57Fe Mossbauer quadrupole splittings and isomer shifts in spin-crossover complexes:: A density functional theory investigation

We report the results of density functional theory (DFT) calculations of the Fe-57 Mossbauer quadrupole splittings DeltaE(Q) and isomer shifts delta(Fe) of both the high-spin (HS) and low-spin (LS) states of two typical spin crossover complexes: the six-coordinate species cis-bis(thiocyanato)bis(1,10-phenanthroline)iron(II), (Fe(phen)(2)(NCS)(2); S = 2 or 0) and the five-coordinate system, [N,N'-ethylenebis(salicylideniminato)]nitrosyl iron(II), (Fe(salen)-(NO); S = 3/2 or 1/2). There is excellent agreement between the experimental data and the theoretical calculations. The wave functions derived are used to clarify some aspects of the differences between the HS and LS electronic states of these materials, and they put on a firm theoretical foundation the use of Mossbauer spectroscopy to investigate spin-crossover complexes.