A Vanadium (VO2+) Metal–Organic Framework: Selective Vapor Adsorption, Magnetic Properties, and Use as a Precursor for a Polyoxovanadate

Abstract

The reaction of VOSO(4) with 2-carboxyethylphosphonic acid (H(2)-CEP) in presence of piperazine (PIP) produces a 3D inorganic-organic hybrid framework, {(H(2)PIP)(0.5)[VO(CEP)]·H(2)O} (1) with bidirectional channels occupied by the H(2)PIP cations and H(2)O molecules. The PO(3)(2-) unit of CEP connects three V(IV) centers to generate a 1D ladder, which is further linked to four such ladders by the CEP linkers to form a 3D hybrid framework. The dehydrated framework, {(H(2)PIP)(0.5)[VO(CEP)]} (1') shows selective and gated adsorption behavior with H(2)O but not with methanol and ethanol. Very interestingly, when 1 is treated with an aqueous solution of LiNO(3)/NaNO(3), the framework breaks down and results in a new polyoxovanadate (POV) cluster, [H(5)(H(2)PIP)(3)][V(V)(12)V(IV)(2)O(38)(PO(4))]·8H(2)O (2) at pH ≈ 2.1. The cluster has been characterized by single-crystal X-ray diffraction, (31)P NMR, EPR, and magnetic studies. The temperature-dependent magnetic susceptibility measurement suggests antiferromagnetic ordering in 1 with T(N) ≈ 3.8 K.