meta-Phenylene-bridged double Schiff base copper(II) complexes as building blocks for 1D coordination polymers:: Synthesis, crystal structure and magnetic properties

The new double Schiff-base ligands H(6)ipa-hyhb and H(6)ipa-hyhh were synthesized by condensation of a 4,6-diformylresoreinol derivative (ipa) with 4-hydroxy-butanoic acid hydrazide (hyhb) and 6-hydroxy-hexanoic acid hydrazide (hyhh). The reaction with copper(II) perchlorate in the presence of an appropriate co-ligand (Him = imidazole, Hpz = pyrazole) leads to the novel coordination polymers {[Cu-2(H(4)ipa-hyhb)(Hpz)(2)](ClO4)(2))(n) (1), {[Cu-2(H(4)ipa-hyhb)(Him)(2)](ClO4)(2)}(n) (2), and {[Cu-2-(H(4)ipa-hyhh)(Hpz)(2)](ClO4)(2)}(n) (3). These coordination polymers are composed of primary building blocks with the general formula [Cu-2(H(4)ipa-X)(L)(2)](2+) (X = hyhb, hyhh; L = Him, Hpz) which are linked by coordination of the hydroxyl groups of the ligand side chains at the apical position of copper(II) centers of adjacent building blocks. The resulting chains possess different topologies and therefore different supramolecular structures due to the variation in length of the ligand alkyl side chains. For the complexes 1 and 2 double- hydroxyalkyl-bridged distorted ladder like chains are formed. Whereas in case of complex 3 single hydroxyalkyl-bridged chains are obtained which assemble to hydrogen bonded double chains. In the case of 1 and 2 these chains are cross-linked by hydrogen bonding interactions with the perchlorate counterions, whereas for 3 additional pi-pi stacking interaction are observed. The temperature-dependent magnetic measurements indicate weak antiferromagnetic interactions with coupling constants J = -26.1 cm(-1) (1), J = -28.2 cm(-1) (2), and J = -26.5 cm(-1) (3). The magnetic exchange interaction is solely the result of a coupling within the dinuclear complex moieties through the central resorcinol moiety. (c) 2007 Elsevier Ltd. All rights reserved.