TRANSITION-METAL CHALCOGENIDES - NEW VIEWS ON AN OLD TOPIC

In this contribution we discuss a group of layered tellurides with mod ular structures (tinker toy phases) and possible low temperature route s for the synthesis of chalcogenides with porous structures. Layer com pounds of general composition [(M(2)Te(2))(ATe(2))](MTe(2))(n) and rel ated phases have been synthesized as main group counterparts of layere d metal-rich early transition metal tellurides. Special features of th ese compounds are (i) the unusual square planar Te coordination of the main group atoms Ga, Si, and Ge and (ii) their modular structure base d on four building blocks. Similarly to layered metal-rich early trans ition metal tellurides these phases are electronically stabilized by e xtensive bonding between early transition metals and main group ''hete roatoms''. Size effects are important for the structural stability of the tinker toy phases; attempts to substitute A=Ga by the group homolo gues B or In lead to the formation of alternate phases such as Ta4BTe8 containing metal clusters with interstitial atoms or intercalate phas es such as InxNb3Te4. Reactions in thiophosphate fluxes and under solv othermal conditions have been explored in order to synthesize material s with microporous structures. The formation of (poly)thiophosphates s uch as K(2)MP(2)S(7) (M=V, Cr) and K4Ti2P6S25 shows that reactions in molten thiophosphates are controlled by the redox equilibria and the b asicity of the flux. The reaction conditions prevent the use of templa tes which are needed for the formation of compounds with porous struct ures. Reaction of telluroarsenates with Cr(CO)(6) under solvothermal c ondition, however, results in the formation of a unique polytelluride [Cr(en)(3)][Te-6] with a microporous structure. Solvated Cr(en)(3)(3+) cations serve as templates in the synthesis of this material.