Reaction of the non-innocent dinucleating ligand 2,5-bis[N,N-bis(carboxymethyl) aminomethyl]hydroquinone (H 6bicah) with VO (2+) and VO 4 (3-) salts in water in the pH range 2 to 4.5 provides a series of novel tetranuclear V (IV) and/or V (V) macrocycles with the main core consisting of the anions [V (V) 4O 4(mu-O) 2(mu-bicah) 2] (4-) isolated at pH = 2.5 and [V (IV) 2V (V) 2O 4(mu-O) 2(mu-bicas)(mu-bicah)] (5-) and [V (IV) 4O 4(mu-O) 2(mu-bicas) 2] (6-) isolated at pH = 4.5 (bicas (*5-) = 2,5-bis[N,N-bis(carboxymethyl) aminomethyl]- p-semiquinonate), whereas at pH = 2 the dinuclear [(V (IV)O) 2(OH 2) 2(mu-bicah)] (2-) was obtained. All vanadium compounds have been characterized, and the charge of the ligand has been assigned in solid state by X-ray crystallography and infrared spectroscopy. The structures of the tetranuclear anions consist of four vanadium atoms arranged at the corners of a rectangle with the two bridging bicas (*5-) and/or bicah (6-) ligands on the long and the two V (IV/V)-O-V (IV/V) bridges on the short sides of the rectangle. UV-vis, (51)V and (1)H NMR spectroscopy and electrochemistry showed that these complexes interconvert to each other by varying the pH. This pH induced redox transformation of the tetranuclear anions has been attributed to the shift of the reduction potential of the bicas (*5-) to higher values by decreasing the pH. The electron is transferred intramolecularly from the metal ion to the electron accepting semiquinones resulting in reduction of bicas (*5-) to bicah (6-) and concurrent oxidation of the V (IV) to V (V). The resulting complexes are further oxidized by atmospheric oxygen. This system as a model for the H (+) coupled redox reactions in metalloenzymes and its relevance is discussed briefly.

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A Blatter radical is oxidized to benzotriazin-7(H)-one which after amination and subsequent acyl- and aroylation gives N-(benzotriazin-6-yl)carboxamides that undergo ring closure with P(2)S(5) to afford the corresponding thiazolo[5',4':4,5]benzo[1,2-e][1,2,4]triazin-4-yls. These highly delocalized radicals are air stable and show good reversible electrochemical behavior.

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Cobalt(II) is an essential metal ion, which can react with biologically relevant substrates in aqueous media, affording discrete soluble forms. D-(-)-quinic acid is a representative metal ion binder, capable of promoting reactions with Co(II) under pH-specific conditions, leading to the isolation of the new species K[Co(C(7)H(11)O(6))(3)] x 3 CH(3)CH(2)OH (1), Na[Co(C(7)H(11)O(6))(3)] x 3 CH(3)CH(2)OH x 2.25 H(2)O (2), and [Co(C(7)H(11)O(6))(2)(H(2)O)(2)] x 3 H(2)O (3). Compounds 1-3 were characterized by elemental analysis, spectroscopic techniques (Fourier-transform infrared, UV-visible, electron paramagnetic resonance (EPR), electrospray ionization mass spectrometry), magnetic studies, and X-ray crystallography. Compound 1 crystallizes in the cubic space group P2(1)3, with a = 15.3148(19) A, V = 3592.0(8) A(3), and Z = 4. Compound 2 crystallizes in the orthorhombic space group P2(1)2(1)2(1), with a = 14.9414(8) A, b = 15.9918(9) A, c = 16.0381(9) A, V = 3832.1(4) A(3), and Z = 4. Compound 3 crystallizes in the monoclinic space group P2(1)/m, with a = 13.2198(10) A, b = 5.8004(6) A, c = 15.3470(12) A, beta = 108.430(7), V = 1116.45(17) A(3), and Z = 4. The lattices in 1-3 reveal the presence of mononuclear Co(II) units bound exclusively to quinate (1 and 2) or quinate and water ligands (3), thus projecting the unique chemical reactivity in each investigated system and suggesting that 3 is an intermediate in the synthetic pathway leading to 1 and 2. The octahedral sites of Co(II) are occupied by oxygens, thereby reflecting the nature of interactions between the divalent metal ion and quinic acid. The magnetic and EPR data on 1 and 3 support the presence of a high-spin octahedral Co(II) in an oxygen environment, having a ground state with an effective spin of S = 1/2. The significance of 3 is further reflected into the aqueous speciation of the binary Co(II)-quinic acid system, in which 3 appears as a competent participant linked to the solid state species 1. The physicochemical profiles of 1-3, in the solid state and in solution, earmark the importance of aqueous structural speciation, which projects chemical reactivity pathways in the binary Co(II)-quinate system, involving soluble Co(II) forms emerging through interactions with low molecular mass O-containing physiological substrates, such as quinic acid.

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The reaction of Cu2+ acetate monohydrate with 2-[N,N'-bis(carboxymethyl)aminomethyl]-4-carboxyphenol (H4cacp), 2-[N,N-bis(carboxymethyl)aminomethyl]hydroquinone (H4cah) and the dinucleating 2,5-bis[N,N-bis(carboxymethyl)aminomethyl]hydroquinone (H6bicah) in water results in the formation of several Cu2+ species, which are in dynamic equilibrium in aqueous solution and their stability is pH dependent. A systematic crystallographic study of these species was pursued, resulting in the characterization of most of the species. Additional techniques were employed to characterize the molecules in the solid state (infrared spectroscopy) and in solution (UV-vis spectroscopy and electrochemistry). These measurements show that the Cu2+ ions are ligated mainly to the iminodiacetate at pH < 6, exhibiting only weak interactions with the phenol oxygen. At pH > 6, the phenol oxygen was deprotonated and dinuclear-bridged species, from the phenolate oxygen complexes exhibiting a Cu2+ 2O2 core, were isolated. The coordination environment around the copper ions varies between trigonal bipyramidal, tetragonal pyramidal and distorted octahedral geometries. The two unpaired electrons of the Cu2+ ions are found to be antiferromagnetically coupled. A survey of the magnetic and structural properties of the dinuclear phenoxide bridged Cu2+ complexes shows that the strength of the antiferromagnetic coupling is linearly dependent on the Cu-Ophenolate bond lengths, at bond distances below 1.98 angstroms. The effect of the Cu-O-Cu angles on the magnetic properties of the complexes is also discussed.

Reaction of the p-hydroquinone derivative H2Na4bicah.4H2O with either VIVOSO(4).3H2O and NaVVO3 in equivalent quantities or with NaVVo3 yields the tetranuclear VIVO2+ macrocycle-semiquinonate compound Na6[(VIVO)4-(mu2-O)2[mu2-bicas.(-5)-N,O,O,O]2].Na2SO(4).20H2O (1.Na2SO(4).20H2O) and the dinuclear cis-VVO2(+)-hydroquinone species Na4[(VVO2)2[mu2-bicah(-6)-N,O,O,O]].11H2O (2.11H2O) respectively. Compounds 1.Na2SO(4).20H2O and 2.11H2O were characterized by X-ray structure analysis and ab initio calculations.