Polyoxometalates from gases: Mineral-inspired synthesis and characterization of novel compounds containing [M⊂Cu12O8(AsO4)8]q- polyoxocuprate clusters (M = Ti(IV), Bi(III))

Abstract

A novel type of polyoxocuprate (POCu) clusters, [M⊂Cu12O8(AsO4)8]q- (M = Ti(IV), Bi(III)), with a cubooctahedral arrangement of Cu2+ cations, have been prepared by chemical vapor transport reactions (CVT) using the methodology inspired by mineralogical discoveries at volcanic fumaroles of the Tolbachik volcano (Kamchatka peninsula, Russia). Three new compounds, Na21Cl6F[TiF6][TiCu12O8(AsO4)8] (1), Na18Cl6[TiCu12O8(AsO4)8] (2), and Na18Cl5[BiCu12O8(AsO4)8] (3), prepared under low-vacuum conditions, contain the {[M⊂Cu12O8](AsO4)8} (M = Ti4+, Fe3+) clusters with a Keggin-ion-like cubooctahedral arrangement of Cu2+ cations encapsulating Mn+ cations strikingly similar to the {[Pd13O8]L8]q- polyoxoanions observed in polyoxopalladates. The packing modes of clusters in different structures are different, with the structures of 1 and 3 based upon cubic-close-packing and hexagonal-close-packing arrangements, respectively. The packing of clusters in 2 is rather complex that results in its extreme structural complexity with the amount of Shannon structural information per unit cell exceeding 3000 bits. In the title compounds, the POCu clusters are embedded into salt matrices and therefore can be considered as an inverse analogue of salt-inclusion compounds, i.e., as inclusion-in-salt compounds. The successful synthesis of new types of POCu clusters using the CVT techniques opens up a new synthetic pathway for the exploration of polyoxocuprates with promising interesting structures and physical properties.