Variations of the coordination of nortricyclane-type 7-atom polypnictides to metal ions were achieved upon reactions of either K₃As₇ with PbI₂ in ethane-1,2-diamine and subsequent layering with toluene or by reacting an extraction solution of ‘K₅Ga₂Bi₄’ in pyridine with [ZnPh₂] prior to layering with toluene. The two procedures were specific for the respective elemental combinations, and they afforded the second compound exhibiting the rare Bi₇ ³⁻ ion in the coordination sphere of transition metal ions.

Abstract

The formation and follow-up chemistry of P₇ ³⁻ has been intensely studied in the recent decades. In contrast, corresponding investigations of its heavier polycyclic polypnictide congeners Pn₇ ³⁻ (Pn=As, Sb, Bi), especially Bi₇ ³⁻, have been done to a much lesser extent. In our report, we add to these rare studies, by reporting new coordination compounds with As₇ ³⁻ and Bi₇ ³⁻, respectively. Addition of PbI₂ to a solution of K₃As₇ in ethane-1,2-diamine (en) afforded the heterometallic cluster anion [(As₇)Pb(As₇)]⁴⁻ (with an 8 % co-crystallization of [PbAs₁₅]³⁻ on the same site), in compound [K_3.92(crypt-222)₄][(As₇)Pb(As₇)]_0.92[PbAs₁₅]_0.08 ⋅ 3en (1). A similar reaction of [ZnPh₂] with a pyridine (py) solution of the ternary solid ‘K₅Ga₂Bi₄’, which was previously shown to release Ga and polybismuthide units in situ under certain reaction conditions, resulted in the formation of [K(crypt-222)]₄[(Bi₇)Zn(Bi₇)] ⋅ 2.5py (2), comprising the related heterometallic anion [(Bi₇)Zn(Bi₇)]⁴⁻. The former represents the first Pb−As binary Zintl anions obtained via solution chemistry, and the latter adds one more piece to the remarkably rare coordination compounds reported for Bi₇ ³⁻.