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The synthesis and characterization of neutral heteroleptic molecular iridium(III) complexes with (2,4-difluoro)phenylpyridine and different pyridine-1,2,4-triazole ligands are described. The studies have shown high external quantum efficiencies and color points better than the standard for blue iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,[C.sup.2]]picolinate.

The synthesis and photophysics properties of new homocysteine-selective sensor based on the iridium(III) complex are described. The studies have shown that the complex can selectively recognize homocysteine over other amino acids and thiol-related peptides through a color change.

The studies about the photophysical and electrochemical properties of [Ir[(ppy or pq).sub.2] (substituted-1,10-phenanthroline)]-[P[F.sub.6]] (ppy = 2-phenypyridine, pq = 2-phenylquinoline) is presented. The results provide insight into nature and number of the phenanthroline substituents to tune the color, quantum yield, and lifetime of the emission.

The roles of carboxylato and sulfonamido ligands is made clear by a comparative synthetic, structural and thermodynamic study of coordinatively unsaturated chelate complexes, which are monomeric in solution and in the solid states. However, the oxalato complex exists as a 'n' oligomer or polymer that serves as a versatile precursor to monomeric adducts 6-L.

Research has been conducted on the bis(mu-chloro)tetracarbonyldirhodium(I) and chlorotricarbonyliridium(I). The reactions of these compounds in conjugate Bronsted-Lewis superacid and in CO atmosphere are described.

Research has been conducted on the iridium(III) nitrosyl complex. Reactions of the complex with hydrosulfide and arenethiolate anions have been investigated.

Research has been conducted on the Rh-Te and Ir-Te binary systems. The use of Huckel calculations in investigating the systems' differences in phase and structure at low temperatures is described.

The article discusses synthesis of different iridium carboxamides that are analogous to intermediates in metal-catalyzed nitrile hydration reactions. Experiments include generation of these carboxamides by addition of Cp (super)* (PMe (sub)3)IrPh(OH) to RCN.

A study was conducted to determine the liquid crystal and nonlinear optical properties of rhodium (I) and iridium (I) complexes containing beta-diketonate or pyrazole ligands. X-ray single-crystal diffraction analysis show that some beta-diketonate compounds have two different polymorphs at the solid state. It was also found that the color and infrared spectra of the solid forms seem to be influenced by a different intermetallic-packing arrangement in the metal centers.

Research was conducted to examine the synthesis of cationic dinuclear hydrido complexes of ruthenium, rhodium, and iridium with bridging thiolato ligands and their reactions with nitrosobenzene. X-ray diffraction studies of the molecular structures of the three nitrosobenzene complexes showed that in each case, nitrosobenzene serves as a mu-eta(super 1):eta(super 1)-N,O ligand. The unpaired electron is considered to be located mainly on the nitrosobenzene ligand in the diruthenium and dirhodium complexes.

Research was conducted to examine the spectroscopic characterization of the cyclometalated complex (IrH(dppf(-H))(dppf))+ that results from the intramolecular oxidative addition of the ortho C-H bond of the phenyl substituents in 1,1'-bis(diphenylphosphino)ferrocene (dppf)(Ir(dppf)2)+. Results provide a rade example of compounds in which the same set of ligands appears to sustain the metal in four different oxidation states. Findings also provide the opportunity to investigate the structural changes of the (IrP4)(super n) moiety on changing the charge of the complex (n = +1, 0, -1).

Research was conducted to examine the synthesis of several functionalized polypyridine ligands and of five new Ir(III) cyclometalated derivatives as well as the absorption spectra, luminescence properties and the redox behavior of the new metal complexes. The ligands present a bidentate 6-phenyl-2,2'-bipyridine framework substituted in the 4'-position with a phenyl ring having different para X substituents. Results suggest that the complexes may be considered as useful building blocks for light- and redox-active, multicomponent supramolecular systems.

A study is conducted on the rhodium(I) and iridium(I) chloride complexes of a tris(phosphinine). The SiMe2-linked tris(phosphinine) reacts with (M(COD)Cl)2 (M = Rh, Ir) to yield the complexes Rh(tris(phosphinine)) and Ir(tris(phosphinine)). Results show that the crystal structure of Rh(tris(phosphinine)) features a highly twisted geometry of (tris(phosphinine)) around the rhodium center. Abstraction of the chloride ligands with AgOtf in the presence of CH3CN also forms corresponding cationic complexes.

The facile decapping of a heptanuclear rhenium-iridium carbido carbonyl cluster and the capping reactions of the cluster with (triphenylphosphine)gold(I) derivatives are described. Both monogold and digold derivatives are formed with the addition of [AuP-Ph3]+ caps to the trianion. While the digold complex exhibits only one structure in both the solid and liquid states, several isomers of the monogold complex are seen in the solution.

Reaction of the monodeprotonated silaborate with the respective pentamethylcyclopentadienyl transition metal chloride allows the synthesis of the sandwich anions [(eta-5-C5Me5)M(MeSiB10H10)]-(M = Co, Rh, Ir). The thermal reaction between a substituted derivative of the carba-nido-undecaborane, derived from bis(trimethylsilyl)acetylene and decarborane(14), and CpCo(Co)2 produces a mixture of two sandwich complexes. The transition metal adopts an 18-electron configuration in the sandwich complex.

The solvent exchange process for (eta5-C5Me5)M(S)3]2+ (M = Rh, S = MeCN) was found to proceed via a dissociative mechanism. Intermolecular exchange with free Me2SO on (eta5-C5Me5)M(S)3]2+ (S = Me2SO) takes place exclusively from a conformational isomer which is in equilibrium with a second, more compact conformer. The rate constants associated with the solvent exchange process on the half-sandwich species were shown to be governed primarily by electronic properties of the ligands.

The electronic influence of an ancillary ligand on metal-diazenido bonding induces a facile rearrangement of an aryldiazenido ligand from a singly-bent to a bridging geometry. This was demonstrated when the strong pi-base ligands I-, Br- and Cp*Ir(CO)2 were separately reacted with the complex ((eta5-C5Me5)Ir(C2H5)(p-N2C6H4OMe))(BF4) to replace its ethylene ligand. The reactions afforded the diiridium complexes ((eta5-C5Me5)IrX)2(mu-eta2-p-N2C6H4OMe)(mu-eta1-p-N2C6H4OMe) where X = I,Br and (((eta5-C6Me5)Ir(CO))2(mu-eta2-p-N2C6H4OMe))(BF4).

Suitable reactions in sealed Nb tubing at 850-950 degrees C produced good yields of a family of oligomeric cluster phases that were characterized by single-crystal X-ray diffraction methods. The basic Y16Z4 units can be obtained from 2+2 condensation of centered Y6Br12Z-type clusters or as tetracapped truncated tetrahedra Y16 that are centered by a large tetrahedral Z4. These are surrounded by 36 bromine atoms which bridge edges or cap faces of the Y16Z4 nuclei and, in part, bridge to metal atoms in other clusters.

The trimetallic complexes of the form (((bpy)2Ru(bpm))2MCl2)5+, where M=Rh(III) or Ir(III), are synthesized and characterized to determine the ability of bpm to act as a bridging ligand in this structural motif. These systems also demonstrate how central metal variation can be employed to tune the characteristics of these complexes. These systems are interesting because the have catalytically active Ir or Rh metal centers covalently connected to two light-absorbing ruthenium chromophores, forming the core of a molecular device for photoinitiated electron collection.

The iridium and ruthenium complexes are reacted with poly(pyrazol)borato complexes to form heterodinuclear species with Co and Ni. The reaction is performed to investigate the coordination capacity of the iridium and ruthenium anions as tridentate ligands. New heterodinuclear complexes with pyrazolate and other mononegative bridging ligands are prepared and their molecular structures reported.

Simple syntheses of dinuclear complexes are provided by protonation of the methoxo groups in M(mu-OMe)(diolefin) 2 (M = Rh, Ir) with acidic proton-bearing binucleating ligands. Py(SH)2 reacts with (Rh mu-OMe cod )2 (cod = 1,5-cyclooctadiene) to form Rh4(mu-PyS2)2(cod)4, 1. Analogous preparations also give the diolefin rhodium complexes Rh4(mu-PyS2)2(nbd)4, 2, and Rh4(mu-PyS2)2(tfbb)4, 3, (nbd = norborna-2,5-diene, tfbb = tetrafluorobenzo 5,6 bicyclo 2.2.2 octa-2,5,7-triene). 1 is a tetranuclear complex with two 2,6-pyridinethiolate groups linking four metal centers.

The synthesis and characterization of phosphino alkylsilanes in which Si is connected to P through a three-carbon framework that incorporates a planar benzenoid unit are described. The complexes were used as precursors to chelate ligand systems to transition metal centers, attaching through a silicon-metal bond supported by intramolecular phosphorus-metal bonds.

The synthesis and characterization of the novel complex hydridophenyl(hydrotris 3,5-dimethylpyrazolyl borato)(trimethyl phosphite)iridium are described. The scheme involves the photolysis of benzene solutions of (hydrotris 3,5-dimethylpyrazolyl borato)IrH2(Z-cyclooctene) in the presence of P(OMe)3. The reaction occurs with the initial loss of cyclooctene. The C-H activation of benzene is also shown to occur at the coordinatively unsaturated iridium(III) intermediate.

The intermolecular NH...H(Ir)...HN interactions of IrH(2-thiazolidinethione)4(PCy3) (BF4)2 were examined in both the solution and crystalline states. The results showed a novel four-membering ring formed by the hydrogen bonds between the NH groups and a fluorine of BF(sub 4)(super -). Intramolecular NH...Ir interactions have also been observed in the complexes Ir(H)2(PCy3)2(L)2 (BF4) for L = 2-thiazolidinethione and 2-benzothiazolethione.

The carbon monoxide addition to iridium(III) fluorosulfate and subsequent evaporation resulted to the crystal formation of mer-Ir(CO)3(SO3F)3. Its molecular structure has an octahedral coordination about the iridium atom with a meridional stereochemistry. The extramolecular C-O interaction molecule connections resulted to an extended three-dimensional structure. The molecular structure also showed significantly reduced pi-back donation. Vibrational spectra of the crystal recorded extensive band splitting in the 1000-800 cm region.

The reactions between C60O and Vaska type iridium complexes were examined. The results showed that reaction with Ir(CO)Cl P(C6H5)3(sub 2) has resulted in partial deoxygenation of the fullerene epoxide. Reaction with Ir(CO)Cl As(C6H5)3(sub 2) has resulted in the formation of crystalline (mu2-C60O)Ir(CO)Cl(AsPh3)2.482C6H6-0.18CHCl3 with the oxygen atom disordered over four positions.

Analysis of the electrocatalysis of iridium porphyrins through a study of the reduction of dioxygen by these porphyrins to water suggests the involvement of a four-electron pathway in electrocatalysis. The most important criteria for catalytic reduction is the axial ligation to the iridium from the edge plane graphite electrode.

Variable-temperature NMR experiments help evaluate the enthalpy and entropy changes associated with the formation of few iridum-dihydrogen complexes. T1 relaxation times of few complexes are determined by the inversion-recovery method. Analysis of spectral data and T helps evaluate the rate of H2 dissociation from these complexes, and enthalpy and entropy changes a associated with the dissociation. Increases in H-H bond length in the H2 ligand decreases the rate of H2 loss. Ir-H2 bond strengths controls the enthalpy changes.

Synthesis of Ir(II)Pd(II)Ir(II) and Ir(III)Pd(II)Ir(III) complexes involves oxidative stepwise addition reactions of trinuclear heterobridged iridium complexes with electrophilic reagents. These syntheses involve formation of metal-metal bonds and their subsequent cleavage. X-ray studies of ((Ir(mu-pz)(mu-S(t)Bu)I2(CO)(P(OMe)3))2Pd) reveal that trans addition of iodide atoms occurs at two distinct metallic centers and X-ray data support the flexibility of the pyrazolate-2-methyl-2-propanethiolate bridges.

Reaction of Vaska-type iridium complexes with C60 results in two double addition products. X-ray crystallographic studies show that the added groups have 'para' orientation. Spectroscopic studies reveal the elongation of the fullerene along the Ir-Ir axis. 31P(1H) NMR analysis indicates the dissociation of adducts at room temperature, resulting in the formation of regioisomers. These para regioisomers are preferentially crystallized due to their low solubility in benzene.

Trace amounts of Cu2+ and Fe2+ catalyze the outer-sphere electron-transfer oxidation of NH2OH by (IrCl6)2- in aqueous solution. Addition of an inhibitor C2O4(2-) inhibits the catalysis, and the rate law is of the first order with respect to each reactant in the presence of the inhibitor. The first step in the oxidation is the formation of NH2OH+, and major structural changes accompanying oxidation lead to a large reorganizational energy. Marcus cross relationship helps determine the self-exchange rate constant for the NH2OH+/NH2OH redox couple.

Examination of the substituent effects in Vaska-type complexes trans-IrL2(CO)X (X = substituent) by ab initio molecular orbital study reveals that electron affinity and ionization potential of the complex increase on moving down the halogen series, complexes with more electronegative halogens undergoing oxidation more easily. Carbonyl stretch frequencies predicted by ab initio studies are greater than experimental values. Ab initio calculations accurately predict the influence of electronic effects of L (L = PH3, NH3 or AsH3) and X on the thermodynamics of H2 dissociative addition.

One equiv of tBuLi deprotonates the bridging amido ligands in Ir2(mu-NH(p-tolyl))2(CO)4, producing a monoanionic mu-amido/mu-imido complex and the addition of another equiv of tBuLi leads to a second deprotonation, generating a dianionic bis(mu-imido) complex of iridium(I). Spectroscopic studies help characterize both monoanionic and dianionic complexes. Solubility and reactivity of the complexes indicate strong cation-anion interaction at the imido nitrogens. Below zero degree Celsius, the dianionic complex exhibits separate 7Li signals, suggesting two unequal lithium ions. The dianionic complex reacts with (PPh3) AuCl, generating a tetranuclear complex.

A new approach involving early transmission microscopic, catalyst isolation, kinetic and quantitative phenomenological studies helps differentiate homogeneous catalysis from heterogeneous catalysis. Application of this approach to the cyclohexene hydrogenation catalyst derived from the polyoxoanion-supported Ir complex reveals the involvement of polyoxoanion/Bu4N+Ir-190-450 nanoclusters as the hybrid homogeneous/heterogeneous catalysts.

Reaction of (IrCl(CO)(PPh3)2) with ligands L(sub s2cx)(super -) and L(sub s2n)(super -), having two sulfur atoms directly linked to the carbon atoms of 7, 8-dicarbenide-undecarborate (1-), in the presence of AgNO3 produces two stable metal complexes. Nature of the S,S' connecting chain influences the reaction of these species with O2. Complexes with a short chain ligand decompose on reaction with O2 while those with a noncyclic ligand form addition complexes. Complexes having seven or eight chain atoms exhibit no reaction with O2.

IrCl(CO)(PPh3)2 reacts with (K)(ReH6(PPh3)2) to form a rhenium-iridium polyhydride complex. NMR and x-ray analyses help the structural characterization of the complex. HBF4.OMe2 reacts with the complex to produce another complex separated as its tetraphenylborate salt, which has a rhenium terminal hydride bond induced by protonation.

IrH5(PPh3)2 reacts with carboxylic acids to produce hydridoiridium complexes of the type IrH2(eta squared-O2CR)(PPh3)2. Analysis of the reactions of these compounds with acetylenedicarboxylic dimethylester and HBF4 shows the alkylene insertion into one of two Ir-H bonds of the starting complexes, leading to the formation of hydrido-vinyl complexes. X-ray analysis helps the structural elucidation of a hydrido-bridged dinuclear complex (Ir2H2(PPh3)4(mu-H)2(mu-eta squared-O2CCH))BF4.

Multinuclear NMR experiments at different temperatures are conducted to analyze the dynamic behavior of (pentamethylcyclopentadienyl)iridium complexes with pyrazole ligands. Argentotropism accounts for the observed properties of these compounds. Heteronuclear coupling constants are related to the structure and dynamic properties of the complex. Line-shape analysis is used to calculate the kinetic parameters.

Analysis of dioxygen and carbon monoxide uptake by Ir(I) complexes, which were stabilized by mixed N, P-donor ligands, revealed a metal cavity that was vital to the metal's interaction with small molecules. Certain Ir(I) complexes were observed to bind to carbon monoxide and dioxygen at low temperature. This binding is attributed to the steric hindrance of the ligands.

A generalized synthesis scheme yields facial tris cyclometalated Rh3+ and Ir3+ complexes using the room-temperature chemical formula, C27H18N3S3Ir. Absorption and luminescence spectroscopy analyze the excited state properties of the complexes. Short luminescence decay times prove the mixing of charge-transfer property in the 3pi-pi excited states.

The action of silver trifluoromethanesulfonate (OTf) on a CH3OH/CH2Cl2 mixture of (Ir(L)2Cl2), where L is ppy or ptpy, yields cyclometalated Ir(III) complexes of the type Ir(L)2(S)2(OTf). The H NMR spectra of the Ir(III) complexes have either six or seven aromatic domain signals due to resonance overlapping. The absorption spectra reveals a sharp band between 300 and 390 nanometers that overlaps a weaker band in the region between 422 and 426 nanometers.

Synthesis and characterization of a Keggin polyoxoanion-supported Ir(1,5-COD)+ complex, (Bu4N)4Na2((1,5-COD)Ir. SiW9Nb3O40) set the stage for a comparison of the catalytic action of existing Keggin-type SiW9Nb3O(sub 40)(super 7-) and the Wells-Dawson-type P2W15Nb3O(sub 62)(super 9-) polyoxoanion-supported Ir(1,5-COD)+ complexes. Oxygen links Ir(1, 5-COD)+ moiety to SiW9Nb3O40.

A study on mixed ligand cyclometalated Ir+3 complexes is presented, including the synthesis of (Ir(thpy)2bpy)+. The lowest energy excited states were characterized using high-resolution optical spectroscopy. Results showed that lowest C and D energy states were localized in the cyclometalating thpy- ligands. The first excited states C and D had more CT character in (Ir(thpy)2bpy)+ than in the (Rh(thpy)2bpy)+ complex. Luminescence in the Ir complex had a typical shape and Stokes shift of a charge-transfer band, as well as a red shift in crsytal spectra.

The absorption, excitation and luminescence spectra of (Ir(ppy)2bpy)+ (ppyH = 2-phenylpyridine, bpy = 2,2'-bipyridine) in various media are reported. Ligand centered transitions at high energy were found to lead to reversals in the order of lowest excited LC and MLCT states. The emitting state of (Ir(ppy)2bpy)+ was described in two ways: as a ligand-centered state if analyzed on the basis of band shape, and in terms of a charge-transfer character if analysis is based on polarization, intensity, lifetime, and zero-field splitting.

The preparation of mixed Langmuir-Blodgett films containing neutral hydrophobic iridium(III) complexes and their spectroscopic properties are reported. The area occupied by the Ir(ppy)3 molecule was calculated as 55 Angstrom. UV-Vis absorption was significant and directly proportional to the number of layers deposited on the substrate. Emission spectra at room temperature and in a rigid glassy solution showed a blue shift as the concentration of the complex in the matrix decreased. Solvent change had no effect on the emission peak.

The displacement of cyclooctaniene from 99cod (M(mu-Cl))2 by dfepe results in quantitative yield of the complex (fluoroalkyl)phosphine complex (dfepe)M(mu-Cl)2 where dfepe = (C2F5)2PCH2CH2P(C2F5)2; M = Rh or Ir. X-ray diffraction data shows that both analogues are isomorphous having identical M2(mu-Cl)2 dihedral angles of 120 degrees. Chemical analyses also show that both the iridium and rhodium complexes have high thermal stability and forms no oxidative addition products with H2, O2 or alkyl halides.

The syntheses and spectroscopic, electrochemical and spectroelectrochemical properties of ((tpy)Ru(tpp)IrCl3)2+ (tpy = 2,2':6',2'-terpyridine; tpp = 2,3,5,6-tetrakis(2-pyridyl)pyrazine), (Ir(tpp)Cl3) and (Ru(tpy)(tpp))2+ were reported. Electronic absorption spectra and electrogeneration of different oxidation states were performed. Emission spectrum analysis revealed a lower metal-to-ligand charge-transfer energy for the ruthenium system compared to that for iridium complexes.

The electronic absorption spectra and emission lifetimes of Ir2(mu-L)2(CO)4, where L = pyrazolyl, 3-methylpyrazolyl and 3,5-dimethylpyrazolyl, were determined at the temperature range of 77 to 300 degrees K. The electronic absorption spectra of the complexes are similar to those of analogues with two to four of the CO ligands replaced by phosphines or alkenes. The band shifts were in the order of Ir2(mu-3,5-Me2pz)2(CO)4 < Ir2(mu-3-Mepz)2(CO)4 < Ir2(mu-pz)2(CO)4. Moreover, emissions at 77 and 300 degrees K showed shifts much smaller than the corresponding absorption bands.

The mechanism of the oxidative addition of halogen gases (Cl2, I2) to trans-(IrCl(CO)(dppm))2 is is described. A structure for the chlorine analog is suggested base on the spectral data showing that it has both cis Cl and CO ligands and exibits bands for two terminal carbonyl groups. The derivatization and the characterization of the iodine analog are also discussed.

The iridium-gold hydride (triphos Ir H C2H4 Au PPh3)PF6 was prepared from the reaction of (Au THF PPh3)PF6 with a THf solution of (triphos)Ir(H)(C2H4). The digold adduct (triphos Cl Ir mu-H Au2 PPh3 2)PF6, on the other hand, was produced from AuCl(PPh3) and the hydride. Likewise, (triphos Cl Ir mu-H Au2 AsPh3 2)PF6 was afforded by the substitution of AuCl(AsPPh3) for AuCl(PPh3). (Triphos Cl Ir mu-H Au2 PPh3 2)PF6 possesses a crystal structure with a discrete (triphos Cl Ir mu-H Au2 PPh3 2)1+ cation, a PF6 anion and a clathrated THF molecule.