EPR studies on melaminium hexachlorodicuprate - a one-dimensional dimeric copper(II) chain system

X-band EPR studies of the monoclinic crystal melaminium hexachlorodicuprate (MHCC) constituted of ladder-like chains of copper (II) dimers (S = 1) run ning parallel to the a-axis are carried out in the temperature interval 77- 295 K. Spectra recorded in the two crystallographic planes (010) and (001) have revealed some features quite distinct from those of true dimeric compo unds such as copper acetate monohydrate. Only a single line spectrum has be en observed in ail orientations of the single crystal. A large disparity wa s observed between the mean g-value (2.11) directly obtained from EPR measu rements and that (2.21) derived from mean magnetic susceptibility data base d on the 'mean field corrected dimer model' of Colombo et al (Colombo A, Me nabue L, Motori A, Pellacani G C, Porzio W, Sandrolini F and Willet R D 198 5 Inorg. Chem. 24 2900). EPR lineshape is Lorentzian in all directions of t he crystal. The linewidth has appreciable anisotropy (1000-600 Oe). The obs erved angular variation of linewidth in the said crystallographic planes ha s been analysed on the basis of the anisotropic exchange theory of Ritter e y al (Ritter M B, Drumheller J E, Kite T M, Snively L O and Emerson K 1983 Phys. Rev. 28 4949) suitably modified to be applicable in the present case of the S = 1 1D system. The thermal dependence of EPR line intensity has al so been investigated, It has been shown that the MHCC system is best descri bed as an antiferromagnetic exchange coupled S = 1 1D system. The presence of orthorhombic anisotropic symmetric exchange has also been confirmed.