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Inorg. Chem. 1987, I 0 -0.4 0.8 V vs. Ag/AgCl Figure 12. Cyclic voltammogram (200 mV/s) for a GClpoly-CobNMez)TPP film (r = 1.4 X mol/cm2) in a CH$N + 0.1 M Et4NCI04 solution (solid curve) and for the same solution after addition of 2 volumes of HzO (dashed curve).potentials for O2 reduction and larger slope. The slope for poly-Co(o-NH2)TPP in 1 M N a O H is in fact very close to the four-electron value; we have confirmed by the rotating ring-disk techniqueI4 that this situation produces virtually no H202 product. 26, 1017-1025 1017Assuming (as we have14) that the two waves for poly-Co(o-NH2)TPP reflect monomeric and dimeric species in the film, then the lower activity of the other cobalt porphyrins may be connected to their lower dimerization constants, as found for Co(p-0H)TPP and Cob-pyr)TPP solutions from absorbance spectroscopy (Table 11) * showed that Co(1) porphyrins placed in solutions and adsorbed or bound to G C electrodes34 react rapidly with water. Figure 12 shows a test for water reduction using an electropolymerized poly-Cob-NMe2)TPP film (GC electrode). Co(II/I) voltammetry of the film in dry 0.1 M Et4NCI04/CH3CN (solid curve) occurs at Eo' = -0.92 V, whereas upon addition of two volumes of water (dashed curve), an irreversible, split (ca. -0.68 and -1.01 V) wave, with greatly enhanced cathodic current and no reverse anodic wave, is observed. While it is reasonable to suppose that these waves represent H2 evolution, they are not very stable (as S p i r~~~ also experienced) and gradually decayed. N o further studies were done. This instability is not characteristic of the polymeric porphyrin films in dry solvent, which in the potential window 0 to -1.5 V are very stable to repeated potential cycling. Acknowledgment.A series of 19 mononuclear oxomolybdenum(V) compounds of the general formula LMoOXY (L = hydrotris(3,5-dimethyl-lpyrazoly1)borate; (X,Y) = C1-, NCS-, NC, OR-, SR-, and the dianions of ethylene glycol, mercaptoethanol, dimercaptoethane, catechol, o-mercaptophenol, o-aminophenol, o-aminobenzenethiol, and toluenedithiol) have been prepared and characterized by electron paramagnetic resonance spectroscopy (EPR), cyclic voltammetry, UV-visible spectroscopy, and mass spectrometry. The LMoO(SR)~ complexes possess the cis sulfur ligands proposed for the molybdenum cofactor. The structure of LMoO(SPh), was determined by X-ray crystallography: space group P2,/c, Z = 4, u = 13.079 (6) A, 6 = 14.438 (7) A, c = 15.836 (9) A, p = 104.73 (4)O. The molecule adopts the expectedfuc six-coordinate stereochemistry with cis thiolate groups. The average Mo-S distance is 2.382 (2) A, and the average Mo-0 distance is 1.676 (4) A. The Mo-N distances range from 2.164 (5) to 2.357 (5) A. The isotropic ( g ) and (A)(95*97Mo) values show an inverse correlation and cluster according to the nature of the donor atoms.Sulfur donor atoms lead to large ( g ) and small ( A ) values. The anisotropies of the g values for LMoO(OR), and LMoO(SR)~ complexes show marked differences between monodentate and chelated ligands. All ...

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The molecular charge-transfer salt bB-(bedt-ttf) 4 [(H 2 O)Cr-(C 2 O 4 ) 3 ]•PhCN [bedt-ttf = bis(ethylenedithio)tetrathiafulvalene], containing paramagnetic Cr III ions (S = 3/2), is a superconductor with T c = 6.0(5) K.

A g,, f gVv f g,, All coincident A x , # A , # A,, gxx + g y y # g,, One axis ofg and gxx # g,, # gz, Complete gxx = g y y # g,, Only g,, and A,,

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Spectroscopic studies have been performed to investigate the high-affinity binding site for copper in human serum albumin (HSA) and dog serum albumin (DSA). A new approach based on exposure to albumin of the copper in the form of a well-characterized histidine (his) chelate has been adopted. This technique has been shown to minimize interaction at the lower affinity sites. The analysis of the S-band EPR spectrum of [Cu(his)2] at pH 7.3 revealed the major component is a complex formed with two histidines in a histamine-like coordination. Detailed analysis of S-band and X-band EPR and optical spectra of [Cu(II)−HSA] revealed that copper forms a complex with HSA involving α-NH2 terminal, two deprotonated peptide nitrogens (NH of Ala2, and NH of His3), and the imidazole nitrogen of His3 in a square planar arrangement. The spectral data were found to be independent of pH in the range 4.5−9.0 and did not confirm axial Asp1 carboxylate chelation. The EPR study of [Cu(II)−DSA] complex at pH 7.3 confirmed the presence of two bonded nitrogens which substantiate the absence of strategically located His3. It has been suggested that residues of non-nitrogen origin localized in the main body of DSA may be involved in copper binding, which would explain the protection from the Sanger reaction.

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