Anion-pi, Lone-Pair-pi, pi-pi and Hydrogen-Bonding Interactions in a Cu-II Complex of 2-Picolinate and Protonated 4,4 '-Bipyridine: Crystal Structure and Theoretical Studies

A Cu-II complex of protonated 4,4'-bipyridine (Hbyp) and 2-picolinate (pic), [Cu-2(pic)(3)(Hbyp)(H2O)(ClO4)(2)], has been synthesised and characterised by single-crystal X-ray analysis. The structure consists of two copper atoms that have different environments, bridged by a carboxylate group. The equatorial plane is formed by the two bidentate picolinate groups in one Cu-II, and one picolinate, one monodentate 4,4'-bipyridyl ligand and a water molecule in the other. Each copper atom is also weakly bonded to a perchlorate anion in an axial position. One of the coordinated perchlorate groups displays anion-pi interaction with the coordinated pyridine ring. The noncoordinated carboxylate oxygen is involved in lone-pair (l.p.)-pi interaction with the protonated pyridine ring. In addition there are pi-pi and H-bonding interactions in the structure. Bader's theory of "atoms in molecules" (AIM) is used to characterise the anion-pi and l.p.-pi interactions observed in the solid state. A high-level ab initio study (RI-MP2/aug-cc-pVTZ level of theory) has been performed to analyse the anion-pi binding affinity of the pyridine ring when it is coordinated to a transition metal and also when the other pyridine ring of the 4,4'-bipyridine moiety is protonated. Theoretical investigations support the experimental findings of an intricate network of intermolecular interactions, which is characterised in the studied complex, and also indicate that protonation as well as coordination to the transition metal have important roles in influencing the pi-binding properties of the aromatic ring. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Solvothermal syntheses, crystal structures and properties of five new thloantimonates(III) containing the [Sb4S7](2-) anion

Five new thioantimonates have been synthesized in the presence of organic amines under solvothermal conditions and their structures determined by single-crystal X-ray diffraction. All of the compounds are layered and contain antimony-sulphide anions of stoichiometry [Sb4S7](2-), but the structure of the anion formed is dependent on the amine used in synthesis. (H3N(CH2)(4)NH3)[Sb4S7] (1) contains [Sb4S7](2-) double chains directed along [010]. Weak interchain Sb-S interactions between neighbouring chains cause the double chains to pack into layers in the ab plane. In the [001] direction, the layers of double chains alternate with doubly protonated diaminobutane molecules to which the chains are hydrogen bonded. Compounds of general formula (TH)(2)[Sb4S7] (T= CH3(CH2)(2)NH2 (2), (CH3)(2)CHNH2 (3), CH3(CH2)(3)NH2 (4) and CH3(CH2)(4)NH2 (5)) adopt a more complex structure in which [Sb3S8](7-) units are linked by Sb-3(3-) pyramids to form chains, which in turn are bridged by sulphur atoms to create sheets containing large heterorings. Pairs of such sheets form double layers of four atoms thickness that are stacked along [001]. Protonated amine molecules are located between anionic antimony-sulphide layers to which they are hydrogen bonded. Thermal analysis reveals that the decomposition temperature of materials containing [Sb4S7](2-) anions is dependent both on the structure of the anion, the lowest decomposition temperature being that of the low-dimensional phase (1) and on the identity of the amine, the decomposition temperature decreasing with an increasing number of carbon atoms and decreasing density. (c) 2005 Elsevier Inc. All rights reserved.

Metal cluster expansion by addition of low-valent group 4B reagents: crystal and molecular structure of [Os3SnH2(CO)10{CH(SiMe3)2}2]; a compound with hydrogen bridging osmium and tin

Cluster expansion of [Os3H2(CO)10] with [SnR2][R = CH(SiMe3)2] take place in high yield to give [Os3SnH2(CO)10R2], the first closed triosmium–main-group metal cluster to be structurally characterized; a novel feature is the presence of a hydrogen atom bridging the tin atom and one of the osmium atoms.

Rational modification of the hierarchy of intermolecular interactions in molecular crystal structures by using tunable halogen bonds

A family of 16 isomolecular salts (3-XpyH)(2)[MX'(4)] (3-XpyH=3-halopyridinium; M=Co, Zn; X=(F), Cl, Br, (I); X'=Cl, Br, I) each containing rigid organic cations and tetrahedral halometallate anions has been prepared and characterized by X-ray single crystal and/or powder diffraction. Their crystal structures reflect the competition and cooperation between non-covalent interactions: N-H center dot center dot center dot X'-M hydrogen bonds, C-X center dot center dot center dot X'-M halogen bonds and pi-pi stacking. The latter are essentially unchanged in strength across the series, but both halogen bonds and hydrogen bonds are modified in strength upon changing the halogens involved. Changing the organic halogen (X) from F to I strengthens the C-X center dot center dot center dot X'-M halogen bonds, whereas an analogous change of the inorganic halogen (X') weakens both halogen bonds and N-H center dot center dot center dot X'-M hydrogen bonds. By so tuning the strength of the putative halogen bonds from repulsive to weak to moderately strong attractive interactions, the hierarchy of the interactions has been modified rationally leading to systematic changes in crystal packing. Three classes of crystal structure are obtained. In type A (C-F center dot center dot center dot X'-M) halogen bonds are absent. The structure is directed by N-H center dot center dot center dot X'-M hydrogen bonds and pi-stacking interactions. In type B structures, involving small organic halogens (X) and large inorganic halogens (X'), long (weak) C-X center dot center dot center dot X'-M interactions are observed with type I halogen-halogen interaction geometries (C-X center dot center dot center dot X' approximate to X center dot center dot center dot X'-M approximate to 155 degrees), but hydrogen bonds still dominate. Thus, minor but quite significant perturbations from the type A structure arise. In type C, involving larger organic halogens (X) and smaller inorganic halogens (X'), stronger halogen bonds are formed with a type II halogen-halogen interaction geometry (C-X center dot center dot center dot X' approximate to 180 degrees; X center dot center dot center dot X'-M approximate to 110 degrees) that is electrostatically attractive. The halogen bonds play a major role alongside hydrogen bonds in directing the type C structures, which as a result are quite different from type A and B.

Molecular structures of benzoic acid and 2-hydroxybenzoic acid, obtained by gas-phase electron diffraction and theoretical calculations

The structures of benzoic acid (C6H5COOH) and 2-hydroxybenzoic acid (C6H4OHCOOH) have been determined in the gas phase by electron diffraction using results from quantum chemical calculations to inform restraints used on the structural parameters. Theoretical methods (HF and MP2/6-311+G(d, p)) predict two conformers for benzoic acid, one which is 25.0 kJ mol(-1) (MP2) lower in energy than the other. In the low-energy form, the carboxyl group is coplanar with the phenyl ring and the O-H group eclipses the C=O bond. Theoretical calculations (HF and MP2/6-311+ G(d, p)) carried out for 2-hydroxybenzoic acid gave evidence for seven stable conformers but one low-energy form (11.7 kJ mol-1 lower in energy (MP2)) which again has the carboxyl group coplanar with the phenyl ring, the O-H of the carboxyl group eclipsing the C=O bond and the C=O of the carboxyl group oriented toward the O-H group of the phenyl ring. The effects of internal hydrogen bonding in 2-hydroxybenzoic acid can be clearly observed by comparison of pertinent structural parameters between the two compounds. These differences for 2-hydroxybenzoic acid include a shorter exocyclic C-C bond, a lengthening of the ring C-C bond between the substituents, and a shortening of the carboxylic single C-O bond.

Synthesis, structure and magnetic characterisation of a new layered ammonium manganese(II) diphosphate hydrate, (NH4)(2)[Mn-3(P2O7)(2)(H2O)(2)]

A new layered ammonium manganese(II) diphosphate, (NH4)(2)[Mn-3(P2O7)(2)(H2O)(2)], has been synthesised under solvothermal conditions at 433 K in ethylene glycol and the structure determined at 293 K using single-crystal X-ray diffraction data (M-r = 584.82, monoclinic, space group P2(1)/a, a = 9.4610( 8), b = 8.3565( 7), c = 9.477(1) Angstrom, beta = 99.908(9) degrees, V = 738.07 Angstrom(3), Z = 2, R = 0.0351 and R-w = 0.0411 for 1262 observed data (I > 3(sigma(I))). The structure consists of chains of cis- and trans-edge sharing MnO6 octahedra linked via P2O7 units to form layers of formula [Mn3P4O14(H2O)(2)](2-) in the ab plane. Ammonium ions lie between the manganese-diphosphate layers. A network of interlayer and ammonium-layer based hydrogen bonding holds the structure together. Magnetic measurements indicate Curie - Weiss behaviour above 30 K with mu(eff) = 5.74(1) mu(B) and theta = -23(1) K, consistent with the presence of high-spin Mn2+ ions and antiferromagnetic interactions. However, the magnetic data reveal a spontaneous magnetisation at 5 K, indicating a canting of Mn2+ moments in the antiferromagnetic ground state. On heating (NH4)(2)[Mn-3(P2O7)(2)(H2O)(2)] in water at 433 K under hydrothermal conditions, Mn-5(HPO4)(2)(PO4)(2).4H(2)O, synthetic hureaulite, is formed.

High-resolution crystal structure of the intramolecular d(TpA) thymine-adenine photoadduct and its mechanistic implications

A high-resolution crystal structure is reported for d(TpA)*, the intramolecular thymine-adenine photoadduct that is produced by direct ultraviolet excitation of the dinucleoside monophosphate d(TpA). It confirms the presence of a central 1,3-diazacyclooctatriene ring linking the remnants of the T and A bases, as previously deduced from heteronuclear NMR measurements by Zhao et al. (The structure of d(TpA)*, the major photoproduct of thymidylyl-(3'-5')-deoxyadenosine. Nucleic Acids Res., 1996, 24, 1554-1560). Within the crystal, the d(TpA)* molecules exist as zwitterions with a protonated amidine fragment of the eight-membered ring neutralizing the charge of the internucleotide phosphate monoanion. The absolute configuration at the original thymine C5 and C6 atoms is determined as 5S,6R. This is consistent with d(TpA)* arising by valence isomerization of a precursor cyclobutane photoproduct with cis-syn stereochemistry that is generated by [2 + 2] photoaddition of the thymine 5,6-double bond across the C6 and C5 positions of adenine. This mode of photoaddition should be favoured by the stacked conformation of adjacent T and A bases in B-form DNA. It is probable that the primary photoreaction is mechanistically analogous to pyrimidine dimerization despite having a much lower quantum yield.

Oxo-rhenium(V) complexes with bidentate phosphine ligands: synthesis, crystal structure and catalytic potentiality in epoxidation of olefins using hydrogen peroxide activated bicarbonate as oxidant

Two oxorhenium(V) complexes with bidentate phosphine ligands were synthesized and isolated as [ReOCl3(dppm)] 1 and [ReOCl3(dppp)] 2 [where dppm = 1,1-bis(diphenylphosphino) methane and dppp = 1.3-bis(diphenylphosphino) propanel. Complex 2 was structurally characterized. Both the complexes were used as catalysts in the epoxidation of olefins using NaHCO3 as co-catalyst and H2O2 as terminal oxidant. (c) 2008 Elsevier B.V. All rights reserved.

The trapping and decomposition of toxic gases such as hydrogen cyanide using modified mesoporous silicates

Selected silicas were modified with the covalently bound ligand 2,6-bis(benzoxazoyl)pyridine (BBOP), equilibrated with copper(II) nitrate, then challenged with toxic vapour containing HCN (8000 mg m(-3) at 80% relative humidity). The modified SBA-15 material (Cu-BBOP-SBA-15) had an improved breakthrough time for HCN (36 min at a flow rate of 30 cm(3) min(-1)) when compared to the other siliceous materials prepared in this study, equating to a hydrogen cyanide capacity of 58 mg g(-1), which is close to a reference activated carbon adsorbent (24 min at 50 cm(3) min(-1)) that can trap 64 mg g(-1). The enhanced performance observed with Cu-BBOP-SBA-15 has been related to the greater accessibility of the functional groups, arising from the ordered nature of the interconnected porous network and large mesopores of 5.5 nm within the material modified with the Cu(II)-BBOP complex. Modified MCM-41 and MCM-48 materials (Cu-BBOP-MCM-41 and Cu-BBOP-MCM-48) were found to have lower hydrogen cyanide capacities (38 and 32 mg g(-1) respectively) than the Cu-BBOP-SBA-15 material owing to the restricted size of the pores (2.2 and <2 nm respectively). The materials with poor nano-structured ordering were found to have low hydrogen cyanide capacities, between 11 and 19 mg g(-1), most likely owing to limited accessibility of the functional groups. (C) 2004 Elsevier Inc. All rights reserved.

Chemistry of mixed-ligand methoxy bonded oxidovanadium(V) complexes with a family of hydrazone ligands containing VO3+ core and their substituent controlled methoxy-bridged dimeric forms

[(VO)-O-IV(acac)(2)] reacts with an equimolar amount of benzoyl hydrazones of 2-hydroxyacetophenone (H2L1), 2-hydroxy-5-methylacetophenone (H2L2) and 5-chloro-2-hydroxyacetophenone (H2L4) in methanol to afford the penta-coordinated mixed-ligand methoxy bonded oxidovanadium(V) complexes [(VO)-O-V(L-1)-(OCHA(3))](1). [(VO)-O-V(L-2)(OCH3)](2), and [(VO)-O-V(L-4)(OCH3)](4), respectively, whereas, the similar reaction with the benzoyl hydrazone of 2-hydroxy-5-methoxyacetophenone (H2L3) producing only the hexa-coordinated dimethoxy-bridged dimeric complex [(VO)-O-V(L-3)(OCH3)](2) (3A). Similar type of hexa-coordinated dimeric analogue of 1 i.e., [(VO)-O-V(L-1)(OCH3)](2) (1A) was obtained from the reaction of [(VO)-O-IV(acac)(2)] with the equimolar amount of H2L1 in presence of half equivalent 4,4'-bipyridine in methanol while the decomposition of [(VO)-O-IV(L-2)(bipy)] complex in methanol afforded the dimeric analogue of 2 i.e., [(VO)-O-V(L-2)(OCH3)](2) (2A). All these dimeric complexes 1A-3A react with an excess amount of imidazole in methanol producing the respective monomeric complex. The X-ray structural analysis of 1-3 and their dimeric analogues 1A-3A indicates that the geometry around the vanadium center in the monomeric form is distorted square-pyramidal while that of their respective dimeric forms is distorted octahedral, where the ligands are bonded to vanadium meridionally in their fully deprotonated enol forms. Due to the formation of bridge, the V-O(methoxy) bond in the dimeric complexes is lengthened to such an extent that it becomes equal in length with the V-O(phenolate) bond in 3A and even longer in 1A and 2A, which is unprecedented. The H-1 NMR spectra of the complexes 1A-3A in CDCl3 solution, indicates that these dimeric complexes are converted appreciably into their respective monomeric form. Complexes are electro-active displaying one quasi-reversible reduction peak near +0.25 V versus SCE in CH2Cl2 solution. The E-1/2 values of the complexes show linear relationship with the Hammett parameter (sigma) of the substituents. All these VO3+-complexes are converted to the corresponding complexes with V2O34+ motif simply on refluxing them in acetone and to the complexes with VO2+ motif on reaction with 2 KOH in methanol. (C) 2008 Elsevier Ltd. All rights reserved.

Synthesis, structure and solution chemistry of a family of dinuclear hydrazonato-vanadium(V) complexes with [OV(mu-O)VO](4+) core

Dinuclear trioxidic [{VOL}(2)mu-O] (1-4) complexes were synthesized from the reaction of [(VO)-O-IV(acac)(2)] with an equimolar amount of H2L [H2L is the general abbreviation of hydrazone ligands (H2L1-4) derived from the condensation of benzoyl hydrazine with either 2-hydroxyacetophenone or its para substituted derivatives] in acetone or CH2Cl2 or acetonitrile. These V2O3L2 complexes were also obtained from the reaction of VOSO4 with H2L in the presence of two equivalents sodium acetate in aqueous-methanolic (50% V/V) medium and also from the decomposition of [(VO)-O-IV(L)(bipy/phen)] complexes in CH2Cl2 Solution. Black monoclinic crystals of 2 and 4 with C2/c space group were obtained from the reaction of [(VO)-O-IV(acac)(2)], respectively, with H2L2 and H2L4 in acetone in which the respective ligands are bonded meridionally to vanadium in their fully deprotonated enol forms. The V-O bond lengths follow the order: V-O(oxo) < V-O(oxo-bridged) < V-O(phenolate) < V-O(enolate). Complexes (1-4) are diamagnetic exhibiting LMCT transition band near 380 nm in CH2Cl2 solution and they are electroactive displaying a quasi-reversible reduction peak in the 0.14-0.30 V versus SCE region. The and the reduction peak potential (E-p(c)) values show linear relationships with the Hammett constant (sigma) of the substituents in the hydrazone ligands. These dinuclear complexes are converted to the corresponding mononuclear cis dioxo complexes K(H2O)(+)[(VO2)-O-V(L)](-) (5-8) and mixed-ligand [(VO)-O-V(L)(hq)] complexes on reaction, respectively, with two equivalents KOH in methanol and two equivalents 8-hydroxyquinoline (Hhq) in CHCl3. Ascorbic acid reduces the dioxovanadium(V) complexes reversibly under aerobic condition. (C) 2008 Elsevier Ltd. All rights reserved.