Two lantern-like 1D polymeric Schiff base copper(I/II) complexes derived from copper(II) salts containing rarely seen [CuI(NCS)4] bridges

Article abstract of DOI:10.1039/c2ce26201k

Two lantern-like 1D polymeric Schiff base copper(i/ii) complexes containing rarely seen [Cu^I(NCS)₄] bridges have been obtained by reaction of tridentate Schiff bases, copper(ii) salts, and ammonium thiocyanate in methanol under mild

Full text of DOI:10.1039/c2ce26201k

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Two lantern-like 1D polymeric Schiff base copper(I/II) complexes
derived from copper(II) salts containing rarely seen [CuI(NCS)4]
bridges{
Zhong-Lu You,* Dong-Mei Xian and Mei Zhang
Received 25th July 2012, Accepted 18th August 2012
DOI: 10.1039/c2ce26201k
coordinated by one N atom and three S atoms from four
thiocyanate ligands, forming a tetrahedral geometry. The Cu1II–
S2i (symmetry code for i: 1 2 y, 1 2 x, 1/2 + z) bond length in 1 is
Two lantern-like 1D polymeric Schiff base copper(I/II) com-
plexes containing rarely seen [CuI(NCS)4] bridges have been
obtained by reaction of tridentate Schiff bases, copper(II) salts,
and ammonium thiocyanate in methanol under mild condition.
II
ii
˚
3.195(2) A, and the Cu1 –S2 (symmetry code for i: 1 2 y, 1 2 x,
˚
21/2 + z) bond length in 2 is 3.119(2) A. In comparison with other
CuII–SCN bond lengths reported previously,4e–4g,5 it can be seen
that the bond lengths of Cu1II–S2i in 1 and Cu1II–S2ii in 2 are
much longer. The coordinate bond angles subtended at the Cu2
atoms are in the ranges 106.7(1)–112.1(1)u for 1 and 107.6(1)–
111.2(1)u for 2, indicating they are slightly distorted tetrahedral
coordination. Each Cu atom in the CuIIL unit is five-coordinated
in a square pyramidal geometry, with the three donor atoms of L,
and one N atom of a thiocyanate ligand defining the basal plane,
and with one S atom of another thiocyanate ligand occupying the
apical position. The square pyramidal coordination in both
complexes are supported by the t parameters7 (0.09 for 1 and
0.22 for 2). It is very interesting that the S atom coordinates
simultaneously to three Cu atoms, generating a flat tetrahedral
geometry (Fig. 1). The S atoms deviate from the planes defined by
Much effort has been focused on the design and controlled
synthesis of polymeric structures of complexes since they possess
wide applications, especially for their magnetic properties.1 The
2
pseudohalide ligands, such as N3 and NCS2, have been
extensively used as bridging groups in the construction of such
complexes.2,3 As an excellent ligand, containing several pairs of
electrons, thiocyanate can readily bridge two or more spin carriers.
It can provide several bridging modes, such as m2-NS, m2-NN, m3-
NNS, etc.4 To our knowledge, very few complexes containing m4-
NSSS bridges have been reported so far.5 It can be seen that the
bridging modes of the thiocyanate groups are relatively simple
than the azide bridges, and the number of polymeric complexes
bridged by thiocyanate groups is much less than that bridged by
azide groups. Thus, more work needs to be carried out to
construct thiocyanate-bridged complexes with novel structures and
bridging modes. In recent years, our research group has reported a
number of Schiff base copper(II) complexes bearing thiocyanate
ligands.6 In our continuous investigation on tridentate Schiff base
copper complexes with thiocyanate bridges, we obtained unex-
pectedly the first two examples of 1D polymeric copper(I/II)
complexes [CuII3L3CuI(NCS)4]n (L = L1 for 1, L = L2 for 2)
containing rarely seen [CuI(NCS)4] bridges with the Schiff bases
4-chloro-2-[(2-diethylaminoethylimino)methyl]phenol (HL1) and
2-[(3-dimethylaminopropylimino)methyl]-6-methylphenol (HL2),
respectively (Scheme 1).
˚
the three Cu atoms by 0.531(1) A for 1 and 0.462(1) A for 2. The
˚
…
˚
Cu Cu distances in the tetrahedral geometries are 5.457(1) A for
II
˚
1 and 5.342(1) A for 2. In both complexes, the Cu L units are
linked via [CuI(NCS)4] bridges, forming infinite 1D chains, as
shown in Fig. 2. It is interesting that the 1D chains are much like
strings of lantern.
In recent years, a number of thiocyanate coordinated copper
complexes derived from Schiff base ligands bearing 2-[(2-
aminoethylimino)methyl]phenol backbones has been reported. In
the complexes, thiocyanate ligands coordinate to the Cu atoms
through terminal,8 m2-NN,9 and m2-NS10 modes. It is very
interesting that for the complexes reported in the present paper,
the Schiff base ligands and the synthetic method are very similar to
Single-crystal X-ray analysis{ reveals that the complexes are
[CuI(NCS)4] bridged polymeric copper(I/II) complexes with
tridentate Schiff bases as co-ligands. The complexes possess
crystallographic three-fold rotation axis symmetry, with the
Cu2–N4–C15–S2 units located at the backbones of the axes. The
asymmetric unit of each complex contains a [CuI(NCS)4] bridge
and three CuIIL units. The Cu2 atom in the [CuI(NCS)4] moiety is
Department of Chemistry and Chemical Engineering, Liaoning Normal
University, Dalian, 116029, P. R. China
{ CCDC reference numbers 638086 and 889124. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/c2ce26201k
Scheme 1 The Schiff bases.
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Fig. 1 The bridging mode of the thiocyanate groups in 1 or 2. The Schiff base ligands have been omitted for clarity.
Fig. 2 The [CuI(NCS)4] bridged 1D polymeric chains for 1 and 2, as well as the lantern-like appearance of the complexes.
Fig. 3 DT-TGA curves of the complexes.
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calculated positions and constrained to ride on their parent atoms. CCDC
638086 (1) and 889124 (2) contain the supplementary crystallographic data
for this paper.{ Crystal data for 1: C43H54Cl3Cu4N10O3S4, Mr = 1247.7,
those reported previously, however, the final structures are totally
different.
˚
˚
The complexes 1 and 2 were prepared by the reaction of
ammonium thiocyanate and CuBr2 with HL1 and HL2, respec-
tively, in methanol at ambient condition.§ At first, we suspected
that the CuII A CuI process may have resulted from the reduction
of Br2 A Br2, however, when CuBr2 was replaced by other copper
salts, such as Cu(CH3COO)2, Cu(NO3)2, CuCl2, and Cu(ClO4)2,
we obtained the same structures of complexes as those prepared
by using CuBr2 without exception. Thus, the Cu+ ions in the
[CuI(NCS)4] units most probably be reduced by the thiocyanate
anions.
hexagonal space group R3c, a = b = 20.925(2) A, c = 20.610(2) A, a = b =
3
90u, c = 120u, V = 7815.2(13) A , Z = 6, Dc = 1.591 g cm23, F(000) = 3822,
˚
S = 1.033, Rint = 0.0489, R1 = 0.0373 [I . 2s(I)], wR2 = 0.0799 (all data).
Crystal data for 2: C43H57Cu4N10O3S4, Mr = 1144.4, hexagonal space
˚
˚
group R3c, a = b = 20.650(1) A, c = 20.332(1) A, a = b = 90u, c = 120u, V =
7508.4(6) A , Z = 6, Dc = 1.519 g cm23, F(000) = 3534, S = 1.029, Rint
=
3
˚
0.0430, R1 = 0.0358 [I . 2s(I)], wR2 = 0.0722 (all data).
§ Synthesis of the complexes: For 1: The Schiff base HL1 was readily
prepared by the condensation reaction of 5-chlorosalicylaldehyde with
N,N-diethylethane-1,2-diamine in methanol. To a methanolic solution
(30 mL) of the Schiff base (0.25 g, 1 mmol) and ammonium thiocyanate
(0.15 g, 2 mmol) was added a methanolic solution (20 mL) of copper
bromide (0.23 g, 1 mmol), with stirring. The mixture was stirred for 30 min
at room temperature and filtered. Diffraction quality single crystals of 1
were obtained after a few days by slow evaporation of the filtrate in open
atmosphere. The crystals were isolated, washed three times with cold
methanol and dried in air. Yield: 0.22 g (71% based on Cu). Anal. Calcd for
C43H54Cl3Cu4N10O3S4: C 41.4, H 4.4, N 11.2; Found: C 41.6, H 4.4, N
11.3. IR (KBr, cm21): 2127 s, 2097 s, 1639 s, 1523 m, 1457 s, 1385 m,
1319 m, 1173 m, 1086 w, 973 w, 830 m, 801 w, 743 w, 706 m, 657 w, 555 w,
467 w, 436 w, 332 w. For 2: The complex 2 was prepared by the same
method as that described for 1, with 5-chlorosalicylaldehyde replaced by
3-methylsalicylaldehyde, and with N,N-diethylethane-1,2-diamine replaced
by N,N-dimethylpropane-1,3-diamine. Diffraction quality single crystals of
2 were obtained after a few days by slow evaporation of the filtrate in open
atmosphere. Yield: 0.19 g (66% based on Cu). Anal. Calcd for
C43H57Cu4N10O3S4: C 45.1, H 5.0, N 12.2; Found: C 45.0, H 5.1, N
12.3. IR (KBr, cm21): 2126 s, 2097 s, 1638 s, 1523 m, 1455 s, 1381 m,
1323 m, 1177 m, 1086 w, 972 w, 817 m, 743 w, 710 m, 645 w, 562 w, 473 w,
428 w, 335 w.
Infrared spectra of the complexes were recorded as KBr discs
in the range 4000–200 cm21 with a Perkin-Elmer FT-IR 1800
spectrometer. The weak and broad bands indicative of the n(O–H)
of the free Schiff bases are absent in the complexes, indicating the
coordination through the deprotonated forms of the Schiff bases.
The intense absorption bands at about 2127 and 2097 cm21 for the
complexes are assigned to the stretching vibrations of two kinds of
thiocyanate ligands. The strong absorption bands at 1639 cm21 in
the spectrum of 1 and 1627 cm21 in the spectrum of 2 are assigned
to the azomethine groups, n(CLN).
Differential thermal (DT) and thermal gravimetric analyses
(TGA) were conducted to examine the stability of the complexes
(Fig. 3). For 1, the complex was decomposed from 153 uC to
673 uC, corresponding to the loss of the Schiff base and
thiocyanate ligands, and the formation of the final products
(CuO and Cu2O). The total observed weight loss of 75.6% is very
close to the calculated value of 75.2%. For 2, the complex was
decomposed from 150 uC to 713 uC, corresponding to the loss of
the Schiff base and thiocyanate ligands, and the formation of the
final products (CuO and Cu2O). The total observed weight loss of
71.6% is very close to the calculated value of 72.9%.
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In conclusion, we have prepared two lantern-like 1D polymeric
copper(I/II) complexes containing rarely seen [CuI(NCS)4] bridges
with tridentate Schiff bases 4-chloro-2-[(2-diethylaminoethylimi-
no)methyl]phenol and 2-[(3-dimethylaminopropylimino)methyl]-6-
methylphenol. Three of the four thiocyanate ligands adopt m2-NS
bridging mode, and the fourth adopts m4-NSSS bridging mode.
The Cu2+ ions in the copper(II) salts might partially be reduced to
Cu+ ions by thiocyanate anions, which have never seen in the
previous literature. The correlation between the substitute groups
of the Schiff bases and the final products of the copper complexes
deserves further study.
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Acknowledgements
This work was financially supported by the Natural Science
Foundation of China (Project No. 20901036), and by the
Distinguished Young Scholars Program of Higher Education
of Liaoning Province (Grant No. LJQ2011114).
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