Tungsten oxide as a universal source for the synthesis of complexes with different nuclearities in WO3/chalcogen/NaCN systems

Abstract

Tungsten trioxide can be used as a readily available source in the one-step preparation of a variety of cyanide and chalcocyanide mononuclear and cluster complexes of tungsten. In our study of phase formation in the system 6WO₃ + 8Q + 32NaCN (Q = S, Se or Te) in the temperature range of 250–700 °C, we determined which soluble complex compounds are formed, the temperature limits of their existence and the influence of synthesis time on the composition of the products. As the temperature increases, the process begins with the formation of mononuclear and then cluster complexes and ends with the formation of tungsten dichalcogenides: [W(CN)₈]⁴⁻ → [WS₄]²⁻/[WS₃O]²⁻ → [{W₃Q₄}(CN)₉]⁵⁻ (Q = S or Se), [{W₃S₃O}(CN)₉]⁵⁻ → [{W₄Q₄}(CN)₁₂]⁶⁻ (Q = S, Se or Te) → WQ₂ (Q = S or Se). Depending on the synthesis conditions, these complexes can either coexist in a mixture or one of them becomes the main product of the reaction. The obtained trinuclear and tetranuclear cluster complexes were studied by ¹³C, ⁷⁷Se and ¹⁸³W NMR spectroscopy using DFT calculations to assign the spectral signals. The crystal structures of the salts Cs₅Na₃[W(CN)₈]₂·2H₂O (1), Cs_2.8Na_2.2[{W₃S₄}(CN)₉]·2.2H₂O (2), Cs₅[{W₃S₃O}(CN)₉]·2H₂O·0.5CsCl (3) and Cs_3.5Na_1.5[{W₃Se₄}(CN)₉]·6.5H₂O (4) were determined by single-crystal X-ray diffraction analysis. It was also revealed that the quantitative ratio of trinuclear complexes [{W₃S₃O}(CN)₉]⁵⁻ and [{W₃S₄}(CN)₉]⁵⁻ with different cluster core compositions formed in the 6WO₃ + 8S + 32NaCN system at 300 °C depends on the synthesis time. Dynamics of the observed transformation of the initially dominant complex with a heteroleptic cluster core {W₃(μ₃-S)(μ-S)₂μ-O} into the complex with a homoleptic core {W₃(μ₃-S)(μ-S)₃} was studied using ¹³C NMR spectroscopy.