Synthesis and Characterisation of Monolacunary Keggin Monovanado-deca-tungstophosphate and Its Complexes with Transition Metal Cations.

Five new complexes with metal cations (Mn 2+ , Fe 3+ , Co 2+ , Ni 2+ , and Cu 2+ ) of monolacunary Keggin monovanado-deca-tungstophosphate, K 8 [PVW 10 O 39 ]·15H 2 O, have been synthesised. The molar ratio of the combination between metal cations and K 8 [PVW 10 O 39 ]·15H 2 O has been established to be 1:1, and its general molecular formulas were found to be: K n [MPVW 10 O 39 (H 2 O)]·xH 2 O ( n = 5 for M = Fe 3+ and n = 6 for M = Mn 2+ , Co 2+ , Ni 2+ , and Cu 2+ ). Optimal conditions for complexes' synthesis (pH, temperature, and reaction time) have been determined. The characterisation of K 8 [PVW 10 O 39 ]·15H 2 O and of its compounds K n [MPVW 10 O 39 (H 2 O)]·xH 2 O have been performed using AAS, TG-DTA-DTG, UV-VIS, IR, Raman, and powder XRD methods. In UV spectra, two maximums of absorption were obtained, at 200 and 250 nm, characteristic of Keggin polycondensate compounds. The coordination of cations Ni 2+ , Co 2+ , and Cu 2+ through oxygen atoms from K 8 [PVW 10 O 39 ]·15H 2 O in an octahedron system has been reflected with VIS spectroscopy. All these methods have proved the compositions and structures of K 8 [PVW 10 O 39 ]·15H 2 O and K n [MPVW 10 O 39 (H 2 O)]·xH 2 O, their similarity with other vanadotungstophosphates, and their achievements in the Keggin class. Additionally, all analysis methods have shown an increase in the degree of structural symmetry and the thermal stability of a polyoxoanion complex after attaching metal cations compared to the monolacunary, K 8 [PVW 10 O 39 ]·15H 2 O.