SYNTHESIS AND PROPERTIES OF THE HOMOPOLYCHALCOGENIDE AND HETEROPOLYCHALCOGENIDE [A(Q5)2]2- FAMILY (A = TE, Q = S, SE - A = SE, Q = SE) - CRYSTAL-STRUCTURES OF (PH4P)2[TE(S5)2] AND BETA-(PH4P)2[SE(SE5)2]

The reaction of Na2Te4 with K2S5 in dimethylformamide in the presence of Ph4 PCl gave (Ph4P)2[Te(S5)2] (I). Under the same conditions, the reaction of elemental tellurium with Na2Se5 afforded (Ph4P)2[Te(Se5)2] (II), while beta-(Ph4P)2[Se(Se5)2] (III) was made by reacting Na2Se5 with I2. The X-ray powder diffraction studies showed that I, II and III are isostructural. The structures of I and III were determined by X-ray single crystal analysis. The [A(Q5)2]2- anions in the two compounds contain either a square-planar Te2+ in I or Se2+ centre in III, which is situated on an inversion centre and chelated by two S-5(2-) or Se-5(2-) ligands. The bond distances between the central A2+ and its surrounding four Q atoms are Te-S(1) = 2.699(2) angstrom and Te-S(5) = 2.752(2) angstrom, or Se-Se(1) = 2.653(2) angstrom and Se-Se(5) = 2.693(2) angstrom. S-S bond distances [av. S-S = 2.075(12) angstrom] or Se-Se bond distances [av. Se-Se = 2.314(13) angstrom] are normal and in good agreement with those found in other polysulphide or polyselenide compounds. The conformation of each AQ5 ring in I and III is very close to a ''chair''. The solution UV-vis spectra of DMF solutions for all three compounds are reported.