Homoleptic 1-D iron selenolate complexes-synthesis, structure, magnetic and thermal behaviour of (1)(infinity)[Fe(SeR)(2)] (R = Ph, Mes)

The first examples of polymeric homoleptic iron chalcogenolato complexes (1)(infinity)[Fe(SePh)(2)] and (1)(infinity)[Fe(SeMes)(2)] (Ph = phenyl = C6H5, Mes = mesityl = C6H2-2,4,6-(CH3)(3)) have been both prepared by reaction of [Fe(N(SiMe3)(2))(2)] with two equivalents of HSeR (R = Ph, Mes) while (1)(infinity)[Fe(SePh)(2)] was found to be also easily accessible through reactions of either FeCl2, Fe(OOCCH3)(2) or FeCl3 with PhSeSiMe3 in THF. In the crystal, the two compounds form one-dimensional chains with bridging selenolate ligands comprising distinctly different Fe-Se-Fe bridging angles, namely 71.15-72.57 degrees in (1)(infinity)[Fe(SePh)(2)] and 91.80 degrees in (1)(infinity)[Fe(SeMes)(2)]. Magnetic measurements supported by DFT calculations reveal that this geometrical change has a pronounced influence on the antiferromagnetic exchange interactions of the unpaired electrons along the chains in the two different compounds with a calculated magnetic exchange coupling constant of J = -137 cm(-1) in (1)(infinity)[Fe(SePh)(2)] and J = -20 cm(-1) in (1)(infinity)[Fe(SeMes)(2)]. In addition we were able to show that the ring molecule [Fe(SePh)(2)](12) which is a structural isomer of (1)(infinity)[Fe(SePh)(2)] behaves magnetically similar to the latter one. Investigations by powder XRD reveal that the ring molecule is only a metastable intermediate which converts in THF completely to form (1)(infinity)[Fe(SePh)(2)]. Thermal gravimetric analysis of (1)(infinity)[Fe(SePh)(2)] under vacuum conditions shows that the compound is thermally labile and already starts to decompose above 30 degrees C in a two step process under cleavage of SePh2 to finally form at 250 degrees C tetragonal PbO-type FeSe. The reaction of (1)(infinity)[Fe(SePh)(2)] with the Lewis base 1,10-phenanthroline yielded, depending on the conditions, the octahedral monomeric complexes [Fe(SePh)(2)(1,10-phen)(2)] and [Fe(1,10-phen)(3)][Fe(SePh)(4)].