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A dimolybdenum molecular pair, [Mo.sub.2][(DAniF).sub.3][([mu]-OH).sub.2][Mo.sub.2][(DAniF).sub.3], is synthesized and characterized by using X-ray crystallography. The results have provided an interesting case of single-crystal-to-single-crystal (SCSC) transformations and described the deprotonation process affected by dioxygen.

A combination of the near-IR, EPR, NMR and magnetic susceptibility measurements are employed to compare the electronic localization and the delocalization that are effectively determined by the binding of a linker in an isomer pair. The results demonstrate that the [alpha] species are electronically localized and are diradical, whereas the [beta] species are electronically delocalized and are essentially diamagnetic.

The compound [Re.sub.2][(hpp).sub.4]F[(TFPB).sub.2] is characterized by both X-ray and neutron diffraction and an EPR spectroscopy of [Re.sub.2][(hpp).sub.4][Cl.sub.2]P[F.sub.6] at multifrequency (9-95 GHz) is studied by using dilute solution, frozen glass and neat powder samples. It is indicated that the unpaired electron in a [Re.sub.2.sup.7+] compound resides in a dominantly metal-based orbital.

Several new polyamidate-linked dimolyhdenum compounds, prepared in good yield and high purity by direct assembly of M[O.sub.2][[DAniF].sub.3]([O.sub.2]CC[H.sub.3]) are reported with polyamides in the presence of strong base [H.sup.-]. It is suggested that M[O.sub.2.sup.5+] is an electron-trapped species with one electron residing on each of the two dimolybdenum units as revealed by electrochemical measurements.

The halide-bridged tetranuclear clusters, [cis-Mo2(DAniF)2]2([mu]-X)4, X=Cl, Br, and I are produced by reactions of [cis-Mo2(DAniF)2(NCCH3)4](BF4)2, DAniF= N,N'-di-p-anisylformamidinate, with an excess of anhydrous. All three compounds show two reversible one-electron oxidation processes with potential separations between the two oxidation processes of 540, 499, and 440 mV.

A study synthesized and crystallographically characterized a pair of isomeric cyclic triads containing three quadruply bonded [Mo2] units, [[Mo2(cis-DAniF)2].sup.2+] bridged by six fluoride. For the [alpha] isomer, the three [Mo2] units are oriented in two orthogonal directions.

Dinickel(II) complexes of the ligands N,N'-di-p-anisylformamidinate (DAniF) and N,N',N'-tripheynlguanidinate (TPG) are synthesized and crystallographically characterized, along with their one-electron oxidized analogues. In both systems, the Ni-Ni distances become shorter by ~0.1 A upon oxidation and it is proposed that this species contains a [Ni.sub.2.sup.6+] core with a single Ni-Ni sigma bond.

Electrochemical studies are provided that show how strongly the bicyclic hpp ligand stabilizes high oxidation states in dimetal units and a comparison of the PES of W(sub 2)(O(sub 2-)CCH(sub 3))(sub 4), W(sub 2)(diphenylformamidinate)(sub 4), and W(sub 2)(hpp)(sub 4). This shows that the metal-metal bonding orbitals are destabilized by axial ligands, which accounts for significant variations in the W-W distances.

The reactions of Pd(sub3)(OAc)(sub 6) with lithium salts of mononegative bidentate N,N-ligands, L, of various types are investigated in a search for ways to obtain Pd(sub 2)(super 4+) compounds that could serve as precursors to paddlewheel complexes with a metal-metal bond and a Pd(sub 2)(super 5+)core. The reactions are found to be complex and that either square planar mononuclear or dinuclear species might form depending on the reaction conditions or the method of isolation.

Linkage isomers bridged oxamidate dianions are used for modifying electronic communication in dimolybdenum units. The results suggest that the pi interaction over the entire fused bicyclic chelating ring could be responsible for the metal-metal interaction and also indicates the presence of a strong electronic communication between the two linked dimetal units.

We report a class of molecules with extremely low ionization enthalpies, one member of which has been determined to have a gas-phase ionization energy (onset, 3.51 electron volts) lower than that of the cesium atom (which has the lowest gas-phase ionization energy of the elements) or of any other known closed-shell molecule or neutral transient species reported. The molecules are dimetal complexes with the general formula [M.sub.2][(hpp).sub.4] (where N is Cr, Mo, or W, and hpp is the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine), structurally characterized in the solid state, spectroscopically characterized in the gas phase, and modeled with theoretical computations. The low-energy ionization of each molecule corresponds to the removal of an electron from the delta bonding orbital of the quadruple metal-metal bond, and a strong interaction of this orbital with a filled orbital on the hpp ligands largely accounts for the low ionization energies., The phenomena of oxidation (electron loss) and reduction (electron gain) are fundamental to chemistry. Even when these processes do not occur as such, more complex chemical processes and properties, such [...]

Research has been conducted on the (Bu (super)n (sub)4 N) (sub)2 H (sub)2{Mo (sub)2[Mo(CO) (sub)4 (PhPO (sub)2) (sub)2](sub)2}. The study of this compound has been carried out and the results indicate that hydrogen atoms are not present in in this formula.

Research has been conducted on the dirhodium(II) tetra(trifuoroacetate) metal complexes. The reactions of these complexes with the N-donor ligands have been investigated and the results indicate that these reactions produce supramolecular assemblies of differing complexity.

Research has been conducted on the molybdenum to molybdenum quadruple bonds. The deviations of the bonds' lengths from the main body of results has been investigated and the details are presented.

Within the broad field called 'supramolecular chemistry,' there is a sector that is based on the use of metal atoms or ions as key elements in promoting the assembly and dictating the main structural features of the supramolecular products. Considerable success has been achieved by using M--M bonded dimetal entities in this role. Metal-metal bonded cationic complexes of the [[[M.sub.2][(DAniF).sub.n][(MeCN).sub.8-2n]].sup.(4-n)+] type, where M = Mo or Rh and DAniF is an N,N'-di-p-anisylformamidinate anion, have been used as subunit precursors and then linked by various equatorial and axial bridging groups such as polycarboxylate anions, polypyridyls, and polynitriles. Characterization of the products by single-crystal x-ray diffraction, cyclic voltammetry, differential pulse voltammetry, NMR, and other spectroscopic techniques has revealed the presence of discrete tetranuclear (pairs or loops), hexanuclear (triangles), octanuclear (squares), and dodecanuclear (cages) species and one-, two-, or three-dimensional molecular nanotubes. These compounds display a rich electrochemical behavior that is affected by the nature of the linkers.

Research has been conducted on the dimolybdenum tetracarboxylato cations. The preparation and structural characterization of these compounds are described.

The author reviews some developments in the transition metal organometallic chemistry emphasising the areas to which the author has contributed himself. The topics of interest include fluxional organometallics, fluxional metal carbonyls and the agostic hydrogen atoms.

Research has been conducted on the localized oxidation of the chromium atoms. The example of such an oxidation where the Cr (sub)2 (super)4+ starting compound and the resulting cationic product have been structurally characterized is described.

Research has been conducted on the dirhenium(III) non-metal-bonded edge-sharing complex. The reduction and oxidation rates of this complex have been investigated and the results are reported.

Research has been conducted on the compounds with the metal-metal bonded Mo (sub)2 (super)4+ and Rh (sub)2 (super)4+ units. The description of these compounds with the units the midpoints of which occupy the vertexes of an octahedron is reported and the results of their study indicate that these units are linked together by the trimesic acid tricarboxylate anions.

Research has been conducted on the molecular loop [Rh (sub)2 (cis-DAniF) (sub)2 (CH (sub)3 CN)] (sub)2 (malonato) (sub)2. The reaction of this loop with the equivalent of 2,2',3,3',5,5',6,6'-octafluoro-4,4'-biphenyldinitrile which produces a liner tubular structure with Rh-Rh distances has been investigated and the results are presented.

Research has been conducted on the monoanion and dianion of 2,6-bis(phenylamino)pyridine. Results indicate that the monoanion supports quadruply bonded Cr (sub)2 (super)4+ and Mo (sub)2 (super)4+ units in Cr (sub)2 (HBPAP) (sub)4 and Mo (sub)2 (HBPAP) (sub)4, and that the dianion stabilizes the trinuclear complexes.

The structural and magnetic behavior of a greater range of solvated crystals of Co(sub 3)(dpa)(sub 4)Cl2, including the temperature dependences of both structures and magnetism are determined. The magnetic susceptibility measurements from 1.8 to 350 K indicate in each case that a gradual spin crossover, from a doublet to a quartet state, occurs over this temperature range.

The preparation and characterization of the three new linear compounds of the type Co3(dpa)(sub 4)X(sub 2) in which X = NCS-, CN- and N(CN)(sub 2)(super -) are reported. For all the compounds, the magnetic behavior is quite similar and as the temperature increases, the effective moments increase gradually, but since saturation is not reached, even at 400 K, the high-spin state cannot be assigned.

The twelve compounds containing two quadruply bonded Mo2(DAniF)(sub 3) (DAniF = N,N'-di-anisylformamidinate) units linked by dicarboxylate anions are prepared in high purity and good yields and these compounds are characterized by crystallography and NMR. The dinuclear pairs display electrochemical behavior that is controlled by the nature of the bridging dicarboxylate group.

The compound W2Cl4(4-Bu(super t)C5H4N)4 is synthesized and obtained in several crystalline forms. The existence of other rational conformers for W(sub 2)(super 4+) complexes with alkyl-substituted pyridines is checked as D(sub 2d) is the only isomer that is considered favorable for steric reasons for quadruply bonded ditungsten compounds of the type W2X4L4.

A study of the paddlewheel complexes with Ir(sub 2)(super 5+) cores having an unpaired electron are prepared by reacting (COD)Ir(super 1)(DArF)(sub 2)Ir(super III)(CF3CO2)(sub 2)(H2O) with two molar equivalents of HDArF (DArF = N,N'-diarylformamidinate, Ar = p-anisyl and p-chlorophenyl, and COD = 1,5-cyclooctadiene). The results show that in the presence of CH2Cl2, the corresponding Ir(sub 2)(mu-DArF)(sub 4)(n(super 1)-O2CCF3).2CH2Cl2 compounds are isolated in ca. 50% yield.

A study of the preparation and characterization of ionic compounds containing linear or zigzag chains of copper ions and linear tetracopper chain cation in [Cu4(DPhIP)(sub 4)][CuCl2](sub 2) is presented. The results show that the dimagnetic nature of the compound, molecular orbital calculations indicate that no direct Cu-Cu bonds are present, instead the bridging ligand effects a strong coupling of the spins.

Two crystalline forms of Di(2-pyridyl)amide (dpa),[Co(sub 3)(dpa)(sub- 4)(CH(sub 3)CN][PF(sub 6)](sub 2) are obtained from the same solution. Chiral crystals of both Delta and Alfa configurations have been isolated and determined by X-ray crystallography and their mirror-image circular dichroism spectra measured.

The series of M(sub 2)(hpp)(sub 4)Cl(sub 2) complexes from M = W to M = Pt have been completed by preparation and characterization of those with M = W, Os, and Pt. W(sub 2)-(hpp)(sub 4)Cl(sub 2) has a W - W distance of 2.250(2) angstrom and is diamagnetic. Os(sub 2)(hpp)(sub 4)Cl(sub 2) has an Os - Os distance of 2.379(2) angstrom and displays small temperature independent paramagnetism while Pt(sub 2)(hpp)(sub 4)Cl(sub 2) has a Pt - Pt distance of 2.440(1) angstrom and is diamagnetic.

The series of M(sub 2)(hpp)(sub 4)Cl(sub 2) complexes from M = W to M = Pt are completed by preparation and characterization of those with M = W, Os, and Pt. W(sub 2)-(hpp)(sub 4)Cl(sub 2) has a W - W distance of 2.250(2) angstrom and is diamagnetic. Os(sub 2)(hpp)(sub 4)Cl(sub 2) has an Os - Os distance of 2.379(2) angstrom and displays small temperature independent paramagnetism while Pt(sub 2)(hpp)(sub 4)Cl(sub 2) has a Pt - Pt distance of 2.440(1) angstrom and is diamagnetic.

Research presents a novel solventless synthesis technique for synthesizing complexes of dirhodium(II) tetra(trifluoroacetate) using demethyl sulfoxide. Crystal structure analysis reveals that dimethyl sulfoxide ligands enter into various bridging mode configurations through sulfur and oxygen atoms to attach to the dirhodium complexes as shown by crystal structure analysis.

In the formation of molecules complexed with three or more metal atoms, two methods are employed following all-in-one fell swoop or step-by-step strategy. Data point out that in the formation of dichromium and dimolybdenum compounds associated with copper(I) atoms, step-by-step strategy is useful.

Research has been conducted on the compounds containing Cr (sub)3 (dipyridylamide) (sub)4 (super)2+ cores. The preparation of the compounds and their magnetic properties are discussed.

Research has been conducted on the quadruply bonded dimolybdenum(II,II) complexes. The substitution reaction of primary amines by tertiary phosphines is analyzed.

Research has been conducted on the solutions of Co (sub)3 (dpa) (sub)4 Cl (sub)2. The results of the NMR study are examined.

Research has been conducted on the electrolytic behavior of the dinuclear platinum complexes. Electrochemically irreversible oxidation and reduction process have been studied.

The authors describe the structure that can arise when the stoichiometry is Rh (sub)2 (O (sub)2 CCF (sub)3) (sub)4 L, and L is a tetrahydrofuran containing only one donor atom. Experiments indicate a crystal structure of the compound.

A study concerning preparation of quadruply bonded dimolybdenum complexes with alkyl-substituted pyridines is presented. X-ray diffraction has been used to examine crystalline structure of different compounds.

The isolation of various new paramagnetic dirhenium(II,III) anions of the formula (Re2Cl6P2)- (P2 = (PPr(super n)3)2, (PEt2Ph)2, dppp)) was conducted in the form of their tetrabutylammonium salts as the kinetic products in the reactions of (Re2Cl8)2- with an appropriate phosphine ligand. Characterization of all three complexes was done in solution by cyclic vovltammetry, electron spin resonance and mass spectrometry.Results show that a compound of the (Re2Cl6(PR3)2 stoichiometry can crystallize not only as the well-known centrosymmetric C(sub 2h) isomer, but also as the noncentrosymmetric C2 isomer.

Research was conducted to examine the remarkable influence of axial pi* coordination on the Cr-Cr quadruple bond in dichromium paddlewheel complexes. The study focused on new, definitive examples that demonstrate how donation of electrons to the pi* orbitals can weaken and lengthen the Cr-Cr bond. Results indicate that the cumulative effect of donation from four nitrogen atoms is very large, which is 0.4 angstrom in the Cr-Cr distance.

Evidences were presented which show that solvent is a reducing agent. Analysis reveals that one-electron reduction of [Re2Cl8]2- under mild environment can still occur even in the presence of PEt3 and PPrn3 provided that propanol is used as the reaction medium. On the other hand, a disproportionation process instead of reduction was noted in the case of benzene for the same phosphine ligands. The occurrence of an intermediate complex in the course of disproportionation reactions was observed in the solution being studied.

Research was conducted to examine the molecular structures of Mo2Cl4(NH2R)4, where R = Pr(super n), Bu(super t) and Cy. The four new complexes were prepared and characterized using infrared, UV-vis, 1H NMR spectroscopy and single-crystal X-ray diffraction methodologies. Results suggest that the newly-synthesized dimolybdenum complex Mo2Cl4(NHET2)4 can act effectively as a starting material for exploring the chemistry of the Mo(sub 2)(super 4+) core.

The first chromium(II) compound with a regular structure of type III, in which X = Cl and L = THF was synthesized and its structure characterized. The crystal structure of (Cr4(mu4-O)(mu-Cl)6(THF)4) showed an oxygen atom coordinated to four chromium atoms and located in the center of a nearly regular tetrahedron. The Cr***Cr distances were almost equal but long. The Cr-O distances were all ca. 1.96 angstroms. Each chromium atom was bound to the central oxygen atom, to three bridging chlorine atoms and to one THF molecule, providing a slightly distorted trigonal bipyramidal coordination to each metal atom.

Chromium compounds with variously fluorinated formamidinate ligands have been synthesized to study the behavior of the Cr-Cr multiple bond to donor capacity of the ligand by varying the substituents of the aromatic rings. The reactions were performed with standard Schlenk or drybox methods under an atmosphere of nitrogen. Results indicate that the fluorine atoms at one or both ortho positions elongate the Cr-Cr bonds because the atoms interact axially with the chromium atoms. It has also been observed that the Cr-Cr quadruple bond lengths are very sensitive to the axial ligands.

Compounds of the stoichiometry Mo2Cl4(phosphine)4 are created by allowing the Mo2Cl4(NHEt2)4 complex to undergo facile substitution reactions of the amine ligands with bidentate and monodentate phosphines. The phosphine compounds formed include those with PMe3, PMe2Ph, PHEt2, dmpm and dmpe. One of these, the quadruply-bonded Mo2Cl4(eta1-dmpm)4, is the first crystallographically characterized member of the M2X4L4 class of compounds.

Research was conducted to examine new methods of making doublets into cyclic quartets. Two new dinuclear metal-metal multiple bonded species were combined to derive cyclic tetranuclear products or quartets. The first type had pairs of quadruply bonded Mo(sub 2)(super 4+) units linked by two bridging ions while the second had Mo2(DArF)2 subunits united by four bridging ions.

The interaction between diethylphosphine and octachlorodirhenium anions was investigated. Novel structures with diethylphosphido-bridges and terminal diethylphosphines were obtained. Experimental results showed that the interaction between diethylphosphine and octachlorodirhenium anions is strongly dependent on reaction conditions, including the amount of phosphine and the nature of the solvent. Mild reaction conditions result in the coordination of PEt2H molecules as neutral terminal ligands, found cis to each other at Re(III) and Re(II) centers.

A study was conducted to extend an investigation of the molybdenum(III) [Mo(III)] species with amines. Specifically the experiment focused on the reaction of Mo(III) with diethylamine NHEt2 at room temperature, which resulted in the isolation of a new dimolybdenum(II) complex Mo2Cl4(NHEt2)4 that features a quadruple bond between the metal atoms. The synthesis of this new complex and some other products of the complex reactions between Mo(III) and amines are discussed.

The novel BH3-bridged ditantalum complex Ta2(mu-BH3)(mu-dmpm)3(nano2- BH4)2 (1) and the acid-base adduct dmpm(BH3)2 (2) were synthesized through the reduction of TaCl5 with LiBH4 in the presence of bidentate ligand bis(dimethylphosphino)methane (dmpm). In the compound 1, the tantalum atom was found to have a formal oxidation state of +1. This compound had a mu-BH3 group bridging the ditantalum metal centers symmetrically to give a metallaborane complex. The Ta2BH3 core in 1 can be formulated as a arachno-tantalaborane with a Ta=Ta double bond.