A new complex salt of composition [Co(phen)(3)](3)(V(4)O(12))(2)Cl·27H(2)O (phen = 1,10-phenanthroline and [V(4)O(12)](4-) = tetrameric dodecaoxotetravanadate ion) was synthesized by reacting appropriate salts in aqueous medium. The complex salt has been characterized by elemental analyses, thermogravimetric analysis (TGA), cyclic voltammetry (CV), FT-IR and UV/Vis spectroscopies, solubility product and conductance measurements. Single crystal X-ray structure determination revealed ionic structure consisting of three complex cations, [Co(phen)(3)](3+), two [V(4)O(12)](4-) anions, one chloride and twenty seven lattice waters. Detailed structural and spectroscopic analyses of [Co(phen)(3)](3)(V(4)O(12))(2)Cl·27H(2)O show that the large anion is stabilized by the large cationic metal complex as there is preferred shape compatibility that leads to a large number of lattice stabilizing non-covalent interactions.

A series of mixed ligand complexes of ruthenium(II) complexes containing 5-methylphenanthroline and trimethylamino-5-methylphenanthroline have been synthesized to investigate the impact of the quaternary amine on the photophysical properties. Thermal stability studies indicate that the quaternary amine group is stable with respect to hydrolysis. Mass spectral analysis of the complexes revealed only fragments consistent with homolytic cleavage of the amines and no parent ions were observed. Both electrochemical and photophysical investigations indicate that the quaternary amine has little or no impact on the properties of the complex when compared to the complexes lacking the amine.

Treatment of cobalt(II) perchlorate hexahydrate with 2 molar equiv. of 2-aminobenzenethiol (Habt) in acetonitrile afforded a tricationic tricobalt complex, [Co{Co(abt)}](ClO)·2CHCN, by aerial oxidation. The molecular structure of the meso (ΔΛ) form of the complex was determined by X-ray crystallography. In the complex cation, the central Co is coordinated by six thiolate groups from two terminal ()-[Co(abt)] units in an octahedral geometry, forming a linear S-bridged tricobalt structure.

Building on our recent report of an active H production catalyst [Ni(P N)] (Prop = phenylpropionic acid, peptide (R10) = WIpPRWTGPR-NH, p = D-proline and PN = 1-aza-3,6-diphosphacycloheptane) that contains structured β-hairpin peptides, here we investigate how H production is effected by: (1) the length of the hairpin (eight or ten residues) and (2) limiting the flexibility between the peptide and the core complex by altering the length of the linker: phenylpropionic acid (three carbons) or benzoic acid (one carbon). Reduction of the peptide chain length from ten to eight residues increases or maintains the catalytic current for H production for all complexes, suggesting a non-productive steric interaction at longer peptide lengths. While the structure of the hairpin appears largely intact for the complexes, NMR data are consistent with differences in dynamic behavior which may contribute to the observed differences in catalytic activity. Molecular dynamics simulations demonstrate that complexes with a one-carbon linker have the desired effect of restricting the motion of the hairpin relative to the complex; however, the catalytic currents are significantly reduced compared to complexes containing a three-carbon linker as a result of the electron withdrawing nature of the -COOH group. These results demonstrate the complexity and interrelated nature of the outer coordination sphere on catalysis.

Imidazolin-2-imines (ImN-), derived from -heterocylic carbenes, have been shown to be strong electron donors when directly coordinated to metals or when used as a substituent in larger ligand frameworks. In an attempt to enhance the electron-donating properties of the popular guanidine ligand class, the effect of appending an ImN- backbone onto a guanidinate scaffold was investigated. Addition of 1 equiv of [Li(EtO)][Im N] to the aryl carbodiimide (dippN)C (dipp = 2,6-diisopropylphenyl) cleanly affords the lithium Im N-functionalized guanidinate [Li(THF)][(Im N)C(Ndipp)] (). Subsequent metalation of the ligand with FeBr gives the yellow Fe(II) complex {[(Im N)C(Ndipp)]FeBr} () in good yield. Solid-state structural analyses of both and shows the Im N- group acts as a non-coordinating backbone substituent. Direct structural comparison of to the closely related guanidinate and ketimine-guanidinate complexes {[(X)C(Ndipp)]FeBr} (X = BuC=N (); N( Pr) ()), differing only in their backbone, reveals a detectable resonance contribution of the Im N- group to the guanidinate ligand electronic structure. Moreover, the Fe(II)/Fe(III) redox couple of (E = -0.67 V) is cathodically shifted by greater than 200 mV from the oxidation potentials of (E = -0.42 V) and (E = -0.45 V), demonstrating the [(Im N)C(Ndipp)] system to be a quantifiably superior electron donor.

The preparation, characterization, and evaluation of a cobalt(III) complex with 13-membered tetraamide macrocyclic ligand (TAML) is described. This is a square-planar (X-ray) = 1 paramagnetic (H NMR) compound, which becomes an = 0 diamagnetic octahedral species in excess d-pyridine. Its one-electron oxidation at an electrode is fully reversible with the lowest value (0.66 V SCE) among all investigated Co TAML complexes. The oxidation results in a neutral blue species which is consistent with a Co/radical-cation ligand. The ease of oxidation is likely due to the two benzene rings incorporated in the ligand structure (whereas there is just one in many other Co TAMLs). The oxidized neutral species are unexpectedly EPR silent, presumably due to the π-stacking aggregation. However, they display eight-line hyperfine patterns in the presence of excess of 4--butylpyridine or 4--butyl isonitrile. The EPR spectra are more consistent with the Co/radical-cation ligand formulation rather than with a Co complex. Attempts to synthesize a similar vanadium complex under the same conditions as for cobalt using [VO(OCHMe)] were not successful. TAML-free decavanadate was isolated instead.

In this research article, we report the synthesis and structural characterization of a family of first-row metal complexes bearing redox-active ligands with tunable H-bonding donors. We observed that these coordination complexes can adopt three different geometries and that they are stabilized by intramolecular multicenter H-bonding interactions, which are systematically modified by changing the metal ion (Co, Ni, Cu, Zn), the ligand scaffold (variations in the diamine and ureanyl substituents used) and the solvent of crystallization.

Cooperativity between organic ligands and transition metals in H-atom (proton/electron) transfer catalysis has been an important recent area of investigation. Tetramethylpiperidine-N-oxyl (TEMPO) radicals feature prominently in this area, prompting us to examine cooperativity between its hydrogenated congener, TEMPOH, and Co centers ligated by dihydrazonopyrrole ligands which have previously been shown to also store H-atom equivalents. Addition of TEMPOH to ( DHP)CoOTf results in formation of an unusual Co-adduct of 1-hydroxy-2,2,6,6-tetramethylpiperidin-1-ium (TEMPOH ) which has been characterized with IR spectroscopy and single crystal X-ray diffraction. This adduct is thermally unstable, and decomposes, putatively via N-O homolysis, to generate 2,2,6,6-tetramethylpiperidine and the Co-hydroxide complex [( DHP)CoOH][OTf]. Computational investigations suggest a proton-coupled electron transfer step to generate the TEMPOH adduct where the Co center serves as an electron acceptor. Despite the prevalence of aminoxyl reagents in catalysis, particularly in aerobic transformations, metal complexes of differently hydrogenated congeners of TEMPO are rare. The isolation of a TEMPOH adduct and investigations into its formation shed light on related transformations that may occur during metal-aminoxyl cooperative catalysis.