Solid-State Structure and Solution Behavior of Eight-Coordinate Sm(III) Poly(pyrazolyl)borate Compounds

[Sm(TpMe2)2(κ2-S2CNR2)] compounds (R = Et (1), Me (2); TpMe2 = HB(3,5-Me2pz)3) have been isolated from reaction of (R2NC(S)S)2 with 2 equiv of [Sm(TpMe2)2]. Reductive cleavage of 2,2‘-dipyridyl disulfide or 2,2‘-dipyridyl diselenide by [Sm(TpMe2)2] afforded good yields of [Sm(TpMe2)2(κ2-Y)] compounds (Y = 2-SC5H4N (3), 2-SeC5H4N (4)). 4 is the first selenopyridine complex of an f-block element. Sm(TpMe2)2(2-OC5H4N) (5) has been synthesized by salt metathesis of [Sm(TpMe2)2Cl] with the sodium salt of the 2-hydroxypyridine. The solid-state structures of 1, 3, 4, and 5 were determined by single-crystal X-ray diffraction analysis and revealed that the compounds are all eight-coordinate with dodecahedral geometry. The samarium atoms are bound in tridentate fashion to two pyrazolylborate ligands and in bidentate fashion by the third ligand. The solution behavior of the compounds was studied by 1H NMR techniques. 1H−1H exchange spectroscopy experiments give evidence for two distinct dynamic regimes occurring in solution.