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A series of luminescent cyclometalated Ir(III) complexes are synthesized and evaluated for use in unimolecular oxygen-sensing materials. The complexes Ir(C6)(sub 2)(vacac) and mer-Ir(ppy)(sub 2)(vppy) displayed the longest luminescence lifetimes and largest quantum efficiencies in solution making them ideal candidates for future oxygen-sensing studies.

Research has been conducted on the rhenium complexes that contain sterically-hindered ligands. The synthesis and electrochemical properties of these complexes are described.

The synthesis and characterization of the trinuclear manganese complex are described. The scheme involves the Ce(IV) oxidation of a concentrated solution of manganese(II) acetate and 1,10-phenanthroline in 1.6 N nitric acid. The preparation of the complex with water coordination to Mn(IV) centers showed the stabilization of coordinated aqua molecules in the environment of high-valence manganese.

The interaction of half-filled x squared-y squared orbitals on the two metal atoms represents the primary reaction between mu-oxalato complexes ((N)4M(C2O4)M(N)4)(super 2+) with M = Mn, Fe, Co, Ni, Cu and Zn. The five complexes possess six-coordinate metal centers bridged by planar bis-bidentate oxalate groups. The J values for Mn(II), Fe(II), Ni(II) and Co(II) are 2, 6, 10, 2 and 33 per centimeter respectively. The experimental procedure for the synthesis of these metal complexes is discussed.

Ligand (2-pyridyl)bis(2-pyridylamino)methane (LI) reacts with Mn(II) and Fe(II), producing novel Mn(III) and Fe(III) mononuclear complexes, while L1 reacts with Ni(II) perchlorate in a medium of acetonitrile producing a Ni(II) bis-chelated complex. X-ray crystallographic studies help study the crystal structures of these complexes. Electronic spectrum of Mn(III) complex shows two weak spin-forbidden d-d transitions accounted for by John-Teller effect. Cyclic voltammetric studies show quasi reversible or reversible one-electron oxidation for Mn(III) and Fe(III) complexes. (Ni(L1)2)2+ cation has a pseudoctahedral geometry for nickel center, and magnetic susceptibility studies help examine the spin-system of these complexes.

A synthetic technique helps synthesize a series of binuclear bis(Mu-oxo)dimanganese (III,III), -(III,IV) and -(IV,IV) complexes that contain ligands related to N,N'-bis(2-pyridylmethyl)-1, 2-ethanediamine. X-ray crystallographic studies help study the structures of these complexes. Magnetic susceptibility and EPR studies reveal the difficulty in preparing pure (III,III) and (IV,IV) complexes without (III,IV) and/or Mn(II) impurities.

The hexadentate ligand, 1,10-bis(2-pyridylmethyl)-1,4,7,10-tetraazadecane reacts with iron(II) and nickel(II) ions to form pseudooctahedral complexes, whereas manganese(II) ions form trigonal prismatic complex. Cyclic voltammetry shows that these complexes form quasi-reversible M(II)/M(III) redox couples. These ligands produce tetranuclear iron(III) complexes in water, having two (mu-oxo)bis(mu-acetate)diiron(III/III) cores.

Synthetic tridentate nitrogen ligands, 2,9-disubstituted phen and pyrazolyl groups, coordinate with nickel(II)chloride hexahydrate to form five- and six-coordinate nickel(II) complexes. Three-dimensional X-ray diffraction methods help in structural characterization and cyclic voltammetry analyzes the redox properties of these compounds. Significant structural changes are observed during transition from one oxidation state to another.

EPR spectroscopic studies validate the existence of dimeric structures in cis-hydroxoaquachromium(III) complexes of tetra- and monodentate ligands. Most of the complexes are strongly antiferromagnetic with triplet energies between 2 and 7 per cm. The chromium(III) core atom is bonded to four ligand-based N atoms and two water- and hydroxo ligand-based cis O atoms.

The synthesis of nitrogen ligand, 2, 9-bis(N-pyrazolylmethyl)-1,10-phen (bpmp), C20H16N6, and the use of three-dimentional X-ray diffraction techniques facilitates the establishing of the structure of the tetrafluoroborate and perchlorate salts of its copper complexes. A reversible wave at 0.037 V vs Ag/AgCl, attributable to the (Cu(bpmp)(H2O))2+/+ couple, is evident in the copper (II) complex.

The reaction of the dithionate form of (Cr A 4 OH H2O) with divalent metal ions resulted in the formation of heteronuclear trinuclear dithionate salts having complex ions of the type (MII Cr A 4 OH 2 )4+. The central divalent metal atom, which was placed between the two paramagnetic chromium molecules, functioned as an effective diamagnetic separator. Reflectance spectra, molecular bondings, structural coordinations and magnetic susceptibility measurements were conducted to further characterize the complexes.

The synthesis, structure and magnetic properties of the trinuclear complex ions Cu(super II) Cr(A)4(OH)2 2 4+ and Cu(super II) Co(A)4(OH)2 2 4+ were reported. The electronic spectra of the perchlorate salt of Cu(OH)2Cr(cyclam)2 4+ was ruled by the two spin-allowed chromium(III) bands. In Cu(OH)2Cr(bispictn)2 (ClO4)4.2H2O bispictn = N,N'-bis(2-pyridylmethyl)-1,3-propanediamine, axial coordination to a perchlorate ion was displayed. In Cu(OH)2Cr(cyclam)2(ClO4)4.4H2O, the copper atom exhibited (4 + 2) axially elongated octahedral geometry.

The synthesis and characterization of M(bispican)2X2 bispicam = bis(2-pyridylmethyl)amine; M = Zn(II), Cd(II), Mn(II) is discussed. The results show although all are facial isomers, the complexes have distinct crystal structures. The manganese complex crystallizes in the space group C2/c with four molecules in a cell. The cadmium complex is isomorphic with the manganese complex. Similarly, the zinc complex lies on site of the C2/c symmetry but with eight molecules in a cell. In addition, there are two crystallographically independent zinc ions in the zinc complex crystals.

The ability of heteroatoms to participate during photooxidations at sulfur is studied by comparing the photooxidation of 1,5-dithiacyclooctane (1,5-DTCO) with those of 1,4-dithiane and pentamethylene sulfide. The photooxidation of 1,5-DTCO differs from those of 1,4-dithiane and pentamethylene sulfide in terms of the large ratio of chemical quenching to total quenching of singlet oxygen, of the nonproduction of sulfone and the large value for the rate constant. It is speculated that these results are due to a new sulfur-sulfur interaction during photooxidation.

IR and NMR studies of the rhenium(V) complex (Re(NPh)(O-bpy)(OEt)(PF6))2 reveal a distorted octahedral structure. The oxygen atom of the ethanolate moiety and nitrogen atom of the imidophenyl group form the axial ligands and the 4 nitrogen atoms from the O-bpy ligand form the equatorial ligands. This complex shows electrochemical reversibility, with a negative redox potential. The bonds between Re and N on the open side are shorter.

Two dinuclear manganese complexes with different Mn-Mn distances, similar to the distances of Mn-Mn in photosystem II oxygen-evolving complex, have been synthesized. Both complexes have (mu-oxo)(mu-acetato)dimanganese(III/III) core and four nitrogen atoms from tetradentate ligands coordinate the manganese atom. Cyclic voltammetry determines the redox properties and magnetic susceptibilities of these complexes.

A monomeric rhenium(V) complex having a multidentate, sterically constrained chelate ligand is prepared. The complex ion has the metal trapped by two aza and two pyridyl nitrogen atoms and two aza and two pyridyl nitrogen atoms are uncoordinated. Bimetallic species with other transition metals are not formed.

Binuclear complex (Cu(C9H19N4O2))2(ClO4)(2).2H2O is synthesized and is found to have O-H-O hydrogen bonds. Structural studies reveal the distorted square planar copper centers. The concepts applicable for lightly bound dimeric systems are applied to these weak hydrogen-bonded binuclear complexes and the studies show accurate results.