Exchange interaction between TCNQ and transition metal ion mediated by hydrogen bonds in [Mn(phen)3](TCNQ)2·H2O and [Co(phen)3](TCNQ)2·H2O

The magnetic properties, specific heat and EPR spectra of anion-radical salts [Mn(phen)3](TCNQ)2·H2O and [Co(phen)3](TCNQ)2·H2O, in which TCNQ molecules and transition metal ions are not connected by covalent bonds and magnetic interactions are mediated via hydrogen bonds, were investigated. Measurements of the magnetic response were performed down to 1.8 K in magnetic fields up to 7 T. The heat capacity of investigated compounds was measured in temperature range from 0.38 K to 35 K in magnetic fields up to 9 T for [Mn(phen)3](TCNQ)2·H2O and up to 3 T for [Co(phen)3](TCNQ)2·H2O. The EPR spectra of studied samples were investigated for both samples in the temperature range from 2 K to 300 K. Theoretical model of weakly-coupled magnetic units composed of four TCNQ anion radicals and of two transition metal ions was proposed for interpretation of obtained data. The energy of exchange interactions between TCNQ molecules and transition metal ion is important for the description of low-temperature behavior of studied anion-radical salts and was estimated to be in the range of 1.3-1.5 K.