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This work is devoted to the comparative study of the lattice specific heat of Cu(en)(H2O)2SO4, Cu(en)2SO4 and Cu(en)2CrO4, where en=ethylenediamine - C2H8N2. Previous studies on the effects of spatial anisotropy of exchange coupling within the magnetic layer showed that quasi-one-dimensional polymer structures based on Cu(II) ions, Cu(en)(H2O)2SO4 and Cu(en)2SO4 represent realizations of spin 1/2 Heisenberg model on the spatially anisotropic zig-zag square lattice and the dimerized square lattice, respectively. The substitution of S-Cr in isomorphic Cu(en)2SO4 and Cu(en)2CrO4 introduces differences in lattice specific heat. The description of the heat capacity of the lattice up to room temperature was carried out considering the contribution of acoustic phonons within the Debye model and optical phonons using Einstein approximation. Deviations of the Debye model from the lattice heat capacity are already observed above 15 K for all compounds, for Debye temperatures θD = 146 K, 101 K and 94 K for Cu(en)(H2O)2SO4, Cu(en)2SO4 and Cu(en)2CrO4, respectively. The effect of acoustic and optical modes on magnetic correlations in these systems is also discussed. [ABSTRACT FROM AUTHOR]

Zeolitic imidazolate frameworks represent new materials falling into the large group of metal–organic frameworks with wide application potential. The present work is focused on the study of fundamental properties of imidazolate compound [{Zn(mIm)2·2H2O}∞],which is referred in literature as ZIF–8. Measurements of infrared spectra in the mid-infrared and far-infrared regions at room temperature as well as heat capacity in the range from 2 to 300 K were performed. The character of the infrared spectra suggests why the specific heat data values are so small, and even at 300 K the values are much lower than the classical value of 3sR resulting from the equipartition principle. Analysis of the specific heat of the ZIF–8 powder sample within the Debye model including only the contribution of three acoustic phonon branches revealed deviations of the model from experimental data already above 20 K. Low–frequency optical modes as indicated by infrared spectra are responsible for the observed deviations. [ABSTRACT FROM AUTHOR]