Structural variations in self-assembled coordination polymers constructed by some carboxylate bridged di-copper(II) nodes and hexamethylenetetramine spacers

Four new copper(II)-hexamethylenetetramine (hint) complexes [Cu-3(2-nbz)(6)(mu(2)-hmt)](n) (1), [Cu-3(pa)(6) (mu(3)-hmt)](n). (2), [Cu3(4-nbz)(6)(mu(3)-hmt)](n), (3) and [Cu(3-nbz)(2)(mu(4)-hmt)center dot H2O]. (4) with three isomeric nitrobenzoates, [2-nbz = 2-nitrobenzoate, 3-nbz = 3-nitrobenzoate, 4-nbz = 4-nitrobenzoate] and phenylacetate (pa) have been synthesized and structurally characterized by X-ray crystallography. Their identities have also been established by elemental analysis and IR studies. In all four complexes, the respective [Cu-2(carboxylato)(4)] unit with four bridging carboxylate ligands in the familiar eta(1):eta(1):mu coordination mode acts as a linear node whereas the spacer hmt coordinates in different ways which result in the observed structural variations. Complex 1 is a 1D zigzag polymer where hint acts as angular spacer. In complexes 2 and 3, mu(3)-hmt is pyramidal and the resulting structures are 2D polymers with fused hexagonal rings. Complex 4 is a very rare example of a 3D diamondoid polymer with mu(4)-hmt acting as a tetrahedral spacer. Various weak forces, i.e. lone pair-pi, pi-pi and CH-pi interactions, play a key role in stabilizing the observed structures. (C) 2013 Elsevier Ltd. All rights reserved.