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The unsymmetrical diruthenium complexes [(bpy)(2)Ru-II(mu-H2L2-)Ru-III(acac)(2)]ClO4 ([3]ClO4), [(pap)(2)Ru-II(mu-H2L2-)Ru-III(acac)(2)]ClO4 ([4]ClO4), and [(bpy)(2)Ru-II(mu-H2L2-)-Ru-II(pap)(2)](ClO4)(2) ([5](ClO4)(2)) have been obtained by way of the mononuclear precursors [(bpy)(2)Ru-II(H3L-)]ClO4 ([1]ClO4) and [(pap)(2)Ru-II(H3L-)]ClO4 ([2]ClO4) (where bpy = 2,2'-bipyridine, pap = 2-phenylazopyridine, acac(-) = 2,4-pentanedionate, and H4L = 1,4-diamino-9,10-anthraquinone). Structural characterization by single-crystal X-ray diffraction and magnetic resonance (nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR)) were used to establish the oxidation state situation in each of the isolated materials. Cyclic voltammetry, EPR, and ultraviolet-visible-near-infrared (UV-vis-NIR) spectroelectrochemistry were used to analyze the multielectron transfer series of the potentially class I mixed-valent dinuclear compounds, considering the redox activities of differently coordinated metals, of the noninnocent bridge and of the terminal ligands. Comparison with symmetrical analogues [L'Ru-2(mu-H2L)RuL'(2)](n) (where L' = bpy, pap, or acac(-)) shows that the redox processes in the unsymmetrical dinuclear compounds are not averaged, with respect to the corresponding symmetrical systems, because of intramolecular charge rearrangements involving the metals, the noninnocent bridge, and the ancillary ligands.

Dinudear compounds [L2Ru(mu-E)RuL2](n) where L is acetylacetonate (acac(-), 2,4-pentanedionate), 2,2'-bipyridine (bpy), or 2-phenylazopyridine (pap) and Eat is ellagic acid, an antioxidative bis-catechol natural product, were studied by voltammetric and spectroelectrochemical techniques (UV-vis-NIR and electron paramagnetic resonance (EPR)). The electronic structures of the isolated forms (NBu4)(2)[(acac)(2)Ru(mu-E)Ru(acac)(2)] ( (NBu4)(2)[1]), (bpy)(2)Ru(mu-E)Ru(bpy)(2)]ClO4 ([2]ClO4), and [(pap)(2)Ru(mu-E)Ru(pap)(2)] ([3]) were characterized by density functional theory (DFT) in conjunction with EPR and UV vis NIR measurements. The crystal structure of (NBu4)(2)[1] revealed the meso form and a largely planar Ru(itE)Ru center. Several additional charge states of the compounds were electrochemically accessible and were identified mostly as complexes with noninnocently behaving pap(0/center dot-) or bridging ellagate (En-) anions (n = 2, 3, 4) but not as mixed-valence intermediates. The free anions En-, n = 1-4, were calculated by time-dependent DFT to reveal NIR transitions for the radical forms with n = 1 and 3 and a triplet ground state for the bis(o-semiquinone) dianion E2-.

The varying coordination modes of the ambidentate ligand 2,2'-bipyridine-3,3'-diol (H2L) in a set of ruthenium complexes were demonstrated with special reference to the electronic features of the coligands, including sigma-donating acac(-) (= acetylacetonate) in Ru-III(acac)(2)(HL-) (1), strongly pi-accepting pap (= 2-phenylazopyridine) in Ru-II(pap)(2)(L2-) (2)/[(pap)(2)Ru-II(mu-L2-)Ru-II(pap)(2)](ClO4)(2) ([4](ClO4)(2)), and reported moderately pi-accepting bpy (= 2,2'-bypiridine) in [Ru-II(bpy)(2)(HL-)]PF6 ([5]PF6)/[(bpy)(2)Ru(mu-L2-)Ru(bpy)(2)](PF6)(2) ([7] (PF6)(2)). The single-crystal X-ray structures reveal that, in paramagnetic and electron paramagnetic resonance active 1 and reported diamagnetic [5]PF6, nearly planar monoanionic HL- coordinates to the metal ion via the N,N donors forming a five-membered chelate ring with hydrogen-bonded O-H center dot center dot center dot O function at the backbone of the ligand framework, as has also been reported in other metal complexes. However, structurally characterized diamagnetic 2 represents O-,O- bonded seven-membered chelate of fully deprotonated but twisted L2-. The nonplanarity of the coordinated L2- in 2 does not permit the second metal fragment {Ru(pap)(2)} or {Ru(bpy)(2)} or {Ru(acac)(2)} to bind with the available N,N donors at the back face of L2-. Further, the deprotonated form of the model ligand 2,2'-biphenol (H2L') yields Ru-II(pap)(2)(L'(2-)) (3); its crystal structure establishes the expected O-,O- bonded seven-membered chelate of nonplanar L'(2-) as in reported Ru-II(bpy)(2)(L'(2-)) (6), although {Ru(acac)(2)} metal precursor altogether fails to react with H2L'. All attempts to make diruthenium complex from {Ru(acac)(2)} and H2L failed; however, the corresponding {Ru(pap)(2)(2+)} derived dimeric [4](ClO4)(2) was structurally characterized. It establishes the symmetric N,O-/N,O- bridging mode of nonplanar L2- as in reported [7](PF6)(2). Besides structural and spectroscopic characterization of the newly developed complexes, the ligand (HL-, L2-, L'(2-), pap)-, metal-, or mixed metal-ligand-based accessible redox processes in 1(n) (n = +2, +1, 0, -1), 2(n)/3(n) (n = +2, +1, 0, -1, -2), and 4(n) (n = +4, +3, +2, +1, 0, -1) were analyzed in conjunction with density functional theory calculations.

Coordination compounds [Ru(acac)(2)(Q)] (acac = acetylacetonate; Q = o-benzoquinone) were prepared as complexes 1 (Q = o-benzoquinone), 2 (Q = 3-methoxy-o-benzoquinone), 3 (Q = 4-methyl-o-benzoquinone), and 4 (Q = 3,5-di-tert-butyl-o-benzoquinone). The structures of 1 and 2 were determined to reveal a Ru(III)/o-benzosemiquinone formulation, supported by analysis of experimental data (spectroscopy, magnetism of 1) and by DFT calculations. The S = 1 ground state calculated for 1 stands in contrast to the spin-paired analogues with arylimino-o-benzosemiquinonato and diimino-o-benzoquinone ligands. The close contacts of about 5.3 angstrom possible between semiquinone O atoms of different molecules in the crystal allow for intermolecular spin-spin interactions and an overall complex magnetic behavior. One quasireversible oxidation and two reversible one-electron reductions yielded the corresponding molecular ions, which were characterized by UV-visible-NIR and EPR spectroelectrochemistry in terms of [Ru(III)(acac)(2)(Q(0))](+), [Ru(III)(acac)(2)(Q(2-))](-), and [Ru(II)(acac)(2)(Q(2-))](2-) descriptions in agreement with DFT results. The use of acceptor-substituted 1,2-dioxolenes resulted in the isolation of ionic species Na[Ru(acac)(2)(Q)] (Na(5); Q = 4-chloro-o-benzoquinone) and Na(6) (Q = 4-nitro-o-benzoquinone), which were similarly investigated as compounds 1-4. Magnetic susceptibility and EPR results confirm an S = 1/2 ground state based on ruthenium(III). The combined studies reveal a remarkable substituent sensitivity, and in comparison to recently analyzed Ru(acac)(2) complexes with o-benzoquinone monoimine and diimine ligands, the all-O-donor-containing new systems are distinguished by a qualitatively different metal-ligand interaction based on closer intermolecular radical-radical contacts and on weaker intramolecular d pi-pi* interactions.

The diruthenium(III) complex [(acac)(2)Ru(mu-L(2-))Ru(acac)(2)] (1) with acac(-) = acetylacetonato = 2,4-pentanedionato and a 2,5-pyrazine-dicarboxylato bridge, L(2-), has been obtained and structurally characterized as the rac (Delta Delta,Lambda Lambda) diastereomer. The Ru(III)Ru(III) configuration in 1 (d(Ru-au) = 6.799 angstrom) results in a triplet ground state (mu = 2.82/2 mu(B) at 300 K) with a density functional theory (DFT) calculated triplet-singlet gap of 10840 cm-and the metal ions as the primary spin-bearing centers (Mulliken spin densities: Ru, 1.711; L, 0.105; acac, 0.184). The paramagnetic 1 exhibits :broad, upfield shifted (1)H NMR signals with delta values ranging from -10 to -65 -65 ppm and an anisotropic electron paramagnetic resonance (EPR), spectrum (< g > = 2.133, g(1) - g(3) = Delta g = 0.512), accompanied by a weak half-field signal at g = 4.420 in glassy frozen acetonitrile at 4 K Compound 1 displays two closely spaced oxidation steps to yield labile cations. In contrast, two well separated reversible reduction steps of 1 signify appreciable electrochemical metal-metal interaction in the Run Rum mixed-valent state 1(-) (K(c) approximate to 10(7)). The intermediate 1(-) shows a weak, broad Ru(II)-> Ru(III) intervalence charge transfer (IVCT) band at about 1040 nm (epsilon = 380 M(-1) cm(-1)); the DFT approach for 1(-) yielded Mulliken spin densities of 0.460 and 0.685 for the two metal centers. The monitoring of the frequencies of the uncoordinated C=O groups of L(2-) in 1" by IR spectroelectrochemistry suggests valence averaging (Ru(2.5)Ru(2.5)) in 1(-) on the vibrational time scale. The mixed-valent 1(-) displays a rhombic EPR signal (< g > = 2.239 and Delta g = 0.32) which reveals non-negligible contributions from the bridging ligand, reflecting a partial hole-transfer mechanism and being confirmed by the DFT-calculated spin distribution (Mulliken spin density of -0.241 for L in 1(-)). The major low energy electronic transitions in 1(n) (n = 0,-,2-) have been assigned as charge transfer processes with the support of TD-DFT analysis.

The complete assignments of H-1 and C-13 signals of 19 pregnenolone and progesterone haptens were accomplished using two-dimensional NMR techniques. Copyright (C) 1999 , Ltd.

Two small-pore silicon-substituted molecular sieves SAPO-34 and SAPO-44 with varying amount of silicon have been synthesized and characterized by XRD, SEM, FT-IR spectroscopy, and thermal analyses. Their acidity has been measured quantitatively by temperature-programmed desorption of ammonia. The results of these studies along with solid-state MAS NMR results show that the major part of silicon substitutes isolated phosphorus atoms in the structure whereas some amount of it forms small silica patches. The extent of formation of such small patches is more noticeable in SAPO-34 than in SAPO-44.

The solution conformation of the title compound, based on one and two dimensional NMR techniques in CDCl 3 and (CD 3 ) 2 SO at 500 MHz, has been deduced as a 3 10 helix initiated by an electrostatically locked type II' reverse turn.