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Reaction of KVO3 with 2-[N,N'-(carboxymethyl)aminomethyl]-5-methylhydro quinone (H4 mecah) in aqueous solution at pH 8.2 results in the isolation of mononuclear K2 [VV (O)2 {Hmecah(-3)}]2H2O complex. On the other hand, reaction with the 2-[N,N'-(carboxymethyl)aminomethyl]-5-tert-butylhydroquinone (H4tbutcah) under the same conditions gives the tetranuclear mixed-valent complex K6 [{VV O(µ-O)VIV O}{µ-tbutbicah(-6)}]210.5H2 O(H6 tbutbicah, 2,2'-({2-[bis(carboxymethyl)amino]-3,6-dihydroxy-4-methylbenzyl}azanediyl)diacetic acid). The structures of both complexes were determined by single-crystal X-ray crystallography. The coordination environment of vanadium ions in both complexes is octahedral, with four out of the six positions to be occupied by the two cis carboxylate oxygens, one hydroquinonate oxygen, and one amine nitrogen atoms of the ligands' tripod binding sites. The importance of the chelate ring strains in the stabilization of the p-semiquinone radical is also discussed. A protonation of the ligated to vanadium(IV) ion hydroquinonate oxygen at low pH was revealed by continuous wave (cw) X-band electron paramagnetic resonance (EPR) and UV-vis spectroscopies. [ABSTRACT FROM AUTHOR]

Reaction of the N,N-disubstituted bis(hydroxylamino) ligand 2,6-bis[hydroxy(methyl)amino]-4-morpholino-l,3,5-triazine (H2bihyat) with eis-[MoVI 02(acac)2] in tetrahydrofuran resulted in isolation of the mononuclear compound cis-[MoVI02(bihyat)] (l). The treatment of Na2Mo2VI04-2H20 with the ligand H2bihyat in aqueous solution gave the dinuclear compounds cis-[Mo2VI04(bihyat)2(H20)2] (2) and trans-[Mo2VI04(bihyat)2(H20)2] (3) at'pH values of 3.5 and 5.5, respectively. The structures for the three molybdenum (VI) compounds were determined by X-ray crystallography. Compound 1 has a square-pyramidal arrangement around molybdenum, while in the two dinuclear compounds, each molybdenum atom is in a distorted pentagonal-bipyramidal environment of two bridging and one terminal oxido groups, a tridentate (0,N,0) bihyat2- ligand that forms two five-membered chelate rings, and a water molecule trans to the terminal oxido group. The dinuclear compounds constitute rare examples containing the {Mo2VI02(μ2-02)}4+ moiety. The potentiometry revealed that the MoVIbihyat2- species exhibit high hydrolytic stability in aqueous solution at a narrow range of pH values, 3--5. A subtle change in the coordination environment of the five-coordinate compound 1 with ligation of a weakly bound water molecule trans to the oxido ligand ( lw) renders the equatorial oxido group in 1 w more nucleophilic than that in 1, and this oxido group attacks a molybdenum atom and thus the dinuclear compounds 2 and 3 are formed. This process might be considered as the first step of the oxido group nucleophilic attack on organic substrates, resulting in oxidation of the substrate, in the active site of molybdenum enzymes such as xanthine oxidase. Theoretical calculations in the gas phase were performed to examine the influence of water on the dimerization process (l→2/3). In addition, the molecular structures, cis/trans geometrical isomerism for the dinuclear molybdenum(VI) species, vibrational spectra, and energetics of the metal--ligand interaction for the three molybdenum(Vl) compounds 1--3 have been studied by means of density functional theory calculations. [ABSTRACT FROM AUTHOR]

Bisphosphonates are biologically relevant therapeutics for bone disorders and cancer. Reaction of γ-chlorobutyric acid, phosphorus acid, and phosphorus trichloride without the use of solvent gave the tetrahydrofuranyl-2,2-bisphosphonate sodium salt (Na2H2L). The Na2H2L was isolated, characterized in solution by ¹H, 13C, and 31P NMR spectroscopy and in solid state by single X-Ray crystallography. The crystal structure showed that the Na2H2L forms in the crystal infinite two-dimensional sheets stacked one parallel to the other. A comparison of the chelating properties of H2L2- with similar hydroxyl bisphosphonate ligands shows that the strength of the Na-O(furanyl/hydroxyl) bond is directly related to the total charge of the ligand anion. [ABSTRACT FROM AUTHOR]

Reaction of NH4VO3 with (phenolate/hydroquinonate) iminodiacetate tripod ligands in aqueous solution in the pH range 7-8 results in the isolation of three new dioxido vanadium(V) complexes, one dinuclear (NH4)4{(VVO)2[μ-bicah(6-)-N,O,O,O]}·8H2O, (H6bicah, 2,5-bis[N,N′-bis(carboxymethyl)aminomethyl]-hydroquinone), and two mono - nuclear (NH4)2{(VVO)2[Hcah(3-)-N,O,O,O]·2H2O, (H4cah, 2-[N,N′-bis(carboxy - methyl)aminomethyl]-hydroquinone) and (NH4)2{(VVO)[Hcacp(3-)-N,O,O,O]} 4H2O, (H4cacp, 2-[N,N′-bis(carboxymethyl)aminomethyl]-4-carboxyphenol). The 51V, 1H, and 13C NMR spectra in D2O show the coordination environment of vanadium in the above complexes to be octahedral, with four out of six positions to be occupied by the two carboxylate oxygen, one hydroquinonate oxygen, and one amine nitrogen atoms of the tripod ligand. The two acetate arms are in cis position to each other. Variable-temperature ¹H and 13C NMR measure ments show that the complexes are kinetically labile. An intramolecular exchange that proceeds through the opening of the phenolate/hydroquinonate chelate ring has been revealed by 2D{¹H} NMR EXSY (exchange spectroscopy). [ABSTRACT FROM AUTHOR]

Reaction of the ligand 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1 ,3,5-thazine (H2bihyat) with NaVVO3 in aqueous solution followed by addition of either Ph4PCI or C(NH2)3C1, respectively, gave the mononuclear vanadium(V) compounds Ph4P[4O2(bihyat)]. 1 .5H2O (1) and C(NH2)3[VVO2(bihyat)] (2). Treatment of VIVOSO2. 5H2O with the ligand H2bihyat in methyl alcohol under specific conditions gave the oxo-b~dged dimer [VV2O2(μ2-O)(bihyat)2] (3). The structures for 1 and 3 were determined by X-ray crystallography and indicate that these compounds have distorted square-pyramidal arrangement around vanadium. The ligand bihyat2- is bonded to vanadium atom in a tridentate fashion at the pydine-like nitrogen atom and the two deprotonated hydroxylamino oxygen atoms. The high electron density of the tnazine ring nitrogen atoms, which results from the resonative contribution of electrons of exocyclic nitrogen atoms (Scheme 4), leads to very strong V-N bonds. The cis-[VVO2(bihyat)]- species exhibits high hydrolytic stability in aqueous solution over a wide pH range, 3.3-11.0, as it was evidenced by 1H and 51V NMR spectroscopy and potentiometry. The high affinity of the H2bihyat ligand for the VVO2+ unit, its tndentate character, as well as its small size, paves the way for potential applications in medicine, analysis, and catalysis for the C(NH2)3[VVO2(bihyat)] compound. The molecular structures, vibrational and electronic spectra, and the energetics of the metal-ligand interaction for compounds 1 and 3 have been studied by means of density functional calculations. [ABSTRACT FROM AUTHOR]