SYNTHESIS OF [TL4SE16]4- - A NOVEL TETRANUCLEAR TL3+ POLYSELENIDE

(Ph4P)4[Tl4Se16] was prepared hydrothermally in a sealed pyrex tube by the reaction of TlCl, K2Se4 and Ph4PCl in a 1:1:1 molar ratio at 110-degrees-C for one day. The red crystals were obtained in 50% yield. Crystals of (Ph4P)4[Tl4Se16]: triclinic P1BAR (No. 2), Z=1, a=12.054(9), b=19.450(10), c=11.799(6) angstrom, alpha=104.63(4), beta=98.86(6), gamma=101.99(6)-degrees and V=2555(3) angstrom3 at 23-degrees-C, 2theta(max)=40.0-degrees, mu=120.7 cm-1, D(calc)=2.23. The structure was solved by direct methods. Number of data collected: 5206. Number of unique data having F(o)2>3sigma(F(o)2): 1723. Final R=0.075 and R(w)=0.089. [Tl4Se16]4- consists of four, almost already linearly arranged, tetrahedral thallium centers which are coordinated by two chelating Se4(2-), two bridging Se2(2-) and four bridging Se2- ligands. [Tl4Se16]4- sits on an inversion center and possesses a central {Tl2Se2}2+ planar core. The Tl(1)-Tl(1)' distance in this core is 3.583(6) angstrom. These two thallium atoms are then each linked to two cyclic Tl(Se4) fragments via bridging Se2(2-) and Se2- ligands forming Tl2Se(Se2) five-membered rings.