Accurate Spin-State Energies for Iron Complexes

A critical assessment of the OPBE functional is made for its performance for the geometries and spin-states of iron complexes. In particular, we have examined its performance for the geometry of first-row transition-metal (di)halides (MnX2, FeX2, COX2, NiX2, CuX, X=[F, CI]), whose results were previously [J. Chem. Theory Comput 2006, 2, 1282] found to be representative for a much larger and more diverse set of 32 metal complexes. For investigating the performance for spin ground-states of iron complexes, we examined a number of small iron complexes (Fe(II)Cl-4(2-), Fe(III)Cl-4(1-), Fe(II)Cl-6(4-), Fe(III)Cl-6(3-), Fe(II)CN64-, Fe(III)CN63-, Fe(VI)O-4(2-), Fe(III)(NH3)(6)(3+)), benchmark systems (Fe(II)(H2O)(6)(2+), Fe(II)(NH3)(6)(2+), Fe(II)(bpy)(3)(2+)), and several challenging iron complexes such as the Fe(II)(phen)(2)(NCS)(2) spin-crossover compound, the monopyridylmethylamine Fe(II)(amp)(2)Cl-2 and dipyridylmethylamine Fe(II)(dpa)(2)(2+), and the bis complex of Fe(III)-1,4,7-triazacyclononane (Fe(III)((9)aneN(3))(2)(3+). In all these cases OPBE gives excellent results.