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Differences in the relative energies of the interconfigurational (IC) transitions for the fully oxidized (+6) states of the osmium systems demonstrate that stereochemical effects lead to fundamental changes in the energy levels of the metal-based dpi orbitals, which are split by spin-orbit coupling and ligand-field asymmetry. An increase in the separation between the IC bands as BL is varied reflects the increase in the degree of electronic coupling through the series of ruthenium and osmium complexes.

A series of C- and Z-shaped complexes of the form cis- and trans-[Re(CO)3(L)2BiBzlm, where L = 4-phenylpyridine, 2,4'-bipyridine, or pyridine and BiBzlm = 2,2'-bisbenzimidizolate, are synthesized. The compounds are acyclic analogues of studied tetraehenium molecular rectangles and are of interest, in part, due to their potential to form ligand-centered mixed-valence compounds upon reduction by one electron.

Research has been conducted on the charge transfer within different (X (sub)2 -bipyridine)Re (super)I (CO) (sub)3 Cl complexes. The use of the transient DC photoconductivity, Stark emission spectroscopy and ground-state dipole moment measurements in examining this charge transfer is discussed.

Electroabsorption and related spectroscopic studies were conducted on bimetallic tetraiminoethylenedimacrocyclic complexes. Additional near-infrared Raman investigations on mixed valent and isovalent diiron species support the observed delocalized mixed-valence ion behavior. Results also show that electroabsorption causes anomalous polarizability and that metal-to-ligand charge transfer excitation causes the blue green electronic absorption band in the mixed-valent complex.

The intrinsic charge localization in the formed state of metal-to-ligand charge transfer (MLCT) excited-state formation was established through utilization of Electronic Starck effect measurements. Data indicated that the transition involved the production of a charge-localized state. It was further indicated that the 'singlet' MLCT excited state of Ru(phenanthroline)3(super)2+ resembled the MLCT state of the bipyridine analogue.

The charge transfer of pyridinium ions that are directly attached to Ru(bpy)sub3super2+ is not observed in the photoexcited state of the donor. The tris(bipyridyl)ruthenium dication has a 4,4'-bipyridinium ion that is attached by nitrogen-carbon bond at the four site of the single 2,2'-bpy ligand. The 2,2'-bipyridine has an interplanar angle of 28 degrees between two 4,4'-bpy rings. The two 4,4'bpy rings have an interplanar angle of 24 degrees. The four ruthenium polypyridyl complexes exhibit metal-to-ligand charge-transfer transitions that are similar to ruthenium(II) bypiridine.

A tricarbonylrhenium (bi)pyridine based donor/crown/acceptor assembly undergoes photoredox reactivity consisting of rhenium-to-pyridine charge-transfer absorption before electron transfer to Re(II) from the pyridine anion reduced nitrobenzene. Quenching and nuclear magnetic resonance spectroscopy at different temperatures reveal that the folding kinetics is accelerated at low temperature, low dielectric strength solvents, and in metal-to-ligand charge transfer excited state than the ground state.

The aqueous (D2O) self-exchange kinetics studies for (trimethylammonio methyl)ferrocenium/ferrocene (TMAFc2+/+) as a function of beta-cyclodextrin encapsulated are described. The results showed that the electron self-exchange rate constant for TMAFc2+/+ in D20 decreased by a ca. 20-50 fold in the presence of beta-cyclodextrin. The decrease has been attributed to the increase in thermal activation barrier, reflecting the incipient need to transfer the cyclodextrin host.

Intervalence absorption spectroscopic studies show that an inert electrolyte exhibits significant influence on the energetics of optical electron transfer (ET) in (NC)5Fe(III)-bis(pyridyl)ethylene-Fe(II)(CN)(sub 5)(super 5-). A model incorporating energetic consequences of stepwise ion pairing explains the above compound in different ionic strength solutions of LaCl3, CaCl2 and NaCl. This model explains the optical intervalence properties of (NH3)5Ru(III)-4, 4'-bpy-Ru(II)(NH3)(sub 5)(super 5+) in aqueous Na2SO4 solution. Ion-pairing-stimulated symmetry reduction and subsequent restoration influence optical electron transfer.

A three-site description of electronic delocalization helps explain quantitatively the intervalence energy effects associated with double crown encapsulation of the Creutz-Taube ion. Increase in the size of the macrocycle increases the energy shifts in both the near-infrared and visible portions of the electronic absorption spectrum. Improved parameterization of the model enhances the agreement between the expected and observed crown effect on MLCT and intervalence energies.

The effects of host (crown ether) size and structure and guest (ruthenium complex) oxidation state and primary ligand environment on binding strength were reported. It was found that binding increases with increased size and flexibility of the crown ether. It also increases with increased availability of ammine ligands, higher oxidation state and increased Lewis acidity of the guest. Small amounts of crown ether can also have substantial effects upon metal-ligand and metal-metal charge-transfer interactions.

The environmental effect of intervalence transition for trans-(py)(NH3)4Ru-pz-Ru(NH3)4(py)5+, a structure comparable to the Creutz-Taube ion, is analyzed according to its response to both solvent and added electrolyte. Using dimethyl sulfoxide as the electrolyte and acetonitrile as solvent, intervalence effects are observed through the absorbance differences obtained.

The electrochemical examination and oscillator strength measurements of Ru(NH3)4(2, 2'-bipyridine)2+ and Ru(NH3)4(1,10-phenanthroline)2+ metal/ligand orbital mixing show differing experimental results. The electrochemical method detects a considerable degree of electronic delocalization while the spectral measurement detects less than two percent delocalization. However, a separate spectroscopic counter-study favors the results obtained from the electrochemical technique. This study shows that the electrochemical study of the two Ru compounds provides an accurate representation of metal/ligand orbital mixing and partial charge-transfer reactions.

A family of anisotropic open-framework compounds is obtained based upon paddle-wheel-type coordination of Zn(II) pairs in two dimensions and pyridyl ligand pillaring in the third. The mixed-ligand approach is used to tune channel dimensions, to introduce otherwise unstable metal/pyridine linkages, and to engender framework redox reactivity.

gA pulse-field gradient nuclear magnetic resonance spectroscopic technique for determining the size of a tetrametallic molecular square is described. The method utilizes molecule's self-diffusion coefficients relative to those from other isostructural compounds with an inverse relationship with hydrodynamic radii, which roughly represents the cube of the assembly's mass.

Research has been conducted on the rhenium-linked porphyrin dimers. The synthesis, photophysical characterization and preliminary energy transfer applications of these dimers based on the rhenium pyridyl ligation are discussed.

Research demonstrates measuring charge-transfer characteristics of the emission properties of the excited states of bipyridine complexes using transient direct current photoconductivity technique.

Research demonstrates the application of transient direct current photoconductivity technique to inorganic systems in the investigation of charge-transfer reactions in solutions of pt(dpphen)(ecda) at room temperature. Result indicate that the technique can be extended to other related compounds to study relationship between one-electron-transfer distances and molecular structure.

Trimethylaminomethyl(ferrocenium/ferrocene) (TMAFc super 2+/+) self-exchange studies in water with the negatively charged molecular host calix 6 arene-p-sulfonate generated two contributing factors. The extent of oxidation-state dependence of the guest/host association constant was smaller for 1(super n-)TMAFc(super 2+/+) than for beta-cyclodextrin/TMAFC(super 2+/+) or the ammine ruthenium/crown ether systems. Another factor was the opposite charges of the free guests and the guest/host assembly which triggered the net acceleration of the exchange kinetics.

The excitation-wavelength-dependent Raman spectra of the species trans-(O)2Re(py-x)4(super 1+), where py-x = pyridine or pyridine derivative, was studied. The trans-dioxo complexes exhibited absorption regions at ca. 440 nm and ca. 350 nm. The ligand-field transition also featured peaks at 822 cm(super -1) and 907 cm(super -1) which were assigned to the asymmetric oxygen-metal and the O-double bond-Re-double bond-O modes, respectively. The near-UV absorption in the charge-transfer region was assigned as rhenium-to-pyridine charge transfer.

The mechanisms involved in the electrochemical reduction of cis- and trans-dioxorhenium(V) species in acidic and neutral solutions is reported and quantitative measurements of the accompanying electrochemical kinetics is made. Results indicate that access to Re(IV) is a significant factor in the differentiation of cis/trans electrochemical kinetics. Moreover, comparisons to isoelectronic osmium species makes possible a semiquantitative reactivity analysis.

The mixed-valence compound (NH3 5 Ru-NC-Fe CN 5)Na was synthesized and its intervalence thermochromism was investigated. A transient thermochromic bleaching and recovery was expected in view of the intervalence absorbance measurements made on the high-energy side of the intervalence band and the negative sign of dE(sub op)/dT. It follows that a sign reversal should result fron measurements on the low energy side. These indicate that the driving force is temperature-dependent and that it is most negative when the temperature is at its lowest.

Eleven linked donor- (chromophore-) acceptor complexes have been synthesized. The complexes consist of the Re(CO)3(ligand) unit as the chromophoric donor, the encapsulation unit linked directly to 2,2'-bipyridine or pyridine and an electron acceptor, another chromophore or a redox-inactive site. The excited-state lifetimes of the complexes revealed that a rhenium-to-pyridine-based charge-transfer state existed with an energetic ordering of py > bpy > py-crown (or py-ester) > bpy-crown (or bpy-ester).

The bridge-mediated charge-transfer kinetics of L(NH3)4Ru(super III)N-triple bond-CFe(super II)(CN 5)1- were studied. Differential-pulse voltammetry indicated positive shifts in E(sub f)(Ru) as NH3 is displaced progressively by 4-methylpyridine and the other electron-withdrawing ligands. Potential shifts of the indirectly disturbed redox site was also revealed. Differences in the estimates of orbital mixing for the species are accounted for by the geometric distance between donor and acceptor metal ions which can exceed the true charge-transfer distance.

The application of redox quenching processes after photochemical excitation is a new method for the assembly of metallopolymeric films. The visible-region photolysis of an acetonitrile solution of Ru(vbpy)2(super 2+) and BPh3R(super 1-) between conductive glass and ordinary glass plates generates a polymeric coating on the plate nearest to the light source. Films are obtained easily from solutions containing triphenyl-n-hexylborate but not from those containing tetraphenylborate. Electrochemical determination indicates that thinner films are more electroactive than the thicker ones.

A 2-fold interwoven metal-organic framework is chemically reduced and doped with [Li.sup.+], [Na.sup.+] and [K.sup.+] and they have displayed enhanced [H.sub.2] uptake at low pressures and temperatures. The absence of large special-site effects has shown that ions might be positioned between frameworks and might not be readily accessible to [H.sub.2].

A molecular rectangle of the form ([Re(CO)3]2BiBzlm)2-mu,mu'-(LL)2, where BiBzlm is 2,2'-bisbenzimidazolate and LL are cofacially aligned [5,15-bis(4-ethynylpyridyl)-10,20-bis(n-hexyl)-porphyrinato]zinc ligands, is examined. The spectroelectromechanical and electroabsorption measurements have shown that the singly reduced rectangle is assigned as a borderline class II/class III mixed-valence species.

Antracene and related compounds function as lifetime-extending cofactors in the (meso-tetraphenylporphine)Mn(super III) chloride-catalyzed epoxidation of olefins. An experiment with a chiral porphyrin catalyst shows that enantioselectivity is preserved in the presence of the cofactor.

Gel-Permeation Chromatography (GPC) can be used in the determination of size and purity of transition-metal-directed supramolecular assemblies (TMDSA), as well as in the deduction of byproducts in the syntheses of these materials. It is found that preparatory GPC can be used in the purification of mixtures of TMDSA.

Resonance Raman and semiempirical electronic structure calculations are performed to determine the electronic nature of the ground-state analogous square planar nickel complex(super 3+) species, as well as the character of the excited state arising from the intense near-infrared absorption. The study reveals that the absorption band is composed of two separate overlapping transitions, which are described as ligand-based transitions rather then ligand-to-metal charge transfer (LMCT) or class III intervalence transitions.

Tetrametallic molecular rectangles have been synthesized, based upon rhenium thiolate dimers combined with difunctional pyrazyl and pyridyl ligands. The composition of the proposed structure is supported by H NMR, IR and MS measurements. It is suggested that such molecules may be useful as a basis for further work, such as the creation of larger-cavitied molecular rectangles which could be used for separations and sieving.

Assemblies of multiporphyrin molecular squares are synthesized from a soluble dipyridylporphyrin ligand and Re(CO)5Cl. Both free multiporphyrin molecular square assemblies and metalated forms using zinc have been synthesized. Squares containing zinc bind particular polyimine ligands strongly in CH2Cl2 solution. The squares are insoluble in water but highly soluble in tetrahydrofuran, CHCl3 and CHCl2.