Fourteen membered hexaaza copper macrocycle: Synthesis, characterization, crystal structures and the consequence of anion coordination

Article abstract of DOI:10.1016/j.ica.2011.12.019

Fourteen membered hexaaza macrocyclic complexes of the type [CuLX ₂] (where L = 3,10-bis(benzyl)1,3,5,8,10,12-hexaazacyclotetradecane and X=ClO4-, SCN^-) and [CuL(CH₃CN)₂](PF ₆)₂(CH₃

Full text of DOI:10.1016/j.ica.2011.12.019

Inorganica Chimica Acta 384 (2012) 309–317
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Inorganica Chimica Acta
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Fourteen membered hexaaza copper macrocycle: Synthesis, characterization,
crystal structures and the consequence of anion coordination
Ahmad Husain a,1, A. Moheman a, Shahab A.A. Nami b, K.S. Siddiqi a,
⇑
a Department of Chemistry, Aligarh Muslim University, Aligarh 202002, India
b Department of Kulliyat, Faculty of Unani Medicine, Aligarh Muslim University, Aligarh 202002, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 October 2010
Received in revised form 10 August 2011
Accepted 13 December 2011
Available online 24 December 2011
Fourteen membered hexaaza macrocyclic complexes of the type [CuLX2] (where L = 3,10-bis(ben-
zyl)1,3,5,8,10,12-hexaazacyclotetradecane and X ¼ ClOꢀ4 , SCNꢀ) and [CuL(CH3CN)2](PF6)2(CH3CN)2 have
been synthesized by template assisted condensation reaction. They have been characterized by spectral
and X-ray crystallographic techniques. It was of interest to investigate the effect of anions on the gross
geometry and chemical properties of Cu(II) ion. The crystal structure of all the complexes show axially
elongated octahedral geometry with weakly coordinated anions. The macrocyclic ring adopts the
trans-III configuration with six- and five-membered chelate rings in chair and gauche conformation,
respectively. The IR and other spectral properties are consistent with the result of X-ray diffraction. It
was observed that in the solid state the arrangement of the coordination sphere is distorted octahedral
whereas in solution, a square-planar structure is predominant. The molar conductivity of the complexes
indicates that the axially bonded anions are almost entirely dissociated in acetonitrile solution. The EPR
Keywords:
Crystal structure
Trans-III conformation
Macrocycle
Cu(II) complex
Axially elongated octahedral
Square-planar
spectra of complexes 1–3 are axial and consistent with a dx2
ground state.
ꢀy2
Crown Copyright Ó 2011 Published by Elsevier B.V. All rights reserved.
1. Introduction
are simple ‘one pot reactions’, inexpensive and high yielding. Metal
template condensation involving amines and formaldehyde have
been employed in the preparation of various saturated polyazamac-
rocyclic complexes containing N–CH2–N linkages [11–14]. Some-
times, the pendant-arms of the macrocycles can also play an
important role in altering their stereochemistry and thermody-
namic parameters, hence affecting their overall physicochemical
properties [15]. However, the presence of rigid aromatic system
gives particular coordination properties to the ligands defining dis-
tinct preorganized binding sites for the metal ions. Copper-contain-
ing macrocycles are of considerable interest as low molecular
weight models for biological copper-containing redox proteins [16].
In the present study, complexes of 14-membered hexaaza mac-
rocyclic ligand with Cu(II) containing different anions have been
characterized by crystallographic studies to investigate the effect
of the anions on the gross geometry and chemical properties of
Cu(II) ion. In order to characterize the [CuLX2] entity structurally
and to assess the consequence of anion coordination, IR, electronic
spectra and EPR were also recorded and analyzed in this work.
There is a continuing interest in the chemistry of polyazamacro-
cycles because of their sturdy chemical and biochemical application.
Structural factors, such as ligand rigidity and the electron-donating
properties of the nitrogen atoms constituting the polyaza network
and their disposition play a significant role in determining the
binding features towards metal cations [1–7]. Moreover, hexaaza
macrocyclic complexes show enhanced thermodynamic and kinetic
stability as compared to their non-cyclic chelate ligands, and have
applications in modern chemical techniques such as magnetic
resonance imaging, imaging with radioisotopes and radiotherapy
[8,9]. The diverse synthetic utility of hexaaza macrocycles may be
attributed due to the liberty offered by these systems in terms of
cavity size, pendant groups and different metal encapsulation
ability. The complexation of hexaaza macrocycles is governed
mainly by the ring size and ionic radii of the metal ions [10].
Out of the two well known strategies of synthesis of polyaza-
macrocyclic systems, metal template procedure is considered as
better as it often provides selective routes toward products that
are not obtainable in the absence of metal ions. Such processes
2. Experimental
⇑
Corresponding author. Mobile: +91 9837284930.
E-mail addresses: ahmad.chem786@hotmail.com (A. Husain), kssiddiqi@gmail.
2.1. Material and methods
com (K.S. Siddiqi).
1
Cu(OOCCH3)2ꢁH2O, HClO4 (Merck India), ethylenediamine (E.
Present address: Centre for Supramolecular Chemistry Research, Department of
Chemistry, University of Cape Town, South Africa.
Merck), benzylamine and formaldehyde (S.D. Finechem India) were
0020-1693/$ - see front matter Crown Copyright Ó 2011 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.12.019

310
A. Husain et al. / Inorganica Chimica Acta 384 (2012) 309–317
used as received. Elemental analysis was done with a FLASH EA
1112 SERIES CHNS analyzer. IR spectra (4000–400 cmꢀ1) were re-
corded with a Spectrolab Interspec FT/IR-2020 spectrometer as
KBr disc. The conductivity measurements were carried out with a
CM–82T Elico conductivity bridge in acetonitrile. The electronic
spectra were recorded with a Perkin Elmer Lambda–35 UV–Vis
spectrophotometer in CH3CN. Magnetic susceptibility measure-
ments in powdered samples were performed at 25 °C by Faraday
method with a Sherwood Scientific magnetic susceptibility balance,
calibrated against Hg[Co(SCN)4]. EPR spectra were recorded in the
solid state and in frozen CH3CN with a JEOL FE3X EPR spectrometer
at X-band microwave frequency. Powder XRD pattern of all samples
were recorded on a Bruker-Axs, D8 Advance diffractometer using
2.4. Synthesis of [CuL(CH3CN)2](PF6)2(CH3CN)2 (3)
To an acetonitrile (20 mL) solution of [CuL(ClO4)2] (1) (1 mM,
0.645 g) was added an excess of potassium hexafluorophosphate
and filtered to remove solid KClO4. The red filtrate was allowed
to stand for a few days at 4 °C to give red crystals. Yield: ꢂ94%
(0.606 g). M.p.: 297 °C. Km: 275
X
ꢀ1 cm2 Mꢀ1. Anal. Calc. for
C
22H34CuF12N6P2 (3): C, 40.03; H, 5.15; N, 15.56. Found: C, 40.23;
H, 5.28; N, 15.45% IR (KBr, cmꢀ1): 3269, 3173, 2916, 2885, 2294,
2259, 1466, 1435, 1379, 1334, 1273, 1188, 1159, 1080, 1057,
999, 823, 738, 702, 638, 557, 445.
2.5. X-ray crystal structure determination and refinements
Cu Ka X-radiation at 35 kV and 25 mA. Diffraction patterns were
collected over 2h range of 5–50° at scan rate of 1°/min.
Caution! Although our samples never exploded during handling,
perchlorate metal complexes are potentially explosive: they should
be handled with care.
Single crystals suitable for X-ray crystallographic analysis were
obtained by slow evaporation of the solvent from the acetonitrile
solution of 1 at room temperature and that of 3 at 4 °C. Crystals
of 2 were grown by slow evaporation of a 1:1 mixture of acetonitrile
and DMF and a few drops of water. X-ray data for 1 were collected
using graphite-monochromated Mo K
a radiation (K = 0.71073 Å)
2.2. Synthesis of [CuL(ClO4)2] (1) [(L = 3,10-bis(benzyl)1,3,5,8,10,12-
hexaazacyclotetradecane)]
on ‘‘Bruker SMART APEX CCD Diffractometer’’ at 100(2) K. The pro-
gram SMART [17] was used for collecting frames of data, indexing
reflections, and determining lattice parameters for 1. The data inte-
gration and reduction were processed with SAINT [17] software. An
empirical absorption correction was applied to the collected reflec-
tions with SADABS [18] using XPREP [19]. X-ray data for 2 and 3 were
collected on Oxford Diffraction Gemini CCD equipped diffractome-
To an ethanolic (50 mL) solution of Cu(OOCCH3)2ꢁH2O (5 mM,
0.998 g) were slowly added ethylenediamine (10 mM, 0.669 mL),
40% formaldehyde (20 mM, 1.600 mL) and benzylamine (10 mM,
1.092 mL) with constant stirring. After refluxing this mixture for
48 h, the red-violet solution was cooled to room temperature and
filtered to remove any insoluble solid. To this filtrate an excess of
70% perchloric acid was added with continuous stirring which
yielded pink colored precipitate (Scheme 1). It was filtered and
washed with ethanol and dried over P2O5. The complex was recrys-
tallized from acetonitrile. Red crystals were obtained after 7 days.
ter at 298(2) K using graphite-monochromated Mo K
a radiation
(K
= 0.71073 Å). The strategy for the data collection was evaluated
by the CRYSALISPRO CCD software and collected by the standard
‘phi-omega scan’ techniques, scaled and reduced using CRYSALISPRO
RED software [20]. The linear absorption coefficients, scattering
factors for the atoms and the anomalous dispersion corrections
were taken from the International Tables for X-ray Crystallography
[21]. The structures were solved by direct method using SHELXS-97
program [22] and were refined on F2 by full-matrix least-square
technique using the SHELXL-97 [22] program. Figures were drawn
using ORTEP-3.2 [23] and MERCURY-2.3 [24]. All non-hydrogen atoms
were refined with anisotropic displacement parameters. H atoms
were refined isotropically. The pertinent crystal data and refine-
ment parameters for compounds 1, 2 and 3 are compiled in Table 1.
Yield: ꢂ80% (2.58 g). M.p.: 255 °C. Km: 247
X
ꢀ1 cm2 Mꢀ1. Anal.
Calc. for C22H34Cl2CuN6O8 (1): C, 40.97; H, 5.31; N, 13.03. Found:
C, 40.81; H, 5.41; N, 13.15%. IR (KBr, cmꢀ1): 3243, 3173, 2924,
2879, 1449, 1421, 1377, 1335, 1275, 1114, 1073, 997, 830, 896,
855, 750, 703, 624, 437.
2.3. Synthesis of [CuL(SCN)2] (2)
To a solution of [CuL(ClO4)2] (1) (1 mM, 0.645 g) in acetonitrile
(20 mL) was added an excess of potassium thiocyanate and stirred
for 1 h. It wasfilteredto remove solid KClO4 and the solventwas evap-
orated to dryness to give purple blue powder. It was dissolved in ace-
tonitrile-DMF mixture with a few drops of water and left to stand at
room temperature. Violet crystals thus obtained after 1 month were
filtered and washed with ethanol. Yield: ꢂ95% (0.612 g). M.p.:
3. Results and discussion
3.1. Crystal structure description of [CuL(ClO4)2] (1)
The molecular structure and the atomic numbering scheme of 1 is
showninFig. 1. Crystallographicdata, selectedbondlengthsand bond
angles are listed in Tables1and2. It wascrystallizesintriclinicsystem
228 °C. Km: 254
X
ꢀ1 cm2 Mꢀ1. Anal. Calc. for C24H34CuN8S2 (2): C,
51.27; H, 6.10; N, 19.93. Found: C, 50.87; H, 5.99; N, 19.73%. IR (KBr,
cmꢀ1): 3194, 2897, 2868, 2049, 1459, 1418, 1269, 1188, 1147, 1060,
1012, 951, 856, 742, 698, 640, 592, 480, 418.
ꢀ
with P1 space group. The asymmetric units comprise of half a mole-
cule and the other half of the molecules are generated through a
Scheme 1. Synthesis of [CuL(ClO4)2] (1).

A. Husain et al. / Inorganica Chimica Acta 384 (2012) 309–317
311
Table 1
Crystallographic data and structure refinement parameters for 1, 2 and 3.
Complex
[CuL(ClO4)2] (1)
22H34Cl2CuN6O8
644.99
100(2)
0.71073
[CuL(SCN)2] (2)
[CuL(CH3CN)2](PF6)2ꢁ2CH3CN (3)
C30H46CuF12N10P2
900.25
298(2)
0.71073
Empirical formula
Formula weight
C
C24H34CuN8S2
562.25
298(2)
T (K)
0
0.71073
k (AÅ)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Triclinic
Rhombohedral
Monoclinic
P2(1)/c
12.5103(9)
16.0648(11)
20.8753(15)
90
ꢀ
ꢀ
P1
R3
10.156(3)
11.433(3)
11.965(3)
86.679(5)
29.766(6)
29.766(6)
7.9265(11)
90
a
(°)
b (°)
75.765(4)
87.829(5)
1344.0(6)
2, 1.594
1.070
670
90
120
6082.2(19)
9, 1.382
0.991
2655
99.8510(10)
90
4133.6(5)
4, 1.447
0.696
c
(°)
V (Å3)
Z, qcalc (g cmꢀ3
)
Absorption coefficient (mmꢀ1
F(000)
)
1852
Crystal size (mm)
h Range for data collection (°)
Limiting indices
0.28 ꢃ 0.20 ꢃ 0.20
0.40 ꢃ 0.20 ꢃ 0.10
0.25 ꢃ 0.20 ꢃ 0.20
1.61–25.00
ꢀ14 6 h 6 14, ꢀ19 6 k 6 19,
ꢀ24 6 l 6 24
39271/7278 [Rint = 0.0400]
0.8734 and 0.8453
2.07–25.00
2.74–24.99
ꢀ12 6 h 6 10, ꢀ12 6 k 6 13,
ꢀ14 6 l 6 14
6855/4664 [Rint = 0.0245]
0.8145 and 0.7539
ꢀ35 6 h 6 27, ꢀ23 6 k 6 34,
ꢀ9 6 l 6 9
Reflections collected/unique
Maximum and minimum
transmission
8105/2381 [Rint = 0.0628]
0.9074 and 0.6926
Refinement method
Full-matrix least-squares on F2
4664/4/371
1.066
Full-matrix least-squares on F2
2381/3/168
0.957
Full-matrix least-squares on F2
7278/2/516
1.039
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2
r
(I)]
R1 = 0.0475, wR2 = 0.1336
R1 = 0.0528, wR2 = 0.1396
1.160 and ꢀ0.815
98.5
R1 = 0.0506, wR2 = 0.1226
R1 = 0.0787, wR2 = 0.1308
0.573 and ꢀ0.360
99.9
R1 = 0.0699, wR2 = 0.1953
R1 = 0.0864, wR2 = 0.2098
1.021 and ꢀ0.426
100.0
R indices (all data)
Largest diff. peak and hole (e Åꢀ3
)
Completeness to h = 25.00 (%)
Table 2
Selected bond lengths (Å) and bond angles (°) for [CuL(ClO4)2] (1).
Bond lengths
Bond angles
N(1B)–Cu(1B)
N(2B)–Cu(1B)
N(1A)–Cu(1A)
N(2A)–Cu(1A)
2.002(2)
2.015(2)
1.994(3)
2.020(3)
N(1B)–Cu(1B)–N(2B)#1
N(1B)–Cu(1B)–N(2B)
N(1A)–Cu(1A)–N(2A)
N(1A)–Cu(1A)–N(2A)#2
93.92(10)
86.08(10)
86.11(10)
93.89(10)
Symmetry transformations used to generate equivalent atoms: #1 ꢀx + 1, ꢀy + 1,
ꢀz + 1 #2 ꢀx + 1, ꢀy, ꢀz.
and (Cu(1B)–N(1B) = 2.002(2) Å, Cu(1B)–N(2B) = 2.015(2) Å]occupy-
ing equatorial plane in an essentially square-planar arrangement and
two weakly coordinated perchlorate anions at the axial position. The
two independent molecules in the asymmetric unit show slightl0y dif-
ferent Cu–O (perchlorate) interactions [Cu(1A)–O(4A) = 2.474 AÅ and
Cu(1B)–O(1B) = 2.651 Å]. The overall coordination geometry around
Cu(II) may therefore, be described as an elongated octahedron which
is expected from the Jahn–Teller distortion.
The six-membered chelate rings adopt a chair conformation,
whereas five-membered rings assume a gauche conformation.
The chelate angles were N(1A)–Cu(1A)–N(2A) = 86.11(10)°,
N(1A)–Cu(1A)–N(2A)#2 = 93.89(10)° and N(1B)–Cu(1B)–N(2B) =
86.08(10)°, N(1B)–Cu(1B)–N(2B)#1 = 93.92(10)° for five- and six-
membered rings in unit A and B, respectively. The Cu–N and Cu–O
bond lengths are similar to other Cu(II) complexes with cyclam-
derived ligands where perchlorate is axially coordinated [25,26].
The trans-III configuration of N-donors enables the hexaaza ring to
adopt least strained conformation, i.e. an eclipsed pair of gauche
five-membered chelate rings and two chair six-membered rings.
The perchlorate ion indicates a lengthening of the Cl–O bond
involving O(4A) and O(1B), which were weakly coordinated to
the Cu atom. The Cl(1A)–O(4A) and Cl(1B)–O(1B) bond length were
1.452(2) and 1.437(2) Å, which were significantly longer than the
Fig. 1. Molecular structure (ORTEP diagram with 50% thermal ellipsoids) of 1, along
with the atomic numbering scheme. Hydrogen atoms have been omitted for clarity.
center of symmetry. There are two metal atoms in the asymmetric
unit sitting on inversion centers. The two resulting molecules have
equivalent geometries (Table 2). The coordination environment of
the Cu(II) ion is (N4O2) coordinated with four secondary amine nitro-
gen atoms [Cu(1A)–N(1A = 1.994(3) Å, Cu(1A)–N(2A) = 2.020(3) Å)

312
A. Husain et al. / Inorganica Chimica Acta 384 (2012) 309–317
Fig. 2. Depicting intermolecular hydrogen bonded 1D polymeric array along a axis for complex 1. Hydrogen atoms except those involved in H-bonding have been omitted for
clarity.
Table 4
Table 3
Selected bond lengths (Å) and bond angles (°) for [CuL(SCN)2] (2).
Intramolecular and intermolecular hydrogen bonds of the N–Hꢁ ꢁ ꢁO and C–Hꢁ ꢁ ꢁO type
in complex [CuL(ClO4)2] (1).
Bond lengths
Bond angles
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–N(4)
S(2)–C(12)
C(12)–N(4)
2.035(3)
2.011(3)
2.528(3)
1.562(5)
1.192(5)
N(2)–Cu(1)–N(1)
N(2)#1–Cu(1)–N(1)
C(11)–N(1)–C(9)
C(8)–N(3)–C(9)
C(8)–N(3)–C(7)
C(9)–N(3)–C(7)
N(1)–Cu(1)–N(4)
N(1)–Cu(1)–N(4)#1
N(2)–Cu(1)–N(4)
N(2)–Cu(1)–N(4)#1
94.14(11)
85.86(11)
113.6(3)
115.1(3)
114.8(3)
115.7(3)
89.93(12)
90.07(12)
87.59(13)
92.40(13)
D–Hꢁ ꢁ ꢁA
d(Dꢁ ꢁ ꢁA)
d(Hꢁ ꢁ ꢁA)
(D–Hꢁ ꢁ ꢁA) (°)
(Å)
(Å)
N(1A)–
2.939
2.187
2.214
2.639
2.293
2.159
145.3 (x, y ꢀ 1, z)
H(N1A)ꢁ ꢁ ꢁO(3B)
N(1B)–
H(N1B)ꢁ ꢁ ꢁO(1A)
N(1B)–
H(N1B)ꢁ ꢁ ꢁO(1B)
N(2A)–
H(N2A)ꢁ ꢁ ꢁO(3A)
N(2B)–
H(N2B)ꢁ ꢁ ꢁO(2B)
2.976
3.131
3.104
2.994
147.07 (ꢀx + 1, ꢀy, ꢀz + 1)
117.33 (ꢀx + 1, ꢀy + 1,
ꢀz + 1)
156.66 (ꢀx + 1, ꢀy, ꢀz)
161.01
Symmetry transformations used to generate equivalent atoms: #1 ꢀx + 1, ꢀy,
ꢀz + 1.
mean of the other three Cl–O bonds [27]. The mononuclear units
are held together by intermolecular hydrogen bonds to form an
infinite one-dimensional polymeric array along a axis (Fig. 2).
The hydrogen bonding parameters are collected in Table 3.
lengths and bond angles are given in Tables 1 and 4. It was crystal-
lizes in rhombohedral system with R3 space group with nine for-
ꢀ
mula units per unit cell (Fig. 4). The asymmetric unit is made up
of half a molecule, the other half of the molecule is generated
through a center of symmetry. The crystallographic asymmetric
unit of 2 consists of [CuL]2+ cation and two thiocyanate anions in
isothiocyanate binding mode. The thiocyanate ion is known to form
both thiocyanato (M–SCN) and isothiocyanato (M–NCS) complexes,
depending on the nature of metal ion [28]. Pearson [29] suggests
3.2. Crystal structure description of [CuL(SCN)2] (2)
The molecular structure of 2 along with the atomic numbering
scheme is shown in Fig. 3. Crystallographic data, selected bond
Fig. 3. Molecular structure (ORTEP diagram with 50% thermal ellipsoids) of complex 2, along with the atomic numbering scheme. Hydrogen atoms have been omitted for
clarity.

A. Husain et al. / Inorganica Chimica Acta 384 (2012) 309–317
313
that S in SCNꢀ is soft and will prefer to coordinate with soft acids
whereas N in SCNꢀ is hard and coordinates with hard acids. The
copper atom is in an axially distorted octahedral (N4 + N2) environ-
ment with four secondary amine nitrogen atoms occupying the
equatorial plane, similar to 1 and two isothiocyanate groups at
the axial positions. Two cross bond angles N(1)–Cu(1)–N(1)#1
and N(2)–Cu(1)–N(2)#1 in equatorial plane show that the Cu(II)
ion is located in a square plane without any axial displacement.
The large Cu(1)–N(4) bond length of 2.528(3) Å in trans configura-
tion, are similar to those found for weakly coordinated axial SCNꢀ
in hexa-coordinate (N4N2) copper complexes such as trans-[Cu
(Me2en)2(NCS)2] [30], trans-[Cu(amepy)2(NCS)2] and [Cu(a-
L)(NCS)2] [31–33]. The thiocyanate groups show small distortions
[N(4)–(C12)–S(2) = 177.74(4)°] from linearity as is usually ob-
served [34]. The Cu–N–C angles related to the thiocyanate anion
are Cu(1)–N(4)–C(12) [119.9(6)°]. Therefore, the overall geometry
of Cu(II) may be described as an elongated octahedron similar to
1. The chelate angles N(1)–Cu(1)–N(2), N(1)–Cu(1)–N(2)#1 were
94.14(11)°, 85.86(11)° for six-membered and five-membered rings,
respectively. Analysis of the crystal packing reveals that mononu-
clear units are held together by intermolecular hydrogen bonds
involving the N(2)–H(2A) protons and S(2) with d(Dꢁ ꢁ ꢁA) = 3.615Å,
Fig. 4. Unit cell diagram of complex 2. Hydrogen atoms have been omitted for
clarity.
Fig. 5. Depicting intermolecular hydrogen bonded 1D polymeric array along a axis in complex 2. Hydrogen atoms except those involved in H-bonding have been omitted for
clarity.
Fig. 6. Molecular structure (ORTEP diagram with 50% thermal ellipsoids) of complex 3, along with the atomic numbering scheme. Hydrogen atoms have been omitted for
clarity.

314
A. Husain et al. / Inorganica Chimica Acta 384 (2012) 309–317
Table 5
Selected bond lengths (Å) and bond angles (°) for [CuL(CH3CN)2](PF6)2ꢁ2CH3CN (3).
Bond lengths
Bond angles
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–N(3)
Cu(1)–N(4)
Cu(1)–N(7)
Cu(1)–N(9)
N(7)–C(27)
N(8)–C(29)
N(9)–C(23)
N(10)–C(25)
2.006(4)
2.002(3)
2.011(3)
2.010(3)
2.747(4)
2.432(4)
1.118(7)
1.127(8)
1.120(5)
1.118(7)
N(2)–Cu(1)–N(1)
N(2)–Cu(1)–N(3)
N(3)–Cu(1)–N(4)
N(1)–Cu(1)–N(4)
N(2)–Cu(1)–N(9)
N(1)–Cu(1)–N(9)
N(3)–Cu(1)–N(9)
N(4)–Cu(1)–N(9)
N(1)–Cu(1)–N(3)
N(2)–Cu(1)–N(4)
C(27)–N(7)–Cu(1)
C(23)–N(9)–Cu(1)
N(1)–Cu(1)–N(7)
N(2)–Cu(1)–N(7)
N(3)–Cu(1)–N(7)
N(1)–Cu(1)–N(9)
N(2)–Cu(1)–N(9)
N(3)–Cu(1)–N(9)
N(4)–Cu(1)–N(7)
N(4)–Cu(1)–N(9)
86.26(14)
92.96(13)
86.57(13)
94.03(14)
93.22(15)
89.96(15)
93.77(15)
89.59(15)
176.23(15)
177.18(15)
143.13(4)
158.2(4)
89.33(17)
85.93(15)
86.93(16)
89.96(14)
93.23(15)
93.77(14)
91.25(15)
89.60(15)
Fig. 7. Unit cell diagram of complex 3. Hydrogen atoms have been omitted for
clarity.
ꢀ
Fig. 8. Solvent-anion interaction for complex 3. Arrangement of PF6 nd two solvent molecules due to Fꢁ ꢁ ꢁH bonding in unit cell. Hydrogen atoms have been omitted for
clarity.

A. Husain et al. / Inorganica Chimica Acta 384 (2012) 309–317
315
Table 6
3.4. IR Spectral studies
ꢀ
Hydrogen bonds of the N–Hꢁ ꢁ ꢁF and N–Hꢁ ꢁ ꢁN type between the macrocycle and PF6
and CH3CN in complex [CuL(CH3CN)2](PF6)2ꢁ2CH3CN (3).
IR spectra of 1–3 (Fig. S1, Supporting information) show common
absorption bands, characteristic of the tetraaza macrocyclic ligand
in the region 3269–3194 cmꢀ1, indicating the presence of NH groups
in the complexes. Complex 1 shows two splitted peaks at 1111 and
D–Hꢁ ꢁ ꢁA
d(Dꢁ ꢁ ꢁA)
d(Hꢁ ꢁ ꢁA)
(D–Hꢁ ꢁ ꢁA) (°)
(Å)
(Å)
N(1)–
3.031(7)
3.210(7)
2.30(5)
2.41(5)
154(5) (x, 1/2 ꢀ y, ꢀ1/
2 + z)
153(4) (ꢀ1 + x, y, z)
1074 cmꢀ1
(m
3-antisymmetric stretching) assigned to perchlorate
ions [35]. This splitting clearly explains the presence of coordinated
perchlorate ion [36]. The band at 999 cmꢀ1
2-symmetric stretch-
ing) further supports that perchlorate ions are coordinated in the
complex [37]. The peak around 621 cmꢀ1
4-antisymmetric bend-
ing) belongs to a perchlorate bending vibration.
The (CN) stretching frequency of the thiocyanate group can be
used for characterization of the coordination mode to the metal ion
[38,39]. The stretching frequency (CN) of thiocyanate are lower in
N-bonded (near 2050 cmꢀ1
than S-bonded complexes (near
2100 cmꢀ1). The (CN) observed at 2050 cmꢀ1 in 2 suggests that
H(1N)ꢁ ꢁ ꢁN(10)
N(2)–
H(2N)ꢁ ꢁ ꢁF(10)
(m
N(3)–H(3N)ꢁ ꢁ ꢁN(8)
2.999(7)
3.347(8)
2.27(5)
2.52
147(4) (ꢀ1 + x, y, z)
C(26)–
145
H(26A)ꢁ ꢁ ꢁF(2)
C(28)–
H(28B)ꢁ ꢁ ꢁF(4)
(m
3.310(10)
2.41
157 (ꢀ1 + x, y, z)
m
m
)
d(Hꢁ ꢁ ꢁA) = 2.882 Å and (D–Hꢁ ꢁ ꢁA) = 143° to form an infinite one-
dimensional polymeric chain along the b axis (Fig. 5).
m
the pseudo-halide is coordinated to copper through the nitrogen
atom (terminal N-bonded) [40].
3.3. Crystal structure description of [CuL(CH3CN)2](PF6)2ꢁ2CH3CN (3)
The spectrum of 3 displays broad and intense bands at 845 and
555 cmꢀ1 consistent with the characteristic
m3(Flu) IR-active modes
The molecular structure of the complex 3 along with the atomic
numbering scheme is shown in Fig. 6. Crystallographic data, selected
bond lengths and bond angles are given in Tables 1 and 5. It was crys-
tallizes in the space group P2(1)/c of the monoclinic system. The unit
cell was shown in Fig. 7. The crystal structure of 3 contains a mono-
meric [CuL(CH3CN)2]2+ cation, two hexafluorophosphate anions and
two lattice acetonitrile molecules. The Cu(1) atom is (N4 + N2) coordi-
nated in a distorted elongated octahedron with four secondary amine
nitrogen atoms [Cu(1)–N(1) = 2.006(4) Å, Cu(1)–N(2) = 2.002(3) Å,
Cu(1)–N(3) = 2.011(3) Å and Cu(1)–N(4) = 2.010(3) Å] occupying
the equatorial plane in an square planar arrangement and coordi-
ꢀ
of the PF6 anions [38]. It showed two bands at 2341 and
2313 cmꢀ1 duetotheasymmetricandsymmetric
m(C„N)ofthecoor-
dinated acetonitrile [41]. A band at 2250 cmꢀ1 is indicative of uncoor-
dinated lattice acetonitrile [42]. When IR spectrum of 3 was taken
after drying at 80 °C for 30 min, (Fig. S1, Supporting information)
nated by two nitrogen atoms from two acetonitrile at the axial posi-
0
tions (Cu(1)–N(9) = 2.432(4) AÅ and Cu(1)–N(7) = 2.747(4) Å). The
two trans bond angles in equatorial plane (N(1)–Cu(1)–N(3) and
N(2)–Cu(1)–N(4) deviate from 180° indicating that the Cu(II) ion is
slightly out of equatorial plane with some axial displacement. The
copper ion is 0.057 Å above the basal plane constituted via N(1),
N(2), N(3), N(4) atoms, towards the N(9) of CH3CN. The two coordi-
nated CH3CN are located at trans positions to each other and are not
exactly at the axial sites of Cu(II) as evident from the bond angle
(N(7)–Cu(1)–N(9) = 178.93°). While in most transition metal com-
plexes of acetonitrile the coordination is approximately linear, it
deviates slightly from linearity. The bond angles N(1)–Cu(1)–N(9),
N(4)–Cu(1)–N(9), N(2)–Cu(1)–N(9), and N(3)–Cu(1)–N(9) are
89.96(15)°, 89.59(15)°, 93.22(15)° and 93.77(15)°, respectively,
suggested that the Cu(1)–N(7) and Cu(1)–N(9) linkages are slightly
bent off the perpendicular to the N(1)–Cu(1)–N(4) and N(2)–Cu(1)–
N(3) plane. The angle between the planes of the two benzene rings
is 23.32° which is possibly due to intramolecular hydrogen.
0
The P–F bond length ranges from 1.454(5) to 1.571(5) ÅA with an
0
average of 1.528(5) ÅA. [CuL(CH3CN)2]2+ cation is linked by intrꢀamo-
lecular N–Hꢁ ꢁ ꢁF hydrogen bonds through uncoordinated PF6 an-
ions and N–Hꢁ ꢁ ꢁNNCMe through two lattice acetonitrile molecules,
which are further linked by C–Hꢁ ꢁ ꢁF hydrogen bonds. In the crystal
packing four PF6ꢀ anions and two lattices CH3CN were arranged in
a square manner by Hꢁ ꢁ ꢁF bonding forming to a 2D network (Fig. 8).
Pertinent structural parameters of the hydrogen-bonded contacts
are collated in Table 6.
During the solving crystal structure, it was suggested that some
F atoms were disordered and multiple splitting was suggested for
single F atoms. The fluorine atoms of PF6ꢀ counter ions have a high
thermal parameter since data was collected at room temperature.
We tried refining those atoms in two positions with reduced occu-
pancy but there was no decrease in R value and, therefore, we con-
sider that our original refinement is the best.
Fig. 9. (a) EPR spectra of 1, 2 and 3 determined at RT on polycrystalline powder
sample. (b) EPR spectra of 1, 2 and 3 determined at 140 K on a frozen CH3CN–
C6H5CH3 (1:1, v/v) glass.

316
A. Husain et al. / Inorganica Chimica Acta 384 (2012) 309–317
Table 7
EPR parameters of the complexes 1–3.
Complex
Temperature
g||
g\
giso
G
A||
[CuL(ClO4)2] (1)
RT
LNT
RT
LNT
RT
LNT
2.180
2.095
2.177
2.067
2.225
2.176
2.043
2.025
2.045
2.019
2.056
2.050
2.088
2.048
2.089
2.035
2.112
2.092
4.366
4.083
4.091
3.874
4.147
3.64
–
96
–
170.6
–
214
[CuL(SCN)2] (2)
[CuL(CH3CN)2](PF6)2ꢁ2CH3CN (3)
acetonitrile bands disappear indicating the complete loss of acetoni-
trile molecules.
[(g|| ꢀ 2.0023)/(g\ ꢀ 2.0023)] > 4 (Table 7) thus, the extent of inter-
action between Cu(II) centers is negligible, indicating an essentially
mononuclear structure [52].
The frozen solution spectra of the complexes are axial with
g|| > g\ > 2.0 and G = 3.6–4.1, confirm the square based geometries
of the complexes, as observed in the X-ray crystal structures of 1–
3. Frozen spectrum of 1 is well resolved with a quartet hyperfine
structure (Cu, I = 3/2) while those of 2 and 3 are partially resolved.
A square-based CuN4 chromophore is expected to show g|| value of
about 2.200 and an A|| value of 180–220 G. The nuclear hyperfine
coupling for 2 and 3 is observed in the g|| signal with three of the
four components clearly resolved, the last one being obscured by
the g\ component. Accordingly, the orbital ground state of the
Cu(II) would be basically dx2 ꢀ dy2 and the polyhedra could be sta-
tistically distorted [53].
3.5. Electronic spectra and magnetic moment
The electronic spectra of 1–3 complexes were measured in ace-
tonitrile solutions. All complexes exhibit very intense bands in the
250–275 nm region assignable to
p ?
p⁄ intraligand charge-trans-
fer bands. The appearance of a single broad d–d band in the visible
spectrum of square-planar or tetragonally distorted octahedral
complexes containing neutral macrocyclic diimine ligands is com-
mon [43]. In the present study, the spectra display one broad d–d
band at Kmax 497, 532 and 498 nm for complex 1, 2 and 3, respec-
tively, contributed from the CuN4 square-based planar coordination
environment which indicates that the M–X (where X = ClO4ꢀ, SCNꢀ
and NCCH3) bonds are entirely dissociated [44]. Similar behavior
has also been reported by Kang et al. [45]. This can be adequately
explained as a d–d transition of Cu(II) ion in the complex with a
D4h symmetry [46].
3.7. PXRD studies
The phase purity of all Cu(II) complexes was confirmed by
PXRD. The experimental PXRD patterns of 1 and 2 are consistent
with the simulated ones, as determined from the single-crystal
X-ray diffraction data (Fig. S2, Supporting information). Difference
in intensities and peak positions between the PXRD patterns of the
two sets of compound 3 is due to the loss of solvent molecules dur-
ing grinding. Intensity of the experimental XRD patterns is a little
weak, due to the preferred orientation of the powder samples and
the instrumental limitations.
Tetragonal distortions involving elongation of the axial bonds
that remove the degeneracy are very common, especially with
r-
bonding ligands such as 1,2-diamines [47]. This fact suggests that
in tetragonally distorted octahedral Cu(II) complexes involving
unidentate ligands, the axially coordinated groups are weakly
bonded and not positioned by lattice packing factors. This is indic-
ative of a reduction of the coordination number of the examined
complex to form a square planar CuN4 chromophore after solva-
tion. The molar conductivity of perchlorate, thiocyanate and hexa-
fluorophosphate salts of Cu(II) complexes measured in acetonitrile
4. Conclusion
solution was found to be in the range of 283–375
X
ꢀ1 cm2 Mꢀ1
corresponding to a 1:2 electrolyte [48]. The contradiction between
the crystal structure of Cu(II) complex and the conductivity data
indicate that the perchlorate and hexafluorophosphate anions are
coordinated to the Cu(II) ion in solid state and are labile in solution.
The magnetic moment at room temperature for 1–3 was in the
range 1.9–1.8 B.M. and these values are within the usual range.
Cu(II) complexes have been synthesized by one-pot template
reaction. It may be proposed that in the solid state, most probably
due to crystal packing effects, the arrangement of the coordination
sphere is distorted octahedral whereas in solution, the square-pla-
nar one is prevalent. Further, oxygen from perchlorate molecule
and nitrogen from thiocyanate and acetonitrile is semi-coordi-
nated to copper, stabilizing an octahedral geometry in the solid
state. The molar conductivity determination reflects that the axi-
ally bonded groups are almost entirely dissociated in acetonitrile
solution.
3.6. EPR studies
The X-band EPR spectra of polycrystalline powder of 1, 2 and 3
were recorded at room temperature and in frozen acetonitrile–tol-
uene (1:1) mixture (Fig. 9). EPR spectral parameters for complexes
1–3 are summarized in Table 7. The powder spectra at RT were
typical for axial-type Cu(II) complexes with two g values and
g|| > g\ > 2.03, suggesting a dx2ꢀy2 ground state which is consistent
with a tetragonally distorted octahedral stereochemistry [49].
The broadening of the spectrum of 2 and 3 is probably due to spin
relaxation. The absence of any half field signal suggests the pres-
ence of only one transition metal ion. The g|| < 2.3 indicate a con-
siderable covalent character [50]. The smaller g|| value indicates
increased delocalization of the unpaired electron away from the
metal nucleus and has been often interpreted in terms of increased
covalency in the metal-ligand bond [51]. The calculated G value
Acknowledgements
We are indebted to the Department of Chemistry, IIT Kanpur
and School of Chemistry, University of Hyderabad, for providing
single crystal X-ray facilities. Dr. Suneel P. Singh, Department of
Chemistry, University of Guelph Ontario, Canada is gratefully
acknowledged for his valuable discussion. We are grateful to the
Council of Scientific and Industrial Research, New Delhi (Research
Scheme No. 21(0685)/07 EMR-II) for the financial support. One of
us (SAAN) thanks Department of Science and Technology for finan-
cial assistance under SERC FAST Scheme, No. SR/FT/CS-031/2008,
NewDelhi, India.

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