Heat capacities of six synthesized complex compounds with apical substituted pyridine ligands were studied by adiabatic calorimetry (AC), differential scanning calorimetry (DSC), and computer simulation. Thermodynamic properties were calculated from experimental heat capacity data and by computer simulation. It was shown that below the structural phase transition temperatures the lattice component of heat capacity has the similar values for all studied complexes and above this temperature structural changes are determined by the nature of apical ligand. (C) 2010 Elsevier B.V. All rights reserved.