Light-induced dissolution and concomitant crystallization of a Keggin-type polyoxometalate mimicking a naturally occurring phenomenon.

A suspension of a yellow polycrystalline compound [PPh][PMoO] in -methylformanilide (NMF) (in which it is not soluble), on irradiation with sunlight, initiates dissolution its reduction followed by its crystallization leading to the isolation of single crystals of compound [PPh][PMoMoO]·3CH(CH)NCHO (1). Compounds [PPh][PMoO]·1.75 CH(CH)NCHO (2) and [PPh][PMoO]·2CH(CH)NCHO (3), each containing an oxidized Keggin anion, are obtained at two different temperatures when the corresponding mother liquor is kept in the dark.