192
R.P. Sharma et al. / Journal of Molecular Structure 918 (2009) 188–193
Fig. 6. Unit cell packing diagram for 2(a) and 3(b) (view along b axis).
In 2, the asymmetric unit contains one p-ethoxybenzoate anion
and a half of the [trans-Cu(en)2(H2O)2]2+ cation, while in 3, the cat-
ion lies on an inversion center. ORTEPIII [23] view of the complex
salts 2 and 3 are shown in Figs. 3 and 4. In both the complex cat-
ions, two chelating ethylenediamine molecules coordinated with
copper metal ion and the slightly distorted octahedral coordination
is completed by two water O atoms in axial positions (Figs. 3 and
4). The values of T parameter [24] (indicating the degree of tetrag-
onal distortion about the Cu(II) atom) in the complex salts 2 and 3
are 0.75 and 0.79 which are within the range 0.76–0.84 reported
for such complex salts [25]. A comparison of T parameter and
structural parameters of the present complex salts with those of
other related Cu(II) complexes showed a substantial agreement
for bond lengths and angles (given in Table S1 in Supplementary
material). The C–O distances in the carboxylate anions of the two
complex salts (Table 2) are very similar and are typical of delocal-
ized bonds. Hydrogen-bonding parameters are reported in Table 3.
Thus, we have shown that the electronic spectrum may be used
to (i) predict the formation of ionic [trans-Cu(en)2(H2O)2]2+and aryl
carboxylates anions in solution which may be confirmed by the so-
lid state X-ray structure determination of the single crystals (ob-
tained after evaporation of solution at room temperature) and (ii)
complex salts are anhydrous and their formation is unaffected by
the substitution on the benzene ring. Further studies are in pro-
gress to establish this spectra–structure relationship for other cop-
per(II) aryl carboxylate complex salts in the presence of
ethylenediamine ligand.
Appendix A. Supplementary data
Crystallographic data for complex salts 2 and 3 have been
deposited with the Cambridge Crystallographic Data Center as sup-
plementary publications CCDC 691637 and CCDC 691638. Copies
of the data can be obtained free of charge on application to CCDC,
12 Union Road, Cambridge CB2 1EZ, UK [fax: +44 1223 336033,
e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated
with this article can be found, in the online version, at
4.2. Packing
In both crystals, the packing architecture is mainly controlled
by the formation of O–HꢁꢁꢁO hydrogen bonds, involving O–H groups
of the coordinated water molecules as donors and the oxygen
atoms of the carboxylate anions as acceptors. The structures are
made more robust by additional N–HꢁꢁꢁO interactions. The H-bond-
ing parameters are reported in Table 3. The OꢁꢁꢁO contact distances,
on average 2.80(9) and 2.789(1) Å for 2 and 3, respectively, are
longer than expected for Charge Assisted Hydrogen Bonds, that
are usually in the range 2.45–2.65 Å [26], due to the fact that the
donor atoms are involved in the formation of the additional N–
HꢁꢁꢁO bonds. Taking into consideration only the strongest interac-
tions, the hydrogen-bond pattern can be described in terms of
graph-set approach [27]. In both cases there is the formation, by
symmetry, of the same R44(12) motif (R = ring) shown in Fig. 5,
which, in turn, leads to two C22(8) chains running, in both structures,
along the b axis. The hydrogen bond links in the crystal lattice re-
sulted the separate columns formation by the cations and the anions
(Fig. 6), the only difference between the two structures being the
mutual orientation of the benzoate derivatives, i.e. the carboxylate
anions are arranged in the herringbone pattern in 2 while in 3 they
are disposed in a parallel way.
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Copper(II)arylcarboxylates react with ethylenediamine (en) in
water–methanol solution to form dark blue coloured crystalline io-
nic solids in which two en molecules displace four water molecules
from the coordination sphere of the hexaaqua copper(II) complex
(in general). On the basis of physico-chemical data available (kmax
ꢀ540), the trans octahedral ionic structure, predicted in the solu-
tion state, has been confirmed by single-crystal X-ray structure
determinations of [trans-Cu(en)2(H2O)2](L)2: 2, 3 in the solid state.
Probably, the same is true for ibuprofenato complex salt 1 also.