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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.

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.

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.