Structural, mesomorphic, photoluminescence and thermoelectric studies of mononuclear and polymeric complexes of copper(II) with 2-hexyldecanoato and 4,4′-bipyridine ligands

[Cu(R)(2)(bpy)(2)]center dot 2RH (1) and [Cu-2(R)(4)(bpy)](x) (2) were obtained from the reaction of [Cu-2(R)(4)(RH)(2)] (R = 2-hexyldecanoato) with 4,4'-bipyridine (bpy) using different work-up procedures. Complex 1 consisted of single crystals and its molecular structure showed a distorted octahedral Cu(II) with two chelating bidentate R. Complex 2 has a similar structure as crystals of a linear-chain coordination polymer, [Cu-2(CH3(CH2)(5)COO)(4)(bpy)](x) (3). Both 1 and 2 were thermally stable (T-dec = 240 degrees C for 1; 220 degrees C for 2), have low melting temperatures (T-m = 52.3 degrees C for 1; T-m = 48.3 degrees C for 2) and exhibited temperature-dependent mesomorphisms. For 1, the mesomorphism arose from the change in the binding mode of R from chelating to bridging during isotropization, while for 2, the mesomorphism arose from the breaking of the Cu-N-bpy bonds. The mesophases for 2 were cubic columnar (Cub, P4(3)32) and rectangular columnar (Col(R), space group p2gg) on cooling from 150 degrees C, Cub and hexagonal columnar (Col(H)) on cooling from 184 degrees C (isotropic liquid phase), and Col(H) and nematic columnar (Col(N)) on cooling from 190 degrees C. These complexes also exhibited photoluminescence upon charge transfer and d-d excitation. Finally, the Seebeck coefficient value (Se) for 2 was -0.47 mV K-1, identifying it as a potential thermoelectric material.