Discrete polyoxovanadate cluster into an organic free metal-oxide-based material: syntheses, crystal structures, and magnetic properties of a new series of lanthanide linked-POV compounds [{Ln(H2O)6}2As8V14O42(SO3)] x 8 H2O (Ln = La3+, Sm3+, and Ce3+).

This article describes the linking propensity of the sulfite encapsulated polyoxovanadate (POV) anion, As(8)V(14)O(42)(SO(3)), with aqua-lanthanide complex cations Ln(H(2)O)(6) in a controlled wet synthesis resulting in a series of organic free metal-oxide-based materials [{Ln(H(2)O)(6)}(2)As(8)V(14)O(42)(SO(3))] x 8 H(2)O, Ln = La(3+) (1), Sm(3+) (2), and Ce(3+) (3). The title compounds have been characterized by elemental analyses, IR, diffuse reflectance, electron paramagnetic resonance, powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), and single-crystal X-ray diffraction studies. All three compounds crystallize in the monoclinic space group P2(1)/n. Crystal data for 1: a = 13.4839(7), b = 12.3388(6), c = 18.3572(10) A, beta = 108.2570 (10) degrees, V = 2900.4(3) A(3). Crystal data for 2: a = 13.4156(3), b = 12.2588(3), c = 18.2501(4) A, beta = 108.049(3) degrees, V = 2853.8(10) A(3). Crystal data for 3: a = 13.4934(3), b = 12.3983(3), c = 18.3992(4) A, beta = 108.025(3), V = 2927.0(10) A(3). Crystal structure shows that each cluster is surrounded by six Ln(H(2)O)(6) complex cations, and each Ln(H(2)O)(6) cation is coordinated to three surrounding POV cluster anions. The electron spin resonance spectra of compounds 1-3 show a typical single line (g = 1.9671 for 1, g = 1.9669 for 2, and g = 1.9704 for 3), characteristic for a V(4+) (d(4)) ion; in addition, a supplementary signal appears for compound 2 at g = 5.9238 due to the presence of the Sm(3+) (f(5)) ion. All vanadium atoms exit in +4 oxidation states that have been confirmed by bond valence sum calculations. Variable-temperature magnetic studies for all three compounds 1-3 are performed and are discussed in terms of antiferromagnetic coupling interactions, giving importance to linking/assembling the {V(14)} cluster anions. TGA/mass analyses of compounds 1-3 (linked system) have been compared with that of the starting precursor NH(4)[As(8)V(14)O(42)(SO(3))] (discrete building unit). Interestingly, the evolution of SO(2) gas takes place for the discrete cluster compound NH(4)[As(8)V(14)O(42)(SO(3))] in a temperature range of 480-520 degrees C with the decomposition of the POV cluster anion, whereas the same evolution occurs at 520-580 degrees C for compounds 1-3. These comparative TGA/mass studies help to understand how the organic free linker elevates the thermal stability of the sulfite encapsulated POV cluster anion in going from a discrete cluster anion to the linked system (molecule to material). It has also been demonstrated that the stability of the sulfite anion increases to a greater extent when it is included in the cluster cage. The powder XRD studies of compounds 1-3 confirm that these are isostructural materials and provide information about the phase purity.