Polyoxovanadatogermanates-based photoelectric bifunctional materials: The ratio of V12Ge8 and V24Ge16 controlled by solvent

Abstract Two isolated polyoxovanadogermanates, [Cd(C 2 H 8 N 2 ) 2 ] 2 {[Cd(C 2 H 8 N 2 )] 2 [Ge 8 V 12 O 40 (OH) 8 ](H 2 O)}·7H 2 O ( 1, V 12 Ge 8 ) and {[Cd(C 2 H 8 N 2 ) 2 ][Cd(C 2 H 8 N 2 )(H 2 O)]}{[Cd(C 2 H 8 N 2 ) 2 ][Cd(C 2 H 8 N 2 )] 2 Ge 8 V 12 O 40 (OH) 8 (H 2 O)} 2 ·4H 2 O ( 2, V 24 Ge 16 ), have been hydro-/solvothermally synthesized and structurally characterized. All the V ions existed in compounds 1 and 2 are demonstrated in the valence of +4 by bond valence calculation (BVC). Notably, it is the first time to investigate the nonlinear optical (NLO) properties of vanadium-based heteropolyacids and obtain strong two photon responses. The results of open aperture Z-scan based on the two compounds manifest that they are the highest value among the reported polyoxovanadates and may be a decent potential NLO materials. At the same time, the electrochemical and electrocatalytic properties of compounds 1 were also measured in detail. More interestingly, the ratio of compounds 1 and 2 in solvent thermal synthesis can be regulated by adjusting the proportion of mixed solvents, which provides a fresh idea and method for the investigation of polyoxometalate chemistry.