Copper-azide-thioarylazoimidazoles - Structure, spectra, redox properties, magnetism and theoretical interpretation

Article abstract of DOI:10.1002/ejic.200900648

Azido-copper(II) and -copper(I) complexes of 1-alkyl-2-[(o-thioalkyl) phenylazo]imidazole (SRaaiNR') have been prepared and studied. Complex 2 [Cu(SRaaiNR')(μ_1.1-N₃)(N₃)]₂ dimerises via end-to-end (μ_1,3)-N₃ to form a tetrameric structure. Azido-copper(I) complexes of the ligands are obtained as MeOH-bridged dimers, [Cu(SRaaiNR')(N₃)(μ-OHMe)]₂ (3). The electronic spectra suggest that a small reorganisation energy (0.08 eV) is associated with the change in electronic configuration, structure and oxidation state from Cu¹¹ to Cu¹. Redox interconversion., Cu ¹¹ Cu¹, [Cu.(SMeaai.NMe)(μ-N₃)(N ₃)]₂ (2a) ? [Cu(SMeaaiNMe)(N₃)(μ- OHCH₃)]₂ (3a), has been performed in one case. The tetranuclear complex shows ferromagnetic and antiferromagnetic interactions. The spectra, redox chemistry and magnetism, are explained by DFT studies.

Full text of DOI:10.1002/ejic.200900648

FULL PAPER
DOI: 10.1002/ejic.200900648
Copper-Azide-Thioarylazoimidazoles – Structure, Spectra, Redox Properties,
Magnetism and Theoretical Interpretation
Prasenjit Bhunia,[a] Debasis Banerjee,[a] Papia Datta,[a] Pallepogu. Raghavaiah,[b]
Alexandra M. Z. Slawin,[c] John D. Woollins,[c] Joan Ribas,[d] and Chittaranjan Sinha*[a]
Keywords: Copper / Bridging ligands / Structure elucidation / Magnetic properties / Redox chemistry
Azido-copper(II) and -copper(I) complexes of 1-alkyl-2-[(o-
thioalkyl)phenylazo]imidazole (SRaaiNRЈ) have been pre-
pared and studied. Complex 2 [Cu(SRaaiNRЈ)(µ1,1-N3)(N3)]2
dimerises via end-to-end (µ1,3)-N3 to form a tetrameric struc-
ture. Azido-copper(I) complexes of the ligands are obtained
as MeOH-bridged dimers, [Cu(SRaaiNRЈ)(N3)(µ-OHMe)]2
(3). The electronic spectra suggest that a small reorganisation
energy (0.08 eV) is associated with the change in electronic
configuration, structure and oxidation state from CuII to CuI.
Redox interconversion, CuII ↔ CuI, [Cu(SMeaaiNMe)(µ-N3)-
(N3)]2 (2a) ↔ [Cu(SMeaaiNMe)(N3)(µ-OHCH3)]2 (3a), has
been performed in one case. The tetranuclear complex shows
ferromagnetic and antiferromagnetic interactions. The spec-
tra, redox chemistry and magnetism are explained by DFT
studies.
of its ability to generate bridging systems with CuII/
CuI.[14–16] Azide may serve as an end-on (µ1,1) and an end-
to-end (µ1,3) bridging agent. In general the end-on coordi-
nation mode is associated with ferromagnetic coupling,
whereas end-to-end bridging leads to antiferromagnetic in-
teractions.[15] In this work, we report copper(I) complexes
of SRaaiNRЈ and ternary complexes of CuII/CuI,
Introduction
Structure and electronic configuration are interrelated
properties in transition metal chemistry.[1–4] The structural
change associated with CuII/CuI reorganisation effects is
utilised by biochemical systems in copper-containing metal-
loenzymes.[4–9] Cu(II)- and Cu(I)-diimine complexes (di-
imine function, –N=C–C=N–) have attracted much re-
search interest in the field of redox chemistry, photochemis-
try and photophysics, supramolecular chemistry, bioinor-
ganic and medicinal chemistry, magnetic materials etc., in-
spiring us to design new ligands isoelectronic to diimine.
We have previously reported 2-(arylazo)imidazoles[10–13]
with the azoimine (–N=N–C=N–) chelating functional
group, which is π-acidic and stabilises low-valent metal oxi-
dation states. 1-Alkyl-2-(arylazo)imidazole successfully sta-
bilises the CuI state.[11,12] 1-Alkyl-2-[(o-thioalkyl)phenyl-
azo]imidazoles (SRaaiNRЈ) are ligands with N(imidazole)
(N), N(azo) (NЈ) and S(thioether) donor centres. The reac-
tion of CuCl2 with SRaaiNRЈ gives a pentacoordinate
square pyramidal Cu(SRaaiNRЈ)Cl2 compound.[13] In this
–
SRaaiNRЈ and azide (N3 ). The complexes have been char-
acterised by spectroscopic and electrochemical techniques.
as well as X-ray diffraction studies. One of the azide-bridg-
ing CuII-SRaaiNRЈ complexes has been used to examine
magnetic coupling at variable temperature, and it shows
strong ferromagnetic (J1 = 13.35 cm–1) and weak antiferro-
magnetic (J2 = –0.55 cm–1) interaction. Redox interconver-
sion has been studied in one case. DFT and TD-DFT com-
putations have been performed on optimised geometries of
selected molecules to define electronic structure, spectra,
magnetism and redox properties of the complexes both in
the gas phase and in solution.
–
work, we have selected azide (N3 ) as counterion, because
Results and Discussion
[a] Inorganic Chemistry Section, Department of Chemistry, Ja-
davpur University,
1-Alkyl-2-[(o-thioalkyl)phenylazo]imidazoles (SRaaiNRЈ)
have three potential donor centres N(imidazole), N(azo)
and S(thioether).[13] They were synthesised by coupling o-
(thioalkyl)phenyldiazonium ions with imidazole in aqueous
sodium carbonate and purified by solvent extraction and
chromatography. The alkylation was carried out by adding
alkyl iodide (MeI, EtI) in dry THF solution to the corre-
sponding 2-[o-(thioalkyl)phenylazo]imidazole in the pres-
ence of sodium hydride.
Kolkata 700032, India
Fax: +91-033-2413-7121
E-mail: c_r_sinha@yahoo.com
[b] Department of Chemistry, Hyderabad Central University,
Hyderabad 500046, India
[c] Department of Chemistry, University of St Andrews,
St Andrews, Fife KY16 9ST, UK
[d] Departament de Química Inorgànica, Universitat de Barcelona,
Diagonal 6487, 08028 Barcelona, Spain
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.200900648.
Eur. J. Inorg. Chem. 2010, 311–321
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
311

C. Sinha et al.
FULL PAPER
Figure 1. Molecular structure of [Cu(SMeaaiNEt)(µ-N3)(N3)]2 (2b) with atom numbering scheme (symmetry codes: –x + 1, –y + 2, –z +
1) (35% ellipsoids shown).
A methanol solution of Cu(ClO4)2·6H2O and the appro-
priate ligand SRaaiNRЈ in a 1:1 mol ratio were treated with
aqueous solutions of NaN3 (2.5 equiv.). Slow evaporation
of the solution gave block-shaped brown crystals. The com-
plexes were characterised by microanalytical, spectroscopic,
redox and magnetic (bulk and EPR) measurements. The X-
ray structure determination in one case shows that 2 has a
tetranuclear structure (see the discussion of crystal structure
and Figure 1). The complexes are soluble in methanol, eth-
anol, chloroform, dichloromethane and acetonitrile but in-
soluble in hydrocarbons (hexane, benzene, toluene). They
are nonconducting. Their magnetic moments at room tem-
perature (1.6–1.7 B.M.) are lower than those for typical S
= ½ (CuII) compounds.
The CuI complexes (Scheme 1) were synthesised by add-
ing SRaaiNRЈ (1) to a well-stirred solution of NaN3 and
[Cu(MeCN)4](ClO4) in methanol under dry nitrogen.
Brown crystalline compounds separated on slow evapora-
tion of the solvent. The complexes were characterised by C,
H,
N
analyses and spectroscopic data as [Cu-
(SRaaiNRЈ)(N3)(µ-OHCH3)]2 (3). Structural confirmation
has been carried out in one case by single-crystal X-ray
crystallography. [Cu(SRaaiNRЈ)2](ClO4) (4) were synthe-
sised by refluxing mixtures of [Cu(MeCN)4](ClO4) and
SRaaiNRЈ in dry MeOH under dry nitrogen. The com-
plexes are fairly soluble in CH3CN, CHCl3, CH2Cl2 and are
insoluble in hydrocarbons. The molar conductance mea-
surement shows that complexes 2 and 3 are nonconducting
and 4 exhibits 1:1 electrolytic conductivity.
Scheme 1.
The X-ray structure (Figure 1) reveals that complex 2b
has a neutral tetranuclear copper(II) centre comprising a
dimer of dinuclear copper(II) subunits. Selected bond metal centre. There are two crystallographically unique cop-
lengths and angles are given in Table 1. The ligand, SMeaai- per(II) environments: one of them is square-based pyrami-
NEt, is a bidentate N(imidazole) (N), N(azo) (NЈ) chela- dal CuN5, and the second is a distorted octahedral CuN6-
tor; –S–Me (thioether) remains free and away from the type environment. The two unique copper atoms are linked
312
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Copper-Azide-Thioarylazoimidazoles
by two µ1,1-azides, whilst dimerisation of the dinuclear mo- ing ligand. The ligand, SMeaaiNEt, has three eligible donor
tif is accomplished through µ1,3-N3 groups. There are two centres: N(imidazole), N(azo) and S(thioether); in this case,
different N-donor centres of SMeaaiNEt: N(imidazole) it acts as an N(imidazole), N(azo) bidentate chelating
[N1, N21 or N1a, N21a] and N(azo) [N7, N27 or N7a, agent. The chelate angle [Cu–N=N–C=N (N–N)] is
N27a]. The Cu–N distances of these two types of N centres 71.69(3)°, which is comparable to the reported data.[11,12]
differ significantly by approximately 0.07 Å {Cu–N(azo) The deviation of the angle from the ideal 90° for a regular
[Cu1–N7, 2.6277(16); Cu2–N27, 2.5837(18) Å] and Cu–N(i- structure is a result of steric requirements of the chelated
midazole) [Cu1–N1, 1.9610(16); Cu2–N21, 1.9788(16) Å]}. ligands. The Cu–N(azo) bond length [Cu1–N4, 2.468(4) Å]
The stronger binding of N(imidazole) to CuII may be due is longer than the Cu–N(imidazole) distance [Cu1–N1,
to the comparable hardness of CuII and N(imidazole). This 1.987(3) Å]. The N=N bond length [N3–N4, 1.268(4) Å] is
is also observed in copper-containing biomolecules.[17] The greater than that of the free ligand value [1.252(1) Å][18] but
N=N distance [N6–N7/N26–N27] is 1.278(2) Å, which is is shorter than that in the CuII analogue (Table 1, Figure 1),
slightly elongated relative to the free ligand value,[18] implies perhaps as a consequence of better dπ(Cu)Ǟπ*(azo) charge
some degree of charge delocalisation, d(Cu)Ǟπ*(azo).[11–13] overlap[12,19,20] in this compound than in 2b. CH3OH acts as
bridging molecule through the O centre, and thus a dimer is
Table 1. Bond lengths and bond angles of 2b and 3b.
formed. The Cu1–O1 distance is 1.939(3) Å. The
Cu1···Cu1A distance is too long (3.052 Å) to consider any
metal–metal interaction. In the dinuclear motif, the bridg-
ing unit Cu2O2 is a distorted four-armed plane of mean
deviation of approximately 0.02 Å. The bridge angle is
Cu1–O1–Cu1A, 103.82(13)° and the remaining angle is O1–
Cu1–O1A, 76.18(13)°. The chelate and bridge planes are
inclined at an angle of 78.39(16)°.
2b
Bond lengths /Å
Bond angles /°
Cu1–N1
1.9610(16) N1–Cu1–N41
1.9633(17) N1–Cu1–N47
1.9936(16) N41–Cu1–N47
2.0120(17) N1–Cu1–N50
98.02(7)
169.52(7)
92.43(7)
91.89(7)
167.41(7)
77.65(7)
100.98(7)
91.17(7)
167.57(7)
168.04(7)
90.97(6)
76.91(7)
70.41(6)
70.86(7)
101.47(7)
102.25(7)
176.3(2)
179.1(2)
102.25(7)
101.47(7)
77.65(7)
76.91(7)
Cu1–N41
Cu1–N47
Cu1–N50
Cu1–N7
2.628(4)
N41–Cu1–N50
Cu2–N44
Cu2–N21
Cu2–N50
Cu2–N47
Cu2–N27
N6–N7
N26–N27
N41–N42
N42–N43
N44–N45
N45–N46
N47–N48
N48–N49
N50–N51
N51–N52
Cu2a–N43
Cu1a–N41a
1.9536(17) N47–Cu1–N50
1.9788(16) N44–Cu2–N21
1.9987(16) N44–Cu2–N50
2.0392(17) N21–Cu2–N50
2.584(3)
1.278(2)
1.278(2)
1.203(2)
1.153(2)
1.205(2)
1.158(2)
1.215(2)
1.145(2)
1.210(2)
1.143(2)
2.732(3)
1.963(4)
N44–Cu2–N47
N21–Cu2–N47
N50–Cu2–N47
N1–Cu1–N7
N21–Cu2–N27
Cu1–N47–Cu2
Cu1–N50–Cu2
N43–N42–N41
N49–N48–N47
Cu1–N50–Cu2
Cu1–N47–Cu2
N50–Cu1–N47
N50–Cu2–N47
Figure 2. Thermal ellipsoidal plot with atom labelling scheme of
[Cu(SMeaaiNEt)(N3)(µ-OHCH3)]2 (3b) (30% probability). Atoms
with label A are generated by symmetry.
3b
Bond lengths /Å
Bond angles /°
Cu1–N1
Cu1–N4
Cu1–N5
Cu1–O1
Cu1–O1a*
N3–N4
N5–N6
N6–N7
Cu1–Cu1a*
1.987(3)
2.468(4)
1.964(4)
1.938(3)
1.939(3)
1.268(5)
1.179(6)
1.156(6)
N1–Cu1–N4
N5–Cu1–N1
N5–Cu1–N4
O1–Cu1–O1a*
O1–Cu1–N5
O1–Cu1–N5
O1–Cu1–N1
O1a*–Cu1–N1
71.69(13)
93.97(16)
89.43(17)
76.18(13)
93.40(15)
167.13(16)
171.76(13)
96.02(13)
112.07(13)
101.41(13)
38.10(8)
Infrared spectra of complexes 2 exhibit ν(N=N) and
ν(C=N) at 1410–1430 and 1580–1595 cm–1, respectively,
and these values are redshifted by 10–25 cm–1 relative to
those of the free ligands. This supports coordination of
N(azo) and N(imine) to CuII. The most significant observa-
tion is the appearance of a strong doublet at 2090–2105 and
2065–2085 cm–1. These correspond to bridging νasym
-
3.0516(11) O1–Cu1–N4
O1–Cu1–N4
(N3).[15,16,21]
O1a*–Cu1–Cu1
O1a*–Cu1a*–Cu1
N7–N6–N5
In complexes 3, ν(N3) appears as a single sharp stretch at
2035–2045 cm–1. The ν(N=N) and ν(C=N) appear at 1410–
1415 and 1580–1590 cm–1, respectively. The stretching fre-
quency of N=N in [Cu(SRaaiNRЈ)(N3)(µ-OHCH3)]2 (3) ap-
pears at a lower value than that for CuII complexes, [Cu(S-
RaaiNRЈ)(µ-N3)(N3)]2 (2) (∆ν = 5–10 cm–1), and this effect
38.08(8)
177.5(5)
103.82(13)
Cu1–O1–Cu1a*
*Symmetry: –x + 1, –y + 2, –z + 1
The single-crystal X-ray structure of [Cu(SMeaaiNEt)- has been attributed to better dπ(Cu)-π*(azo of ligand) back
(N3)(µ-OHCH3)]2 (3b) is shown in Figure 2. Selected bond bonding in copper(I) complexes[11–13,19] than in copper(II)
lengths and angles are given in Table 1. The copper(I) cen- complexes (also supported by N=N bond length data, vide
tre exhibits a distorted tetrahedral CuN3O coordination supra). In [Cu(SRaaiNRЈ)2](ClO4) (4), ν(N=N) and
sphere bridged by OHCH3 and two N centres from chelat- ν(C=N) appear at 1390–1400 and 1560–1575 cm–1, respec-
Eur. J. Inorg. Chem. 2010, 311–321
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C. Sinha et al.
FULL PAPER
Table 2. FTIR[a] and UV/Vis spectra[b] of the complexes in CH3CN.
Compound
UV/Vis spectra
IR spectra /cm–1
ν(N3 )
–
–
λmax /nm (10–3 ϫ ε /dm3 mol–1 cm–1)
ν(ClO4 )
ν(C=N)
ν(N=N)
2a
2b
2c
2d
3a
3b
3c
3d
4a
4b
4c
4d
725(0.37), 410(27.01), 362(38.11), 265(11.03)
759(0.12), 413(9.57), 367(13.73), 269(9.31)
728(0.15), 416(18.31), 364(21.05), 263(9.23)
726(0.48), 403(20.10), 367(26.34), 268(14.12)
711(0.18), 434(13.96), 369(13.59), 251(8.41)
715(0.16), 428(12.24), 368(13.27), 259(8.77)
737(0.18), 436(10.45), 371(12.71), 254(7.93)
735(0.18), 434(13.57), 373(12.71), 253(8.19)
762(0.45), 415 (16.54), 359(22.19), 262(15.74)
756(0.41), 410 (14.66), 358(21.47), 260(14.52)
752(0.47), 419 (14.14), 362(21.30), 260(14.15)
765(0.38), 419 (20.11), 352(26.24), 257(15.13)
2092, 2065
2102, 2071
2090, 2068
2098, 2069
2040
2035
2043
1581
1587
1585
1590
1589
1586
1590
1576
1591
1587
1585
1590
1423
1420
1426
1443
1421
1429
1455
1446
1429
1428
1423
1428
2040
1094
1089
1089
1090
[a] In KBr disk. [b] In MeCN solution.
tively. The ν(ClO4) frequency appears as a high intense 435 nm (Figure 3), which are characteristic features of CuI
sharp band at 1085–1090 cm–1 with a weak signal at complexes when bonded with conjugated organic chromo-
625 cm–1. Some interesting IR data are given in Table 2.
The electronic spectra of 2 exhibit multiple highly intense
transitions (ε ≈ 104 –1 cm–1) in the visible region, 400–
445 nm, along with a broad weak band at 725–760 nm. In
the free ligand SRaaiNRЈ, the intraligand charge transi-
tions, n–π* and π–π*, appear at 370–380 and 250–260 nm,
respectively. Some of the transitions are new (Table 2, Fig-
ure 3) in the complexes: these are characteristic of cop-
per(II) azoheterocycles[16,19,22] and are the MLCT transi-
tions involving dπ(Cu)Ǟπ*(arylazoheterocycle). By com-
paring them with values for copper(II)-1-alkyl-2-(arylazo)-
imidazoles,[11–13,16] copper(II)-2(arylazo)pyridine,[19] cop-
per(II)-pyridylthioazophenolates[22] and other pyridylthio-
ethers,[23] we can assign the transitions at approximately
410 nm to the MLCT [dπ(Cu)Ǟπ*(azoimidazole)] band,
and the absorption at approximately 740 nm is undoubtedly
a d–d transition.[24] The visible ranges of the spectra of cop-
per(I) complexes (3, 4) show similar metal-to-ligand charge-
transfer (MLCT) transitions at 710–765 nm and 410–
phores.[14–16]
EPR Spectra
Solid state EPR spectra of 2 at room temperature
(298 K) are weakly resolved. Copper(I) complexes 3 and 4
are EPR silent. The hyperfine splitting in the EPR spectra
of 2 is poor. The resolution is better at 77 K in MeCN solu-
tion (Figure 4). The complexes show the expected four-line
(63Cu, I = 3/2) EPR spectra and are anisotropic at higher
magnetic field, exhibiting axial spectra having gII values
varying from 2.188 to 2.226 and AII in a range from
140ϫ10–4 to 165ϫ10–4 cm–1. The results are in general
agreement with the electronic spectra, which also suggest
the existence of distorted geometry. From the observed g-
tensor values of the CuII complexes, it is clear that gʈ Ͼ
gЌϾ 2.0023, which agrees with the ground state configura-
2
tion of dx2–y2, giving B1g.
Figure 4. EPR spectrum of [Cu(SEtaaiNEt)(µ-N3)(N3)]2 (2d) in
MeCN at 77 K.
The stereochemistry of [Cu(SRaaiNRЈ)(N3)(µ-OH-
CH3)]2 (3) and [Cu(SRaaiNRЈ)2](ClO4) (4) was studied by
1H NMR spectroscopy. The aromatic and imidazole pro-
Figure 3. UV/Vis spectra of 2b (Ϫ) and 3b (- - -) in DMF at 298 K. tons are shifted downfield on coordination of SRaaiNRЈ to
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Copper-Azide-Thioarylazoimidazoles
1
Table 3. H NMR spectroscopic data of [Cu(SRaaiNRЈ)]2(ClO4) (4) and [Cu(SRaaiNRЈ)(N3)(µ-OH CH3)]2 (3a) in CDCl3 at room tem-
perature.
Compound δ /ppm (J /Hz)
4-Hb[a]
7.34
5-Hb
7.22
8Hd
9, 10-Hm 11-Hd
N1-CH3
N1-CH2
N1-CH2CH3
S-CH3
S-CH2
S-(CH2)CH3
s
q
t
s
q
t
3a
3b
3c
3d
4a
4b
4c
4d
7.45
(7.0)
7.50
(7.0)
7.40
(7.0)
7.45
(7.0)
7.44
(7.0)
7.46
(7.5)
7.43
(7.5)
7.47
(7.5)
7.57
7.55
7.60
7.56
7.53
7.53
7.54
7.56
7.84
(7.5)
7.87
(7.5)
7.85
(7.5)
7.88
(7.5)
7.86
(8.0)
7.84
(8.0)
7.89
(7.5)
7.83
(7.5)
4.28
4.31
4.22
4.24
2.72
2.68
7.38
7.36
7.30
7.28
7.27
7.31
7.30
7.24
7.20
7.30
7.27
7.24
7.25
7.28
4.48
(9.0)
1.68
(8.0)
3.36
(7.5)
3.40
(7.5)
1.52
(8.0)
1.57
(8.0)
4.40
(9.0)
1.62
(8.0)
2.70
2.72
4.74
(9.0)
1.78
(8.0)
3.42
(9.0)
3.40
(9.0)
1.56
(8.0)
1.57
(8.0)
4.72
(9.0)
1.75
(8.0)
[a] b Broad singlet; d doublet; m multiplet; s singlet; t triplet; q quartet.
CuI relative to the free ligand data[11,12] (Table 3). This im-
plies significant bonding interaction of the metal ion with
the ligand. Imidazole protons (4- and 5-H) and aryl protons
(8–11-H) suffer approximately 0.10 to 0.15 ppm downfield
shift. The S–R and N1–RЈ do not shift significantly, which
implies a non-coordinated –S–R centre. Ligands SRaaiNRЈ
are capable of showing a tridentate N,NЈ,S donor system.
1
However, H NMR spectroscopic data reflect no coordina-
tion of –S–R to CuI, thus these ligands serve as bidentate
N,NЈ chelators.
The magnetic properties of complex 2b are shown in Fig-
ure 5 as a χMT vs. T plot (χM is the molar magnetic suscep-
tibility for two CuII ions). The value of χMT at 300 K is
0.86 cm3 mol–1 K, a typical value for two copper(II) ions
with g Ͼ 2.00, as expected. On lowering the temperature,
there is a rapid increase in χMT to 1.03 cm3 mol–1 K at 5 K
and then a decrease to 0.91 cm3 mol–1 K at 2 K. These fea-
tures indicate noticeable intramolecular ferromagnetic cou-
pling with the presence of weak intermolecular antiferro-
magnetic interactions, always present at very low tempera-
ture.
Figure 5. Plot of the susceptibility data, χMT vs. T, for 2b, assuming
a dinuclear entity. The solid line represents the best fit using the J2
parameter with the mean field approach (see text for explanation).
Inset: plot of the reduced magnetisation M/N µB vs. H data at 2 K.
The plot of the reduced magnetisation at 2 K is included
in Figure 5. The M/N µB value at saturation (5 T) is 2.00,
in agreement with the presence of two electrons in the
ground state.
Complex 2b is a tetranuclear entity, constituted by dimer-
isation of two Cu2 “dinuclear entities”. In the “dinuclear
entity” each CuII is linked by two azido ligands in an end-
on (µ1,1-N3) coordination mode. Furthermore, one of the
terminal azido ligands of each dinuclear unit links the
neighbouring dinuclear entity by means a long apical Cu–
N(azido) bond. (Figure 1). The resulting tetranuclear entity,
together with the two different magnetic pathways (J1 and
J2) are depicted in Scheme 2.
Scheme 2.
ing a J2 parameter through the mean-field approach for cal-
For calculating the values of J1 and J2 two approaches culating the intermolecular interactions.[26,27] This approach
have been carried out. First, we have considered the Cu2 is valid because of the long apical Cu–N(azido) distance,
“dinuclear entity” by applying the Bleaney–Bowers for- which allows to assume a very weak magnetic coupling. The
mula,[25] with the Hamiltonian H = –J1ΣSiSj, and introduc- best-fit parameters were: J1 = 13.35Ϯ0.5 cm–1, g =
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315

C. Sinha et al.
FULL PAPER
2.12Ϯ0.002, J2 = –0.55Ϯ0.01 cm–1 and R = 4.0ϫ10–5 –1.0 to –1.2 V (∆Ep Ͼ 140 mV) (Figure 6), which may be
{R is the agreement factor defined as Σi[(χmT)obs
–
assigned to reduction of the azo groups [(–N=N–)/
(χmT)calc]2/Σi[(χmT)obs]2}.
(–N=N–)–] of the chelated ligands. The free ligand does not
The second approach consists of considering the tetranu- show any oxidation, but irreversible reductive responses ap-
clear complex as an isolated entity. The corresponding fit pear at Ͻ –1.0 V. The voltammogram also shows a sharp
can be made by applying the corresponding formula for the anodic part at approximately –0.2 V, possibly due to the
model indicated in Scheme 2 or, more easily, by working CuI/Cu0 couple.[12,33] The reduced Cu0 is absorbed on the
with the Clumag program,[28] using the same Hamiltonian electrode surface, as evidenced by the narrow width of the
and with the coupling values shown in Scheme 2. Both anodic response with a large peak current.
models are exact, and thus the results are identical and in-
dependent of the method. The best-fit parameters are: J1 =
11.25Ϯ0.5 cm–1, J2 = –0.85Ϯ0.02 cm–1, g = 2.12Ϯ0.01
and R = 3.7ϫ10–3 {R is the agreement factor defined as
Σi[(χmT)obs – (χmT)calc]2/Σi[(χmT)obs]2}.
By applying two different methods, we have obtained
very similar results, as expected: J1 is medium and positive
(ferromagnetic) and J2 is weak and negative (antiferromag-
netic).
All experimentally reported complexes,[29] as well as
theoretical studies,[30] have demonstrated that almost all di-
nuclear complexes with double azido ligand bridges in the
µ1,1 coordination mode create ferromagnetic coupling. All
data seem to indicate that the main parameter is the M–N–
M angle (N referring to the N3 bridging ligand). For CuII,
when this angle is extraordinarily large, for example greater
than 108°, the magnetic coupling becomes antiferromag-
netic.[31] In fact, almost all complexes have a Cu–N–Cu an-
gle between 96° and 104°, thus being ferromagnetic. Many
other structural factors may influence the J value, such as
the Cu–N distance and the Cu–N3–Cu torsion angle.[32]
A
clear dependence of the exchange coupling constant on the
Cu–N distance has been found, the ferromagnetic coupling
decreasing as the Cu–N distance increases.[30] The J1 value
found for complex 2b is rather small compared to those
reported in the literature.[30] The three most important fac-
tors are: the Cu–N–Cu angles [Cu1–N50–Cu2 102.25(7)°
and Cu1–N47–Cu2 101.47(7)°], the Cu–N distances (these
are rather long, from 1.994 to 2.039 Å) and the τ torsion
angles (these are very large). The sum of these factors
causes the relatively small J1 parameter. Assuming a tetra-
nuclear entity, the J2 value (–0.85 cm–1) is easily understood
by taking into account the long Cu(apical)–N(azido) dis-
tance (2.73 Å).
Copper(I) complexes [Cu(SRaaiNRЈ)(N3)(µ-OHCH3)]2
(3) show oxidative responses at approximately 0.4 V. This is
quasireversible, as estimated from peak-to-peak separation
(∆Ep Ͼ 100 mV) and is assigned to the CuII/CuI couple by
comparison with literature reports.[11,12,19] Complexes
[Cu(SRaaiNRЈ)2](ClO4) (4) show a higher CuII/CuI poten-
tial, which may be due to the presence of two π-acid-coordi-
nated azoimine functions. Figure 6 shows the cyclic voltam-
mogram (CV) of the complexes in MeOH (Table 4). The
CV plots of copper(II) complexes 2 show a reductive re-
sponse at approximately 0.4 V vs. SCE. On comparing with
the CV of Cu(RaaiRЈ)2X2 (X = N3, NCS),[10] the couple is
assigned to a CuII/CuI couple. On scanning in the negative
Figure 6. Cyclic voltammogram of (a) 2a, (b) 3a and (c) 4a in
CH2Cl2.
Table 4. Cyclic voltammetric data.[a]
Complex
Metal redox couple
Ligand redox couple
E /V (∆Ep /mV)
E /V (∆Ep /mV)
CuII/CuI
CuI/Cu0
azo/azo–
azo=/azo–
2a
2b
2c
2d
3a
3b
3c
3d
4a
4b
4c
4d
0.33 (150)
0.37 (170)
0.38 (160)
0.40 (140)
0.37 (120)
0.35 (128)
0.30 (130)
0.38 (140)
0.44 (180)
0.42 (180)
0.40 (180)
0.44 (110)
–0.25[b]
–0.22[b]
–0.22[b]
–0.24[b]
–0.48 (160) –1.40 (170)
–0.44 (180) –1.35 (200)
–0.44 (160) –1.30 (200)
–0.48 (180) –1.38 (180)
–0.58 (150) –1.42 (170)
–0.54 (170) –1.38 (200)
–0.56 (180) –1.42 (200)
–0.58 (160) –1.38 (180)
–0.40 (140) –1.22 (190)
–0.47 (160) –1.24 (200)
–0.44 (170) –1.27 (200)
–0.44 (160) –1.24 (140)
[a] Solvent: MeCN; Pt-disk working electrode, supporting electro-
lyte: TBAP (0.01 ); reference: SCE; solute concentration: 10–3 ;
scan rate: 0.05 Vs–1; ∆Ep = |Epa – Epc| mV; Epa = anodic peak
potential, Epc = cathodic peak potential in V; E1/2 = 0.5(Epa
Epc) V. [b] Epc.
+
DFT calculation has been performed for two different
direction up to –1.8 V, we observe an irreversible response, molecules, 2b and 3b. The optimised structure of these
Epc, at approximately –0.4 V and a quasireversible one at molecules are developed by using the Gaussian 03 analysis
316
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Copper-Azide-Thioarylazoimidazoles
package. The orbital energies along with contributions (ca. 39%). The chelating ligand SMeaaiNEt, in general, is
from the ligands and metal are given in the Supporting the main constituent of unoccupied MOs (2b: LUMO to
Information. Figure 7 depicts selected occupied and unoc- LUMO+10, 99–100% and 3b: LUMO, 73%; LUMO+1,
cupied frontier orbitals. In CuII complex 2b, the highest 95%). The charge-transfer transition in the visible region
occupied molecular orbital (MO) is singly occupied, so it not observed in the free ligand is assigned to pure MLCT
is abbreviated as SOMO. The occupied MOs are stabilised, rather than an admixture of dπ(Cu)Ǟπ*(azoimine)
whereas unoccupied MOs are destabilised on going from and π(azide)Ǟπ*(azoimine) transitions involving the
the CuII (2b) to the CuI (3b) compounds: ESOMO(2b) = SOMOǞLUMO/LUMO+1/LUMO+2 and HOMO-1/
–4.9 eV and EHOMO(3b) = –4.17 eV. This may be due to HOMO-2/HOMO-3ǞLUMO/LUMO+1//LUMO+2 func-
better electron donation from CuI (d10) compared to that tions. The ILCT π(thioazoimidazole)Ǟπ*(azoimine) tran-
from CuII (d9) toward the π-acidic azoimine function. Sol- sitions may appear in the high energy region. In CuI complex
vent polarity stabilises occupied MOs more efficiently than 3b, the transitions HOMO/HOMO-1/HOMO-3ǞLUMO/
unoccupied MOs. Thus, the energy separation (∆E) be- LUMO+1/LUMO+2 have significant dπ(Cu)Ǟπ*(thioazo-
tween the SOMO (for 2b) or HOMO (for 3b) and the imidazole) contribution.
LUMO increases on going from the gas phase to the
Cyclic voltammetric behaviour of 3 and 4 are readily ra-
MeCN phase. The occupied MOs (HOMO-1 and HOMO- tionalised by using the DFT calculation. Because of higher
2) of 2b have a significant contribution from Cu (ca. 10%). metal (Cu) function in occupied MOs in 3b, the complexes
The bridging azide (µ1,1 and µ1,3-N3) contributes 7% to show metal oxidation. Unoccupied MOs are significantly
the HOMO, while the terminal azide contributes 89%. In dominated by the azoimine function, thus reduction may
complex 3b copper contributes 42% to the HOMO and refer to electron addition at the azo-dominated orbital of
13% to the LUMO. Azide contributes to the HOMO the ligand.
Figure 7. Selected molecular orbital pictures of 2b and 3b.
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317

C. Sinha et al.
FULL PAPER
The spin density calculated for the triplet state from a
DFT study determines the exchange coupling between the
two metal centres. The degree of delocalisation of the un-
paired electron increases if the coordinating atoms of the
ligand participate in the singly occupied molecular orbital
(SOMO), which leads to the enhancement of the electron
density of the donor atoms. Interestingly, the spin density
is mainly distributed among the copper dx2–y2 magnetic or-
Conclusion
1-Alkyl-2-[(o-thioalkyl)phenylazo](SRaaiNRЈ)
coordi-
–
bital and µ1,1-N3 bridging between two Cu centres nates to CuII and CuI in the presence of azide (N3 ) as a
[Cu1···Cu2] in the dinuclear entity. It is to be noted that the bidentate N,NЈ-chelator. Tetranuclear CuII-azido-bridged
exchange coupling constant for 2b calculated by using the complexes show ferromagnetic and antiferromagnetic cou-
crystal coordinates suggests a ferromagnetic interaction (J) pling. Electrochemistry shows a quasireversible CuII/CuI re-
of 10.76 cm–1. For the optimised geometry, the calculated dox couple along with CuI/Cu0 response at –0.2 V. The
(UB3LYP) average Cu-µ-N(µ1,1-N3) bond length is 1.98 Å, solution spectra show highly intense metal-to-azoimine
which is comparable with the average X-ray value (2.03 Å). charge transfer. CuII (2) and CuI (3) complexes undergo
The other bond lengths within the coordination sphere de- redox interconversion; CuII complex 2b is reduced by ascor-
viate marginally from the experimentally observed values. bic acid to a CuI complex in methanol in the presence of
In terms of magnetic properties, the Cu1–µ-N(µ1,1-N3)–Cu2 excess NaN3, whilst CuI complex 3a is oxidised by chlorine
angle is the most important. According to the Hay water to CuII complex (2). The spectra, magnetism and re-
model,[33] the antiferromagnetic exchange coupling con- dox properties are explained by using DFT computation on
stant for the binuclear metal complexes, each bearing one optimised geometries.
unpaired electron, is linearly proportional to the square of
the energy difference between the two SOMOs. The overlap
Experimental Section
between the magnetic orbitals of the copper atoms takes
place via the bonding between the dx2–y2 magnetic orbital
of copper and the hybrid orbital of the bridging azido-N.
Thus, the spin delocalisation on the bridging group corro-
borates the antiferromagnetic interaction.
Materials: All starting organic compounds were purchased from
Aldrich Chemical Co. and used without further purification.
CuCl2·2H2O and NaN3 were E. Merck reagent grade. Solvents
were distilled from appropriate drying agents under appropriate
conditions as per literature in a N2 atmosphere.[34] [Cu(MeCN)4]-
(ClO4) was used as copper(I) precursor. All experiments were car-
ried out under N2. The syntheses of the ligands were carried out by
following the common procedure[13] of coupling the o-(thioalkyl)-
phenyldiazonium ion [obtained by diazotisation of o-(thioalkyl)ani-
line] with imidazole at pH 7 followed by N1-alkylation using alkyl
iodide in the presence of NaH in dry THF under dry and inert
conditions.
Redox Interconversion CuII ↔ CuI
The CuII–CuI interconversion experiment was carried
out by using a representative compound of the series,
[Cu(SMeaaiNMe)(µ-N3)(N3)]2 (2a). Compound 2a reacts
with ascorbic acid in aqueous methanol in the presence of
NaN3 (an excess amount of NaN3 is added to resist dissoci-
ation), and a brown-red copper(I) complex precipitates. The
identity of the reduced product has been established by
matching the spectroscopic and cyclic voltammetric results
(Table 2 and Table 4). The compound is diamagnetic. The
structure of the coordinated CuI compound was established
by its 1H NMR spectrum and by comparison with the spec-
trum of directly synthesised [Cu(SMeaaiNMe)(N3)(µ-
OHCH3)]2 (3a) (Table 3). Microanalytical data (C,H,N)
also confirm the composition of the compound. In a second
experiment, to a suspension of [Cu(SMeaaiNMe)(N3)(µ-
Caution! Perchlorate salts of metal complexes can be explosive. Al-
though no detonation tendencies have been observed, care is ad-
vised and handling of only small quantities recommended.
Physical Measurements: Microanalytical data (C,H,N) were col-
lected with a Perkin–Elmer 2400 CHNS/O elemental analyser.
Spectroscopic data were obtained by using the following instru-
ments: Perkin–Elmer model Lambda 25 spectrophotometer (UV/
Vis), Perkin–Elmer model RX-1 spectrometer on KBr disks at
4000–450 cm–1 (IR), Bruker (AC) 300 MHz FTNMR spectrometer
(1H NMR). Electrochemical measurements were performed by
using computer-controlled PAR model 250 VersaStat electrochemi-
cal instruments with Pt disk electrodes. All measurements were car-
OHCH3)]2 (3a) in methanol was added chlorine water, and ried out under nitrogen at 298 K with reference to SCE in acetoni-
trile and by using [nBu4N][ClO4] as supporting electrolyte. The re-
ported potentials are uncorrected for the junction potential. Room
temperature (298 K) magnetic susceptibility was measured with a
Sherwood Scientific (Cambridge, UK) instrument at 298 K, and
data were corrected by subtracting the diamagnetic contribution.
The diamagnetic correction was calculated by individually adding
the diamagnetic contribution of each atom using Pascal’s constants.
EPR spectra were recorded in MeCN solution at room temperature
(298 K) and liquid nitrogen temperature (77 K) by using a Bruker
model EMX 10/12 ESR spectrometer with an X-band ER 4119 HS
cylindrical resonator.
the mixture was stirred in air. Nitrogen gas was bubbled
through the solution to remove chlorine followed by the
addition of excess NaN3, whereupon the colour of the solu-
tion changed to brown-red. A crystalline compound was
precipitated by reducing the volume of the solution to half.
The compound so obtained was purified by crystallisation
from CH2Cl2/MeOH. The spectroscopic (IR and UV/Vis),
magnetic and voltammetric identification support the for-
mation of copper(II) complex 2a, which is supported by
microanalytical data and spectral measurements.
318
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Copper-Azide-Thioarylazoimidazoles
Synthesis of Complexes
[%] for [Cu(SMeaaiNMe)2](ClO4) (4a), (C22H24N8O4S2 ClCu)
(627): C, 42.04 (42.11); H, 3.88 (3.83); N, 17.92 (17.86). [Cu-
(SMeaaiNEt)2](ClO4) (4b), (C24H28N8O4S2ClCu) (655): C, 43.84
(43.97); H, 4.33 (4.27); N, 17.00 (17.10). [Cu(SEtaaiNMe)2](ClO4)
(4c), (C24H28N8O4S2ClCu) (655): C, 44.04 (43.97); H, 4.20 (4.27);
N, 17.21 (17.10). [Cu(SEtaaiNEt)2](ClO4) (4d), (C26H32N8O4-
S2ClCu) (683): C: 45.63 (45.68); H, 4.75 (4.69); N, 16.32 (16.40).
Copper(II) Complexes. Preparation of [Cu(SMeaaiNMe)(µ-N3)-
(N3)]2
(2a):
1-Methyl-2-[o-(thiomethyl)phenylazo]imidazole
(SMeaaiNMe) (200 mg, 0.86 mmol) in methanol (10 mL) was
added dropwise to a methanol solution (10 mL) of Cu(ClO4)2·
6H2O (330 mg, 0.89 mmol) at 298 K under N2. The brown-red
solution was stirred for 10 min, and a methanol solution of NaN3
(145 mg, 2.22 mmol) was added. It was then filtered and left undis-
turbed for a week. Dark brown crystalline compounds were sepa-
rated. The crystals were filtered, washed with water and cold meth-
anol and dried in vacuo. The yield was 200 mg (61%).
Copper(II)–Copper(I) Interconversion
[Cu(SMeaaiNMe)(µ-N3)(N3)]2 (2a)
Ǟ [Cu(SMeaaiNMe)(N3)(µ-
OHCH3)]2 (3a): To a suspension (15 mL) of [Cu(SMeaaiNMe)(µ-
N3)(N3)]2 (2a) (0.20 g, 0.26 mmol) in methanol was added with stir-
ring under N2 ascorbic acid (0.09 g, 0.50 mmol) in water (5 mL).
The brown suspension quickly changed to deep red-brown, and
stirring was continued for 30 min. NaN3 (0.2 g, excess amount) was
added to this solution and stirred. The volume of the solution was
reduced by bubbling off N2 gas, and a precipitate appeared within
a short while. The precipitated mass was filtered, washed with water
and cold methanol. The residue was dried with CaCl2 and recrys-
tallised by diffusion of CH2Cl2 solution to hexane. Brown shining
crystals were isolated. The yield of [Cu(SMeaaiNMe)(N3)(µ-
OHCH3)]2 (3a) was 0.08 g (42%). Microanalytical data: found
(calcd.) [%] for [Cu(SMeaaiNMe)(N3)(µ-OHCH3)]2 (3a),
(C12H16N7OSCu)2 (739): C, 38.92 (38.97); H, 4.36 (4.33); N, 26.45
(26.52).
All other complexes were prepared by the same procedure. The
yield varied from 60 to 75%. Microanalytical data: found (calcd.)
[%] for [Cu(SMeaaiNMe)(µ-N3)(N3)]2 (2a), (C11H12N10SCu)2
(759): C, 34.84 (34.78); H, 3.07 (3.16); N, 36.96 (36.89). [Cu(S-
MeaaiNEt)(µ-N3)(N3)]2 (2b), (C12H14N10SCu)2 (787): C, 36.55
(36.59); H, 3.47 (3.56); N, 35.65 (35.58). [Cu (SEtaaiNMe)(µ-
N3)(N3)]2 (2c), (C12H14N10SCu)2 (787): C, 36.50 (36.59); H, 3.61
(3.56); N, 35.68 (35.58). [Cu(SEtaaiNEt)(µ-N3)(N3)]2 (2d),
(C13H16N10SCu)2 (815): C, 38.18 (38.28); H, 3.88 (3.93); N, 34.48
(34.36).
Copper(I) Complexes. Preparation of [Cu(SMeaaiNMe)(N3)(µ-
OHCH3)]2 (3a): To a dry methanol solution of [Cu(MeCN)4](ClO4)
(133 mg, 0.40 mmol) was added solid sodium azide (5 equiv.,
132 mg, 2.03 mmol) whilst stirring at room temperature in an inert
atmosphere (N2). Then a dry methanol solution of SMeaaiNMe
(95 mg, 0.41 mmol) was added by a syringe in an inert atmosphere.
The resultant deep brown solution was stirred for one hour and
then heated under reflux for another one hour. The solution was
filtered, and the filtrate was kept undisturbed for crystallisation.
After a few days, deep brown crystals appeared, which were sepa-
rated by filtration. The crystals were washed with dilute methanol
(1:1, v/v) and dried with CaCl2 in a desiccator. The complexes were
characterised by C,H,N analysis, and spectroscopic data support
the composition [Cu(SMeaaiNMe)(N3)(µ-OHCH3)]2 (3a).
[Cu(SMeaaiNMe)(N3)(µ-OHCH3)]2 (3a) Ǟ [Cu(SMeaaiNMe)(µ1,1
-
N3)(N3)]2 (2a): To a methanol suspension of [Cu(SMeaaiN-
Me)(N3)(µ-OHCH3)]2 (3a) (0.20 g, 0.27 mmol) methanol saturated
with chlorine was added in drops and the mixture was stirred in
air. Immediately, the colour changed from red-brown to deep
brown. The stirring was continued for 45 min, and then N2 gas was
bubbled for a few minutes with constant stirring. Excess NaN3
(0.2 g) in water was added, and air was bubbled through the mix-
ture for 30 min and methanol was added from time to time to main-
tain the volume of the solution at 25 mL. The mixture was filtered
and kept in the freezer for 4 h. The brown precipitate was filtered
and washed with water and cold methanol. The compound was
soluble in the mixture of 2-methoxy ethanol and methanol (1:5,
v/v) and was crystallised by concentration in air for a week. The
yield of [Cu(SMeaaiNMe)(µ1,1-N3)(N3)]2 (2a) was 0.12 g (58%).
All other complexes were prepared by the same procedure. The
yield varied from 65 to 75%. Microanalytical data: found (calcd.)
[%] for [Cu(SMeaaiNMe)(N3)(µ-OHCH3)]2 (3a), (C12H16N7-
OSCu)2 (739): C, 38.88 (38.97); H, 4.26 (4.33); N, 26.56 (26.52).
[Cu(SMeaaiNEt)(N3)(µ-OHCH3)]2
(3b),
(C13H18N7OSCu)2
Microanalytical data: found (calcd.) [%] for [Cu(SMeaaiNMe)(µ1,1
-
(767):C, 40.59 (40.68); H, 4.72 (4.69); N, 25.48 (25.55). [Cu(SE-
taaiNMe)(N3)(µ-OHCH3)]2 (3c), (C13H18N7OSCu)2 (767): C, 40.62
(40.68); H, 4.64 (4.69); N, 25.50 (25.55). [Cu(SEtaaiNEt)(N3)(µ-
OHCH3)]2 (3d), (C14H20N7OSCu)2 (795): C, 42.17 (42.26); H, 5.00
(5.03); N, 24.58 (24.65).
N3)(N3)]2 (2a), (C11H12N10SCu)2 (759): C, 34.74 (34.78); H, 3.19
(3.16); N, 36.92 (36.89).
X-ray Crystal Structure Analysis of 2b and 3b: Details of crystal
analysis, data collection and structure refinement are given in
Table 5. Data for 2b (blue colour, prism shape, size
0.20ϫ0.20ϫ0.05 mm) were collected at 93(2) K by using a Rigaku
MM007/Mercury CCD diffractometer (Mo-Kα radiation, confocal
optics λ = 0.71073 Å). All refinements were performed by using
SHELXTL.[35] Data for 3b (brown colour, plate shape, size
0.36ϫ0.18ϫ0.10 mm) were collected with a Bruker SMART CCD
area detector using fine-focus sealed tube graphite monochro-
matised Mo-Kα radiation (λ = 0.71073 Å) at 293(2) K. Data were
corrected for Lorentz polarisation effects and for linear decay. Sem-
iempirical absorption corrections based on ψ-scans were applied.
The structure was solved by direct methods using SHELXS-97[35]
and successive difference Fourier syntheses.[36] All non-hydrogen
atoms were refined anisotropically. The hydrogen atoms were fixed
geometrically and refined by using the riding model. In the final
difference Fourier map, the residual minima and maxima were
–0.315 and 0.455 e/Å3 for 2b and –0.400 and 0.647 e/Å3 for 3b. The
structures were drawn by using the ORTEP-32[37] and PLATON-
99[38] programs.
Preparation of [Cu(SMeaaiNMe)2](ClO4) (4a): The ligand
SMeaaiNMe (100 mg, 0.43 mmol) in dry MeOH (25 mL) was
added to a methanol solution (20 mL) of [Cu(MeCN)4][ClO4]
(70 mg, 0.21 mmol) in N2 at room temperature. The dark-brown
solution was stirred for 3 h. The solution was reduced to half of its
original volume by bubbling N2 gas through it, a brown-red crystal-
line precipitate appeared, which was filtered, washed with meth-
anol/water (1:1, v/v) and dried with CaCl2. The dried compound
was purified by column chromatography. A column alumina (neu-
tral) was prepared in benzene. A chloroform solution of the com-
plex was absorbed in the column and eluted first by chloroform.
Initially a light yellow band was eluted and rejected. The desired
deep brown/red band was collected by elution by using a methanol/
chloroform (4:1, v/v) mixture and concentrated slowly in air. The
yield was 0.28 g (52%).
All other complexes were prepared by following identical pro-
cedures with yields of 55–70%. Microanalytical data: found (calcd.)
Eur. J. Inorg. Chem. 2010, 311–321
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319

C. Sinha et al.
FULL PAPER
Table 5. Summary of crystallographic data for 2b and 3b.
[1]
A. C. Steenabergen, E. Bouwman, R. A. G. de Graft, W. L.
Driessen, J. Reedijk, J. P. Zanello, J. Chem. Soc., Dalton Trans.
1990, 3175; R. Bastida, S. Gongalez, T. Rodrignez, A. Sousa,
D. E. Fenton, J. Chem. Soc., Dalton Trans. 1990, 3643; M. R.
Malachonsk, M. Adams, N. Elia, A. L. Rheingold, R. S. Kelly,
J. Chem. Soc., Dalton Trans. 1999, 2177; L. Casella, M. Gul-
lotti, R. Vigato, Inorg. Chim. Acta 1986, 124, 121; R. A. Allred,
S. A. Hufner, K. Rudzka, A. M. Arif, L. M. Berreau, Dalton
Trans. 2007, 351–357.
2b
3b
Empirical formula
Formula weight
Temperature /K
Crystal system
Space group
Crystal size /mm
a /Å
C24H28Cu2N20S2
787.86
93(2)
monoclinic
P21/n
0.20ϫ0.20ϫ0.05
14.951(4)
14.922(3)
15.245(4)
100.474(7)
3344.6(14)
4
C26H34Cu2N14O2S2
765.87
293(2)
monoclinic
P21/c
0.36ϫ0.18ϫ0.10
10.8091(19)
13.737(2)
15.4200(19)
133.081(7)
1672.3(4)
2
[2]
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V /Å3
Z
µ (Mo-Kα) /mm–1
θ range /°
hkl range
1.448
1.445
2.22–25.35
–17 Յ h Յ 18;
–16 Յ k Յ 17;
–18 Յ l Յ 14
1.565
2.34–25.36
–13 Ͻ h Ͻ 13;
–16 Ͻ k Ͻ 16;
–18 Ͻ l Ͻ 18
1.521
[4]
Dcalc /Mgm–3
Refined parameters
Total reflections
Unique reflections
436
19901
5971
0.0286
211
16956
3259
0.0529
[a]
R1 [I Ͼ 2σ(I)]
[b]
wR2
0.0703
0.1607
Goodness of fit
1.025
1.063
[a] R = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = [Σw(Fo – Fc ) /Σw(Fo2)2]1/2, w
2
2 2
= 1/[σ2(Fo)2 + (0.0336P)2 + (2.7488P)] for 2b; w = 1/[σ2(F0)2
+
(0.0942P)2 + (1.1087P)] for 3b where P = (Fo + 2Fc )/3.
2
2
[5]
[6]
CCDC-691681 {[Cu(SMeaaiNEt)(µ-N3)(N3)]2 (2b)} and -691682
{[Cu(SMeaaiNEt)(N3)(µ-OHCH3)]2 (3b)} contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Computational Methods: All computations were performed by
using the Gaussian03 (G03)[39] software package running under
Windows. Becke’s three-parameter hybrid exchange functional and
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symmetry constraints. In all cases, vibrational frequencies were cal-
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Supporting Information (see also the footnote on the first page of
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Financial support from University Grants Commission, New Delhi
is thankfully acknowledged. J. R. acknowledges the financial sup-
port given by the Spanish Government (Grant CTQ2006-03949).
320
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Received: July 10, 2009
Published Online: November 24, 2009
Eur. J. Inorg. Chem. 2010, 311–321
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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