Mononuclear to polynuclear transition induced by ligand coordination: Synthesis, X-ray structure, and properties of mono-, di-, and polynuclear copper(II) complexes of pyridyl-containing azo ligands

Article abstract of DOI:10.1021/ic051029c

Reactions of two hydrated cupric salts (CuCl₂·2H ₂O and Cu(ClO₄)₂·6H₂O) with three azopyridyl ligands, viz. 2-[(arylamino)phenylazo]pyridine [aryl = phenyl (HL^1a), p-tolyl (HL^1b), and 2-thiomethyl phenyl (HL ^1c)], 2-[2-(pyridylamino)phenylazo]pyridine (HL²), and 2-[3-(pyridylamino)phenylazo]pyridine (HL³), afford the mononuclear [CuClL¹] (1), dinuclear [Cu₂X₂L ²₂]ⁿ⁺ (X = Cl, H₂O, ClO₄; n = 0, 1; 2, 3), and polynuclear [CuClL³]_n (4) complexes, respectively, in high yields. Representative X-ray structures of these complexes 1-4 are reported. X-ray structure analysis of 4 reveals an infinite 1D zigzag chain that adopts a saw-tooth-like structure. Variable-temperature cryomagnetic measurements (2-300 K) on the complexes 2-4 have revealed weak magnetic interactions between the copper centers with J values -1.04, 9.88, and -1.31 cm^-1, respectively. Positive ion ESI mass spectra of the soluble complexes 1-3 are studied which provide the evidence for the integrity of the complexes also in solution. Visible range spectra of the complexes 1-3 in solution consist of intense and broad transitions in the range 700-600 nm. The solid-state spectrum of the insoluble copper complex 4, on the other hand, shows a structured band near 700 nm. The intensities of the transitions of the dinuclear complexes are much higher than those of the corresponding mononuclear copper complexes. Redox properties of the present copper complexes are reported. Notably, the dinuclear complex, 3, displays two successive redox processes: Cu^IICu^II ? Cu^IICu^I ? Cu^ICu^I. It catalyzes aerial oxidation of L-ascorbic acid. The catalytic cycle is most effective up to H₂A/3 (H₂A = L-ascorbic acid) molar ratio of 20:1.

Full text of DOI:10.1021/ic051029c

Inorg. Chem. 2006, 45, 562−570
Mononuclear to Polynuclear Transition Induced by Ligand
Coordination: Synthesis, X-ray Structure, and Properties of Mono-, Di-,
and Polynuclear Copper(II) Complexes of Pyridyl-Containing Azo
Ligands
Srijit Das,† Priyabrata Banerjee,† Shie-Ming Peng,‡ Gene-Hsiang Lee,‡ Jinkwon Kim,§ and
Sreebrata Goswami*,†
Department of Inorganic Chemistry, Indian Association for the CultiVation of Science,
Kolkata 700 032, India, Department of Chemistry, National Taiwan UniVersity, Taipei, Taiwan,
Republic of China, and Department of Chemistry, Kongju National UniVersity, 182 Shinkwan,
Kongju, Chungnam 314-701, Republic of Korea
Received June 23, 2005
Reactions of two hydrated cupric salts (CuCl2
2-[(arylamino)phenylazo]pyridine [aryl
phenyl (HL1a), p-tolyl (HL1b), and 2-thiomethyl phenyl (HL1c)], 2-[2-
(pyridylamino)phenylazo]pyridine (HL2), and 2-[3-(pyridylamino)phenylazo]pyridine (HL3), afford the mononuclear
‚2H2O and Cu(ClO4)2‚6H2O) with three azopyridyl ligands, viz.
)
n
+
[CuClL1] (1), dinuclear [Cu2X2L2
]
2
(X
respectively, in high yields. Representative X-ray structures of these complexes 1
analysis of 4 reveals an infinite 1D zigzag chain that adopts a saw-tooth-like structure. Variable-temperature
cryomagnetic measurements (2 300 K) on the complexes 2 4 have revealed weak magnetic interactions between
the copper centers with J values 1.04, 9.88, and
1.31 cm-1, respectively. Positive ion ESI mass spectra of the
soluble complexes 1 3 are studied which provide the evidence for the integrity of the complexes also in solution.
Visible range spectra of the complexes 1 3 in solution consist of intense and broad transitions in the range 700
)
Cl, H2O, ClO4; n
)
0, 1; 2, 3), and polynuclear [CuClL3]n (4) complexes,
4 are reported. X-ray structure
−
−
−
−
−
−
−
−
600 nm. The solid-state spectrum of the insoluble copper complex 4, on the other hand, shows a structured band
near 700 nm. The intensities of the transitions of the dinuclear complexes are much higher than those of the
corresponding mononuclear copper complexes. Redox properties of the present copper complexes are reported.
Notably, the dinuclear complex, 3, displays two successive redox processes: CuIICuII
catalyzes aerial oxidation of L-ascorbic acid. The catalytic cycle is most effective up to H2A/3 (H2A
acid) molar ratio of 20:1.
h
CuIICuI
h
CuICuI. It
L-ascorbic
)
Introduction
azo-based ligands that are suitable for the construction of
polynuclear frameworks.
Azoaromatic compounds have been known to have wide
application1,2 in the dyestuff industry and also more recently
in the field of optical data storage and nonlinear optics.
However, examples of well-characterized azo-based di- and
polynuclear systems are limited in the literature primarily
due to lack of availability3 of suitable bridging ligands.
Therefore, there is an obvious need to develop syntheses of
(1) (a) Bach, H.; Anderle, K.; Fuhrmann, Th.; Wendorff, J. H. J. Phys.
Chem. 1996, 100, 17337. (b) Taniike, K.; Matsumoto, T.; Sato, T.;
Ozaki, Y.; Nakashima, K.; Iriyama, K. J. Phys. Chem. 1996, 100,
15508 (c) Clark, R. J. H.; Hester, R. E. AdVances in Material Science
Spectroscopy; Wiley: New York, 1991. (d) Rou, H. Photochromism.
Molecules and Systems; Durr, H., Bouaslourent, H., Eds.; Elsevier:
Amsterdam, 1990; Chapter 4, p 165. (e) Zollinger, H. Color Chemistry,
Syntheses, Properties and Applications of Organic Dyes and Pigments;
VCH: New York, 1987; p 92.
(2) (a) Willner, I.; Rubin, S. Angew. Chem., Int. Ed. Engl. 1996, 35, 367.
(b) Ramanujam, P. S.; Hvilsted, S.; Zebger, I.; Siesler, H. W.
Macromol. Rapid Commun. 1995, 16, 455. (c) Lee, G. J.; Kim. D.;
Lee, M. Appl. Opt. 1995, 34, 138. (d) Ramanujam, P. S.; Hvilsted,
S.; Andruzzi, F. Appl. Phys. Lett. 1993, 62, 1041. (e) Hvilsted, S.;
Andruzzi, F. Ramanujam, P. S. Opt. Lett. 1992, 17, 1234.
* To whom correspondence should be addressed. E-mail:icsg@
iacs.res.in. Fax: +91 33 2473 2805.
† Indian Association for the Cultivation of Science.
‡ National Taiwan University.
§ Kongju National University.
562 Inorganic Chemistry, Vol. 45, No. 2, 2006
10.1021/ic051029c CCC: $33.50
© 2006 American Chemical Society
Published on Web 12/16/2005

Mononuclear to Polynuclear Transition
Scheme 1
During recent years we have been working on the designed
synthesis4 of a new class of azo-containing polydentate
ligands. A tridentate ligand, 2-[(arylamino)phenylazo]pyri-
dine (HL1), was first isolated via regioselective ortho-fusion
of primary aromatic amines on cobalt(II)-coordinated 2-(phe-
nylazo)pyridine (pap). The coordination chemistry of this
bis-chelating ligand has some unique features. For example,
it stabilizes uncommon low-spin states5 of manganese(II) and
iron(II) and also produces complexes of stable azo-radical
ions.6 The success in this area has persuaded us to develop
azo-containing bridging ligands. Accordingly, positional
isomers of pyridylamines are chosen as the reagents for the
above amine fusion reaction. The ligands used in this work
are shown in Chart 1.
compounds. In contrast, the coordination chemistry of
3-aminopyridine is unknown and molecular modeling on the
coordination mode9 of [L3]- indicates the possibility of
formation of coordination polymers (Scheme 1).
In this work we have investigated the coordination
chemistry of copper complexes involving the above aromatic
amine-substituted aryl azo ligands, HL1-HL3. There has been
an increasing interest in the coordination chemistry of
multinuclear systems due to their modified properties10 that
primarily originate due to the interactions between different
metal centers. For similar reasons the chemistry of copper
complexes of high nuclearity involving the pyridyl-based
ligands are of interest.11 Furthermore, we note that structure
building and the deliberate design of polynuclear coordina-
tion compound12 are also important due to their potential as
new functional solid materials.
Chart 1
Results and Discussion
A. Synthesis and X-ray Structures. (i) Mononuclear
Copper(II) Complexes. Hydrated CuCl2‚2H2O reacted
almost instantaneously with an equimolar quantity of the
deprotonated ligands, [L1]-, in methanol resulting in mo-
lecular complexes of formula [CuClL1] (1) in high yields
(>80%). There was distinct color change from red (free
[L1]-) to green complexes, 1. The copper complex 1c of the
substituted ligand, [L1c]-, produced suitable crystals for X-ray
diffraction.
It was hoped that introduction of a pyridyl function in the
place of the phenyl ring would produce the desired bridging
ligands. The ability of the 2-aminopyridine functionality to
serve as three-atom bridge has long been known,7 and thus,
the deprotonated ligand [L2]- primarily forms binuclear8
(3) (a) Kaim, W. Coord. Chem. ReV. 2001, 219-221, 463. (b) Hartmann,
H.; Scheiring, T.; Fiedler, J.; Kaim, W. J. Organomet. Chem. 2000,
604, 267.
(4) Saha, A.; Ghosh, A. K.; Majumdar, P.; Mitra, K. N.; Mondal, S.; Rajak,
K. K.; Falvello, L. R.; Goswami, S. Organometallics 1999, 18, 3772.
(5) (a) Saha, A.; Majumdar P.; Goswami, S. J. Chem. Soc., Dalton Trans.
2000, 1703. (b) Saha, A.; Majumdar, P.; Peng, S.-M.; Goswami, S.
Eur. J. Inorg. Chem. 2000, 2631.
(6) Sanyal, A.; Banerjee, P.; Lee, G.-H.; Peng, S.-M. Hung, C.-H.;
Goswami, S. Inorg. Chem. 2004, 43, 7456.
(7) (a) Chakravarty, A. R.; Cotton F. A.; Falvello, L. R. Inorg. Chem.
1986, 25, 214. (b) Chakravarty, A. R.; Cotton F. A.; Tocher. D. A.
Organometallics 1985, 4, 863.
The molecular structure of 1c is shown in Figure 1, and
its selected bond parameters are collected in Table 1. The
Cu(II) ion in this complex is four-coordinate, and the
(9) Banerjee, P.; Lee, G.-H.; Peng, S.-M.; Goswami, S. Manuscript in
preparation.
(10) Ambrosi, G.; Formica, M.; Fusi, V.; Giorgi, L.; Guerri, A.; Lucarini,
S.; Micheloni, M.; Paoli, P.; Rossi, P.; Zappia, G. Inorg. Chem. 2005,
44, 3249.
(11) Mirica, L. M.; Ottenwaelder, X.; Stack, T. D. P. Chem. ReV. 2004,
(8) (a) Das, S.; Hung, C.-H.; Goswami, S. Inorg. Chem. 2003, 42, 5153.
(b) Kamar, K. K.; Das, S.; Hung, C.-H.; Castin˜eiras, A.; Rillo, C.;
Kuzmin, M.; Goswami, S. Inorg. Chem. 2003, 42, 5367. (c) Das, S.;
Hung, C.-H.; Goswami, S. Inorg. Chem. 2003, 42, 8592.
104, 1013.
(12) (a) Gao, E.-Q.; Bai, S.-Q.; Wang, C.-F.; Yue, Y.-F.; Yan, C.-H. Inorg.
Chem. 2003, 42, 8456. (b) Zaman, M. B.; Smith, M. B.; Ciurtin, D.
M.; Zurloye, H.-C. Inorg. Chem. 2002, 41, 4895.
Inorganic Chemistry, Vol. 45, No. 2, 2006 563

Das et al.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for the Complexes 1c and 2-4
Complex 1c
Cu-N(1)
2.0092(16)
2.1965(5)
1.436(3)
77.52(6)
98.67(5)
Cu-N(3)
1.9603(15)
1.285(2)
1.331(2)
81.78(6)
Cu-N(4)
1.9706(16)
Cu-Cl
N(2)-N(3)
C(11)-N(4)
N(3)-Cu-N(4)
N(3)-C(6)
N(4)-C(12)
N(4)-Cu-Cl
1.351(2)
1.420(2)
102.07(5)
C(6)-C(11)
N(1)-Cu-N(3)
Cl-Cu-N(1)
Complex 2
Cu(1)-N(1)
2.020(4)
2.3947(11)
1.356(5)
1.406(5)
77.13(15)
98.60(10)
Cu(1)N(3)
Cu(1)-N(5A)
C(6)-C(11)
1.996(3)
2.108(3)
1.434(6)
Cu(1)-N(4)
N(2)-N(3)
C(11)-N(4)
1.985(3)
1.284(5)
1.333(5)
Cu(1)-Cl(1)
N(3)-C(6)
N(4)-C(12)
N(1)-Cu(1)-N(3)
N(5A)-Cu(1)-Cl(1)
N(3)-Cu(1)-N(4)
80.05(15)
N(4)-Cu(1)-N(5A)
97.13(13)
Complex 3
Cu(1)-N(6)
1.996(9)
2.000(8)
1.952(6)
2.465(7)
1.417(14)
1.239(11)
1.396(12)
75.9(3)
Cu(1)-N(8)
Cu(1)-O(1)
Cu(2)-N(4)
N(7)-N(8)
1.966(6)
2.378(7)
1.968(6)
1.209(10)
1.381(12)
1.431(11)
1.387(11)
82.4(2)
Cu(1)-N(9)
Cu(2)-N(1)
Cu(2)-N(10)
N(8)-C(22)
N(9)-C(28)
C(6)-C(11)
1.946(6)
1.979(8)
1.997(8)
1.447(11)
1.459(10)
1.380(15)
Cu(1)-N(5)
Cu(2)-N(3)
Cu(2)-O(2)
C(22)-C(27)
N(2)-N(3)
C(27)-N(9)
N(3)-C(6)
C(11)-N(4)
N(4)-C(12)
N(9)-Cu(1)-N(8)
N(8)-Cu(1)-N(6)
N(3)-Cu(2)-N(4)
N(3)-Cu(2)-N(1)
77.1(3)
83.1(2)
Complex 4
Cu(a)-N(1a)
2.024(3)
2.2408(11)
1.356(4)
1.411(4)
77.23(12)
102.15(9)
Cu(a)-N(3a)
Cu(a)-N(5)
C(6a)-C(11a)
1.963(3)
2.205(3)
1.435(5)
Cu(a)-N(4a)
N(2a)-N(3a)
C(11a)-N(4a)
2.029(3)
1.295(4)
1.329(4)
Cu(a)-Cl(a)
N(3a)-C(6a)
N(4a)-C(12a)
N(1a)-Cu(a)-N(3a)
Cl(a)-Cu(a)-N(5)
N(3a)-Cu(a)-N(4a)
80.18(12)
N(4a)-Cu(a)-Cl(a)
102.85(9)
geometry around it is a distorted square planar. The metal
atom is located 0.0272(3) Å above the mean basal plane
formed by the coordinating atoms, viz. N(1), N(3), N(4),
and Cl. Deviation from the idealized square geometry is due
to geometric constraints imposed by the tridentate ligand.
The Cu-N lengths showed expected variation with that to
the middle nitrogen (N(3)) being shorter than those to the
other two terminal nitrogen atoms, viz. N(1) and N(4). The
chelate bite angles are in agreement with those of the
previously reported4 complexes of [L1]-. Crystal packing of
complex 1c reveals an array of intra- and intermolecular
C-H‚‚‚‚Cl hydrogen-bonding interactions (Figure S1). Two
distinct types of C-H‚‚‚‚Cl interactions13 are present between
the acceptors, i.e., the metal bound chloride ion and the C-H
moieties (donors) on the same or an adjacent molecule. The
identified donors are the H(1) atom of a pyridine ring
(intramolecular donor in nature) and H(3) atom of the
pyridine ring of an adjacent molecule (intermolecular donor
in nature). The intra- and intermolecular distances are 2.8465-
(6) and 2.8600(5) Å, respectively. These distances are
appreciably shorter than the sum of the van der Waals radii
for the hydrogen and the neutral chlorine atoms (2.95 Å).
These noncovalent interactions have led to a 1D sinusoidal
architecture along the a axis.
(ii) Dinuclear Copper(II) Complexes. (a) [Cu2Cl2L2 ]‚
2
H2O (2). The reaction of hydrated salt CuCl2‚2H2O with an
equimolar quantity of the deprotonated [L2]- in methanol
produced a sky-blue solution from which a molecular
dicopper complex, [Cu2Cl2L2 ]‚H2O (2), was obtained in a
2
high yield (75%). The X-ray structure of the complex 2 is
shown in Figure 2, and its bond parameters are collected in
Table 1. The complex 2 is located at the crystallographic
2-fold axis; only half of it occupies the asymmetric unit. Each
copper atom in this molecule is in a pentacoordinated N4Cl
environment. The three coordinating nitrogen atoms, viz.
N(1), N(3), and the deprotonated secondary amine N(4), of
one [L2]- bind to Cu(1) as a bis-chelating tridentate ligand
while the second pyridyl nitrogen N(5) bridges8a to another
Cu(1A) atom. Tridentate coordination of one [L2]- and
pyridyl nitrogen of a second [L2]- ligand, together with one
chloride, thus completes five-coordination about each copper.
The three coordinating nitrogen atoms, viz. N(1), N(3), and
N(4), form a good plane, and Cu(1) sits above this plane by
0.0500(4) Å. The geometry around each Cu atom is highly
distorted; the angular structural parameter,14 τ, value equals
0.55 suggesting more likely a trigonal bipyramidal structure.
(13) (a) Balamurugan, V.; Hundal, M. S.; Mukherjee, R. Chem.sEur. J.
2004, 1683. (b) Aakero¨y, C. B.; Evans, T. A.; Seddon, K. R.; Pa´linko´,
I. New J. Chem. 1999, 145.
Figure 1. ORTEP and atom-numbering scheme for [CuCl(L1c)] (1c).
Hydrogen atoms are omitted for clarity.
564 Inorganic Chemistry, Vol. 45, No. 2, 2006

Mononuclear to Polynuclear Transition
Figure 2. ORTEP and atom-numbering scheme for [Cu2Cl2L2 ]‚H2O (2).
2
Hydrogen atoms are omitted for clarity.
The four Cu-N lengths along with Cu-Cl lengths are
normal. Notably, the separation between Cu(1)···N(4A) is
3.144(4) Å, which is longer than a typical covalent Cu-N
length, but is shorter than the sum of van der Waals radii15
of Cu and N. The separation between the two copper atoms
in the present complex is 4.182 Å. Complex 2 also contains
one molecule of H2O as a solvent of crystallization. In the
crystal packing, the dimeric units of the complex 2 are
connected through an extensive network16 of hydrogen bonds.
The void volume/unit cell is filled by uncoordinated water
molecules. Furthermore, the hydrogen of solvated water
molecules is connected through strong intermolecular O-H‚
‚‚‚Cl hydrogen-bonding interactions (O-H‚‚‚‚Cl: 2.43(11)
Å; 171(10)°) between coordinated chlorine atoms of two
adjacent Cu2 dimers (Figure S2).
Figure 3. ORTEP and atom-numbering scheme for [Cu2(OH2)(ClO4)L2 ]-
(ClO4) (3). Hydrogen atoms and uncoordinated perchlorate ion are omitted
for clarity.
2
(b) [Cu2(OH2)(ClO4)L2 ](ClO4) (3). A similar reaction
2
of the hydrated salt Cu(ClO4)2‚6H2O with an equimolar
quantity of the deprotonated ligand [L2]- in methanol
produced a cationic dicopper complex [Cu2(OH2)(ClO4)L2 ]-
2
(ClO4) (3) (yield, 70%). The bonding pattern of the two
anionic ligands in 3 is identical with that of 2; however, the
geometry of 3 is different. While complex 2 is distorted
trigonal bipyramid, complex 3, in contrast, is a distorted
square pyramidal.14 The value of τ for Cu(1) is 0.33 and for
Cu(2) is 0.37. Figure 3 shows the ORTEP and atom-
numbering scheme for 3, and its bond parameters are
collected in Table 1. The tridentate coordination of one [L2]-
and a pyridyl nitrogen atom of a second [L2]- ligand, together
with the oxygen atom of H2O, completes five-coordination
about Cu(1). The coordination mode of the organic ligand
about Cu(2) is similar to that of Cu(1), with only the
difference of a ClO4 coordination in place of H2O coordina-
tion. The three coordinating nitrogen atoms, viz. N(6), N(8),
and N(9), form a good plane, and Cu(1) sits above the plane
by 0.2475(12) Å. Similarly, the second metal ion, Cu(2),
Figure 4. ORTEP and atom-numbering scheme for [CuClL3]n (4).
Hydrogen atoms are omitted for clarity.
lies below the plane formed by three coordinated nitrogen
atoms, viz. N(1), N(3), and N(4), by 0.1802(12) Å. The
nonbonded distance between the two copper atoms is 3.4207
Å. There also exist two longer Cu···N contacts [Cu(1)-N(10)
3.50037 Å and Cu(2)-N(5) 3.4925 Å] as it is observed in
the case of the compound 2. The molecule also contains one
CH3CN as a solvent of crystallization.
(iii) Polynuclear Copper(II) Complex. The ligand HL3
in methanol reacted instantaneously with an aqueous solution
of hydrated cupric chloride in the presence of triethylamine
(14) Addison, A. W.; Rao, T. N.; Reedijk, J.; Rijn, J. V.; Verschoor, G. C.
J. Chem. Soc., Dalton Trans. 1984, 1349.
(15) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D.
G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, 12, S1-S83.
(16) (a) Shi, X.; Zhu, G.; Wang, X.; Li, G.; Fang, Q.; Wu, G.; Tian, G.;
Xue, M.; Zhao, X.; Wang, R.; Qiu, S. Cryst. Growth Des. 2005, 5,
207. (b) Castillo, O.; Luque, A.; Iglesias, S.; Vitoria, P.; Roma´n, P.
New. J. Chem. 2000, 24, 771.
Inorganic Chemistry, Vol. 45, No. 2, 2006 565

Das et al.
Figure 5. (a) Space-filling model of the zigzag chain of [CuClL3]n (4) producing a saw-tooth-like backbone. (b) Segmented ellipsoid view of the 1D chain
of the copper(II) polymer.
to produce an insoluble dark green complex [CuClL3]n (4).
X-ray-quality crystals of it were grown by slow diffusion of
an aqueous solution of CuCl2‚2H2O into a deprotonated
methanolic solution of [L3]-. A similar reaction of Cu-
(ClO4)2‚6H2O with [L3]- also produced a very short-lived
green solution, which turned brown quickly, and no pure
compound could be isolated from the above mixture.
Structural analysis of 4 reveals infinite 1D chain. Figure 4
shows its ORTEP along with atom numbering scheme, and
the bond parameters are collected in Table 1. In this molecule
each copper atom is surrounded in a pentacoordinated N4Cl
environment. The geometry of each copper(II) ion may be
described14 as square pyramidal (τ ) 0.02). In complex 4
the three coordinating nitrogen atoms, viz. N(1a), N(3a), and
N(4a), form a good plane and Cu(1a) sits above the plane
by 0.1383(4) Å. Interestingly, the coordination mode of the
deprotonated ligand, [L3]-, is found to be different from that
of its positional isomer [L2]- and is perfectly suited for a
metal-ligand extended network. The bending of the ligand
and its coordination about the copper center results in a
zigzag chain17 that adopts a saw-tooth-like structure (Figure
5). In this lattice, the polymeric network runs along the b
axis, where Cu(a)-N(5) of the bridging pyridine distance is
2.205(3) Å. Hence, the bridging pyridyl nitrogen of the next
molecule interacts with the copper of the earlier molecule
axially forming a 1D chain. There are two polymeric chains,
which are mirror images. The interchain Cu···Cu distance
across the bridging ligand is 7.0450(7) Å.
B. Spectral Studies. The positive ion ESI mass spectra
of the soluble complexes 1-3 were recorded in dichlo-
romethane. The representative mononuclear copper complex
1a shows an intense peak at m/z 337 amu which is assigned
to [Mc - X]+, where Mc and X represent the molecule and
Cl-, respectively. Each of the two dinuclear copper(II)
complexes, viz. 2 and 3, shows a peak at m/z 711 and 775
amu, respectively, due to [2 - (Cl + H2O)]+ and [3 - (ClO4
+ H2O)]+. In all the cases the experimental isotopic
distributions for the above molecular ions corresponded to
the simulated pattern. Each spectrum is associated with
daughter peaks due to fragmentation. Thus, the ESIMS data
provide evidence for the integrity of the complexes also in
solution.
IR spectra of the copper(II) complexes show the presence
of all characteristic bands4,8 for the coordinated ligands with
νCdN and νNdN appearing in the ranges 1590-1595 and
1305-1325 cm-1, respectively. Notably, complex 3 shows
three peaks near 1100 cm-1 and one peak near 620 cm-1.
Among these, two peaks are due to the coordinated18
perchlorate ion and one peak is due to uncoordinated
perchlorate. While the complexes 1-3 are soluble in
common organic solvents, complex 4, on the other hand, is
insoluble. The solution electronic spectra of the complexes
(18) Thirumavalavan, L.; Akilan, P.; Kantaswamy, M.; Chinnakali, K.;
(17) Moulton, B.; Zaworotko, M. J. Chem. ReV. 2001, 101, 1629.
566 Inorganic Chemistry, Vol. 45, No. 2, 2006
Kumar, G. S.; Fun, H. K. Inorg. Chem. 2003, 42, 3308.

Mononuclear to Polynuclear Transition
1-3 dominated by a moderately intense (ꢀ: ca. 3600 for 1
and 12 300 and 13 100 M-1 cm-1 for 2 and 3, respectively)
and broad charge-transfer transition in the visible range
(700-650 nm). In addition, these also show transitions in
the UV-region, which are ascribed to intraligand charge
transfer. The solid-state absorption spectrum of 4 shows a
low-energy structured band near 700 nm. Interestingly, the
intensities of transitions for the dicopper complexes, 2 and
3, are much higher than those for the mononuclear copper
complexes, 1. Such observations were noted19 before in di-
and polynuclear systems having a repetition of units that are
responsible for the reference electronic transitions. Semiem-
pirical EHMO calculations on the complex 2 using the
CACAO program20 by Mealli and Proserpio indicated that
while the HOMO is an admixture of metal and ligand
orbitals, the LUMO is predominantly ligand orbitals. On the
other hand, the HOMO for each of the complexes 1, 3, and
4 is predominantly ligand orbitals while the LUMO is a
mixture of metal and ligand orbitals. Hence, the lowest
energy transition in the present copper(II) complexes may
be described as a π-π* transition,8 where the π-orbitals are
either an admixture of metal and ligand orbitals or ligand
orbitals.
C. Magnetic Studies. Room-temperature magnetic mo-
ments of the mononuclear copper(II) complexes 1a-c fall
in the range, 1.68-1.72 µB that are close to the spin-only
value 1.73 µB for a single unpaired electron. Variable-
temperature magnetic susceptibility data for the di- and
polynuclear complexes 2-4 were measured at temperature
ranging from 2.0 to 300 K. The dinuclear complex 2 showed
very weak antiferromagnetic behavior. The resulting plots
of the øM versus T and the øMT versus T are submitted as
Supporting Information (Figure S3). From the curve it is
observed that the øMT value is 0.91 cm3 K mol-1 at room
temperature, which decreases gradually with lowering of
temperature. The ømT ) 0.91 cm3 K mol-1 at 300 K is higher
than the spin-only value ømT ) 0.75 cm3 K mol-1 for the
uncorrelated two CuII (S ) 1/2) with g ) 2.00. Such a high
øMT value has been reported21 for other dinuclear copper(II)
complex such as [Cu2(t-bupy)4(N3)2](ClO4)2, where t-bupy
stands for 4-tert-butylpyridine. The temperature dependence
of ømT indicates that two CuII ions are coupled antiferro-
magnetically22 through the bridging ligands. The susceptibil-
ity data were fitted by the following expression derived23
by Bleany and Bowers:
Boltzman’s constant. A good-fitting curve was obtained for
the following parameters: J ) -1.04 cm-1; g ) 2.04.
The resulting plot of the øMT versus T for 3 is submitted
as Supporting Information (Figure S4). At room temperature
øMT is equal to 0.76 cm3 K mol-1 (300 K). This value at
room temperature is consistent with the spin-only value øMT
) 0.75 cm3 K mol-1 for the uncorrelated two CuII (S ) 1/2)
with g ) 2.00, and øMT is almost constant until 100 K. On
further cooling, øMT increases rapidly and reaches a maxi-
mum (0.95 cm3 K mol-1) at 5.0 K, after which it decreases
slightly to 0.90 cm3 K mol-1 at 2 K. This curve is as expected
for a dominant ferromagnetic coupling with weak intermo-
lecular antiferromagnetic interactions and/or zero-field split-
ting of the triplet ground state which would account for the
decrease of øMT at 5 K. The øMT data for temperature range
from 2 to 300 K were fitted by the modified Bleany and
Bowers expression:23
2Ng2â2
ø )
k(T - Θ)[3 + exp(-J/kT)]
A good-fitting curve was obtained for the following param-
eters: J ) 9.88 cm-1; g ) 2.01; Θ ) -0.24 K. The small
positive J value indicates a weak ferromagnetic24 coupling
between the two copper(II) ions.
The resulting plot of the øMT versus T for 4 is submitted
as Supporting Information (Figure S5). The room-tempera-
ture øMT is equal to 0.76 cm3 K mol-1 (300 K), which is
consistent with the spin-only value øMT ) 0.75 cm3 K mol-1
for the uncorrelated two CuII (S ) 1/2) with g ) 2.00, and
øMT decreases slowly until 20 K and then decreases rapidly
due to weak antiferromagnetic coupling of Cu ions. The
room-temperature magnetic moment of the polycrystalline
powder of complex 4 showed an experimental effective
magnetic moment (µexp) of 1.80 µB, which is slightly higher
than the spin-only magnetic moment for copper(II) ion (1.73
µB). The molar magnetic susceptibility data for temperature
range from 2 to 300 K were fitted by Bonner and Fisher’s
model,25 and the best-fitted parameters obtained were J )
-1.31 cm-1 and g ) 2.09.
The room-temperature EPR spectrum of each of the
mononuclear complexes 1a-c in dichloromethane solution
exhibits a four-line spectrum with hyperfine coupling
constant (A) of 75-80 G and gav ) 2.10. In contrast, the
solutions of the dinuclear complexes 2 and 3 both are EPR
inactive at room temperature. However, the frozen solution
(dichloromethane-toluene, 1:1) of 2 shows a broad axial
spectrum (2: gII, 2.03; AII, 83 G; g , 2.00) with ill-defined
hyperfine components of the gII signals. A very broad
spectrum centered at g ) 2.01-2.04 is observed for the
frozen solution of compound 3. Compound 4 is insoluble,
and hence, its solution spectrum could not be recorded. It
exhibits an axial spectrum (gII, 2.10; g-, 2.07) in the solid
state, but no hyperfine component was observed. Broadening
2Ng2â2
ø )
kT[3 + exp(-J/kT)]
Here N is Avogadro’s number, â the Bohr magneton, and k
(19) Rillema, D. P.; Sahai, R.; Matthvews, P.; Edwarts, A. K.; Shaver, R.
J.; Morgan, L. Inorg. Chem. 1990, 29, 167.
(20) Mealli, C.; Proserpio, D. M. J. Chem. Educ. 1990, 67, 399.
(21) Sikorav, S.; Bkouche-Waksman, I.; Khan, O. Inorg. Chem. 1984, 23,
490.
(22) (a) Castillo, O.; Luque, A.; Sertucha, J.; Roma´n, P.; Lloret, F. Inorg.
Chem. 2000, 39, 6142. (b) Girerd, J. J.; Khan, O.; Verdaguer, M. Inorg.
Chem. 1980, 19, 274.
(23) Bleany, B.; Bowers, K. D. Proc. R. Soc. London, Ser. A 1952, 214,
451.
(24) (a) Reddy, P. A. M.; Nethaji, M.; Chakravarty, A. R. Eur. J. Inorg.
Chem. 2003 2318. (b) Fitzgerald, W.; Foley, J.; McSweeney, D.; Ray,
N.; Sheahan, D.; Tyagi, S. J. Chem. Soc., Dalton Trans. 1982, 1117.
(25) Kahn, O. Molecular Magnetism; VCH: New York, 1993; p 252.
Inorganic Chemistry, Vol. 45, No. 2, 2006 567

Das et al.
of the EPR spectra in magnetically coupled systems is
documented18 in the literature. However, the extent of
interactions in the present complexes is weak as evidenced
by the cryomagnetic data for the above complexes. Very
weak magnetic interactions in the present complexes may
be ascribed to unfavorable overlaps of magnetic orbitals for
the distorted complexes.26 Furthermore, we note that the
magnitudes of separation between the copper centers are also
considerably high.
D. Redox and Catalytic Activity of Complex 3. Redox
behavior of the soluble copper(II) complexes 1-3 was
studied by cyclic voltammetry in dichloromethane solvent
using a platinum working electrode. The complexes 1 and 2
display multiple irreversible and quasireversible ill-natured
responses, which are not considered further. Complex 3,
however, displays two closely spaced one-electron reversible
responses at +0.06 and -0.05 V. The separation between
the two-reduction processes is small, and differential pulse
voltammetry indeed identifies two successive steps. Constant-
potential electrolysis of 3 was performed at -0.4 V, which
confirmed an overall two-electron transfer for the above
response. The two-redox processes are assigned as follows:
CuIICuII h CuIICuI h CuICuI
Figure 6. Voltammograms of [Cu2(OH2)(ClO4)L2 ](ClO4) (3) in dichlo-
2
romethane (0.1 M TBAP): cyclic voltammogram (- -); differential pulse
voltammetry (---); cyclic voltammogram of electrogenerated [3]2- (s).
The above processes are electrochemically reversible; the
CuI2 (green) regenerates CuII2 (sky blue) almost quantitatively
upon electrolysis at 0.35 V. The reference ligand has a unique
combination of hard as well as soft donor sites4 and is known
to stabilize variable valence states of different metal ions.
Furthermore, the lability of the fifth coordinating ligands in
3 is believed to be a key factor for the electrochemical
reversibility. The voltammogram of 3 in dichloromethane is
displayed in Figure 6, and the visible range spectra of the
Inset: Visible range spectra of (i) [Cu2(OH2)(ClO4)L2 ](ClO4) (3) (s) and
2
(ii) electrogenerated [3]2- (---).
I
starting complex 3 and the electrogenarated Cu2 complex
([3]2-) are shown as an inset of Figure 6.
Electrochemical reversibility of complex 3 persuaded us
to examine its catalytic properties. Compound 3 reacts27 with
L-ascorbic acid (H2A) in aqueous methanol instantaneously
to form a brownish-violet solution presumably due to the
formation of copper(I) species. The color of the solution is
stable in an inert atmosphere but regenerates the parent
complex 3 quantitatively upon exposure to air. The above
catalytic reaction is followed spectrophotometrically using
an air-saturated solvent mixture. The catalytic cycle is most
effective up to H2A/3 molar ratio of 20:1 with quantitative
regeneration of 3 (Figure 7), but complete regeneration of 3
is not be achieved at higher concentrations of H2A. For
example, for a molar ratio of 30:1, 53% of 3 is regenerated
after 7 h. When the concentration of H2A exceeds 50 times
that of 3, its catalytic activity is completely lost. The overall
rates of regeneration of the parent complex 3 are measured
with H2A/3 molar ratio of 10:1, 15:1, and 20:1 and the
observed rates are 5.75, 4.79, and 2.87 M-1 s-1, respectively.
Figure 7. Time-dependence spectra of [Cu2(OH2)(ClO4)L2 ](ClO4) (3) at
a molar ratio H2A/3 of 20:1 in the air-saturated methanol-water solvent.
2
In contrast, complexes 1 and 2 both react with H2A
irreversibly to produce brown solutions of unknown com-
positions via the transient violet intermediates. The above
catalytic process involving 3 consists of several steps that
primarily include reduction of 3 by L-ascorbic acid and
reoxidation of copper(I) species by aerial oxygen.28 Catalytic
activity of copper(II) complexes toward oxidation29 of
potential bioreductant L-ascorbic acid is of interest for the
construction of possible models for copper enzymes.
(26) Mikuriya, M.; Okawa, H.; Kida, S. Bull. Chem. Soc. Jpn. 1982, 55,
1086.
(27) (a) Santra, B. K.; Reddy, P. A. N.; Nethaji, M.; Chakravarty, A. Inorg.
Chem. 2002, 41, 1328. (b) Taquikhan, M. M.; Martell, A. E. J. Am.
Chem. Soc. 1967, 89, 6.
(28) Scarpa. M.; Vianello, F.; Signor, L.; Zennaro, L.; Rigo, A. Inorg. Chem.
1996, 35, 5201.
(29) Davies, M. B. Polyhedron 1992, 11, 285.
568 Inorganic Chemistry, Vol. 45, No. 2, 2006

Mononuclear to Polynuclear Transition
Table 2. Crystallographic Data
param
1c
2
3
4
empirical formula
molecular mass
cryst syst
space group
a (Å)
C18H15ClSN4Cu
418.39
monoclinic
C2/c
27.2036(11)
9.0209(4)
15.4178(6)
90
112.2120(10)
90
3502.8(3)
8
1.58
0.40 × 0.35 × 0.12
2.40-27.50
0.710 73
14 334
C32H26Cl2N10Cu2O
764.61
orthorhombic
Fdd2
28.6584(5)
11.7238(2)
18.0082(3)
90
C34H29Cl2N11Cu2O9
933.66
monoclinic
P21/c
10.5476(2)
23.3966(3)
15.1012(2)
90
94.3235(6)
90
3716.04(10)
4
1.669
0.40 × 0.20 × 0.08
1.61-25.00
0.710 73
20 139
C16H12ClN5Cu
373.30
monoclinic
P21/c
7.7002(5)
7.8855(5)
24.6440(16)
90
95.929(2)
90
1488.38(17)
4
1.666
0.40 × 0.10 × 0.02
1.66-27.50
0.710 73
14 423
b (Å)
c (Å)
R (deg)
â (deg)
90
90
γ (deg)
V (Å3)
6050.49(18)
8
1.679
0.20 × 0.20 × 0.1
2.19-27.50
0.710 73
18 155
Z
D
calcd (Mg/m3)
cryst dimens (mm3)
θ range for data collcn (deg)
wavelength (Å)
reflcns collcd
unique reflcns
4022
3372
6535
3416
final R indices (I > 2σ(I))
R1 ) 0.0328
wR2 ) 0.0886
R1 ) 0.0445
wR2 ) 0.1019
R1 ) 0.1159
wR2 ) 0.2911
R1 ) 0.0580
wR2 ) 0.1185
magnetometer fitted with a walker scientific L75FBAL magnet.
Variable-temperature, direct current (dc) magnetic susceptibility data
on polycrystalline dicopper samples, viz. 2 and 3 (ca. 25 mg each),
were collected using a Quantum Design MPMS5-XL SQUID sus-
ceptometer in the temperature range of 2-300 K and in an applied
magnetic field of 10 000 Oe. The diamagnetic correction was esti-
mated from Pascal’s constants and was subtracted from the experi-
mental susceptibility to give the molar paramagnetic susceptibility.
The room-temperature and low-temperature (77 K) EPR measure-
ments were made with a Varian 109C E-line X-band spectrometer
fitted with a flat cell and equipped with quartz Dewar flask. Spectra
were calibrated against the spectrum of DPPH (g ) 2.0037). The
catalytic activity of the complex 3 toward aerial oxidation of L-
ascorbic acid was studied in a 10-3 M air-saturated methanol-
water (9:1) solvent mixture. The reaction was followed spectro-
photometrically by choosing the strongest absorbance at 650 nm
and monitoring the increase in the absorbance at this wavelength
as a function of time.
E. Conclusion. In this work we have successfully dem-
onstrated how rational design of a ligand system can bring
about mononuclear to polynuclear transition. In the present
cupric complexes, while the noncovalent hydrogen-bonding
interactions were observed in mono- and dinuclear copper
systems, a 1D zigzag framework, through covalent interac-
tions, was resulted in the polynuclear system. We note here
that there has been an upsurge in research for the construction
of new metal organic frameworks (MOF’s) through the
combination of suitable ligands and metal ions. Our work
in this direction using the ligand HL3 and the d10-metal ions
is in progress. Furthermore, redox behavior of the Cu2
complex 3 is noteworthy. It catalyzes aerial oxidation of
L-ascorbic acid, which may be useful in extracting further
insights into biochemical Cu2-based O2 activation processes.
Experimental Section
Synthesis of Compounds. A. Mononuclear Copper(II) Com-
plexes. [CuClL1a] (1a). The methanolic solution (25 mL) of the
ligand HL1a (100 mg, 0.365 mmol) was deprotonated by addition
of a few drops of dilute triethylamine solution. To this solution a
methanolic solution of CuCl2‚2H2O (65 mg, 0.365 mmol) was
added, and the whole mixture was stirred for 1 h at room
temperature. The color of the resultant solution changed from red
to dark green. The resultant mixture was filtered, and the solvent
was evaporated under vacuum. The green compound, thus obtained,
was crystallized from a dichloromethane-hexane solvent mixture.
Yield: 80%. Anal. Calcd for C17H13N4ClCu: C, 54.8; H, 3.5; N,
15.0. Found: C, 54.9; H, 3.4; N, 15.0. IR (KBr disk, ν, cm-1 ):
1595 (CdN), 1320 (NdN). UV-visible spectrum (dichlo-
romethane) [λmax, nm (ꢀ, M-1 cm-1)]: 705 (3570), 420 (3360), 310
(14 135), 275 (15 900), 205 (56 410). µeff (298 K): 1.68 µB.
ESIMS: m/z 337, [M - Cl]+.
The other substituted complexes were prepared similarly by using
the appropriate ligands, HL1b-HL1c. Their yields and characteriza-
tion data are as follows:
[CuClL1b] (1b). Yield: 80%. Anal. Calcd for C18H15N4ClCu:
C, 56.0; H, 3.9; N, 14.5. Found: C, 56.1; H, 3.9; N, 14.6. IR (KBr
disk, ν, cm-1): 1595 (CdN), 1330 (NdN). UV-visible spectrum
(dichloromethane) [λmax, nm (ꢀ, M-1 cm-1)]: 715 (3470), 435
(4680), 315 (16 580), 280 (20 615), 205 (65 840). µeff (298 K): 1.72
µB. ESIMS: m/z 351, [M - Cl]+.
Materials. All solvents and chemicals used for synthesis were
of analytical grade. The ligands HL1-HL3 were prepared by
following the reported4a,8b procedure using the appropriate aromatic
monoamines.
Caution! Perchlorate salts of metal complexes can be explosive.
Although no detonation tendencies have been observed, care is
advised and handling of only small quantities recommended.
Physical Measurements. A JASCO V-570 spectrometer was
used to record electronic spectra. The IR spectrums were recorded
with a Perkin-Elmer 783 spectrophotometer. A Perkin-Elmer 240C
elemental analyzer was used to collect microanalytical data (C, H,
N). Electrochemical measurements were performed under a dry
nitrogen atmosphere at 298 K on a PAR model 370-4 electrochem-
istry system as described before.30 The potentials reported herein
are referenced to the saturated calomel electrode (SCE) and are
uncorrected for junction contribution. The value for the ferroce-
nium-ferrocene couple under our experimental conditions is 0.40
V. Tetrabutylammonium perchlorate was used as the supporting
electrolyte. ESI mass spectra were recorded on a micro mass Q-TOF
mass spectrometer (serial no. YA 263). Room-temperature magnetic
moments were carried out with a PAR 155 vibrating-sample
(30) Goswami, S.; Mukerjee, R.; Chakravorty, A. Inorg. Chem. 1983, 22,
2825.
Inorganic Chemistry, Vol. 45, No. 2, 2006 569

Das et al.
[CuClL1c] (1c). Yield: 75%. Anal. Calcd for C18H15N4ClSCu:
C, 51.6; H, 3.6; N, 13.4. Found: C, 51.9; H, 3.4; N, 13.6. IR (KBr
disk, ν, cm-1): 1595 (CdN), 1305 (NdN). UV-visible spectrum
(dichloromethane) [λmax, nm (ꢀ, M-1 cm-1)]: 720 (3200), 450
(3790), 320 (14 690), 260 (16 110), 210 (56 550). µeff (298 K): 1.70
µB. ESIMS: m/z 383, [M - Cl]+.
Mo KR radiation (λ ) 0.710 73 Å) and were corrected for Lorentz-
polarization effects. A total of 14 334 reflections were collected
out of which 4022 were unique (Rint ) 0.0229) and were used in
subsequent analysis.
[Cu2Cl2L2 ]‚H2O (2). The suitable X-ray-quality crystals (0.20
2
× 0.20 × 0.10 mm3) of [Cu2Cl2L2 ]‚H2O (2) were obtained by slow
2
B. Dinuclear Copper(II) Complexes. (i) [Cu2Cl2L2 ]‚H2O (2).
evaporation of a concentrated methanol solution of the compound.
The data were collected as noted above. A total of 18 155 reflections
were collected out of which 3372 were unique (Rint ) 0.0473) and
were used in subsequent analysis.
2
The ligand HL2 (100 mg, 0.365 mmol) was dissolved in 25 mL of
methanol and was deprotonated by the addition of a few drops of
dilute triethylamine. To this solution a methanolic solution of CuCl2‚
2H2O (64 mg, 0.365 mmol) was added, and the whole solution
was stirred for 1 h at room temperature. The color of the solution
changed from orange to sky blue. The resultant mixture was filtered,
and the solvent was evaporated under vacuum. A dark crystalline
compound was obtained through slow evaporation of a concentrated
methanolic solution of the compound. Yield: 75%. Anal. Calcd
for C32H24N10Cl2Cu2‚H2O: C, 50.2; H, 3.4; N, 18.3. Found: C,
50.5; H, 3.4; N, 18.1. IR (KBr disk, ν, cm-1): 1600 (CdN), 1315
(NdN). UV-visible spectrum (dichloromethane) [λmax, nm (ꢀ, M-1
cm-1)]: 635 (12 300), 360 (25 000), 300 (34 450), 235 (32 415).
ESIMS: m/z 711, [M - (Cl + H2O)]+.
[Cu2(OH2)(ClO4)L2 ](ClO4) (3). The suitable X-ray-quality
2
crystals (0.40 × 0.20 × 0.08 mm3) of [Cu2(OH2)(ClO4)L2 ](ClO4)
2
(3) were obtained by slow diffusion of toluene into acetonitrile
solution of the compound. The data were collected as noted above.
A total of 20 139 reflections were collected out of which 6535 were
unique (Rint ) 0.0487) and were used in subsequent analysis.
Complex 3 has two unreasonable peaks. One peak has 7.26 e-/Å3
near the atom of Cu(2) and N(4) (1.037, 1.059 Å); the other peak
has 6.36 e-/Å3 near the atoms of Cu(1) and N(9) (1.417, 0.704 Å).
So the structure has a higher R1 value.
[CuClL3]n (4). The suitable X-ray-quality crystals (0.40 × 0.10
× 0.02 mm3) of [CuClL3]n (4) were obtained by slow diffusion of
aqueous solution of CuCl2‚2H2O into the deprotonated methanolic
solution of the ligand, [L3]-. The data were collected as noted above.
A total of 14 423 reflections were collected out of which 3416 were
unique (Rint ) 0.0468) and were used in subsequent analysis.
All structures were solved by employing the SHELXS 97
program package31 and refined by full-matrix least squares based
on F2 (SHELXL-97).32
(ii) [Cu2(OH2)(ClO4)L2 ](ClO4) (3). This was prepared similarly
2
by reacting appropriate quantities of Cu(ClO4)2‚6H2O (135 mg,
0.365 mmol) and the deprotonated ligand [L2]- as described above.
Crystals were grown by slow diffusion of toluene into acetonitrile
solution of the compound. Yield: 75%. Anal. Calcd for C32H29N11-
Cl2O9Cu2: C, 43.7; H, 3.1; N, 16.5. Found: C, 43.6; H, 3.4; N,
16.3. IR (KBr disk, ν, cm-1): 1600 (CdN), 1310 (NdN) 1100,
620 (ClO4-). UV-visible spectrum (dichloromethane) [λmax, nm
(ꢀ, M-1 cm-1)]: 655 (13 000), 380 (18 985), 305 (32 320), 245
(41 185). ESIMS: m/z 775, [M - (ClO4 + H2O)]+.
Acknowledgment. Financial support received from the
Department of Science and Technology, New Delhi, and the
Council of Scientific and Industrial Research, New Delhi,
is gratefully acknowledged. We are thankful to Prof. R.
Mukherjee, IIT, Kanpur, India, for his help in studying the
crystal packing in the present complexes. S.D. also thanks
the Council of Scientific and Industrial Research for his
fellowship. J.K. thanks the MOST (NRL program) of Korea.
We are also grateful to the reviewers for their suggestions.
C. Polynuclear Copper(II) Complex. [CuClL3]n (4). In a long
neck crystal tube, an aqueous solution (5 mL) containing CuCl2‚
2H2O (65 mg, 0.365 mmol), a blank methanol solvent (2 mL), and
the deprotonated methanolic solution of [L3]- (100 mg, 0.65 mmol)
were added gradually. Between the water and methanol solvent
layer, a green ring was formed. The tube was stoppered and left to
stand at room temperature. Slow diffusion between the two solutions
afforded dark green crystals of 4 within 2 weeks. Yield: 70%. Anal.
Calcd for C16H12N5ClCu: C, 51.4; H, 3.2; N, 18.8. Found: C, 51.6;
H, 3.0; N, 18.9. IR (KBr disk, ν, cm-1): 1595 (CdN), 1300 (Nd
N). UV-visible spectrum (solid; λmax, nm): 700, 425, 365, 345,
320, 250.
Crystallography. Crystallographic data for the compounds 1c
and 2-4 are collected in Table 2. Specific details are given below.
[CuClL1c] (1c). The suitable X-ray-quality crystals (0.40 × 0.35
× 0.12 mm3) of [CuClL1c] (1c) were obtained by slow diffusion
of hexane into dichloromethane solution of the compound. The data
were collected on a Bruker SMART diffractometer equipped with
Supporting Information Available: X-ray crystallographic data
in cif format; figures of 1c and 2; øM vs T plots for various
compounds. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC051029C
(31) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(32) Sheldrick, G. M. SHELXL 97. Program for the refinement of crystal
structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
570 Inorganic Chemistry, Vol. 45, No. 2, 2006