Covalent Attachment of Thiophene Groups to Polyoxomolybdates or Polyoxotungstates for the Formation of Hybrid Films

Abstract

A novel bisphosphonate ligand bearing a thiophene group (AleThio) was synthesized and its covalent grafting to polyoxometalates (POMs) investigated. The hybrid polyoxomolybdate [(Mo3O8)4(O3PC(O)(C3H6NH2CH2C4H3S)PO3)4]8- [Mo12(AleThio)4] was synthesized in water by the reaction of Na2MoO4 with AleThio. It is built of four {MoVI3O8} units connected by phosphonate groups around a central Na+ ion. The reaction of the trivacant [PW9O34]9- units with CoII or NiII ions in the presence of AleThio led to the sandwich-type anions [(PW9O34)2(OH)2(H2O)4M7(O3PC(O)(C3H6NH2CH2C4H3S)PO3)2]14- [M = Ni, Co; M7(AleThio)2]. Salts soluble in organic solvent were prepared by cation-exchange with bis(triphenylphosphine)iminium ions. 31P NMR spectroscopy showed that Mo12(AleThio)4 is stable in acidic medium (pH ≤ 4) while the M7(AleThio)2 POMs are stable in alkaline medium (6 ≤ pH ≤ 13). Their cyclovoltammograms were recorded in solution. Attempts to surface immobilize the POMs through homo-polymerization were unsuccessful but co-polymerization employing 3-methylthiophene led to polymeric films with covalently attached POMs.