Isonicotinate-functionalized cross-shaped tetrameric Ce(III)-containing arsenotungstate as a heterogeneous catalyst for pyrazole synthesis.

An isonicotinate-functionalized Ce(III)-containing arsenotungstate, Na12[H2N(CH3)2]26{[Ce2W3O13(AsW9O33)2][Ce(Ac)(INA)]}2·85H2O (Ce6INA2), was successfully synthesized. Ce6INA2 features a unique cross-shaped tetrameric architecture, in which two {Ce2W3(AsW9)2} subunits are bridged by isonicotinate linkers. As a rigid ligand, isonicotinate enforces near-orthogonal spatial alignment of the two subunits, with an inter-subunit dihedral angle of 84.77°, in contrast to the coplanar or low-dihedral-angle stacking geometries formed with flexible multidentate carboxylates. Moreover, Ce6INA2 serves as an efficient heterogeneous catalyst to construct valuable pyrazoles via the cyclocondensation of hydrazides with 1,3-diketones. This work underscores the decisive impact of ligand backbone rigidity on regulating the spatial packing of polyoxometalate subunits.