, respectively.^[15]The of the o-benezenediamidate fragment to the Cu^IIIcenter

observed g values for [1^{Ox +}and [2^{Ox +}

are in good agree- helps to delocalize the unpaired spin onto the ligand’s π

ment with those for other nickel(III) complexes with a sim- orbitals.^[14,31]

ilar electronic ground state,^[14,15,31]whereas [3^{Ox +}

displays Complex 6 was oxidized in a similar fashion at 0.74 V

g values of 2.140 and 2.008 and a g_avvalue of 2.074, which to obtain a brown species ([6^Ox]⁺) with λ_max= 470 (ε =

is quite close to that for a free electron.^[27,31c,33]In contrast 1200 ^–1cm^–1) and

shoulder at 380 nm (ε

]

a

=

to the higher intensity noted for the organic-based radical, 1900 ^–1cm^–1).^[34]Finally, complex 7 was oxidized at 0.75 V

the reason for the observed low intensity of the [3^Ox]⁺EPR to generate a brown-colored solution with λ_max= 788 nm

signal is not clear. The observed EPR signal for [3^Ox]⁺sug- (ε = 270 ^–1cm^–1) and a weak shoulder at 465 nm (ε =

gests that the SOMO may have significantly developed on 600 ^–1cm^–1). As was the case for the MeO-substituted

the ligand, although with some contribution from the metal nickel complex [3^Ox]⁺, the MeO-substituted copper com-

center.^[28,31c][3^{Ox +}may therefore best be described as a plex [7^{Ox +}

] ] also displays a different absorption spectrum,

nickel(II) complex with a semiquinone-type ligand-based thus indicating a different chromophore than in [4^Ox]⁺,

radical. The different nature of these oxidized species is also [5^Ox]⁺, or [6^Ox]⁺.

reflected in the different absorption spectrum of species

The absorption spectra of the solution-generated Cu^III

species with tetraanionic, tetradentate oxamide-based li-

gands reported by Journaux and co-workers have features

at around 380, 435–460, and 540–600 nm.^[10]A similar situ-

ation has been observed for the Cu^IIIspecies [4^Ox]⁺, [5^Ox]⁺,

and [6^Ox]⁺. These authors suggested that three transitions

(from four low-lying fully occupied d orbitals to the upper

empty d orbital) would be expected for a diamagnetic Cu^III

ion with a d⁸electronic configuration in a square-planar

environment. However, their closeness in energy may result

in the overlap of these three transitions.^[10a,10b,34]This is the

situation, for example, for the isoelectronic nickel(II) com-

plexes 1–3, where a single absorption feature is observed

[3^Ox]⁺compared with those for [1^Ox]⁺, [2^Ox]⁺and [C^Ox]⁺.

+

Cu^IIISpecies [4^Oxto 7^Ox

]

The singly oxidized forms of complexes 4–7 were gener-

ated electrochemically in CH₃CN solution and charac-

terized by absorption spectroscopy (Figure 14). The absorp-

tion spectra of these oxidized complexes display several

charge-transfer bands,^[34]some of which are exceptionally

intense (ε values up to 15500 ^–1cm^–1). The oxidized species

of complex 4 ([4^Ox]⁺) was generated by oxidizing the solu-

tion at 0.78 V vs. SCE, which gave a brown solution. This

solution displays absorption features at λ = 455 (ε =

1050 ^–1cm^–1) and 372 nm (ε = 1500 ^–1cm^–1).^[34]The new

features are quite different from the original Cu^IIcomplex

(λ_max= 573 nm; ε = 110 ^–1cm^–1), thus indicating that oxi-

dation probably results in a change of geometry.^[10]

in the range 442–450 nm. Interestingly, [7^{Ox +}

] shows quite

different spectra, as is also the case for the analogous nicke-

l(III) species [3^Ox]⁺, thereby strongly suggesting the dif-

ferent nature of the oxidized species.

Our efforts to characterize the doubly oxidized species

were unsuccessful, owing to their very unstable nature. It

should be noted, however, that all these redox processes are

one-electron in nature, as determined by the coulometric

experiments.

Chemical Oxidation and Justification of Electrochemical

Findings

The accessible redox potentials (cf. Table 3) of complexes

1–7 and the successful electrochemical generation of the

singly oxidized forms [1^{Ox +}to [7^{Ox +}

] ] impelled us to at-

[35]

Figure 14. UV/Vis spectra of electrochemically generated Cu^IIIspe-

tempt chemical oxidation with Cu(OTf)₂at the first oxi-

dation potential (E_1/2= 0.8 V in CH₃CN vs. SCE). Thus,

addition of 1.2 equiv. of Cu(OTf)₂to a CH₃CN solution of

the respective Ni^IIand Cu^IIcomplex resulted in a clean one-

cies in CH₃CN: [4^{Ox +}(––––––), [5^{Ox +}(------), [6^{Ox +}

] ] ] (······), and

[7^{Ox +}

] (-·-·-·).

The oxidized species [5^{Ox +}was generated at a potential electron oxidation.^[14,15]Chemical oxidation of solutions

]

of 0.88 V vs. SCE and produced a brown-colored solution containing the respective Ni complexes generated green to

similar to that for [4^Ox]⁺, with absorption bands at λ = 466 greenish-brown species, as observed electrochemically. A

(ε = 10200 ^–1cm^–1) and 377 nm (ε = 15500 ^–1cm^–1).^[34]brown-colored species was generated in a similar fashion in

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631

S. K. Sharma, G. Hundal, R. Gupta

FULL PAPER

were purified by washing with 5% sodium carbonate solution fol-

lowed by water and finally drying with anhydrous CaCl₂, before

final reflux and distillation. Petroleum ether (boiling range: 60–

80 °C) and hexanes (boiling range: 60–80 °C) were dried by re-

fluxing and distilling from sodium wire. N,NЈ-Bis(chloroacetyl)-1,2-

phenylenediamine and N,NЈ-bis(chloroacetyl)-4,5-dimethoxy-1,2-

phenylenediamine were synthesized according to published pro-

cedures.^[36,37]

the case of copper complexes. The UV/Vis spectra of the

chemically oxidized species were recorded and found to be

identical to the electrochemically generated ones, as shown

in Figures 12 and 14.

Conclusions

The present work has reported the synthesis and charac-

terization of several square-planar Ni^IIand square-pyrami-

dal Cu^IIcomplexes with amine/amide-based macrocyclic li-

gands. The important findings of the present study can be

summarized as follows:

Physical Measurements: Conductivity measurements were per-

formed in organic solvents by using a digital conductivity bridge

from Popular Traders, India (model number: PT-825). Elemental

analysis data were obtained by using an Elementar Analysen Sy-

steme GmbH Vario EL-III instrument. NMR spectra were re-

ocrded with an Avance Bruker (300 MHz) instrument. IR spectra

(as either a KBr pellet or a mull in mineral oil) were recorded by

using a Perkin–Elmer FTIR-2000 spectrometer. Absorption spectra

were recorded by using a Perkin–Elmer Lambda-25 spectropho-

tometer. X-band EPR spectra were recorded by using either a Var-

ian 109 C or a Bruker EMX 1444 spectrometer fitted with a quartz

dewar vessel for measurements at 77 K and 120 K, respectively. The

EPR spectra were calibrated with diphenylpicrylhydrazyl radical

(DPPH, g = 2.0037). Solution-state magnetic susceptibilities were

obtained by the Evans technique^[18]in dmf with a Hitachi R-600

FT NMR (60 MHz) spectrometer. Diamagnetic corrections were

applied with the use of appropriate constants. ESI mass spectra

were obtained by using an LC-TOF (KC-455) mass spectrometer.

(1) To the best of our knowledge, this is the first systematic

investigation aimed at understanding the structural, spec-

troscopic and redox properties of Ni^IIand Cu^IIions bound

to a set of 12-membered macrocyclic ligands containing

electron-donating and -withdrawing substituents.

(2) The crystal structures of these complexes show that the

Cu–N_amidebonds are shorter than the Ni–N_amidebonds.

Furthermore, the Cu ion lies around 0.5 Å above the basal

plane of the macrocyclic ligand, whereas the Ni ion is only

about 0.17 Å above the basal plane.

(3) The Ni^IIand Cu^IIcomplexes are capable of undergoing

one- and two-electron oxidations that are successively met-

al- and ligand-centered.

Electrochemical Measurements: Cyclic voltammetric and coulomet-

ric experiments were performed by using a CH instruments electro-

chemical analyzer (Model No. 600B or 1100A Series). The cell con-

tained a glassy-carbon or a Pt working electrode, a Pt wire auxiliary

electrode, and a saturated calomel electrode (SCE) as reference

electrode. A salt bridge [containing supporting electrolyte, tetra-n-

butylammonium perchlorate (TBAP) dissolved in either MeCN or

dmf] was used to connect the SCE with the electrochemistry solu-

tion.^[38]For constant-potential electrolysis experiments a Pt mesh

was used as the working electrode. The solutions were ca. 1 m in

complex and ca. 0.1  in supporting electrolyte (TBAP). Under our

experimental conditions, the E_1/2values (in V) for the couple Fc⁺/

Fc was found to be 0.40 in MeCN vs. SCE.^[39]

(4) The electrochemical results indicate that the Ni^III/IIpo-

tentials are more positive than the Cu^III/IIpotentials.

(5) Electron-donating substituents on the ring shift the re-

dox potentials towards less positive values or better stabilize

the higher oxidation state of a metal ion; out of three sub-

stituents, OCH₃was found to be the best.

(6) The Ni^IIIand Cu^IIIspecies can be generated in solution

both electrochemically and chemically [after oxidizing with

Cu(OTf)₂] and have been shown to have rich spectroscopic

features.

(7) The metastable 1e^–-oxidized species [1^Ox]⁺, [2^Ox]⁺, and

[4^Ox]⁺to [6^Ox]⁺are concluded to be Ni^IIIand Cu^IIIspecies

on the basis of their absorption spectral features.

(8) The anisotropic EPR spectra for nickel species indicate

a Ni^IIIion in a square-planar environment.

N,NЈ-Bis(chloroacetyl)-4,5-dimethyl-o-phenylenediamine:

4,5-Di-

methyl-o-phenylenediamine (1.0 g, 7.0 mmol) in toluene (60 mL)

was stirred at 60–65 °C, then chloroacetyl chloride (1.8 g, 14 mmol)

was added dropwise and the solution refluxed for 6 h. The solid

thus obtained was filtered, washed with toluene and petroleum

ether, and dried. Yield: 1.79 g (85%). M.p. 194–198 °C. FT-IR

(9) The spectroscopic data for [3^{Ox +}and [7^Ox]⁺, both of

]

which bear an MeO group on the phenylene ring, point

towards a metal complex with a semiquinone-type ligand-

based radical.

(10) It can therefore be concluded that changing the elec-

tronic substituent on the ligand shifts the locus of the oxi-

dation.

(KBr disk): ν = 3288, 3048, 2943, 2921, 2863, 1703 cm^–1. ¹H NMR

˜

([D₆]dmso, 60 MHz, 25 °C): δ = 2.30 (s, 6 H, CH₃), 4.30 [s, 4 H,

CH₂C(O)], 7.45 (s, 2 H, aromatic H), 9.70 (br. s., 2 H, NH) ppm.

MS (EI⁺): calcd. for C₁₂H₁₄Cl₂N₂O₂289.16; found for [M⁺], [M⁺

+ 2] 288.15, 290.14.

N,NЈ-Bis(chloroacetyl)-4,5-dichloro-o-phenylenediamine: This rea-

gent was prepared in a similar manner to above from 4,5-dichloro-

o-phenylenediamine (1.0 g, 5.0 mmol) and chloroacetyl chloride

(1.4 g, 10 mmol). Yield: 1.29 g (70%). M.p. 155–160 °C. FT-IR

Experimental Section

(KBr disk): ν = 3254, 3111, 3039, 1688 cm^–1. ¹H NMR ([D ]dmso,

˜

6

Materials and Reagents: All reagents were obtained from commer-

cial sources and used as received unless otherwise stated. N,N-Di-

methylformamide (dmf) was dried and distilled from molecular

sieves (4 Å) and then stored over sieves. Acetonitrile was dried by

distillation from anhydrous CaH₂. Diethyl ether was dried by re-

fluxing in the presence of sodium wire under an inert gas. Ethanol

and methanol were distilled from magnesium ethoxide and magne-

sium methoxide, respectively. Chloroform and dichloromethane

60 MHz, 25 °C): δ = 4.30 [s, 4 H, CH₂C(O)], 7.90 (s, 2 H, aromatic

H), 9.89 (br. s.,

2

H, NH) ppm. MS (EI⁺): calcd. for

C₁₀H₈Cl₄N₂NaO₂352.98; found for [M⁺], [M + 2], [M + 4] 350.08,

352.07, 354.08.

N,NЈ-Bis(chloroacetyl)-4,5-dimethoxy-o-phenylenediamine:

This

compound was prepared according to a slightly modified literature

procedure.^[35,36]Yield: 9.85 g (70%). FT-IR (KBr disk): ν = 3260,

˜

632

www.eurjic.org

Eur. J. Inorg. Chem. 2010, 621–636

Nickel and Copper Complexes of Amide-Based Macrocycles

1

3072, 3006, 2961, 2835, 1749 cm^–1. H NMR ([D₆]dmso, 60 MHz,

filtered and dried under vacuum. Yield: 0.082 g (45%).

C₁₄H₁₆Cl₂N₄NiO₂(401.92): calcd. C 41.82, H 3.98, N 13.94; found

25 °C): δ = 4.0 (s, 6 H, OCH₃), 4.32 [s, 4 H, CH₂C(O)], 7.02 (s, 2

H, aromatic H), 8.30 (br. s., 2 H, NH) ppm. MS (EI⁺): calcd. for

C₁₂H₁₄Cl₂N₂O₄321.15; found for [M + Na⁺] 344.00.

C 41.42, H 4.41, N 13.77. FT-IR (KBr disk): ν = 3400, 2933,

˜

1632 cm^–1. Conductivity (CH₃CN, ca. 1 m solution, 298 K): Λ_M

=

20 Ω^–1cm²mol^–1. UV/Vis (CH₃CN): λ_max(ε)

= 275 nm

H₂L^Cl: LiBr (0.57 g, 6 mmol), Na₂CO₃(2.54 g, 24 mmol) and N,NЈ-

bis(chloroacetyl)-4,5-dichloro-o-phenylenediamine (1.0 g, 3 mmol)

were mixed in MeCN (140 mL) and the mixture refluxed with stir-

ring for 1 h. A solution of N,NЈ-dimethylethylenediamine (0.26 g,

3 mmol) in MeCN (20 mL) was then added. The resulting mixture

was refluxed whilst stirring for an additional 48 h. The mixture was

cooled, filtered, and the solvent removed under reduced pressure

to afford a sticky material. The crude product was further purified

by column chromatography on silica gel (100–200 mesh) with 3–

4% MeOH/CHCl₃(R_f= 0.46) to give a white solid. Yield: 0.230 g

(22%). An analytically pure product (in ca. 75% yield) was ob-

tained by recrystallizing the crude product by layering the CHCl₃

(34200 ^–1cm^–1), 298 (25400), 313 sh (18690), 329 (12400), 442

(460). MS (EI⁺): calcd. for C₁₄H₁₆Cl₂N₄NiO₂401.90; found for

{[Ni(L^Cl)⁺], [Ni(L^Cl) + 2], [Ni(L^Cl) + 4]} 399.4, 402.4, 404.4. ¹H

NMR ([D₆]dmso, 300 MHz, 25 °C): δ = 2.85 (m, 2 H, CH₂), 2.62

(s, 6 H, CH₃), 3.99 (m, 2 H, CH₂), 3.27 [d, 16.15 Hz, 2 H,

CH₂C(O)], 4.27 [d, 16.18 Hz, 2 H, CH₂C(O)], 7.62 (s, 2 H, Ar-f)

ppm. ¹³C NMR ([D₆]dmso, 75.46 MHz): δ = 47.78 (CH₃), 59.86

(CH₂CH₂), 69.50 [C(O)CH₂], 119.12 (Ar-j), 121.23 (Ar-k), 142.43

(Ar-i), 172.46 (C=O) ppm.

[Ni^II(L^Me)] (2): This complex was synthesized according to a similar

procedure to that for 1. The product was isolated as dark yellow

blocks. Yield: 0.085 g (42%). C₁₆H₂₂N₄NiO₂(361.09): calcd. C

53.23, H 6.09, N 15.53; found C 53.08, H 6.62, N 15.61. FT-IR

solution with hexane. M.p. 135–140 °C. FT-IR (KBr disk): ν =

˜

3344, 2947, 2840, 1673 cm^–1. H NMR (CDCl₃, 300 MHz, 25 °C):

1

(KBr disk): ν = 2990, 2953, 2921, 1627, 1585, 1485 cm^–1. Conduc-

δ = 2.50 (s, 6 H, CH₃), 2.70 (s, 4 H, CH₂CH₂), 3.23 [s, 4 H,

CH₂C(O)], 7.79 (s, 2 H, aromatic H), 9.54 (br. s., 2 H, NH) ppm.

MS (EI⁺): calcd. for C₁₄H₁₈Cl₂N₄O₂345.23; found for [M⁺], [M +

2], [M + 4] 344.6, 346.6, 348.6 (6:9:1) and for [H₂L^Cl+ Na⁺] 366.5,

368.56, 370.58.

˜

tivity (CH₃CN, ca. 1 m solution, 298 K): Λ_M= 30 Ω^–1cm²mol^–1.

UV/Vis (CH₃CN): λ_max(ε) = 214 nm (40600 ^–1cm^–1), 262 (15100),

270 (15270), 290 (12800), 318 sh (5900), 445 (245). UV/Vis (dmf):

λ_max(ε) = 270 nm (13000 ^–1cm^–1), 292 (11140), 319 sh (4750), 444

(200). MS (EI⁺): calcd. for C₁₆H₂₂N₄NiO₂360.693; found for

H₂L^Me: This ligand was synthesized in a similar manner to H₂L^Cl

from LiBr (3.05 g, 35 mmol), Na₂CO₃(15.0 g, 140 mmol), N,NЈ-

bis(chloroacetyl)-4,5-dimethyl-o-phenylenediamine (5.09 g, 18

mmol), and N,NЈ-dimethylethylenediamine (1.55 g, 18 mmol). The

crude product was further purified by column chromatography on

silica gel (100–200 mesh) with 2–3% MeOH/CHCl₃(R_f= 0.44) to

give a white solid. Yield: 1.8 g (33%). An analytically pure product

(in ca. 85% yield) was obtained by recrystallizing the crude product

by layering the CHCl₃solution with hexane. M.p. 120–130 °C. FT-

1

[Ni(L^Me) + H⁺] 362.57. H NMR ([D₆]dmso, 300 MHz, 25 °C): δ

= 2.71 (s, 6 H, CH₃), 2.87 (m, 2 H, CH₂), 3.32 [d, 14.9 Hz, 2 H,

CH₂C(O)], 4.05 (m, 2 H, CH₂), 4.28 [d, 15.7 Hz, 2 H, CH₂C(O)],

2.08 (s, 6 H, Ar-CH₃), 7.95 (s, 2 H, Ar-f) ppm. ¹³C NMR ([D₆]-

dmso, 75.46 MHz, 25 °C): δ = 18.82 (Ar-CH₃), 47.72 (CH₃), 59.74

(CH₂CH₂), 69.53 [C(O)CH₂], 120.23 (Ar-k), 127.27 (Ar-i), 140.2

(Ar-i), 171.10 (C=O) ppm.

[Ni^II(L^OMe)] (3): H₂L^OMe(0.10 g, 0.2979 mmol) was dissolved in

MeOH (5 mL) then treated with solid NaOH (0.024 g,

IR (KBr disk): ν = 3239, 2944, 2842, 1667 cm^–1. ¹H NMR (CDCl ,

˜

3

300 MHz, 25 °C): δ = 2.21 (s, 6 H, CH₃), 2.34 (s, 6 H, CH₃), 2.66

(s, 4 H, CH₂CH₂), 3.18 [s, 4 H, CH₂C(O)], 7.53 (s, 2 H, aromatic

H), 9.45 (br. s., 2 H, NH) ppm. MS (EI⁺): calcd. for C₁₆H₂₄N₄O₂

304.39; found for [H₂L^Me+ H⁺] 304.10.

0.595 mmol).

A

solution of [Ni(H₂O)₆](ClO₄)₂(0.11 g,

0.2979 mmol) in MeOH (6 mL) was then added dropwise and the

resulting orange-yellow solution stirred at room temperature for

2 h. The solvent was removed under reduced pressure and the crude

compound isolated after washing with diethyl ether. Recrystalli-

zation was performed by dissolving the crude compound in MeCN

and diffusing diethyl ether. The orange crystalline product thus ob-

tained was filtered, washed with diethyl ether and dried under

vacuum. Yield: 0.02 g (18%). C₁₆H₂₂N₄NiO₄(393.08): calcd. C

48.89, H 5.64, N 14.25; found C 49.08, H 5.92, N 14.61. FT-IR

H₂L^OMe: This ligand was synthesized in a similar manner to H₂L^Cl

from LiBr (0.57 g, 6 mmol), Na₂CO₃(3.0 g, 24 mmol), N,NЈ-

bis(chloroacetyl)-4,5-dimethoxy-o-phenylenediamine

mmol), and N,NЈ-dimethylethylenediamine (0.26 g, 3 mmol). The

crude product was purified by column chromatography on silica

gel (100–200 mesh) with 1% MeOH/CHCl₃(R_f= 0.53) to give a

white solid after layering a CH₂Cl₂solution with hexane. Yield:

(1.0 g,

3

(KBr disk): ν = 3567, 2964, 2922, 1624, 1583, 1103 cm^–1. Conduc-

˜

tivity (CH₃CN, ca. 1 m solution, 298 K): Λ_M= 20 Ω^–1cm²mol^–1.

UV/Vis (CH₃CN): λ_max(ε) = 213 nm (23480 ^–1cm^–1), 257 (15700),

292 (12520), 324 sh (6560), 450 (210). MS (EI⁺): calcd. for

C₁₆H₂₂N₄NiO₄393.06; found for [Ni(L^OMe) + H⁺] 392.51. ¹H

NMR ([D₆]dmso, 300 MHz, 25 °C): δ = 2.60 (s, 6 H, CH₃), 2.81

(m, 2 H, CH₂), 3.21 [d, 16.1 Hz, 2 H, CH₂C(O)], 3.94 (m, 2 H,

CH₂), 4.20 [d, 15.9 Hz, 2 H, CH₂C(O)], 3.58 (s, 6 H, OCH₃), 7.23

(s, 2 H, Ar-f) ppm. ¹³C NMR ([D₆]dmso, 75.46 MHz, 25 °C): δ =

55.91 (OCH₃), 47.91 (CH₃), 59.79 (CH₂CH₂), 69.58 [C(O)CH₂],

142.58 (Ar-k), 135.60 (Ar-i), 104.87 (Ar-j), 171.36 (C=O) ppm.

[Cu^II(L^H)] (4): H₂L^H(0.15 g, 0.54 mmol) was dissolved in dmf

(15 mL) with stirring, and solid NaH (0.03 g, 1.08 mmol) was

added under nitrogen. The resulting mixture was stirred until H₂

evolution ceased. Solid Cu(OTf)₂(0.20 g, 0.54 mmol) was added to

this mixture, and the resulting dark blue solution was stirred at

room temperature for 3 h. The solvent was evaporated under re-

duced pressure and the crude compound isolated after washing

with diethyl ether. The crude compound was further dissolved in

0.33 g (30%). FT-IR (KBr disk): ν = 3241, 2919, 2837, 2781, 1666,

˜

1

1599, 1144 cm^–1. H NMR (CDCl₃, 300 MHz, 25 °C): δ = 2.39 (s,

6 H, CH₃), 2.67 (s, 4 H, CH₂CH₂), 3.24 [s, 4 H, CH₂C(O)], 3.84 (s,

6 H, OCH₃), 7.46 (s, 2 H, aromatic H), 9.29 (br. s, 2 H, NH) ppm.

MS (EI⁺): calcd. for C₁₆H₂₄N₄O₄336.39; found for [H₂(L^OMe) +

H⁺] 336.7 and for [H₂(L^OMe) + Na⁺] 358.6.

[Ni^II(L^Cl)] (1): H₂L^Cl(0.20 g, 0.579 mmol) was dissolved in dmf

(15 mL) with stirring then treated with solid NaH (0.03 g,

1.275 mmol) under nitrogen. The resulting mixture was stirred until

H₂evolution ceased. A solution of NiCl₂(0.075 g, 0.579 mmol) in

dmf (10 mL) was then added. The resulting dark yellow solution

was stirred at room temperature for 3 h. The solvent was evapo-

rated under reduced pressure and the crude compound isolated af-

ter washing with diethyl ether. The crude compound thus obtained

was dissolved in MeCN (15 mL) and passed through a pad of Ce-

lite on a medium-porosity frit. The filtrate was concentrated to one

third of its original volume, and diffusion of diethyl ether resulted

in a dark yellow crystalline product after 1 d. The product was

Eur. J. Inorg. Chem. 2010, 621–636

www.eurjic.org

633

S. K. Sharma, G. Hundal, R. Gupta

FULL PAPER

MeOH (15 mL) and passed through a pad of Celite on a medium-

porosity frit. The filtrate was concentrated to one third of its origi-

nal volume, and diffusion of diethyl ether resulted in a dark blue

crystalline product in 1 d. The product was filtered and dried under

vacuum. Yield: 0.082 g (45%). C₁₄H₁₈CuN₄O₂(337.87): calcd. C

49.77, H 5.37, N 16.58; found C 50.22, H 5.62, N 16.16. FT-IR

rect methods and refined by full-matrix least-squares refinement

techniques on F². All non-hydrogen atoms were refined anisotropi-

cally. All hydrogen atoms were attached with U_isovalues of 1.2

times (for methylene and phenylene carbon atoms) and 1.5 times

(methyl carbon atoms) the U_isovalues of their respective carrier

atoms. Intensity data for complexes 5 and 6 were collected by using

a Bruker SMART APEX CCD diffractometer at 100(2) K with

graphite-monochromated Mo-K_αradiation (λ = 0.71073 Å).^[40,41]

(KBr disk): ν = 3424, 2918, 1628, 1564 cm^–1. Conductivity

˜

(CH₃CN, ca. 1 m solution, 298 K): Λ_M= 35 Ω^–1cm²mol^–1. UV/

Vis (CH₃CN): λ_max(ε) = 273 nm (4860 ^–1cm^–1), 297 (12160), 573 Intensity data were corrected for Lorentz polarization effects, and

(110). UV/Vis (dmf): λ_max(ε) = 275 nm (15540 ^–1cm^–1), 298

(7450), 573 (240). MS (EI⁺): calcd. for C₁₄H₁₈CuN₄O₂337.87;

found for [CuL^H+ Na⁺] and [CuL^H)₂+ Na⁺] 360.27 and 697.60.

an empirical absorption correction (SADABS) was applied.^[42]The

structures were solved with SIR-97, expanded by Fourier-difference

syntheses and refined with SHELXL-97, incorporated in the

WinGX 1.64 crystallographic software package.^[43]Hydrogen

atoms were placed in idealized positions and treated by using a

riding-model approximation with displacement parameters derived

from those of the atoms to which they are bonded. All non-hydro-

gen atoms were refined with anisotropic thermal parameters by

full-matrix least-squares procedures on F². Convergence was mea-

sured by the factors R and R_w, where R = Σ(||F_o| – |F_c||)/Σ|F_o| and R_w

[Cu^II(L^Cl)] (5): This complex was synthesized according to a similar

procedure to that for 4. The product was isolated as royal blue

blocks. Yield: 0.075 g (45%). C₁₄H₂₃Cl₂CuN₄O_5.5(including

3.5H₂O): calcd. C 35.79, H 4.93, N 11.90; found C 35.77, H 4.89, N

11.92. FT-IR (KBr disk): ν = 3426, 2925, 1613 cm^–1. Conductivity

˜

(CH₃CN, ca. 1 m solution, 298 K): Λ_M= 30 Ω^–1cm²mol^–1. UV/

Vis (CH₃CN): λ_max(ε) = 575 nm (210 ^–1cm^–1). UV/Vis (CH₃OH):

λ_max(ε) = 269 nm (22400 ^–1cm^–1), 307 sh (7440), 587 (240). UV/

Vis (dmf): λ_max(ε) = 280 nm (20110 ^–1cm^–1), 320 (7690), 578

(200).

2

2 2

= {Σ[w(F_o– F_c) ]/Σ[w(F_o²)²]}^1/2. The crystal quality of complex 2

was not very good, and a number of crystals were tried before

measuring the present data set. This poor crystal quality is reflected

in the rather high value of R_int(0.4898) and an A-evel error in the

CIF file. For complex 6, a total of 22908 reflections were collected,

of which 16450 were unique and 11453 were considered observed.

An empirical absorption correction was applied by using SAD-

ABS.^[41]The structure was initially solved in the triclinic space

[Cu^II(L^Me)] (6): This complex was synthesized according to a sim-

ilar procedure to that for 4. The product was isolated as royal blue

blocks. Yield: 0.078 g (45%). C₁₆H₂₅CuN₄O_3.5(including 1.5H₂O):

calcd. C 48.91, H 6.41, N 14.26; found C 48.91, H 6.36, N 14.26.

¯

group P1 with an R factor of 0.12 for observed reflections, al-

FT-IR (KBr disk): ν = 3434, 2916, 1604 cm^–1. Conductivity (dmf,

˜

though the Addsym command in Platon showed additional sym-

metry in the lattice. The data were then transformed to the mono-

clinic space group C2/c and the structure solved by the heavy-atom

method with Patterson maps in SHELX-86. It was refined by the

SHELXL-97 package in the WinGX program.^[43]The structure has

two crystallographically independent units, one of which shows

high disorder in four atoms of one of the phenyl groups, two methyl

groups C29 and C30 attached to this group, one methylene group

C26 and two lattice water molecules O1W and O2W. This disorder

in the phenyl ring C17–C22 could be resolved for four of the atoms

(C18–C21) and methyl groups C29 and C30 by splitting each of

these atoms into two, but not for the water molecules, which had

higher U_isovalues. Treatment of this disorder did not help to im-

prove the model to any significant extent, therefore the final model

omitted this treatment, and the phenyl group C17–C22 was refined

as a rigid group. All non-hydrogen atoms were refined anisotropi-

cally, except for the two water molecules, which were refined iso-

tropically with a fixed U_isovalue of 0.25. The hydrogen atoms of

these two water molecules were located from the difference-Fourier

map, not refined and assigned a U_isovalue of 1.2 times that of the

oxygen atoms. They were fixed at a distance of 0.926(3) Å from

their respective oxygen atoms. All other hydrogen atoms were fixed

geometrically and were not refined. The CIF file shows a few “A”-

level errors, which are due to the above-mentioned disorder and are

explainable. Intermolecular C–H···Cl and C–H···O contacts were

examined with the DIAMOND 2.0 package.^[44]C–H distances were

normalized along the same vectors to the neutron-derived values

of 1.083 Å. CCDC-735978 (5), -735979 (6), -735980 (1), and

-735981 (2) contain the supplementary crystallographic data for

this paper. These data can be obtained free of charges from The

Cambridge Data Center via www.ccdc.cam.ac.uk/data_request/cif.

ca. 1 m solution, 298 K): Λ_M

=

10 Ω^–1cm²mol^–1. UV/Vis

(CH₃CN): λ_max(ε) = 575 (220 ^–1cm^–1). UV/Vis (dmf): λ_max(ε) =

274 (21590 ^–1cm^–1), 307 (8420), 573 (220). MS (EI⁺, m/z): calcd.

for C₁₆H₂₂CuN₄O₂365.92; found for [CuL^Me+ H⁺] and [CuL^Me

+ Na⁺] 366.583 and 388.547.

[Cu^II(L^OMe)] (7): H₂L^OMe(0.10 g, 0.2979 mmol) was dissolved in

MeOH (5 mL) and treated with solid NaOH (0.03 g, 0.60 mmol)

whilst stirring.

A

solution of [Cu(H₂O)₆](ClO₄)₂(0.11 g,

0.2979 mmol) in MeOH (6 mL) was then added dropwise and the

resulting green solution stirred at room temperature for 2 h. The

solvent was removed under reduced pressure, and the crude com-

pound was isolated after washing with diethyl ether. Recrystalli-

zation was achieved by dissolving the crude compound in MeCN

and diffusing diethyl ether. The green product thus obtained was

filtered, washed with diethyl ether and dried under vacuum. Yield:

0.06 g (55%). C₁₇H₂₆CuN₄O₅(including 1CH₃OH): calcd. C 47.49,

H 6.10, N 13.03; found C 47.10, H 6.44, N 13.26. FT-IR (KBr

disk): ν = 3433, 2926, 1562, 1511, 1132 cm^–1. Conductivity

˜

(CH₃CN, ca. 1 m solution, 298 K): Λ_M= 20 Ω^–1cm²mol^–1. UV/

Vis (CH₃CN): λ_max(ε) = 430 nm (1000 ^–1cm^–1), 593 (300). UV/

Vis (CH₃OH): λ_max(ε) = 294 nm (5230 ^–1cm^–1), 326 (2460), 424

(830), 593 (270).

Crystallography: Single crystals suitable for X-ray diffraction stud-

ies were grown by vapor diffusion of diethyl ether into a CH₃CN

(for 1 and 2) or MeOH solution (for 5 and 6) of the complexes

(Table 4). Intensity data for complexes 1 and 2 were collected at

295 K by using a Siemens P4 X-ray diffractometer in θ-2θ scan

mode with graphite-monochromated Mo-K_αradiation. A total of

13300 reflections were measured for complex 2, of which 5922 were

unique and 3977 were considered observed [I Ͼ 2σ (I)]. For com-

plex 1, a total of 3242 reflections were measured, of which 3041

were unique and 2742 were considered observed. The data were

corrected for Lorentz and polarization effects and a ψ-scan absorp-

tion correction was also applied. The structures were solved by di-

Supporting Information (see footnote on the first page of this arti-

cle): Figures showing crystal structures, packing diagrams, and

weak interactions; NMR spectra; EPR spectra; tables of H-bond-

ing interactions and NMR spectroscopic data.

634

www.eurjic.org

Eur. J. Inorg. Chem. 2010, 621–636

Nickel and Copper Complexes of Amide-Based Macrocycles

Table 4. Crystallographic data for Ni^IIcomplexes [Ni(L^Cl)]·H₂O (1) and [Ni(L^Me)] (2) and Cu^IIcomplexes [Cu(L^Cl)] (5) and [Cu(L^Me)]·

2H₂O·CH₃OH (6).

[Ni(L^Cl)] (1·H₂O)

[Ni(L^Me)] (2)

[Cu(L^Cl)] (5)

[Cu(L^Me)] (6·2H₂O·CH₃OH)

Empirical formula

Formula mass

T [K]

C₁₄H₁₈Cl₂N₄NiO₃

419.93

295(2)

C₁₆H₂₂N₄NiO₂

361.07

295(2)

C₁₄H₁₆Cl₂CuN₄O₂

406.75

100(2)

C₆₆H₁₀₂N₁₆O₁₃Cu₄

1581.82

100(2)

Crystal system

Space group

triclinic

P1

monoclinic

P2₁/c

monoclinic

P2₁/c

monoclinic

C2/c

¯

Color, shape

a [Å]

b [Å]

c [Å]

α [°]

β [°]

yellow, prism

9.5602(10)

9.6891(12)

10.5312(13)

84.869(7)

69.457(8)

63.919(6)

818.01(17)

2

1.705

1.534

0.0368

0.0914

yellow, prism

8.719(8)

12.465(6)

29.922(13)

90

95.03

90

3239(4)

8

1.481

blue, block

11.9992(10)

14.1922(11)

10.0039(8)

90

114.224(10)

90

1553.6(2)

4

1.739

1.764

0.0504

0.1311

1.129

blue, block

47.699(10)

9.018(5)

17.330(5)

90

111.024(5)

90

6958(5)

4

1.510

1.281

0.0982

0.2319

1.087

γ [°]

V [Å³]

Z

D_calcd.[gcm^–3]

Absorption coefficient [mm^–1]

1.213

R^[a]

0.0802

0.2245

1.067

[b]

R_w

GOF on F²

1.090

[a] R = Σ||F_o| – |F_c||/Σ|F_o|. [b] R_w= {[Σ(|F_o|²|F_c|²)²]}^1/2

.

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Acknowledgments

R. G. gratefully acknowledges the generous financial support from

the Department of Science and Technology (DST), Government of

India, New Delhi and the University of Delhi under the scheme to

strengthen R&D. The authors also thank the DST-FIST-funded

MS facility at this department and the XRD facility at IIT, Kanpur

for data collection for a few samples. S. K. S. thanks the Council

for Scientific and Industrial Research (CSIR) for an SRF fellow-

ship. We also thank one of the anonymous reviewers for helpful

suggestions.

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Published Online: December 22, 2009

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Article Doi

The effect of ligand architecture on the structure and properties of nickel and copper complexes of amide-based macrocycles

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