SIMPLIFIED FORMULA FOR THE (1)A(1)REVERSIBLE-ARROW-T-5(2) SPIN TRANSITION-TEMPERATURE IN FE(II) COMPLEXES

A formula relating the (1)A(1) reversible arrow T-5(2) spin transition temperature (T-c) in Fe(II) complexes to characteristics of the compo unds is derived. With certain assumptions, T-c is determined by the sp litting parameter Delta(LS) of e(g)- and t(2g)-orbitals for the low-sp in complexes and by the frequency ratio of normal vibrations of the lo w- and high-spin phases. Fbr the group of compounds possessing spilt t ransitions, the values of Delta(LS) are found and analyzed Correlation s between T-c and Delta(LS) are established; the values of the change in the probability of the Mossbauer effect are correlated with those o f entropy of spin transition. The correlations are substantiated. It i s concluded that for mononuclear Fe(II) complexes possessing sharp spi n transitions, T-c may not be significantly higher than for Fe(Phy)(2) (BF4)(2)(T-c = 282 K).