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Research has been conducted on the (bpym)PtCl (sub)2 complexes where bpym= 2,2'-bipyrimidine. The results of the complexes' crystallization in solvent-free form for X-ray diffraction are presented.

The UV-visible absorption spectra of [Ru(E)(E')(CO)(sub 2)(iPr-DAB)] (E=E'=SnPh3 or Cl; E = SnPh3 or Cl, E'=CH3; iPr-DAB=N,N'-di-isopropyl-1,4-diaza-1,3-butadiene) are determined using the combination of CASSCF/CASPT2 and TD-DFT calculations on model complexes. The results indicate the difficulty for the DFT approach in describing excited states in systems containing bonding between a halide and a low-valent metal atom.

Research demonstrates that the alpha-diimine enhances the photostability of the coordination and organometallic compounds. Data indicate that at absolute temperature of 80, the photostability extends from four microseconds to one millisecond due to an inefficient decay to the sigma-bond-to-ligand charge transfer state.

A detailed Fourier transform EPR spectroscopy study of the methyl radicals photogenerated from organometallic complexes [Ru(R)(SnPh3)(CO)2(iPr-DAB)], where R=Ch3, CD3, and [Pt(Me)4(iPr-DAB)] is presented.

(Re(R)(CO)3(4,4'-Me2-bipyridine)) where R = CH3, CD3, Et, iPr, Bz yields (Re(CO)3(4,4'-Me2-bipyridine)) and R radicals with the cleavage of the Re-R bond induced by radiation. Nanosecond time-resolved spectra reveal that the (Re(CO)3(4,4'-Me2-bipyridine)) radical is generated within the 7 nanosecond laser pulse. Ultraviolet, infrared and Fourier transform electron paramagnetic resonance spectroscopies were used to characterize the radicals generated by irradiation.

The triosmium clusters Os3(CO)10(N-N) (N-N = alpha-diimine ligand) underwent the reversible formation of biradicals in toluene which last for only a number of nanoseconds and zwitterions in acetonitrile which last for a number of seconds, when exposed to visible light. Photochemical investigations showed that the visibl absorption band of these clusters can be attributed to electronic transitions with Os-to-alpha-diimine charge transfer character with a variable degree of pi-delocalization within the Os(alpha-diimine) moiety.

The photochemistry of manganese pentacarbonyl chloride (MnCl(CO)5) was studied using the density functional calculations on both the ground and excited states of the organometallic compound. Potential energy curves have shown that the lowest excited states are dissociative for axial and equatorial CO loss. Comparison of the photochemical behavior of Mn2-(CO)10, MnH(CO)5 was conducted which revealed similar CO loss mechanism but a difference in breaking of the bond.

Solvents play a key role in electron donor-acceptor interactions between the -NH2 lone pairs on the remote 3- and 4-amino groups and the ruthenium benzoquinonediimine unit in the highly solvatochromic (Ru(bpy)2(dad9b))(PF6)2 where dadib = 3,4-diamino-3',4'-diimino,3'4'-dihydrobiphenyl and bpy = 2,2'-bipyridine. Its influence results in a dihedral angle orientation towards 90 degrees in water and a twist angle of zero in dimethyl sulfoxide for the two ligands.

One-electron reduction of the complexes (Re(Br)(CO)3(R'-DAB)) in nPrCN has led to the establishment of an equilibrium between the radical anions and the solvento radical. The Re-Br bond becomes more stable with the electron-withdrawing character of R' and with decreasing temperature. Reduction of the radicals can be undertaken in a subsequent one-electron step to give the five-coordinate anions, together with the six-coordinate anions, as the minor products.

The inorganometallic complex Ru(SnPh3)2(CO)2(iPr-DAB), where iPr-DAB = N,N'-diisopropyl-1,4-diaza-1,3-butadiene, is synthesized and subjected to UV-vis, IR, 1H NMR, 13C NMR, 119Sn NMR and mass (FAB+) spectroscopy and X-ray diffraction. The complex has two trans Ru-Sn sigma-bonds which determine its bonding properties. It also has a delocalized 3-center, 4-electron Sn-Ru-Sn sigma-bond, a highly mixed Ru-d(pi), Ru-5pz, Sn-sp3, and DAB-pi* characters in the highest occupied molecular orbital and the lowest unoccupied MO, and undergoes one-electron reduction to a radical anion.

Mono and dinuclear Ru(bpy)2 complexes, bpy = 2,2'bipyridine, containing the bridging ligand 2,2'-bis (benzimidazol-2-yl)-4,4'-bipyridine (bbbpyH2) exhibit electrochemical and photophysical properties dependent on the solvent and solution pH. The UV spectra and the oxidation potentials change with the pH. In the mononuclear complex, the ruthenium(II) ion possess an octahedral geometry. Deprotonation of the dinuclear complex leads to hole-type superexchange via the Ru(II) d-pie-bbbpyH2 pie* interaction.

The lowest energy electronic transition of Re(X)(CO)3(alpha-diimine) (X = Cl, Br, I; alpha-diimine = bpy, iPr-PyCa, iPr-DAB) changes from Re to alpha-diimine (MLCT) to X to alpha-diimine (XLCT) on moving from Cl to Br. Resonance Raman spectra and time-resolved absorption and emission spectroscopy show that the change in excited state is attributed to an irregular mixing of the d(sub pi)(Re) and p(sub pi)(X) orbitals. The emission from the XLCT excited state exhibits a longer lifetime due to the slow nonradiative decomposition to the ground state.

The measurement of potential energy curves (PEC) for Mn2(CO)10 using density functionals indicates that the transition from 3B(sub 2) sigma to sigma* excited state is Mn-Mn dissociative and not Mn-CO dissociative. The PEC associated with the equilibrium geometry is Mn-CO dissociative. The Mn-CO dissociative character is attributed to the lowering of the high-lying Mn-CO sigma-anti-bonding orbitals on Mn-CO bond lengthening.

The pk(sub a) of protonation of an oxygen bridge of (Mn{super IV}{sub 2-}{mu - O}3L'2)2+ has been found to exhibit electrochemical properties. Various experiments suggested the protonation of the reduced species. A pH-dependent reduction potential is found in aqueous buffer solutions. This reduced species was seen to reacts with the carboxylate group of the buffer. In this the potential of the reduction peak shifts to higher values when the pH is lowered.

Density functional analysis of the photoactive excited states of Mn(sub 2)(CO)(sub 10) to investigate the excitation energies and the nature of excited state show that (sigma to sigma*)B(sub 2) and (d-pi to sigma*) E(sub 1) are responsible for the low-energy excitation bands I and II observed at 337-355 nanometer. The LF excitation for Mn-CO(sub ax) dissociative excited state and Mn-CO(sub eq) dissociative excited state are confirmed.

UV-Vis absorption and resonance Raman spectroscopic analyses of complexes such as (Ru(X)R(CO)2(L)) show the influence of X and R ligands on the ground and excited state electronic environments of these complexes. Change of halides in the complex affects the charge transfer transitions associated with mixed metal-halide orbitals. Variations of alkyl ligands shift absorption bonds and change their relative intensities.

Time-resolved UV-vis absorption spectroscopy and nano-second flash photolysis analyze the photoreactions of three (CO)(5)ReMn(CO)(3) (alpha-diimine) complexes at different temperatures and pressures. Primary photoprocess in the metal-to-ligand charge-transfer excitation of these complexes is a fast CO dissociation from Mn center. High reactivities of these complexes are due to an available Mn coordination site and a weak Re-M bond.

The photochemical synthesis and X-ray characterization of new complexes derived from the reaction of orthopalladated N, N-dimethylbenzylamine and azobenzene. The spectral and thermochroic properties of three complexes and the kinetics of thermal composition are also discussed. The behavior of cis-Azobenzene in reaction was notable in its role as a bridging, bidentate ligand. This resulted in two platinum centers in close proximity and platinum planes almost perpendicular to the plane of the N=N double bond.

Characteristics of the ligands of 3,5-di-tert-butyl-1, 2-dioxobenzene (DBDiox) are examined by electronic absorption, infra-red and resonance Raman spectroscopic techniques, and explained as functions of their oxidation states. These DBDiox ligands form a homologous series existing in four different oxidation states that are responsible for chemical behavior changes in the DBDiox ligand. The lowest electron transitions change character to show the varying of the DBDiox ligands.

The redox-controlled photochemical reactivity of the novel cluster [Os3(CO)10(AcPy-MV)](super 2+) is reported. The redox control of the charge separation is highlighted in [Os3(CO)10(AcPy-MV)](super 2+), with the aim to restore the photoreactivity of the ordinary [Os3(CO)10(alpha-diimine)] clusters.

Research has been conducted on NO/CO metal complexes. The authors present the electrochemical, IR-spectroelectrochemical and spectroscopic characterization of these complexes, and report the use of density functional theory methodology in investigating low-energy absorption features, especially with respect to NO ligand's role.

Surface-enhanced Raman scattering (SERS) spectra and excitation profiles of one of Ag-2,2'-bipyridine surface complex show a selective enhancement of several fundamentals, overtones and combination bands that manifests itself by a distinct maximum at ca. 540 nm on their excitation profiles. The results show that the magnitude of the charge transfer (CT) resonance enhancement in a system in which the CT and the electromagnetic (EM) mechanism operate simultaneously is comparable to that achieved in a system in which the CT resonance is the only enhancement mechanism.

The time resolved UV-Vis and IR spectroscopies of Re(bz)(CO)3(iPr-DAB), where Bz is benzyl and iPr-DAB is N,N'-diisopropyl-1,4-diazabutadiene, detect the reactive sigma-pi* excited state. During the photochemical homolysis of the Re-Bz bond, this excited state acts as an intermediate. The complex after excitation to its MLCT visible absorption band suffers homolysis. The spin-triplet nature of the sigma-pi* excited state and small excited state distortion makes it highly stable.

The twist angle of bis(bipyridine)ruthenium(II)3,4-diamino-3', 4'-diamino-3',4'-dihydrobiphenyl contributes to the alteration in the rate of electron transport through the molecule, and is a characteristic feature of molecular switches involving biphenyl linkages. Lewis acid and base solvents change the twist angle of the model compound in the complex (Ru(bpy)2(dadib))2+, where dadib refers to 3,4-diamino-3',4'-diamino-3', 4'-dihydrobiphenyl and bpy refers to 2,2'-bipyridine. The twist angle approaches 90 degrees due to the influence of Lewis acids, and approaches zero degrees as a result of the effect of Lewis bases.

The irradiation of the visible absorption band of the complexes Mn(CO)3(bpy)X, where X = Cl, Br and I, produces the dimer Mn2(CO)6(bpy)2 possibly from the lowest ligand to ligand charge-transfer (LLTC) state. This is evidenced by the absorption spectrum of the Re(CO)3(pTol-DAB)X (pTol-DAB = para-tolyl-1,4-diaza-1,3-butadiene) complexes which showed a weak band at the low-energy side of the MLCT. This suggests that the properties of the lowest excited states of these Re(CO)3(alpha-diimine)X complexes are dependent on the alpha-diimine ligand used.