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The interaction of electron rich imidazol-2-ylidenes with electron poor cyanocarbons is reported. Contrary to previous reports of electron transfer products from imidazol-2-ylidenes and tetracyanoethylene, a number of ring forming cyanocarbon ring structures are isolated and characterized. Cyanation of the imidazole ring was explored by the addition of cyanogen chloride to imidazol-2-ylidenes. Backbone cyanation often occurs when hydrogen atoms are in the C-4/5 positions. When tetrasubstituted imidazol-2-ylidenes are employed, 2-cyanoimidazolium halide salts can be isolated. These salts maintain an electrophilic cyano group and are precursors to thermally stable high nitrogen content imidazolium tetrazolides.

The formation of products derived from competing reactions in Rh-catalyzed alkene hydroborations prompted us to study in situ interactions of several hydroborating reagents with unsaturated phosphinorhodium complexes. The reaction of [Rh(μ-H)(DiPPE)]2 (1) with borane–dimethylsulfide gave several rhodium–boron containing products including the structurally characterized metallaborane [RhH(DiPPE)]2B3H7 (2) [DiPPE=1,2-bis(diisopropylphosphino)ethane]. Addition of thexylborane and 9-H-BBN dimers, containing alkyl groups, to 1 gave the corresponding mononuclear substituted borohydride complexes Rh(η2-H2BRR′)(DiPPE) (4: R=H, R′=C(CH3)2CH(CH3)2; 5: R,R′=bicyclo-[3.3.1]-nonane [C8H14]). The analogous monodentate phosphine complex Rh(η2-H2BC8H14)(PPri3)2 (6) was isolated and structurally characterized. Addition of catecholborane (HBcat; cat=1,2-O2C6H4) to 1 gave the unusual dinuclear species Rh(DiPPE)(μ-H)2(μ-Bcat)RhH(DiPPE) (7) containing a semi-bridging Bcat group, confirmed by single-crystal X-ray diffraction, and zwitterionic Rh(η6-catBcat)(DiPPE) (8). Implications for rhodium-catalyzed hydroborations are addressed.

The first three-dimensional structure of phenylalanine ammonia lyase (PAL) has been determined at 2.1 A resolution for PAL from Rhodosporidium toruloides. The enzyme is structurally similar to the mechanistically related histidine ammonia lyase (HAL), with PAL having an additional approximately 160 residues extending from the common fold. We propose that catalysis (including lowering the pK(a) of nonacidic C3 of l-phenylalanine for an E1cb mechanism) is potentially governed by dipole moments of seven alpha helices associated with the PAL active site (six positive poles and one negative pole). Cofactor 3,5-dihydro-5-methylidene-4H-imidazol-4-one (MIO) resides atop the positive poles of three helices, for increasing its electrophilicity. The helix dipoles appear fully compatible with a model of phenylalanine docked in the active site of PAL having the first covalent bond formed between the amino group of substrate and the methylidene group of MIO: 12 highly conserved residues (near the N termini of helices for enhancing function) are poised to serve roles in substrate recognition, MIO activation, product separation, proton donation, or polarizing electrons from the phenyl ring of substrate for activation of C3; and a highly conserved His residue (near the C terminus of the one helix that directs its negative pole toward the active site to increase the residue's basicity) is positioned to act as a general base, abstracting the pro-S hydrogen from C3 of substrate. A similar mechanism is proposed for HAL, which has a similar disposition of seven alpha helices and similar active-site residues. The helix dipoles appear incompatible with a proposed mechanism that invokes a carbocation intermediate.

Background: Riboflavin synthase catalyzes the dismutation of two molecules of 6,7-dimethyl-8-(1′-D-ribityl)-lumazine to yield riboflavin and 4-ribitylamino-5-amino-2,6-dihydroxypyrimidine. The homotrimer of 23 kDa subunits has no cofactor requirements for catalysis. The enzyme is nonexistent in humans and is an attractive target for antimicrobial agents of organisms whose pathogenicity depends on their ability to biosynthesize riboflavin. Results: The first three-dimensional structure of the enzyme was determined at 2.0 A resolution using the multiwavelength anomalous diffraction (MAD) method on the Escherichia coli protein containing selenomethionine residues. The homotrimer consists of an asymmetric assembly of monomers, each of which comprises two similar β barrels and a C-terminal α helix. The similar β barrels within the monomer confirm a prediction of pseudo two-fold symmetry that is inferred from the sequence similarity between the two halves of the protein. The β barrels closely resemble folds found in phthalate dioxygenase reductase and other flavoproteins. Conclusions: The three active sites of the trimer are proposed to lie between pairs of monomers in which residues conserved among species reside, including two Asp-His-Ser triads and dyads of Cys-Ser and His-Thr. The proposed active sites are located where FMN (an analog of riboflavin) is modeled from an overlay of the β barrels of phthalate dioxygenase reductase and riboflavin synthase. In the trimer, one active site is formed, and the other two active sites are wide open and exposed to solvent. The nature of the trimer configuration suggests that only one active site can be formed and be catalytically competent at a time.

The reaction of Fe(II)(C5Me5)(C5H5), FeCpCp, with percyano acceptors, A [A = C4(CN)6 (hexacyanobutadiene), TCNQF4 (perfluoro-7,7,8,8-tetracyano-p-quinodimethane), and DDQ (2,3-dichloro-5,6-dicyanobenzoquinone)], results in formation of 1:1 charge-transfer salts of [Fe(III)CpCp]*]*+[A]*- composition. With A = TCNQ (7,7,8,8-tetracyano-p-quinodimethane) a 1:2 electron-transfer salt with FeCpCp forms. With A = TCNE (tetracyanoethylene) a pair of 1:1 salts as well as a pair of 2:3 salts of [FeCpCp]2[TCNE]3.S (S = CH2Cl2, THF) have been isolated and characterized by single-crystal X-ray diffraction. [FeCpCp][TCNE] consists of parallel 1-D.D(*+)A(*-)D(*+)A(*-)D(*+)A(*-). chains, while [FeCpCp][TCNE].MeCN has a herringbone array of D(*+)A2(2-)D(*+) dimers separated by solvent molecules. Although each [TCNE](-) is disordered, the diamagnetic [TCNE]2(2-) dimer is structurally different from those observed earlier with an intradimer separation of 2.79 A. The [TCNE](-) in the 2:3 [FeCpCp]2[TCNE]3.S exists as an eclipsed diamagnetic [TCNE]2(2-) dimer with an intradimer ethylene C.C separation of 2.833 and 2.903 A for the CH2Cl2- and THF-containing materials, respectively. The bond distances and angles for all the cations are essentially equivalent, and the distances are essentially equivalent to those previously reported for [FeCp2](*+) and [FeCp2](*+) cations. The average Fe-C5H5-ring and Fe-C5Me5-ring centroid distances are 1.71 and 1.69 A, respectively, which are 0.05 A longer than reported for Fe(II)CpCp. The one-electron reduction potential for Fe(II)CpCp is 0.11 V (vs SCE). The 5 K EPR of [FeCpCp](*+)[BF4](-) exhibits an axially symmetric powder pattern with g(parallel) = 4.36 and g(perpendicular) = 1.24, and the EPR parameters are essentially identical to those reported for ferrocenium and decamethylferrocenium. The high-temperature magnetic susceptibility for polycrystalline samples of these complexes can be fit by the Curie-Weiss law, chi = C/(T - theta), with low theta values and mu(eff) values from 2.08 to 3.43 mu(B), suggesting that the polycrystalline samples measured had varying degrees of orientation. [FeCpCp][TCNE] exhibits the highest effective moment of 3.43 mu(B)/Fe and weak ferromagnetic coupling, as evidenced from the theta of 3.3 K; however, unexpectedly, it does not magnetically order above 2 K. The formation of the four phases comprising FeCpCp and TCNE emphasizes the diversity of materials that may form and the present inability to predict neither solid-state compositions nor structure types.

Escherichia coli riboflavin synthase crystallizes at 22 C in the presence of 7-10percent by volume diglyme, 20-50 mM MgCl2 and pH 7.0. In this medium diffraction quality crystals are routinely obtained within 5 h and they are stable for 10 weeks. The crystals are orthogonal in space group P212121 with unit cell dimensions of a=52.4 A , b = 62.1 A, c = 218.8 A. A 97percent complete data set was collected at 2.1 A resolution.

Background: 3,4-Dihydroxy-2-butanone-4-phosphate synthase catalyzes a commitment step in the biosynthesis of riboflavin. On the enzyme, ribulose 5-phosphate is converted to 3,4-dihydroxy-2-butanone 4-phosphate and formate in steps involving enolization, ketonization, dehydration, skeleton rearrangement, and formate elimination. The enzyme is absent in humans and an attractive target for the discovery of antimicrobials for pathogens incapable of acquiring sufficient riboflavin from their hosts. The homodimer of 23 kDa subunits requires Mg 2+ for activity. Results: The first three-dimensional structure of the enzyme was determined at 1.4 A resolution using the multiwavelength anomalous diffraction (MAD) method on Escherichia coli protein crystals containing gold. The protein consists of an α + β fold having a complex linkage of β strands. Intersubunit contacts are mediated by numerous hydrophobic interactions and three hydrogen bond networks. Conclusions: A proposed active site was identified on the basis of amino acid residues that are conserved among the enzyme from 19 species. There are two well-separated active sites per dimer, each of which comprise residues from both subunits. In addition to three arginines and two threonines, which may be used for recognizing the phosphate group of the substrate, the active site consists of three glutamates, two aspartates, two histidines, and a cysteine which may provide the means for general acid and base catalysis and for coordinating the Mg 2+ cofactor within the active site.

The preparation of (DIPPP)Pd(PR3) and [(DIPPP)(PR3)PdH][OR‘] (DIPPP = bis(1,3-diisopropylphosphino)propane; R = Cy, Et; R‘ = Ar, CF3SO2) is reported. (DIPPP)Pd(PCy3) and [(DIPPP)(PCy3)PdH][CF3SO3] have been structurally characterized. (DIPPP)Pd(PR3) complexes catalyze the reaction of ethylene with carbon monoxide and phenols to give aryl propionates. In situ 31P NMR experiments have shown that the resting state of the catalyst in these transformations is the binuclear species [{(DIPPP)Pd}2(μ-H)(μ-CO)][OPh].

A series of 1,4,8,11-tetraazabicyclo[6.6.2]hexadecane ligands, including the parent compound, N,N‘-dialkyl variants, and the first N,N‘-di-pendant-arm derivatives have been synthesized by a short, efficient, and conceptually novel approach. Their copper(II) complexes have been prepared, and four of these were structurally characterized by X-ray diffraction. In all four complexes, the cross-bridged tetraamine ligand was found to be cis-folded, coordinating the metal cation within its molecular cleft using all four nitrogen lone pairs. Geometries intermediate between idealized square pyramidal and trigonal bipyramidal coordination were found for three of the complexes, whereas a distorted octahedral copper coordination was found for the complex of a di-pendant-arm cross-bridged cyclam.

Syntheses and characterizations are described for C−H insertion products derived from 1,3-dimesityldihydroimidazol-2-ylidene (1) with acetylene, acetonitrile, methyl phenyl sulfone, and chloroform. In the reaction with acetylene, both acetylenic H-atoms are reactive so that 1 : 1 and 2 : 1 adducts can be obtained. The acetylene and methyl-phenyl-sulfone adducts are structurally characterized by means of single-crystal X-ray structure determinations. The reactions of 1,3,4,5-tetramethylimidazolidin-2-ylidene (8) with chloroform or chlorodifluoromethane are shown to yield 2-(dihaloalkyl)imidazolium salts that arise from a failure of the intermediate 2-protioimidazolium salt to capture the initially formed halocarbanion.

Enantioselectivity of Rh(I)-catalyzed asymmetric hydrogenation of dehydroamino acid derivatives and dimethyl itaconate can be enhanced by the appropriate choice of substituents on the aromatic rings of vicinal diarylphosphinites derived from carbohydrates as well as trans-cyclohexane-1,2-diol. For example, the use of phosphinites with electron-donating bis(3,5-dimethylphenyl) groups at phosphorus provide high ee's in these reactions whereas electron-withdrawing aryl substituents decrease the enantioselectivity. In this paper, an attempt is made to clarify the origin of these remarkable electronic effects at two levels. First, crystal structures of a number of precatalysts ([phosphinite](2)Rh(+)[diolefin]X(-)) were determined and their structures were studied in detail to examine the electronic effects, if any, on the ground-state conformations of these molecules. A study of six of these complexes reveals that the gross conformational features of these precatalysts are largely unaffected by electronic effects, which suggests that other explanations have to be sought for the electronic amplification of enantioselectivity. One possibility is a change in the diastereomeric equilibrium between the initially formed [substrate]Rh(+)[phosphinite] complexes as a function of electronic effect of the ligand. In the Rh-catalyzed hydrogenation of dimethyl itaconate, we have examined this equilibrium between the major and minor complexes by (31)P NMR. There is a clear difference in the ratio of these two diastereomers when 3,5-dimethylphenylphosphinite vis-à-vis the unsubstituted diphenylphosphinite is used. Electron-deficient ligands such as 1,2-bis-3,5-diflurophenylphosphinite and 1,2-bis-3,5-bis-trifluromethylphenylphosphinite appear to form these diastereomers more readily at room temperature, even though the exact ratio of the diastereomers could not be established with any certainty.

We report the synthesis, characterization, spectroscopy, and photochemistry of s-dipentacene (see Figure 1). The symmetric addition product dimer of pentacene (s-dipentacene) is formed upon irradiation of a solution of pentacene. The structure of s-dipentacene was determined by X-ray crystallography. The crystals had a space group symmetry of P1 with two molecules per unit cell. One molecule in the unit cell was accompanied by two dichloromethane molecules of solvation. Photodecomposition of s-dipentacene, dispersed in a poly(methyl methacrylate) (PMMA) host matrix, to pentacene was studied. Spectroscopic evidence shows that this photodecomposition proceeds through a trapped intermediate both at low temperature (∼12 K) and at room temperature under high pressure (13 kbar). This intermediate is assigned as a “broken dimer” of two pentacene molecules trapped in the PMMA host. We previously reported similar results in the photolysis of both dianthracene and ditetracene at low temperatures, but this is the f...

Dethiobiotin synthetase (DTBS; E.C. 6.6.6.6), the penultimate enzyme in the biosynthesis of the essential vitamin biotin, is a new potential target for novel herbicides. Inhibitors were designed based on mechanistic and structural information. The in-vitro activities of these potential inhibitors versus the bacterial enzyme are reported here. Mimics of 7,8-diaminopelargonic acid (DAPA) or the DAPA carbamate reaction intermediate were substrates or partial substrates for the enzyme. Synergistic binding with ATP was noted with compounds which contained an amino functionality. NMR studies and X-ray structures confirmed that the inhibitors could be phosphorylated by the enzyme. Several series of potential inhibitors were designed to take advantage of this partial substrate activity by generating potentially more tightly bound phosphorylated inhibitors in situ. Structure-activity relationships for these series based on both substrate and inhibitory activity are described herein. An X-ray structure for one of these inhibitors is also discussed. Although considerable potential for inhibitors of this type was demonstrated, none of the compounds reported showed sufficient herbicidal activity to be a commercial proposition.

One important factor influencing the affinity of a flexible ligand for a receptor is the internal strain energy required to attain the bound conformation. Calculation of fully equilibrated ensembles of bound and free ligand and receptor conformations are computationally not possible for most systems of biological interest; therefore, the qualitative evaluation of a novel structure as a potential high-affinity ligand for a given receptor can benefit from taking into account both the bound and unbound (usually aqueous) low-energy geometries of the ligand and the difference in their internal energies. Although many techniques for computationally generating and evaluating the conformational preferences of small molecules are available, there are a limited number of studies of complex organics that compare calculated and experimentally observed conformations. To assess our ability to predict a priori favored conformations of cyclic HIV protease (HIV-1 PR) inhibitors, conformational minima for nine 4,7-bis(phen...

Comparison of the high-resolution X-ray structures of the native HIV-1 protease and its complexes with the inhibitors suggested that the enzyme flaps are flexible. The movement at the tip of the flaps could be as large as 7 A. On the basis of this observation, cyclic cyanoguanidines have been designed, synthesized, and evaluated as HIV-1 protease (PR) inhibitors. Cyclic cyanoguanidines were found to be very potent inhibitors of HIV-1 protease. The choice of cyclic cyanoguanidines over cyclic guanidines was based on the reduced basicity of the former. X-ray structure studies of the HIV PR complex with cyclic cyanoguanidine demonstrated that in analogy to cyclic urea, cyclic cyanoguanidines also displace the unique structural water molecule. The structure-activity relationship of the cyclic cyanoguanidines is compared with that of the corresponding cyclic urea analogues. The differences in binding constants of the two series of compounds have been rationalized using high-resolution X-ray structure information.

Vicinal diarylphosphinites derived from carbohydrates are excellent ligands for the Rh(I)-catalyzed enantioselective asymmetric hydrogenation of dehydroamino acid derivatives, producing the highest enantioselectivity of any ligands directly prepared from natural products. The enantioselectivity can be enhanced by the appropriate choice of substituents on the aromatic rings of the phosphinites. For example, the use of phosphinites with electron-donating bis(3,5-dimethylphenyl) groups on phosphorus provides ee's up to 99% for a wide range of amino acids including some with easily removable N-protecting groups. Electron-withdrawing aryl substituents, on the other hand, decrease the enantioselectivity. Sense of chiral induction in the amino acid product depends on the relative juxtaposition of the vicinal diphosphinites on a given sugar backbone. When readily available d-glucopyranosides are used as the starting sugars, 2,3-phosphinites give the S-amino acids and 3,4-phosphinites give the R-amino acids. In th...

Treatment of benzaldehyde l-(2-propenyl)-4-methylsulfonylphenylhydrazone (1f) with 45% sulfuric acid gave 2-(4-methylsulfonylphenyl)-6-phenylhexahydro-4-pyridazinol (2f) in 35% yield rather than the expected 1-(4-methylsulfonylphenyl)-1-(2-propenyl)hydrazine. The halogen-substituted hydrazones 1c-1e and benzaldehyde 1-(2-methyl-2-propenyl)phenylhydrazone (1b) gave similar results.

(meso-Tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)porphinato)manganese(III) tetracyanoethenide, [MnTP'P][TCNE], has been structurally and magnetically characterized. [MnTP'P][TCNE] (C(96)H(108)MnN(8)O(4)) belongs to the triclinicPonemacr; (No. 2) space group with a = 8.597(2) Å, b = 14.756(4) Å, c = 17.573(5) Å, alpha = 101.16 (2) degrees, beta = 100.56(2) degrees, gamma = 96.37(2) degrees, and Z = 1. Due to the oxidative instability of the phenoxy groups, [Mn(III)TP'P][TCNE] was prepared from the reaction of [Mn(III)TP'P]OAc with the strong acid H(2)TCNE (pK(a) = 3.6) in the presence of TCNE to form acetic acid and the product. [MnTP'P][TCNE] is a coordination polymer with the Mn(III) sites bridged by trans-mgr;(2)-bound [TCNE](*)(-) with relatively short (8.587 Å) intrachain and long (/=14.756 Å) interchain Mn.Mn separations. The magnetic data above 210 K obey the Curie-Weiss expression with an effectiveTHETAV; value of 90.0 K, the largest yet reported for a soluble molecule-based magnet. In addition to a 15 K T(c) hysteretic behavior with a coercive field of 100 Oe is observed at 5 K. Despite the significant steric bulk leading to the substantially decreased interchain interactions that are crucial for magnetic ordering, the T(c) is unexpectedly high and suggests that other linear chain systems may be expected to exhibit magnetic ordering at higher temperatures.

Addition of TCNQ to a solution of tetrakis(dimethylamino)ethylene in MeCN produces the salt [TDAE][TCNQ]2; the dipositive cation, [{(CH3)2N}2C–C{N(CH3)2}2]2+, is nonplanar, with a dihedral angle of 63.9°, while the TCNQ anions crystallize as [TCNQ]22– dimers with an interplanar separation of 3.16 A. The complex [TDAE][TCNE] was prepared in a similar manner; the [TDAE]2+ cation and [TCNE]2– anion are nonplanar, with dihedral angles of 71.3 and 76.6°, respectively. The four CN groups in the [TCNE]2– anion each accept three C–H ⋯ N hydrogen bonds. In each case, one C–N ⋯ H angle is in the range 134–156°, while the other two are near 90°(81–100°).

The structures of the two isostructural compounds Cs (TiAs)O 5 (CTA) and Cs(TiP)O 5 (CTP) were solved and refined by application of the Rietveld profile technique to high-resolution synchrotron X-ray and neutron powder data. The structures are cubic, space group F d 3 m with a = 10.23415(5) A (CTA) and a = 10.08733(2) A (CTP), and are characterized by an unusual framework consisting of randomly disordered TiO 6 octahedra and X O 4 ( X = As, P) tetrahedra with the Cs + cation occupying large cavities within this framework. The lack of long-range order between octahedra and tetrahedra simulates partially occupied octahedra shared by Ti and X with large displacement parameters for both cations and oxygens. The Ti, X -site can be resolved as a split-atom position where the tetrahedral metal is shifted from the center toward the edge formed by the octahedral oxygens. Split-oxygen positions were refined from a combination of X-ray and neutron data for CTA. The cubic structure is related to the orthorhombic KTiOPO 4 -type structure in that the latter can be derived from the former by ordering of the TiO 6 octahedra and PO 4 tetrahedra. Since different ordering schemes applied to the cubic CTA/CTP structure lead to other known ordered structures of the same stoichiometry such as K(Mg 1/3 Nb 2/3 )OPO 4 and γ-NaTiOPO 4 , cubic CTA/CTP can be viewed as the "mother of all ABOCO 4 -structures." The elucidation of the cubic structure allows us to propose a quantified "threatened structure model," which helps in the understanding of the mechanism of this phase transition.

The preparation of several new coinage metal complexes containing bulky, chelating bis(phosphine) ligands is described. The molecular structures of [AuCl(μ-DiPPE)]n (4), [Cu(μ-Cl)(DHP)]2 (6a), and [Au(DHP)(PEt3)]Cl (8) have been determined (DiPPE = 1,2-bis(diisopropylphosphino)ethane, DHP = deerhead phosphine, o-phenylenebis(diisopropylphosphine). These new complexes are selective catalysts for the hydroboration of imines and thiazolinesus ing catecholborane. The molecular structure of (11) is also reported.

The enthalpies of reaction of CpRu(COD)Cl (1) (Cp = eta(5)-C5H5; COD = cyclooctadiene) with a series of monodentate ligands, leading to the formation of CpRu(ER(3))(2)Cl (E = P, As), have been measured by anaerobic solution calorimetry in THF at 30.0 degrees C. These reactions are rapid and quantitatively lead to the formation of the corresponding CpRu(ER(3))(2)Cl complexes. The overall relative order of stability established for the preceding complexes is as follows: AsEt(3) < PPh(3) < PPh(2)Me < P(OPh)(3) < PEt(3) < P(n)Bu(3) < PPhMe(2) < PMe(3) < P(OMe)(3). Comparisons with other organometallic systems providing insights into factors influencing the Ru-L bond disruption enthalpies and metal basicity are discussed. Structural studies of two of these CpRu(ER(3))(2)Cl complexes (ER(3) = AsEt(3) (2) and PEt(3) (3)) have also been performed. Data for 2: monoclinic, C2/c; a = 30.549(5); b =. 10.523(2); c = 13.503(3) Angstrom; alpha gamma = 90 degrees; beta = 103.71(2)degrees; V = 4217.1 Angstrom(3); Z = 8; d(calcd) 2 = 1.656g cm(-1);n(obsd) 5328; R = 0.032. Data for 3: monoclinic, P2(1)/c; a 13.553(1); b = 8.283(2); c = 19.359(3) Angstrom; beta = 109.74(1)degrees; V = 2045.5 Angstrom 3; Z = 4; dcalcd = 1.422 g cm(-1); n(obsd) = 5152; R = 0.030. A relationship between bond distances and relative bond energies is made possible by the present data. This correlation is good and represents a rare example of such a relationship.

Two new, noncentrosymmetric, rubidium titanium phosphate phases have been synthesized by hydrothermal and flux methods and structurally characterized by single crystal X-ray diffraction methods. Rb2Ti3O2(PO4)2(HPO4)2 (Rb2Ti3P4) consists of a three-dimensional framework of vertex-sharing TiO6, PO4, and HPO4 polyhedra interconnected via Ti-O-Ti and Ti-O-P bonds, surrounding large, one-dimensional channels occupied by eight-coordinate "guest" Rb+ cations: these channels propagate along the a-crystallographic direction. The framework includes [Ti3O16] units built up from three adjacent TiO6 octahedra sharing trans-O-Ti-O links, crosslinked by the (hydrogen)phosphate groups. Rb3Ti3O (P2O7)(PO4)3 (Rb3Ti3P5) is built up from a network of TiO6 and PO4 groups, linked via Ti-O-Ti, Ti-O-P, and P-O-P bonds, enclosing channels occupied by the guest rubidium cations. The structural motif of the framework includes isolated TiO6 and [Ti2O11] groups, interconnected by (pyro)phosphate groups. The Rb+ cations occupying the one-dimensional channels are eighffold coordinate by oxygen atoms. Rb3Ti3O(P2O7)(PO4)3 (2 linked octahedra) and RbaTi3O2(PO4)2(HPO4)2(3 linked octahedra) are considered in relation to the nonlinear optical materials KTiOPO4 (KTP) and RbTiOPO4 (RbTP) which contain infinite -O-Ti-O-Ti-O-chains. The typical short, "titanyl" Ti[ ]O bond found in KTP and RbTP is barely apparent in Rb2Ti3O2(PO4)2(HPO4)2 and Rb3 Ti3O(P2O7)(PO4)3, and the poor nonlinear response of the title compounds is discussed in relation to the extended Ti/O chain structure in RbTP. Crystal data: Rb2Ti3P4O18H2, Mr = 728.5, monoclinic, P21, a = 5.1851(4) A, b = 16.770(2) A, c = 8.4939(6) A β = 90.940(3) °, V = 738.48 A3, Z = 2. Final residuals of R = 4,24% and Rw = 4.40% were obtained for 2331 unique reflections with I > 3σ(I). Rb3Ti3P5O20, Mr = 874.96, orthorhombic, Pca21, a = 18.280(1) A, b = 6.295(1) A, c = 14.773(1) A, V = 1700.0 A3, Z = 4, R = 4.00%, and Rw = 3.70% for 1498 unique reflections with I > 3σ(I).

The hypervalent phosphorus compound, 3,7-di-t-butyl-5-aza-2,8-dioxa-1-phosphabicyclo-[3.3.0]octa-2,4,6-triene (ADPO) forms adducts with chromium, tungsten, nickel and palladium metal centers. All four new adducts contain tetrahedral phosphorus atoms as a result of folding of the ADPO unit. This folding of the planar 10-P-3 ADPO molecule to provide an 8-P-3 center for coordination to the transition metal center is the result of the close energy balance between 10-P-3 ADPO and 8-P-3 ADPO and the strength of the phosphorus-metal interaction. In the case of a homoleptic palladium(II) complex, dimerizati on of the coordinated ADPO unit was observed.

Two zinc phosphate layered materials, each containing unique 3-rings yet differing hydrogen bonding schemes, have been prepared by hydrothermal methods and characterized by single-crystal X-ray diffraction, TGA, and MAS NMR. These phases consist of a two-dimensional network of ZnO4 and PO4 tetrahedra, linked through oxygen vertices, to form structures whose interlayers are occupied by charge-balancing cations. The layers are notable because of the formation of 3-rings comprised of the tetrahedral atoms, Zn and P, and the oxygen atoms, resulting in "terminal" -OH bonds off the P(2) atom, in the sodium analog, and off the P(1) atom in the cesium analog. The topology of the layers is controlled by the templating cation. While the small interlayer sodium cation allows for hydrogen bonding between the layers which results in "puckered" sheets, the larger cesium cation does not allow interlayer hydrogen bonding, resulting in flat sheets. Sodium hydrogen zinc orthophosphate (NaH(ZnPO4)2) is a triclinic crystal: space group P1 (no. 2), with a = 8.641 (2), b = 8.817 (3), and c = 5.1268 (9) A; α = 100.401 (8)°, β = 105.684 (8)°, and γ = 96.924 (9)°; V = 363.9 (1) A3 and Z = 2, with R = 5.21% and Rw, = 4.96% for 1873 observed reflections, according to the criterion I > 3σ(I). Cesium hydrogen zinc orthophosphate (CsH(ZnPO4)2) is orthorhombic: space group Abma (no. 64), with a = 7.739 (8), b = 6.594 (7), and c = 15.94 (2) A; α = 90°, β = 90°, and γ = 90°; V = 813.56 (5) A3 and Z = 4, with R = 4.56% and Rw = 5.23% for 762 observed reflections, according to the criterion I > 3σ(I).

We have systematically investigated the structural stability of the KTiOPO4 family of crystals, specifically of CsTiOAsO4. High temperature differential thermal analysis (DTA) reveals for the first time that CsTiOAsO4 thermally decomposes into a non-stiochiometric, Cs-deficient cubic compound at ∼960°C. This decomposition is actually more general, and is observed in two other KTiOPO4 isomorphs, namely RbTiOPO4 and TITiOPO4. A “threatened-structure model” is proposed to explain the decomposition and evidence supporting the validity of this model are presented. The model further explains the observed anomaly in CsTiOAsO4's crystal growth properties using various fluxes. CsTiOAsO4's relatively low decomposition temperature creates problems for bulk crystal growth and methods for reducing these growth problems are proposed.

Reactions of certain iridium complexes with catecholborane (HBcat) gave boron-substituent redistribution products ([Bcat2]−, B2cat3) with concomitant formation of a complex mixture of iridium hydrides. While "IrCl(PPh3)(COE)n" generated in situ from [Ir(μ-Cl)(COE)2]2 (COE = cyclooctene) (2) plus 2 equivalents of PPh3 also promoted HBcat degradation, this catalyst system was extremely active and selective for alkene hydroborations. Oxidative addition of HBcat to the metal centre can be the sole reaction pathway, however, with iridium complexes containing electron-rich phosphines. The unsaturated boryl complex IrHCl(Bcat)(PPri3)2 was prepared and isolated in high yield from reaction of HBcat with 2 in the presence of four equivalents of PPri3. Ancillary carbonyl ligands also appear to facilitate oxidative addition of HBcat to an iridium centre. Addition of HBcat to trans-IrCl(CO)(PPh3)2 gives the first structurally characterized metal-carbonyl boryl complex trans-IrHCl(CO)(Bcat)(PPh3)2 (7). Colourless crystals of 7 are triclinic, [Formula: see text] (No.2) with two molecules per unit cell of dimensions a = 12.223(2) Å, b = 12.684(2) Å, c = 14.652(1) Å, α = 70.81(1)°, β = 72.47(1)°, and γ = 71.92(1)°.

Rearrangement of allylic cyclic sulfites 2 to allylic sultones 8 upon treatment with boron triflouride etherate is described.

Single crystals of low temperature form of BiNbO4 (α-form) are grown from BiOF flux below 900°C. The crystals are colorless, trapezodial in shape and electrically insulating. The compound has orthorhombic [a = 5.673 (2), b = 11.714 (4) and c = 4.978(2) Ȧ] symmetry with a centric space group Pnna (No. 52) and z = 4. The crystal structure was solved by means of single crystal x-ray diffraction and refined to R = 0.031. Both Bi and Nb have distorted octahedral oxygen coordination. The NbO6 octahedra are linked over four corners and thus the structure can be viewed as consisting of sheets of [NbO4]3− units separated by Bi3+ cations. The structure of α-BiNbO4 is essentially same as that of the low temperature form of α-Sn2+W6+O4.

Reactions of tertiary phosphines or phosphinorhodium complexes with catecholborane (HB(cat)) give boron-substituent redistribution products. While sterically compact phosphines (PMe 3 , PEt 3 , PMe 2 Ph) react with 1 equiv of HBcat to give [(PR 3 ) 2 BH 2 ] + [B(cat) 2 ] - , bulkier phosphines (PPh 3 , PPr i 3 , PCy 3 ) afford phosphine-boranes H 3 B.PR 3 and tris(catecholato)diboron, B 2 (cat) 3 .

K(Mg1/3Nb2/3)PO5 (KMNP) is an aliovalent analogue of potassium titanyl phosphate, KTiOPO4 (KTP). Single crystals of KMNP were grown from a 3K2O/2P2O5 flux and their structure was determined. KMNP is not isostructural with KTP (noncentrosymmetric orthorhombic space group Pna21). Instead, it crystallizes in the noncentrosymmetric, enantiomorphic space groups P 4122 and P4322 (tetragonal; a = 6.5366(3), c = 10.847(1) A). Unlike KTP, KMNP exhibits vanishingly small (∼0) second harmonic generation (SHG). The main structural differences between KMNP and KTP are the lack of a (Mg, Nb)—O bond equivalent to the very short titanyl Ti O bond found in KTP and a change in the connectivity of the MO6/2 octahedra—instead of the cis-trans arrangement of the TiO6/2 chains in KTP, the (Mg1/3Nb2/3)O6/2 chains of KMNP are linked in an all-cis configuration. Phase evolution in and SHG data for the system K[Ti1-x(Mg1/3Nb2/3)x]PO5 (K[T1-x(MN)x]P) are also reported. The results of this study suggest that the aliovalent substitution of (Mg1/3Nb2/3) for Ti is primarily responsible for the dramatic loss of SHG and that the change in space group is only of minimal importance.

We report a new procedure for the synthesis of a strong acceptor tetracyano-1,4-benzoquinone, cyanil, Q together with a wide range of physical and theorical studies for Q,[QH] - ,QH 2 ,[Q] .- and [Q] 2

The electron-transfer salt 4[Cr(C5Me5)2]+[TCNE]˙–(TCNE = tetracyanoethylene) has been prepared and structurally characterized by single-crystal X-ray diffraction. It possesses a solid-state motif of parallel 1D chains of alternating radical rations and anions similar to, but not isostructural to, the ferromagnet [Fe(C5Me5)2]˙+[TCNE]˙–·4[Cr(C5Me5)2]+[TCNE]˙– is a soft ferromagnet with no hysteretic effects observed and Tc= 3.65 K.