Crystal structure of the new compound Pb3+xSb3−xS7−xCl1+x(x∼0.45): The homologous series Pb(2+2N)(Sb,Pb)(2+2N)S(2+2N)(S,Cl)(4+2N)ClN and its polychalcogenide derivatives (N=1–3)

The new chloro-sulfosalt Pb3+xSb3−xS7−xCl1+x (x∼0.45) has been synthesized at 500 °C from a mixture of PbS, PbCl2 and Sb2S3. It crystallizes in the orthorhombic system (space group Pbam), with a=15.194(3) Å, b=23.035(5) Å, c=4.0591(8) Å, V=1420.6 Å3, Z=4. The crystal structure has been solved by X-ray single-crystal study, with a final R=0.0497. Deviation from stoichiometric Pb3Sb3S7Cl (x coefficient) follows the substitution rule Sb3++S2−→Pb2++Cl−. Sb and Pb sub-positions within mixed (Sb,Pb) sites are discussed; Pb excess precludes any superstructure along c. A unique pure Cl position is bound only to Pb atoms with a distorted square coordination. The title compound is a rod-type structure derived from the SnS archetype, homeotypic with Pb6Sb6S14(S3), where the (S3)2− trimer is replaced by two Cl−; this substitution is quite isovolumic. Other similar structures are: three polychalcogenides Sr6Sb6S14(S3), Pb6Sb6Se14(Se3) and Eu6Sb6S14(S3); KLa1.28Bi3.72S8 and its Ln isotypes; dadsonite, Pb23Sb25S60Cl. Pb3+xSb3−xS7−xCl1+x is the N=2 member of the homologous series Pb(2+2N)(Sb,Pb)(2+2N)S(2+2N)(S,Cl)(4+2N)ClN; the N=1 member corresponds to the previously known ∼Pb4.3Sb3.7S8.7Cl2.3 compound. Other polychalcogenide derivatives of this homologous series are K2Pr2−xSb4+xSe8(Se4) and its Ln isotypes (N=1), as well as SrBiSe3 (N=3). Such a comparative modular analysis allowed to propose a structural model for the previous synthetic “Phase Y”, ∼Pb10Sb10S23Cl4, corresponding to the combined N=(1+2) homolog.