Seven-coordinate [ReVON4X2]+ complexes (X = O and Cl).

The oxorhenium(V) complexes with ligands containing N4 (H2pmen) and N4O2 (H2bbpen, H2Clbbpen, and H2bped) donor atom sets have been synthesized. X-ray crystallographic analyses of the [ReO(H2pmen)Cl2]+, [ReO(bbpen)]+, and [ReO(bped)]+ complexes showed that all three cations share a rare seven-coordinate structure with a distorted pentagonal bipyramidal geometry, which represents a novel and potentially general structural motif in ReV = O complexes. 1H NMR spectroscopy shows that the structures of the complexes are retained in the solution.

Homotrinuclear lanthanide(III) arrays: assembly of and conversion from mononuclear and dinuclear units.

The reactions of potentially hexadentate H2bbpen (N,N'-bis(2-hydroxybenzyl)-N,N'-bis(2-pyridylmethyl)-ethylenediamine, H2L1), H2(Cl)bbpen (N,N'-bis(5-chloro-2-hydroxybenzyl)-N,N'-bis(2-pyridylmethyl)ethylenediamine, H2L2), and H2(Br)bbpen (N,N'-bis(5-bromo-2-hydroxybenzyl)-N,N'-bis(2-pyridylmethyl)ethylenediamine, H2L3) with Ln(III) ions in the presence of a base in methanol resulted in three types of complexes: neutral mononuclear ([LnL(NO3)]), monocationic dinuclear ([Ln2L2(NO3)]+), and monocationic trinuclear ([Ln3L2(X)n(CH3OH)]+), where X = bridging (CH3COO-) and bidentate ligands (NO3-, CH3COO-, ClO4-) and n is 4. The formation of a complex depends on the base (hydroxide or acetate) and the size of the respective Ln(III) ion. All complexes were characterized by infrared spectroscopy, mass spectrometry, and elemental analyses; in some cases, X-ray diffraction studies were also performed. The structures of the neutral mononuclear [Yb(L1)(NO3)], dinuclear [Pr2(L1)2(NO3)(H2O)]NO3.CH3OH and [Gd2(L1)2(NO3)]NO3.CH3OH.3H2O, and trinuclear [Gd3(L3)2(CH3COO)4(CH3OH)]ClO4.5CH3OH and [Sm3(L1)2(CH3COO)2(NO3)2(CH3OH)]NO3.CH3OH.3.65H2O were solved by X-ray crystallography. The [LnL(NO3)] or [Ln2L2(NO3)]+ complexes could be converted to [Ln3L2(X)n(CH3OH)]+ complexes by the addition of 1 equiv of a Ln(III) salt and 2-3 equiv of sodium acetate in methanol. The trinuclear complexes were found to be the most stable of the three types, which was evident from the presence of the intact monocationic high molecular weight parent peaks ([Ln3L2(X)n]+) in the mass spectra of all the trinuclear complexes and from the ease of conversion from the mononuclear or dinuclear to the trinuclear species. The incompatibility of the ligand denticity with the coordination requirements of the Ln(III) ions was proven to be a useful tool in the construction of multinuclear Ln(III) metal ion arrays.

Kinetic analysis and comparison of uptake, distribution, and excretion of 48V-labeled compounds in rats.

Vanadium has been found to be orally active in lowering plasma glucose levels; thus it provides a potential treatment for diabetes mellitus. Bis(maltolato)oxovanadium(IV) (BMOV) is a well-characterized organovanadium compound that has been shown in preliminary studies to have a potentially useful absorption profile. Tissue distributions of BMOV compared with those of vanadyl sulfate (VS) were studied in Wistar rats by using 48V as a tracer. In this study, the compounds were administered in carrier-added forms by either oral gavage or intraperitoneal injection. Data analyzed by a compartmental model, by using simulation, analysis, and modeling (i.e., SAAM II) software, showed a pattern of increased tissue uptake with use of 48V-BMOV compared with 48VS. The highest 48V concentrations at 24 h after gavage were in bone, followed by kidney and liver. Most ingested 48V was eliminated unabsorbed by fecal excretion. On average, 48V concentrations in bone, kidney, and liver 24 h after oral administration of 48V-BMOV were two to three times higher than those of 48VS, which is consistent with the increased glucose-lowering potency of BMOV in acute glucose lowering compared with VS.

Glucose-lowering properties of vanadium compounds: comparison of coordination complexes with maltol or kojic acid as ligands.

Bis(kojato)oxovanadium(IV) [abbreviated VO(ka)2], a close chemical analog of the insulin-mimetic lead compound bis(maltolato)oxovanadium(IV)--abbreviated BMOV or VO(ma)2--is reported and its reaction chemistry and insulin-mimetic properties are presented. VO(ka)2 [log K1 = 7.61(10), log K2 = 6.89(6), log beta 2 = 14.50(16)] has a reaction chemistry which directly parallels that of VO(ma)2. In aqueous solution it is more slowly oxidized by molecular oxygen to [VO2(ka)2]- than is VO(ma)2 to [VO2(ma)2]-. Variable pH electrochemistry and variable pH 51V NMR of solutions of VO(ka)2 are presented and contrasted with the corresponding results for VO(ma)2. Time course studies (24 hr) in STZ-diabetic rats following the oral or i.p. administration of VO(ka)2, VO(ma)2, VO2+ (vanadyl) as vanadyl sulfate (VOSO4), and [VO2(ma)2]- as its [NH4]+ salt have been performed, as have chronic oral studies comparing VO(ka)2 and VO(ma)2 over a six week period. In all studies, the most potent form of vanadium was the neutrally charged, water soluble, complex VO(ma)2.