Metal polychalcogenides

Heavy ketones have been synthesized by several synthetic methods shown in Scheme 19 (i) the reaction of divalent group 14 element species with chalcogen sources, (ii) the reaction of dihydrometallanes with chalcogen sources, (iii) the dechalcogenation of metal polychalcogenides, (iv) the reaction of dilithiomet-allanes with dihalochalcogenides, and (v) substitution of the chloro group of heavy acyl chlorides. The methods used for the synthesis of heavy ketones are summarized in Tables 3-5. 

This means that addition of elemental E to alkali metal polychalcogenide fluxes (200-600°C) will promote the formation of longer chains as potential ligands, when such molten salts are employed as reaction media for the preparation of polychalcogenide complexes. Speciation analysis for polychalcogenides in solution has been performed by a variety of physical methods including UV/vis absorption spectroscopy, Raman spectroscopy, Se, Te and Te NMR, electron spin resonance and electrospray mass spectrometry. 

Metal powders can readily react with alkali metal polychalcogenide melts at typical temperatures in the range 200 600°C to afford chalcogen-rich complexes. As discussed in an excellent review article,10 the highly ionic nature of the melt greatly enhances the solubility of the chosen metal and often facilitates the growth of single crystals. 

The hydrothermal method has been employed in recent years to synthesize a variety of solids that include aluminium phosphates (ALPOs) and other microporous transition-metal phosphates and transition-metal polychalcogenides (Davis Lobo, 1992 Haushalter Mundi, 1992 Liao Kanatzidis, 1990, 1992). Unlike zeolites, synthesis of ALPOs requires acidic or mildly basic conditions and no alkali metal cations. A typical synthetic mixture for making ALPO consists of alumina, H3PO4, water and an organic material such as a quaternary ammonium salt or an amine. The hydrothermal reaction occurs around 373-573 K. The use of fluoride ions, instead of hydroxide ions as mineralizer, allows synthesis of novel microporous materials under acidic conditions (Estermann et al, 1991 Ferey et ai, 1994). 

Both reactive and nonreactive molten salts can be used in nontopochemical routes. An example of a nontopochemical route to inorganic materials utilizing reactive molten salts is when a metallic element is reduced in a low-melting alkali metal polychalcogenide (hiQn, where Q = O, S, Se, Te) to form a ternary metal chalcogenide. Potassium bismuth sulfide (KBi3Ss) has been prepared in... 

Figure 60 Possible chalcophosphate anion equilibria present in alkali metal polychalcogenide fluxes...

One permutation that has proven productive is the combination of lanthanides with late transition metals. From the reaction of the elemental copper and either lanthanides or actinides in molten alkali metal/polychalcogenide salts, several new quaternary phases have been discovered. Specifically, these phases are ACuRE2Qe (where A = K, M = La, Q = S A = Cs, M = Ce, Q = S or A = K, M = Ce, Q = Se),i 8 i50 ACuREQj (where A = Cs, RE = lanthanide or actinide, Q = S, Se) and the structurally related BaREMQs (RE = rare earth, M = coinage metal, Q = Se or Te), ARE2CUQ4 (Q = S, ARE2CU3Q5,... 

Four important characteristics of this chemistry will be illustrated in the following paragraphs they all demonstrate the special significance of supramolecular influences for metal polychalcogenides. 

Metal polychalcogenide complexes in solution are not necessarily the same as those in the crystals which grow from those solutions ... 

The clear conclusions from these observations are that (1) metal polychalcogenides are unusually adaptable coordination systems, which is not surprising, and (2) the crystal fields in many of the solids are demonstrably distorting both the compositions and the stereochemistries. The structures of the crystals do not faithfully represent the most stable coordination chemistry. 

The chemistry of metal polychalcogenide clusters represents an area of increasing activity due to the structural diversity as well as the potential for the use of these clusters as precursors to new... 

ABSTRACT Several new metal-(poly)chalcogenide compounds with extended structures are reported. The S5mthetic techniques used include classical solution chemistry in organic solvents, molten salt techniques using alkali metal polychalcogenides as fluxes at 200-400 °C and hydrothermal methods. Several new network structures with transition and main group metals and Sex - are reported. 

Metal polychalcogenide polymers which have been crystallized directly out of the reaction mixture at room temperature are rare. Recently we published several silver polyselenide compounds which were synthesized according to eq. 1... 

Molten alkali-metal polyselenide fluxes also prove to be useful in the syntheses of unusual quaternaries, here illustrated by the synthesis of the onedimensional polyselenide K3CuNb2Sei2-Both of these polychalcogenides are synthesized at 870° or above. The use of low temperatures (< 450°) is not a necessary condition for the synthesis of metal polychalcogenides, as has been implied. ... 

---