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Research is presented describing the synthesis of stable neutral silaaromatic compounds, 2-silanaphthalenes, which were found to have almost as much aromatic character as naphthalene.

One-electron oxidation of Re(II)-Re(II) compounds and one-electron reduction of Re(III)-Re(III) compounds result in compounds containing Re2Cl5(PMe3)3 molecules. The reaction of PhI.Cl2 and Re2Cl4(PMe3)4 creates a crystalline product, 1,3,6-/1,2,7-Re2Cl5(PMe3)3, containing two isomers in its unit cell. The reaction of ((n-Bu)4N)2Re2Cl8 with PMe3 in propanol forms 1,2,7-Re2Cl5(PMe3)3.(n-Bu)4NCl. A dichloromethane solution of this, when heated, gives pure 1,2,7-Re2Cl5(PMe3)3. X-ray crystallographic studies help to disclose the crystal parameters for these compounds.

Electrochemical reduction of a microcrystalline mixture of Bi2SnSe4, SnSe2, and Se, in an electrolyte solution of NEt4Br in ethylenediamine creates the group 15 selenometalate, (NEt4)(BiSe2). Another such compound, (Ge(en)3)(enH)(SbSe4) is the result of reduction of a microcrystalline mixture of Sb2Se3, GeSe2, and Se. X-ray crystallography suggests a rhombohedral structure for (NEt4)(BiSe2) and triclinic structure for (Ge(en)3)(enH)(SbSe4). Unit cell dimensions and other crystallographic parameters have been computed for both the compounds.

Electrochemical reduction of metal-chalcogen alloys in ethylenediamine synthesizes chalcogenometalates. Single crystal X-ray methods and NMR studies help to reveal their crystal structures. (NEt4)2(enH)2(Ge2Se6) crystallizes in the triclinic system, while (NEt4)4(Sn4Se10) is cubic. The (Ge(sub 2)Se(sub 6))(super 4-) anion has a pair of edge-sharing tetrahedra, and the (Sn(sub 4)Se(sub 10))(super 4-) anion has adamantine-type structure. Both the new anions have group 14 structural analogues. Unit cell computations are provided.

Anionic heterobinuclear complexes (NBu4)({C6F5}3Pt{mu-X}Pt{C6F5}3)(X = Cl, OH) are formed by the reaction of (NBu4)(Pt{C6F5}3X) (X = Cl,I) and Pb(ClO4)2.3H2O in CH2Cl2 or by the substitution of the Cl group by OH group. The stability of the compound is due to the Pt-Pb donor-acceptor interactions between the platinate(II) moieties and Pb2+. Single crystal X-ray diffraction is used for determining the structure of the heterobinuclear complexes.

Bridging dinitrogen complex {Mo(CO)(Et2PC2H4PEt2)2}2 (mu-N2) is synthesized by reacting trans-Mo(N2)2(Et2PC2H4PEt2)2 with ethyl acetate. X-ray crystallography reveals a agostic Mo...H-C interaction between the molybdenum atom and an aliphatic gamma-C-H bond of the alkyldiphosphine ligand. The observed interaction is stronger in the nitrogen free compound when compared to the compound involving an ortho-aromatic C-H bond of the diphosphine ligand.

Extended X-ray absorption fine structure (EXAFS) studies are used for determining the crystal structure of iron oxychloride and its alkoxy substituents. The method uses a minimal set of structurally adjustable parameters for getting the detailed long range crystal structure over a range nearly equal to six angstrom. EXAFS analysis of FeOCl and methoxy substituent shows that the local symmetry around the iron becomes greater than that of FeOCl. EXAFS method can be effectively applied to some two-dimensional systems with very poor crystallinity.

Iron-centered (Cp*Co{Et2C2B3H2X})2FeH sandwiches are synthesized and isolated through metal-stacking reactions of Cp*Co(Et2C2B3H2X)- anions with metal halides. These iron-centered sandwiches are converted to Cp*2Co2(Et4C4B6H4X2) (X =Cl,Me), on exposure to silica in air. The geometry of various species is determined by X-ray crystallography. An effort to isolate and characterize iron centered tetradeckers and to establish that they indeed undergo oxidative cage fusion is made.

Trivalent transition metal complexes are formed by the air oxidation of (FeIIL)(ClO4) and (COIIL) (ClO4)2 in acetonitrile in the presence of NEt3. Crystallization of(MnIV {L-3H})BPh4Mn(IV) as determined by X-ray crystallography takes place in orthorhombic space group. The Mn(IV) ion is in a distorted octahedral environment of three facially coordinated tertiary nitrogen donor atoms and three anilido nitrogen donors possessing C3 symmetry.

The hexadentate ligand 1,4,7-tris(o-aminobenzyl)-1,4,7-triazacyclononane (L) forms stable metal complexes of (LM{II})(ClO4)2, where M denotes Mn, Fe, Co, Ni, Cu or Pd, with perchlorate salts of divalent transition metal ions. The dicationic species (ML)2+ has a preference for octahedral over trigonal prismatic coordination due to the steric necessities of the ligand. The ligand forms five coordinate square-based pyramidal polyhedron with Cu and Pd ions, and a six coordinate distorted octahedral polyhedron with Ni ions. The X-ray crystallography determines the crystal structures of the complexes.

The mixed metal carbonl telluride clusters (Phsub4P)sub2[ Fesub2MTesub3(CO)sub11] and Na(Etsub4N)sub2[Fesub3Wsub2Tesub8(TeMe)COsub12] where M = Mo,W are synthesized using mixtures of Fe(CO)sub12, M(CO)sub6 and Nasub2Tesub2 with Phsub4PBr in a sealed pyrex tube. The reaction is carried out metanothermally at 80 degree centigrade. The compound (Ph4P)2{Fe2MTe3(CO)11} crystallizes in monoclinic space group. The compound Na(Et4N)2{Fe3W2Te8(TeMe)CO12} has seven singlets. The hetrometallic cluster {Fe3W2Te8(TeMe)CO12} is a hybrid between {Fe4Te6(TeMe)2CO8}2- and {W6Te8(CO)18}2.

Cp*TiF3 and CpTiF3 with Me3SiOCOCF3 and Me3SiOCOC6F5, respectively, yields the dimers (Cp*TiF2OCOCF3)2 (1) (Cp*TiF2OCOC6F5)2 (2), (CpTiF2OCOCF3)2 (3) and {Cp*TiF(OCOCF3)2}2. X-ray crystallographical study of these dimeric Cp- and Cp*- titanium carboxylates show that compounds 1 and 2 crystallize in the triclinic space group P1. The Ti atoms are bridged by two carboxlate groups and two F atoms having non-equal distances to the Ti atoms. The 19F NMR confirms the presence of dimer structures in solution.

The synthesis of a new copper(II) coordination polymer Cu(sub 2)(oxalate)(sub 2)(pyrazine)(sub 3)n reveals the crystallographic structure of the copper (II) units. The coordination polymer crystallizes in the triclinic space group and displays an extended sheet structure of copper(II) ions joined by oxalate anions and pyrazine. The recurring unit of the polymer contains two types of 4 + 2 coordination systems with O4N2. The Cu-ox-Cu-arrangement demonstrates a pleated ribbon, which shows that the planes of Cu-ox-Cu form a boat conformation.

Alcaligenes xylosoxidans grown under denitrifying conditions are capable of synthesizing two biochemically distinct azurins, and both of these proteins can donate electrons to purified nitrite reductase. These two azurins crystallize distinctly; azurin I crystallizes as thin needles while azurin II grows as blue elongate rectangular prisms with the tetragonal space group P4122 and unit cell parameters a=b=52.65 angstrom = 100.63 angstrom. X-ray crystallographic and other spectrochemical data for both of these azurins are also presented.

A study covers the synthesis and structures of 1,3,6-W2Cl5(PMe3)(sub 3) and (HPMe3)2(W2Cl8PMe3). The molecular structure determined by x-ray crystallography reveals W-W distances. Crystal data reveals an orientational disorder. The 1,3,6-compound is the first known case of a complex with a W(sub 2)(super 5+) core in shape of sigma(super 2)pi(super 4)delta.

The bond length of C2h in 1,2-diphenylethane is 1.54 angstroms, as obtained from high-level split valence ab initio calculations. Using the novel electronic interactions, an anomalously short Csp3-Csp3 (central) bond for 1,2-diphenylethane and a few derivatives is reflected more likely showing experimental displacement of parameters than an actual anomaly because this violates the conception of average molecular geometry.

X-ray absorption spectroscopic studies of the iron-zinc center of purple acid phosphatase obtained from red kidney beans reveal the absence of oxo groups and that phosphate induction causes a shift in the zinc and iron edges to higher and lower energies, respectively. The binding of phosphate is indicated by the reduction in the iron-zinc bond distance and this binding is unaffected by a reduction in pH. The first coordination spheres of the iron-zinc complexes contain a protonated equilibrium and all the observations from this study concur with those from earlier crystallographic studies.

X-ray crystallographic studies of the three-dimensional structures of XYNI and XYNII, two endo-1,4-xylanases from Trichoderma reesi, reveal a homology in the amino acid sequences of the two enzymes, which are present as a single domain. There is a variation in the number of subsites and width of the active site left of XYNI and XYNII. These enzymes also exhibit a difference in pH optimum, due to changes in the environment of the catalytic residue Glu164XYNI Glu177XYNII.

Dichlorophenylphosine reacts with 2,2'-dilithio-1,1'-binaphthalene to produce 7-phenyldinaphthol(2,1-b:1',2'-d)phosphole, which undergoes a dephenylation alkylation reaction, involving a lithium-stimulated phosphole anion formation, generating unsubstituted- and alkyl-substituted phospholes. X-ray analysis reveals the strain in the phosphole ring and rapid interconversion of atropisomeric conformers is responsible for the fluxional nature of dinaphthophospholes. Variable-temperature NMR studies help determine the energy barrier for the interconversion while P-substituted dinaphthophosphepines do not exhibit atropisomerism.

The synthesis of (6R)-isodolastatin 10 involves the use of a side reaction associated with the synthesis of dolaphenine. X-ray crystallographic studies of (6R)-isodolastatin 10 reveal the absence of intramolecular hydrogen bonding involving carbonyl groups or amide hydrogens. However, intermolecular hydrogen bonding occurs at N7, O16a, N23 and O24a with adjacent molecules. Molecular modeling studies help determine the energy barrier between cis and trans conformers.

X-ray crystallographic studies of (deloc-2,3,5)-6-endo-chloro-1,2,3,4,5,6-exo-hexamethylbicyclo (2.1. 1)hex-2-en-5-ylium tetrachloroborate reveal the presence of an unusually strong 3c,2e bond involving C2, C3 and C5. Displacement parameters support the static structure in the crystal, and results from X-ray studies of the 6-hydrogen-substituted complex are less precise. Anion disorder is responsible for the less precise crystal structure of the hydrogen-substituted complex.

X-ray crystallographic studies at 2. 2-angstrom resolution help determine the three dimensional structure of peptide-N4-(N-acetyl-beta-D-glucosaminyl)asparagine amidase F (PNGase F). The protein has two domains, each with eight-stranded antiparallel beta-sandwich motifs, and the interface between the domains has extensive hydrogen-bonding contacts. Active sites of the enzyme exist in three different regions, all in the interface between the domain. The three regions are a hydrophobic bowl on the surface, a long polar cleft on the opposite side and a cleft at the bottom.

X-ray diffraction, transmission electron microscopy and optical diffractogram analysis of the structure, magnetic properties and magnetoresistance of Co/Cu multilayer films grown by sputtering on Si(100) wafers reveals that Co/Cu films are polycrystalline and have layered structures. The films have columnar face-centered cube crystallographic features extending through many layers. Magnetic domain structure and image contrast, examined by Lorentz microscopy, depend on Cu layer thickness and magnetoresistance. Annealed samples exhibit a more ordered domain structure, lower saturating field and magnetoresistance than as-sputtered samples.

1H and P-NMR spectroscopy and X-ray crystallography were used to examine the configurations of heterocyclic six-membered rings possessing O,N,S and P atoms and the different steric and stereoelectronic reactions which function in the conformational equilbria of 1,3,2-oxazaphosphorinanes. The differing conformational characteristics of 1,3,2-dioxa- and 1,3,2-oxazaphosphorinanes which contain three-coordinate phosphorus, were observed.

X-ray crystallography is used in resolving the three dimensional structure of bovine profilin-beta-actin. Several local variations in the structure of beta-actin are present in comparison with alpha-actin. A five degree rotation between some of its primary domains is also noticed. Actin molecules are similar in structure to the oligomeric protein arrangements. The actin crystal has molecules in the form of ribbons, which is caused due to intermolecular contacts two of which have profilin.

X-ray-crystallography facilitates the reestablishing of the structures of ammonium Tutton salts, and the hexafluorosilicates of the divalent hexaaqua species that are formed by V, Cr, Mn, Fe, Co, Ni, Cu and Zn, the elements of the first transition sites. Minima is evident in vanadium and nickel for the metal-to-water bond distances of Tutton salts.

Crystal structure is determined for (LiBr.Et2O4), obtained as a byproduct of the reaction of mesitylene and lithium metal. The (LiBr.Et2O4) consists of discrete tetramers with hetrocubane structures in which the Li is coordinated to three Br anions and one oxygen of diethyl ether. Polymerization of tetramers leads to a decrease in entropy but formation of ladder structure increases entropy due to rise or fall in the number of particles.

Stable chromium complexes of coordination type CrS2N2O2 are formed from an acyclic hexadentate triazine 1-oxide substituted thioether ligand. This is first example of a structurally characterized chromium(III)-thioether complexes having thioether coordination. The chromium(III) binds preferably to thioether sulphur than to high-spin iron(III).

The density functional theory was used to study the structures and energetic of the experimentally known Os[(CO).sub.n] (n= 3-5), [Os.sub.2][(CO).sub.9], and [Os.sub.2][(CO).sub.8]. All the triplet structures of osmium carbonyls were found have significantly higher energies than the corresponding singlet structures.

A pH-metric, UV, and NMR spectroscopic studies of the aqueous solutions of arsenous acid with the meso and racemic forms of 1,4-dithiol-butane-2,3-diol, namely, dithioerythritol and dithiothreitol is reported. The results reveal that arsenous(III) exhibit high affinity for thiolates and show even higher affinity for hydroxide.

The reaction of Fe[Cl.sub.3] with oxalic acid ([H.sub.2]OX) and XCL, where X = substituted univalent ammonium or an alkaline cation, was used to obtain a series of oxalate-bridged iron(III) complexes. The magnetic measurements showed all the 3D compounds to exhibit strong guest-dependent magnetic behavior and are considered as molecule-based spin-canted magnets with relatively high and tunable [T.sub.c] values.

The simple synthesis and reactions of trithio-chloro molybdate [[MoCl[S.sub.3]].sup.-] from trithiomolybdate [[MoO[S.sub.3]].sup.2-] and trimethylchlorosilane are described. The new complexes could be used as versatile precursor to obtain a series of monomeric trisulfido complexes of molybdenum, Cp*, thiolato, amido, and alkoxo complexes as well as building blocks to prepare a citrate derivative of molybdenum trisulfide and structural and reaction models of the FeMo-cofactor.

A series of compounds containing the d-block unit [[Os(phen)[(CN).sub.4]].sup.2-] in combination with various near-infrared-emissive Ln(III) cations are reported. The results from the measurement of the energy transfer rates for Yb(III), Er(III), Nd(III), and Pr(III) provide insight into energy-accepting f-f states of the different Ln(III) ions.

The synthesis and characterization of two new copper complexes, [Cu(pbt)[Br.sub.2], [[Cu(pbt)[Br.sub.2](dmf)].sub.2] and a zinc complex, [Zn(pbt)[Cl.sub.2]], where pbt = 2-(2-pyridyl)benzthiazole) and dmf = dimethylformamide are reported. Both the pure ligand and [Cu(pbt)[Br.sub.2] were found to exhibit remarkable cytotoxic effects against selected cancer cell lines and [Cu(pbt)[Br.sub.2] in DMF cleaved with DNA oxidatively while the pure ligand pbt did not.

The synthesis and comprehensive characterization of a new mercury-alanine complex, [[Hg.sub.6][(alanine).sub.4][(N[O.sub.3]).sub.4]].[H.sub.2]O from the reaction mixtures of mercurous nitrate dihydrate and alanine (L and D enantiomers) is reported. The complex is the first polymeric array containing distinct environment for mercury(I) and mercury(II) coordinated by L-alanine.

The synthesis and characterization of a series of glycolato complexes obtained from (PyH).sub.5][[[Mo.sup.V]O[Cl.sub.4]([H.sub.2]O)].sub.3][Cl.sub.2] or [(PyH).sub.n][[[Mo.sup.V]O[Br.sub.4]].sub.n] is reported. The results provide insight into the binding of glycolate with the alkoxyl oxygen to the site opposite the Mo=O bond that is energetically more favorable in [{[Mo.sup.V.sub.2][O.sub.4]}.sup.2+] species and the reversed orientation of the ligand preferred in Mo(VI) complexes.

The synthesis and characterization of three new [Mn.sup.II] complexes was carried out by using [N.sub.3]O-donor amino-carboxylate ligands. The complexes were found to be good structural models for the oxalate metabolizing enzymes.

The design of a new highly efficient lead(II)-selective optical chemosensor for detection of [Pb.sup.2+] at the levels as low as 2.5 ppb, is described. The sensor was obtained by covalent attachment of two pendent proton-ionizable dansylcarboamide groups to the calix[4]arene preorganized in the partial cone conformation.

The synthesis of four homochiral and one racemic chiral metal camphorate architectures via the integration of transition metals with a dual-ligand assembly approach is reported. The compounds exhibit an unusual homochiral three-dimensional supramolecular assembly as well as homochiral 3-fold interpenetrating diamond net and a noninterpenetrating primitive cubic net.

A practical and efficient synthesis of spirobarbiturates of type III in presence of NH acidity of the imide function of the hydrophilic linker element is reported. The structural characterization based on both X-ray crystallography and spectroscopic analysis showed type II [beta]-turn formation.

Constrained versions of anabasine, a naturally occurring nAChR ligand was designed and synthesized to generate nicotinic acetylcholine receptor (nAChR) ligands selective for the [alpha]4[beta]2 and [alpha]7 subtype receptors. All compounds synthesized exhibited high affinity of the [alpha]4[beta]2 nAChR subtype, a subset bound with high affinity for the [alpha]7 receptor subtype, selectively over the [alpha]3[beta]4 receptor subtype.

The density functional theory electronic structure calculations are carried out to study the various stereoelectronic effects observed on the molecular geometries and state-energy splittings of ligated monocopper dioxygen complexes.

A set of optimized parameters for continuum solvation calculations of carbohydrates in conjunction with the Carbohydrate Solution Force Field are presented. The results obtained for the solvation free energies for explicit and implicit solvents could be applied to design models of mixed carbohydrate-protein systems.

The CrpE P450 epoxidase is characterized by using an engineered maltose binding protein (MBP)-CrpE fusion and its substrate tolerance is examined with a series of structurally related cryptophycin analogues generated by chemoenzymatic synthesis. Binding analysis has disclosed cooperativity of MBP-CrpE toward natural and unnatural desepoxy cryptophycin substrates.

The di- and tetranuclear metal sandwich-type silicotungstates [[[([gamma]-Si[W.sub.10][O.sub.36]).sub.2][M.sub.2][([mu]-OH).sub.2]].sup.10-] and [[[([gamma]-Si[W.sub.10][O.sub.36]).sub.2][M.sub.4]([[mu].sub.4]-O)[([mu]-OH).sub.6]].sup.8-] (M = Zr or Hf) are obtained as single crystals suitable for X-ray crystallographic analyses. The tetranuclear zirconium and hafnium complexes have displayed high catalytic activity for the intramolecular cyclization of (+)-citronellal, while the dinuclear zirconium and hafnium complexes are inactive.

The ratio of the second-order rate constants for reduction of dihydroxyacetone phosphate (DHAP) and of the neutral truncated substrate glycolaldehyde (GLY) is used for calculating the intrinsic phosphate binding energy. Study proposes that the loop motion and associated protein conformational changes accompanying the binding of phosphite dianion and phosphodianion substrates has led to encapsulation of the substrate.

Pyrido- and pyrrolo[2,3-d]oxazoles are prepared from the Ritter reaction of nitriles and in situ generated chiral cyclic N-acyliminium ions. cis-4-Hydroxy-5-acylaminopyrrolidines and cis-5-hydroxy-6-acylaminopiperidines are obtained by acid hydrolysis of these bicyclic heterocyclic compounds, respectively.

The reaction of asymmetrical 1,3-disubstituted thioureas with diacetoxyiodobenzene (DIB) has produced N-acetylurea regioselectively. The correlation is found between the regioselectivity and the p[K.sub.a] of the amine.

A step-economical synthesis of a new family of substituted [4.6.4.6]fenestradienes and [4.6.4.6]fenestrenes through a unique 8[pi]-6[pi]-[[O.sub.2]-oxi] cascade electrocyclization sequence is described. The high yields and the limited number of steps of the reaction sequence have made this process very attractive for preparing new fenestranes.