TETRAPNICTIDOTITANATES(IV) M(4)TIX(4) (M= SR, BA, X=P, AS), HIERARCHICAL DERIVATIVES OF THE KGE STRUCTURE K-4-SQUARE-GE-4

The four new tetrapnictidotitanates(IV) Sr4TiP4, Sr4TiAs4, Ba4TiP4 and Ba4TiAs4 are synthesized from the binary pnictides MX (M = Sr, Ba and X = P, As) and elementary titanium in tantalum ampoules. The compound s are isotypic and isoelectronic with Ba4SiAs4 (space group <P(4)over bar 3n> (no. 218); cP72; Z = 8; Sr4TiP4: a = 1259.0(1) pm; Sr4TiAs4: a = 1288.3(4) pm; Ba4TiP4: a = 1316.6(2) pm; Ba4TiAs4: a = 1346.9(2) pm ). The transition metal compounds form cubic, metallic reflecting crys tals (Sr4TiP4 (green); Sr4TiAs4 (silver coloured); Ba4TiP4 (silver col oured); Ba4TiAs4 (violet). They are semiconducting and very sensitive against air and moisture. The structure is a hierarchical derivative o f Cr3Si (A15) and KGe type: Cr6Si2 corresponds to (square Ge4K4)(6)(sq uare Ge4K4)(2) corresponds to (TiX(4)M(4))(6)(TiX(4)M(4))(2), where Ti occupies the positions of the Cr3Si structure, and the alkaline-earth metal and pnicogen atoms occupy the positions of the KGe structure. T herefore, Ti is surrounded by four X and four more distant M atoms for ming a heterocubane. The mean bond lengths are: (d) over bar(Ti-P) = 2 38.0(5) pm; 307 less than or equal to d(Sr-P)less than or equal to 333 pm; (d) over bar(Ti-As) = 245.9(4); 313 less than or equal to d(Sr-As ) less than or equal to 341 pm; (d) over bar(Ti-P) = 240.5(5); 324 les s than or equal to d(Ba-P) less than or equal to 348 pm; (d) over bar( Ti-As) = 248.3(3) pm; 331 less than or equal to d(Ba-As) less than or equal to 355 pm.