Complexation of a heptanuclear polyoxotantalate anion with K(+): formation of a supramolecular [K6-(mu-OH2)6-(OH2)8](6+) ring structure

Oxalate-assisted assembly of two polyoxotantalate supramolecular frameworks with proton conduction properties

An oxalate-assisted strategy was first developed for creating new polyoxotantalates (POTas). With this strategy, two brand-new POTa supramolecular frameworks based on uncommon dimeric POTa secondary building units (SBUs) were constructed and characterized. Interestingly, the oxalate ligand can not only serve as a coordination ligand to form unique POTa SBUs but also act as a key hydrogen bond acceptor to construct supramolecular architectures. Besides, the architectures show outstanding proton conductivity. The strategy opens up new opportunities for developing new POTa materials.

Synthesis and Characterization of Vanadium(IV) Complexes with cis-Inositol in Aqueous Solution and in the Solid-State

The complex formation of vanadium(IV) with cis-inositol (ino) and the corresponding trimethyl ether 1,3,5-trideoxy-1,3,5-trimethoxy-cis-inositol (tmci) was studied in aqueous solution and in the solid-state. With increasing pH, the formation of [VO(H-2L)], [(VO)2L2H-5]-, [VO(H-3L)]- (L = ino) or [(VO)2L2H-6]2- (L = tmci), [V(H-3L)2]2-, and [VO(H-3L)(OH)2]3- was observed. For the vanadium(IV)/ino system, [(VO)2L2H-7]3- was observed as an additional dinuclear species. The formation constants of these complexes were determined by potentiometric titrations (25 degrees C, 0.1 M KCl). In addition, the vanadium(IV)/ino system was investigated by means of UV-vis spectrophotometric methods. EPR spectroscopy and cyclic voltammetry confirmed this complexation scheme. EPR measurements indicated the formation of three distinct isomers of the non-oxo complex [V(H-3ino)2]2- in weakly basic solution. This type of isomerism, which is not observed for the vanadium(IV)/tmci system, was assigned to the ability of ino to bind the vanadium(IV) center with three alkoxo groups having either a 1,3,5-triaxial or an 1,2,3-axial-equatorial-axial arrangement. The structures of [V(H-3ino)2][K2(ino)2].4H2O (1) and [Na6V(H-3ino)2](SO4)2.6H2O (2) were determined by single-crystal X-ray analysis. In both compounds, the coordination of each ino molecule to the vanadium(IV) center via three axial deprotonated oxygen donors was confirmed. The centrosymmetric structure of the coordination spheres corresponds to an almost regular octahedral geometry with a twist angle of 60 degrees. The crystal structure of the potassium complex 1 represents an unusual 1:1 packing of [V(H-3ino)2]2- dianions and [K2(ino)2]2+ dications, in which both K+ ions have a coordination number of nine and are bonded simultaneously to a 1,3,5-triaxial and an 1,2,3-axial-equatorial-axial site of ino. In 2, the [V(H-3ino)2]2- complexes are surrounded by six Na+ counterions that are bonded to the axial alkoxo oxygens and to the equatorial hydroxy oxygens of the cis-inositolato moieties. The six Na+ centers are further interlinked by bridging sulfate ions. According to EPR spectroscopy, the D3d symmetric structure of the [V(H-3ino)2]2- anion is retained in H2O, in dimethylformamide, and in a mixture of CHCl3/toluene 60:40 v/v.

The novel sandwich-type heteropolyoxotungstates [M2Bi2(β-B-MW9O34)2]14– (M = CoII, ZnII): β-type dimeric heteropolyanions with a transition metal as the central heteroatom and BiIII and M as linking atoms

Two new sandwich-type heteropolyoxometalates, Na(14)[Co(2)Bi(2)(beta-B-CoW(9)O(34))(2)].48H(2)O (1) and Na(14)[beta-B-Zn(2)Bi(2)(ZnW(9)O(34))(2)].51H(2)O (2), have been synthesized at pH = 7.5-8 and characterized by elemental analysis, IR, UV-vis, TG-DSC and electrochemistry. Structural analysis indicates that both polyanions, M(2)Bi(2)(beta-B-MW(9)O(34))(2)](14-) (M = Co(II) and Zn(II)), are isomorphic and consist of two unprecedented [beta-B-MW(9)O(34)](12-) subunits linked by two M(II) and two Bi(III) which are coplanar. The polyanions are also the first examples of dimeric heteropolyanions with Bi(III) only as the second (linking) heteroatom and the transition metals (Co(II) or Zn(II)) as the first and second heteroatoms as well. The lower absorption of nu(W-O(d)) (915 cm(-1)) in the IR is a simple and feasible judgment of sandwich-type polyanions with a transition metal ion as a central heteroatom.

Tris(1,2-dimethyl-3-hydroxy-4(1H)-pyridone)oxotantalum(v): a new water-soluble tantalum complex containing the [TaO]3+core

The synthesis, the characterization and the X-ray crystal structure of a novel tantalum(v) complex tris(1,2-dimethyl-3-hydroxy-4(1H)-pyridone)oxotantalum(v) [TaO(C7H8O2N)3] 1 is reported. Starting from the tantalum pentaethoxide a two-step reaction was carried out observing rigorous anhydrous conditions in methanol in the first step, while the insertion of the oxo group was achieved using water as oxygen donor in the second step. X-Ray diffraction analysis of a crystal of 1 obtained upon evaporation of an aqueous solution shows a seven-coordinate monomeric complex containing the [Ta=O]3+ core in the triclinic space group P1, a = 7.282(3), b = 14.055(5), c = 16.987(6) A, alpha = 65.704(5), beta = 89.155(6), gamma = 75.270(6) degrees, V = 1525(1)A3, Z = 2. Spectroscopic investigation reveals that the complex is highly soluble and stable in water at physiological pH values; as a consequence the complex may represent a potential candidate for the development of new studies on aqueous tantalum(v) chemistry for radiopharmaceutical applications.