Macrocyclic nickel(II) complexes coligated by hydrosulfide and hexasulfide ions: syntheses, structures, and magnetic properties of [NiII2L(mu-SH)]+ and [(LNiII2)2(mu-S6)]2+

The borohydride complex Ni(II)2L(mu-BH4)]+ (3) where L(2-) represents a sterically demanding hexaaza-dithiophenolate ligand reacts rapidly with elemental sulfur in acetonitrile at ambient temperature to produce the cationic complexes Ni(II)2L(mu-SH)]+ (4) and (Ni(II)2L) 2(mu-S6)]2+ (6). Both complexes were isolated as ClO4(-) or BPh4(-) salts and characterized by IR and UV/vis spectroscopy and X-ray crystallography. Complex 4 (also accessible from Ni(II)2L(ClO4)]+ (5) and Na2S.9H2O) features an unprecedented N3Ni(II)(mu-SR)2(mu-SH)Ni(II)N3 core structure, the hydrosulfide ligand being deeply buried in the binding-cavity of the bowl-shaped Ni(II)2L]2+ complex. In 6, a helical S6(2-) chain, with a structure reminiscent to that of plastic sulfur, is almost completely encapsulated by two Ni(II)2L]2+ subunits. In contrast to other triply sulfur-bridged N3Ni(II)(SR)3Ni(II)N3 structures whose ground states are typically of S = 0, 4 reveals an S = 2 ground-state which is attained by a ferromagnetic exchange interaction between the two Ni(II) (S = 1) ions ( J = 18 cm (-1), H = -2JS1S2). Intradimer ferromagnetic exchange interactions are also present in 6 ( J = 23 cm (-1)). A qualitative explanation for this difference is offered.