Synthesis and Characterization of Homoleptic Zintl Anions [(Pn${}_7$)M(Pn${}_7$)]${}^{4-}$ (M/Pn = Pb/As, Zn/Bi)

The formation and follow-up chemistry of P${}_7^{3-}$ has been intensely studied in the recent decades. In contrast, corresponding investigations of its heavier polycyclic polypnictide congeners Pn${}_7^{3-}$ (Pn=As, Sb, Bi), especially Bi${}_7^{3-}$, have been done to a much lesser extent. In our report, we add to these rare studies, by reporting new coordination compounds with As${}_7^{3-}$ and Bi${}_7^{3-}$, respectively. Addition of PbI${}_2$ to a solution of K${}_3$As${}_7$ in ethane-1,2-diamine (en) afforded the heterometallic cluster anion [(As${}_7$)Pb(As${}_7$)]${}^{4-}$ (with an 8 % co-crystallization of [PbAs${}_{15}$]${}^{3-}$ on the same site), in compound [K${}_{3.92}$(crypt-222)${}_4$][(As${}_7$)Pb(As${}_7$)]${}_{0.92}$[PbAs${}_{15}$]${}_{0.08}$ ⋅ 3en (1). A similar reaction of [ZnPh${}_2$] with a pyridine (py) solution of the ternary solid ‘K${}_5$Ga${}_2$Bi${}_4$’, which was previously shown to release Ga and polybismuthide units in situ under certain reaction conditions, resulted in the formation of [K(crypt-222)]${}_4$[(Bi${}_7$)Zn(Bi${}_7$)] ⋅ 2.5py (2), comprising the related heterometallic anion [(Bi${}_7$)Zn(Bi${}_7$)]${}^{4-}$. 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 Bi${}_7^{3-}$.