Zr-7(Sb,Se)(4) - a polar variant of the Nb7P4 structure type

Single crystals of Zr7Sb1.6(1)Se2,4 were obtained by are-melting of compres sed mixtures of Zr, ZrSb2, and ZrSe2, followed by annealing at 1300 degrees C in an induction furnace using traces of iodine to promote crystal growth . The crystal structure (a = 375.98(4), b = 1662.6(2), c = 1476.7(2)pm, V = 923.1(2) 10(6) pm(3) Cmc2(1), Z = 4) was determined by single crystal X-ra y means. Zr7Sb1.6(1)Se2.4 forms a unique polar structure composed of conden sed tri-capped trigonal prismatic Zr-9 clusters, being stabilized by inters titial Sb/Se atoms. The remaining Sb and Se atoms reside in mono- and bi-ca pped trigonal prismatic Zr-7 and Zr-8 clusters, respectively, of the extend ed cluster network. Characteristic structural distinctions and relations be tween Zr-7(Sb,Se)(4) and congeneric Zr7P4 are highlighted.