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).

Abstract The new chloro-sulfosalt Pb 3+ x Sb 3− x S 7− x Cl 1+ x ( x ∼0.45) has been synthesized at 500 °C from a mixture of PbS, PbCl 2 and Sb 2 S 3 . It crystallizes in the orthorhombic system (space group Pbam ), with a =15.194(3) A, b =23.035(5) A, c =4.0591(8) A, V =1420.6 A 3 , Z =4. The crystal structure has been solved by X-ray single-crystal study, with a final R =0.0497. Deviation from stoichiometric Pb 3 Sb 3 S 7 Cl ( x coefficient) follows the substitution rule Sb 3+ +S 2− →Pb 2+ +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 Pb 6 Sb 6 S 14 (S 3 ), where the (S 3 ) 2− trimer is replaced by two Cl − ; this substitution is quite isovolumic. Other similar structures are: three polychalcogenides Sr 6 Sb 6 S 14 (S 3 ), Pb 6 Sb 6 Se 14 (Se 3 ) and Eu 6 Sb 6 S 14 (S 3 ); KLa 1.28 Bi 3.72 S 8 and its Ln isotypes; dadsonite, Pb 23 Sb 25 S 60 Cl. Pb 3+ x Sb 3− x S 7− x Cl 1+ x is the N =2 member of the homologous series Pb (2+2 N ) (Sb,Pb) (2+2 N ) S (2+2 N ) (S,Cl) (4+2 N ) Cl N ; the N =1 member corresponds to the previously known ∼Pb 4.3 Sb 3.7 S 8.7 Cl 2.3 compound. Other polychalcogenide derivatives of this homologous series are K 2 Pr 2− x Sb 4+ x Se 8 (Se 4 ) and its Ln isotypes ( N =1), as well as SrBiSe 3 ( N =3). Such a comparative modular analysis allowed to propose a structural model for the previous synthetic “Phase Y”, ∼Pb 10 Sb 10 S 23 Cl 4 , corresponding to the combined N =(1+2) homolog.