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]·2RH (1) and [Cu2(R)4(bpy)]x (2) were obtained from the reaction of [Cu2(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, [Cu2(CH3(CH2)5COO)4(bpy)]x (3). Both 1 and 2 were thermally stable (Tdec = 240 °C for 1; 220 °C for 2), have low melting temperatures (Tm = 52.3 °C for 1; Tm = 48.3 °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–Nbpy bonds. The mesophases for 2 were cubic columnar (Cub, P4332) and rectangular columnar (ColR, space group p2gg) on cooling from 150 °C, Cub and hexagonal columnar (ColH) on cooling from 184 °C (isotropic liquid phase), and ColH and nematic columnar (ColN) on cooling from 190 °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.