Synthesis and characterization of complexes of thiomolybdates and thiotungstates with copper(I) and silver(I) cyanides, including molybdenum-95 and tungsten-183 NMR properties and the crystal and molecular structures of (n-Pr4N)2[(CN)CuS2MoS2], (n-Pr4N)2[(CN)AgS2WS2], and (Ph4As)2[(CN)CuS2MoS2Cu(CN)