Crystal structures of two trinuclear Schiff-base copper(II) complexes

Abstract

The crystal structures of (I), [{Cu(es)}₂Cu(H₂O)₂][ClO₄]₂,H₂O, [es =NN′-ethylenebis(salicylaldimine)] and (II)[{Cu(eha)}₂Cu(H₂O)][ClO₄]₂, [eha =NN′-ethylenebis-(o-hydroxyacetophenimine)], have been determined by single-crystal X-ray diffraction by use of diffractometer data, and refined by least-squares to R(I) 5·9 (3226, all reflections) and (II) 7·4%(2015 observed reflections).

Crystal data : (I), monoclinic, space group P2₁/n, a= 15·488(2), b= 21·883(4), c= 10·884(1)Å, β= 94·28(1)°, Z= 4; (II), orthorhombic, space group Pbca, a= 26·884(4), b= 19·093(4), c= 15·740(2)Å, Z= 8.

In both these complexes, a pair of Cu(es) and Cu(eha) chelate complexes act as bidentate ligands to the central copper atom, bonding through the oxygen atoms which act as bridges. In (I), the central copper atom has appreciably longer Cu–O bonds owing to its higher co-ordination number of 6, the pair of Cu(es)‘ligands’ effectively occupying ‘cis’ positions in a Jahn–Teller distorted configuration [Cu–O 2·324, 2·050, 2·025, and 2·328(6)Å], the remaining pair of equatorial co-ordination sites being filled by water molecules [Cu–OH₂ 1·950 and 2·000(6)Å]. Cu–Cu–Cu is 97·3(4)° and Cu ⋯ Cu 3·052 and 2·993(2)Å. In (II), the water molecule occupies an equatorisl site in a trigonal bipyramidal configuration on the central copper [Cu–OH₂ 2·18(2)Å], the Cu(eha)‘ligands’ bridging axial and equatorial sites [Cu–O 1·98, 1·93, 1·95, and 2·06(1)Å]. Cu–Cu–Cu is 156·2(4)° and Cu ⋯ Cu 2·950 and 2·975(5)Å. In both complexes, the perchlorate ions could not be precisely located owing to very high thermal motion in the lattice. The large change caused in the Cu–Cu–Cu angle is probably not the reason for the remarkably different magnetic behaviour of the two complexes. The reason for the steric difference between the two structures is not clear, and the system appears to give another example of the extreme sensitivity of complexes of this type to display polymorphism in response to subtle differences in crystal-packing and hydrogen-bonding forces.