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The density functional theory (DFT) calculations are used to investigate the possibility of stabilizing the unstable acepentalene (acp) molecule through coordination to transition metals. The comparison of the results with pentalene complexes has indicated that their acp homologues are slightly less stable, suggesting that they can be synthesized and isolated

A stoichiometric system in which changes of a metallaborane is mediated by insertion of two alkynes into an irdaborane framework through a disposable molybdenum chaperone carbonyl fragment is presented. The complete procedure, 1+2alkyne= 8+B [H.sub.3]+2[H.sub.2], promoted by (arene)(Mo)[(CO).sub.3], serves as an example of a transition-metal-facilitated process analogous to metal-facilitated organic transformations seen in organometallic chemistry.

DFT calculations on the Cu(mu(sub 3)-X)(sub 4)L(sub 4) series indicated that X-to-Cu Pi- donation remains small, regardless of the nature of X. Therefore all the considered X- ligands are better described as two-electron ligands, and the covalent part of the Cu. Cu bonding depends mainly upon the a(sub 1) component of the alpha-type interaction between the L(sub 4)Cu(sub 4)(super 4+) and X(sub 4)(super 4-) fragments.

The synthesis of the characterization of a series of dirhenium metallaboranes containing 5-10m boron atoms is described. Competition between main group and transition metal electronic properties is also presented.

The synthesis of the characterization of a series of dirhenium metallaboranes containing 5-10m boron atoms is described. Competition between main group and transition metal electronic properties is also presented.

Research has been conducted on the rhenium trifluoroacetate compound. The synthesis and structure of this compound have been investigated and the details are reported.

Results demonstrate that organometallic carboxylic acid reacts with copper(II) methoxide to form a new inorganometallic cluster exhibiting a traiangular copper(I) core surrounded by three CCHCo(sub)2(CO)(sub)6 fragments.The bonding in the cluster measures 2.500 and 2.540 angstrom, respectively, for Cu-Cu and Cu-Co distances.

Research has been conducted on the transition-metal chalcogenide clusters. The electronic structures of these electron-rich octahedrally condensed clusters have been investigated via the use of Huckel and density functional molecular orbital calculations and the results are reported.

Research has been conducted on the dithiolato edge-bridged cubic clusters. The extended Huckel and density function calculations used in investigating these cluster demonstrate that the chelating effects of the ligands affect the stability of the clusters.

New allotropic forms of carbon dioxide and carbon disulfide were sought using density functional studies of CX2-based oligomers.

There have been many experimental and theoretical studies on edge-bridged octahedral cluster compounds, although there has been no systematic detailed analysis on their stabilization. A study aims to understand the stability of octahedral cluster compounds, based on recent experimental results, such as the new CsErTa(sub6)C1(sub18) and Cs(sub2)UTa(sub6)C1(sub15)O(sub3) compounds. Density functional theory (DFT) calculations accompany the experimental results.

An experiment was conducted to determine the interaction of the distorted transition-metal cubic clusters [Bi4Co9(CO)16]2- and [Bi8Co14(CO)20]2- and analyze the configurations of the cluster compounds based upon a hexacapped M8 cube. A single-crystal X-ray diffraction was utilized to characterize the transition metal compounds. Results showed HOMO/LUMO region is slightly antibonding between the interstitial Co atoms and the surrounding Bi and peripheral Co Atoms but their rich electron contents contribute to the compounds' strong bonding to interstitial cobalt atoms.

The reactions of salts of the cluster anion (Bi4Fe4(CO)13)2- with MePCl2 are very dependent on the stoichiometry. (HFe2(CO)6Bi2(Fe(CO)4))-, (Bi3Cl4(mu-Cl)4(Fe(CO)3))3-, ((HFe2(CO)6Bi2Cl2)-)infinity, or (Fe(CO)4Bi2Cl6)2- can be isolated depending on conditions. An unusual characteristic of these complexes is the tendency of Bi to adopt hypervalent bonding modes and additionally, in (Bi3Cl4(mu-Cl)4(Fe(CO)3))3-, to adopt such bonding situations in a reduced oxidation state.

The electrochemical and spectroscopic characteristics of dicobalt compounds in aprotic solvents were examined to ascertain their behavior and reactivity toward dioxygen. Findings revealed that their face-to-face configuration strongly affected their electrochemical properties. Some of the compounds were good electrocatalysts for the four-electron reduction of dioxygen upon adsorption on a graphite electrode in aqueous acid. Their electrochemical and spectroscopic behavior indicated that the neutral form has no reaction to dioxygen. The one- and two-electron-oxidized forms of the dimer react to dioxygen, which results in two complexes at room temperature.

Square-pyramidal clusters of [NEt4]2[Fe3(CO)9Bi2] were synthesized by the pyrolysis of [NEt4]2[Bi4Fe4(CO)13] in MeCN. The [NEt4]2[Fe3(CO)9(mu3-Bi)2] square-pyramidal cluster is composed of anion packs that are arranged in discrete units on a crystal lattice with no intermolecular interactions. The cluster also contains two crystallographically unique [NEt4]+ cations per anion in its crystal lattice. Furthermore, the metal carbonyl clusters contain a square-pyramidal E2M3 core with short nonbonding E-E interactions.

(PhCH2NMe3)2(Bi2Cl4(mu-Cl)2(mu-Fe(CO)4)) is prepared from BiCl3 and (PhCH2NMe3)2(Fe(CO)4). It exhibits a high degree of stability inspite of the presence of a nucleophilic iron carbonyl anion and BiCl3 as a lewis acid. The two BiCl3 groups are bridged by an (Fe(CO)4)2- moiety. The coordination geometry at Bi is square-pyramidal with two chloride ligands being shared between Bi-atoms whereas at Fe it is octahedral. The charge transfer from Fe-carbonyl group to Bi2Cl6 results in a delocalization of electron density over chloride ligands contributing towards the stability of the complex.

An extremely sensitive 17e complex is synthesized using either any of two neutral precursors by one-electron oxidation using (FeIIICp2)+PF6-. The complex is characterized using elemental analysis, ESR and Mossbauer spectroscopic techniques. It is also characterized by its one-electron reduction to an isostructural FeII complex using another electron-reservoir complex.

Different approaches were used to examine the synthesis and molecular structure of a transition metal-heavy main group element compound, (Et4N)2(OC)5MoAsMo3(CO)9-(mu-3-OR)3Mo(CO)3, where R is methanol or ethanol. X-ray crystallography showed that the compound is electron rich and contains an extra electron pair that resides in an a2 orbital, equally delocalized over three molybdenum atoms.

Examination of the bonding characteristics and electronic structures of the rare earth metal boron carbide (MBC) compounds having boron-carbon zigzag chains by extended Huckel tight-binding calculations reveals an ionic picture between the metallic framework. Boron-carbon chains account for the metallic framework. Regular chains associated with YBC and UBC are explained by a formal charge of 3- per BC unit, while distorted chains result due to a formal charge higher than 3- per BC unit.

Single-crystal X-ray counter data provided the crystal structure of Gd2B3C2. The boron-carbon structural alignment of the B-C net in Gd2B3C2 explains a formal charge of 5- per B3C2 unit. The electronic structure of the boron-carbon layers observed in ThB2C and alpha-UB2C structures is strongly associated with that of the anionic two-dimensional boron-carbon layers.

Huckel and self-consistent field multiple-scattering Xalpha computation which formed the basis of a study of the bonding in cubic M8(mu4 - E)(6)Ln cluster compounds confirm that electronegative metals and/or terminal pi-acceptor ligands support optimal metallic valence electrons. However, space M-M interactions and bond M-E interactions are responsible for the comparatively powerful M-M bonding.

Extended Huckel tight-binding computations formed the basis of a study of the electronic structure and bonding characteristics of ligand borocarbide compounds with the ThB2C, alpha-UB2C and YB2C structures. They confirmed that an ionic picture between the metallic and the boron-carbon sublattices accounts for the alignment in the various nonmetal networks. A formal charge of the B-C net in ThB2C and alpha-UB2C, but a formal charge of 3-, is due to the one in YB2C.

The replacement of two equatorial bridging carbonyl ligands of the triruthenium complex, Ru3 mu3-eta2-P(C6H5)(C5H4N) (mu-P(C6H5)2)-(CO6)(mu-CO)2, by two diphenylphosphido groups results in the formation of the electron rich cluster, Ru3 mu3-eta2-(P(C6H5)(C5H4M)) mu-P(C6H5)23(CO)6. X-ray diffraction analysis shows that the complex is formed by a triangular array of ruthenium atoms capped by phenylpyridylphosphido ligands with each Ru-Ru corners stabilized by diphenylphosphido groups which occupy the equatorial coordination points. An electrochemical study of the complex is also discussed.

An investigation of the stability of the singlet and triplet states of tetraoxocyclobutane (c4O4, the tetramer of carbon monoxide) at various levels of theory is presented. Second order perturbation favors the singlet state, whereas the triplet and open-shell singlet states are computed to be more stable using the hybrid B3LYP density functional method.

The synthesis and the electronic properties of the highly conjugated molecular wires trans-[[Cl-[(dppe).sub.2]Ru[double bond]C[double bond]C[double bond](Ph)C-CH[double bond](C[H.sub.3])C-C[triple bond]C-[(X).sub.2]Ru-C[triple bond]C-C(C[H.sub.3])[double bond]CH-C(Ph)[double bond]C[double bond]C[double bond]Ru[(dppe).sub.2]Cl].sup.n+] (n = 2, X = dppe and dppm) with three similar metal centers spanned by two odd-numbered unsaturated [C.sub.7] chains providing a long conjugated path and displaying five well-separated redox states are described. Electronic communication is evidenced and tuned in homonuclear trimetallic oligomeric carbon-rich systems in either an oxidation or a reduction process.

The synthesis and structural characterization of an octanuclear Cu(I) cluster [[Cu.sub.8]{[Se.sub.2]P[([O.sub.i]Pr).sub.2]}6][(P[F.sub.6]).sub.2] (1) with an empty [Cu.sub.8] cubic core involving diisopropyl diselenophosphate (dsep) ligand is demonstrated. This is the first example of the reduction of molecular symmetry of hydride by simply changing the encapsulated species without altering the general bonding pattern of the surrounding ligands and also demonstrated the easy replacement of hydride with other anions ([Cl(-), Br(-), F(-), [S.sup.2-], [Se.sup.2-]) to produce hydride-centered species.

The synthesis of alkynyl ruthenium colorimetric sensors whose receptors contains thiazolidinedione, rhodanine or barbituric heads as recognition centers for anions is reported. The results have rationalized the long-range electronic communication as a main characteristic of the alkynyl ruthenium species and as a key to improve the selectivity of alkynyl ruthenium-based sensors toward anions.

A series of four new covalently bonded charge-transfer molecular hybrids were synthesized and characterized. These hybrid complexes consist of an organometallic acceptor fragment and an inorganic donor group connected by an [eta]-conjugated aryldiazenido spacer in a [mu]-[eta.sup.6]:[eta.sup.1] mode.

A report is presented on two novel methodologies of C-C bond formation to control the extension of an odd numbered carbon chain via the achievement of a class of bridged cationic carbon-rich homobimetallic complexes with seven conjugated carbons between remote metals with highly delocalized extended conjugated structures. The proposed mechanisms for the C7 and C9 reactions arise from an unusually reactivity of the polyynyl ruthenium complexes that are protonated at the terminal carbon atom to generate a cumulenic intermediate and especially the novel hexapentaenylidene species, reactive toward nucleophilic carbon-rich systems.

The topological analysis of electron density in the ketene complex (eta(super 5)-MeC5H4)CO)2Mn[eta(super 2)-O=C=C(mu-eta(super 2)-C=CPh)CO2(CO))Ph] is discussed. A predisposition for the carbene component of the ketene ligand for binding to the neighboring C atom of the adjacent CO ligand is observed.

The original solution for creating electronic communication between two carbon-rich chains connected via a metal arised from the reduction of a is(allenylidene) metal leads to the single-electron delocalization.

Analysis of the electronic structure of the electron-deficient cluster cation [Ru(sub 4)(eta(super 6)-C6H6)(sub 4)H4](super 2+) by density functional theory calculations show a very small energy gap(0.06 eV) between the diamagnetic singlet state and the paramagnetic triplet state.

Research describes synthesis and coordination chemistry of the imino nitroxide raical bearing ligand in combination with platinum(II) and palladium(II) metal ions. Results indicate that while the platinum derivative exhibits ferromagnetic intermolecular interactions, the palladium derivative shows an overall antiferromagnetic behavior.

The synthesis, characterization and the structural analysis using arc-melting techniques and single-crystal X-ray structure and the theoretical analysis of Gd4B3C4 is presented, where it is seen that the boron and carbon atoms form two different types of nonmetal arrangements. Results suggest that the group oxidation states for the anions is not fully oxidized and indicates that the results tend to favor full metal oxidation, which could correspond to the different group oxidation states.

A study was undertaken to examine the electronic structure of cubane structures such as the [E4(PdL2)4][Ph2EX2]2 (L = PPh2Me, 1: E =Sb, X = Cl; 2: E = Bi, X = Br). These compounds were characterized spectroscopically and by-single crystal X-ray diffraction for [Sb4(PdL2)4][Ph2SbCl2]2*0.5THF and [Bi4(PdL2)4][Ph2BiBr2]2. Results of the density functional theory and extended Huckel theory calculations revealed large high and low occupied molecular orbit gaps, consistent with the agreement regarding the stability of compounds 1 and 2.

The electrochemical single-electron oxidation of the 18-electron compounds (M(II)(C5R5)-(arene)) + (M = Fe or Ru; R = H or Me)(20) at very high potentials with different arenes was described. In addition, the oxidation of the polymethylated compounds in the series (R = Me, arene = durene, pentamethylbenzene and hexamethylbenzene) with SbCl5 in CH2Cl2 was examined. Experimental results showed that the (Fe(II)Cp(arene))+ compounds exhibit a high degree of functional chemistry that resulted in the synthesis of an extremely large number of complexes.