A series of organic hybrid polyoxovanadate clusters incorporating tris(hydroxymethyl)methane derivatives.

A series of new organic hybrid polyoxovanadate clusters [V4O4(μ-OH)2(acac)2(Htri)2] (1, H3tri = tris(hydroxymethyl) aminomethane, acac = acetylacetone), [V4O4(acac)2(Htri)2(L)2] {HL = methanol (2), ethanol (3a and 3b), ethylene glycol (4) and benzyl alcohol (5)}, {V4O4(H2O)2(tri-acetamide)2(CH3COO)2} (6, H3tri-acetamide = N-(2-hydroxy-1,1-bis-hydroxymethyl-ethyl)-acetamide), [V6O8(μ-OH)2(Htri)3]·6H2O (7) and [V14O18(tri)2(Htri)6(HCOO)(CH3COO)]·2H2O (8) were prepared by hydro(solvo)thermal methods and characterized structurally. 1 contains [VO(OH)(acac)] and [VO2(Htri)] units, which are further interconnected via common edges to build a tetravanadyl cluster [V4O4(OH)2(acac)2(Htri)2] with the double-deficient cube [V4O6]. The tetravanadyl cluster frameworks of 2-5 can be derived from the tetravanadyl cluster of 1 by replacing two -OH groups with two deprotonated organic alcohol ligands, namely, CH3O- (2), CH3CH2O- (3a and 3b), HO(CH2)2O- (4) and C6H5CH2O- (5). Interestingly, both 3a and 3b have the same chemical structure, but they exhibit different conformational polymorphisms [denoted as α-type (3a) and β-type (3b)]. Such conformational polymorphisms within the polyoxovanadate clusters incorporating tris(hydroxymethyl)methane derivatives emerged for the first time. 6 displays another tetravanadyl cluster {V4O4(H2O)2(tri-acetamide)2(CH3COO)2} with a [V4O16] fragment, where the tri-acetamide unit comes from the amidation reaction of H3tri and acetic acid and caps the tetrahedral void of the tetravanadyl cluster. The polyoxovanadate cluster of 7 can originate from the Lindqvist-type hexavanadyl cluster [V6O19] by replacing nine μ-oxides with nine alkoxides of three tri-acetamide3- ligands. 8 exhibits a fully reduced tetradecavanadyl cluster based on the linkage of two heptavanadyl clusters via two O bridges. The magnetic properties of 1-8 show typical antiferromagnetic interactions.