A comparative study of solid carbon acid catalysts for the esterification of free fatty acids for biodiesel production. Evidence for the leaching of colloidal carbon.

The preparation of a variety of sulfonated carbons and their use in the esterification of oleic acid is reported. All sulfonated materials show some loss in activity associated with the leaching of active sites. Exhaustive leaching shows that a finite amount of activity is lost from the carbons in the form of colloids. Fully leached catalysts show no loss in activity upon recycling. The best catalysts; 1, 3, and 6; show initial TOFs of 0.07 s(-1), 0.05 s(-1), and 0.14 s(-1), respectively. These compare favorably with literature values. Significantly, the leachate solutions obtained from catalysts 1, 3, and 6, also show excellent esterification activity. The results of TEM and catalyst poisoning experiments on the leachate solutions associate the catalytic activity of these solutions with carbon colloids. This mechanism for leaching active sites from sulfonated carbons is previously unrecognized.

Pressure-induced cooperative bond rearrangement in a zinc imidazolate framework: a high-pressure single-crystal X-ray diffraction study.

The pressure-dependent structural evolution of a neutral zinc-imidazolate framework [Zn(2)(C(3)H(3)N(2))(4)](n) (ZnIm) has been investigated. The as-synthesized three-dimensional ZnIm network (alpha-phase) crystallizes in the tetragonal space group I4(1)cd (a = 23.5028(4) A, c = 12.4607(3) A). The ZnIm crystal undergoes a phase transition to a previously unknown beta-phase within the 0.543(5)-0.847(5) GPa pressure range. The tetragonal crystal system is conserved during this transformation, and the beta-phase space group is I4(1) (a = 22.7482(3) A, c = 13.0168(3) A). The physical mechanism by which the transition occurs involves a complex cooperative bond rearrangement process. The room-temperature bulk modulus for ZnIm is estimated to be approximately 14 GPa. This study represents the first example of a high-pressure single-crystal X-ray diffraction analysis of a metal-organic framework.

Disorder and pseudo-symmetry in octakis(trivinylsilyl)octasilicate.

Octakis(trivinylsilyl)octasilicate was prepared by capping octaspherosilicate cubes, [Si(8)O(20)](8-), with trivinylsilyl groups in methanol solution. Crystals grown from CCl(4) crystallize in the tetragonal space group I4(1). Systematic absences are consistent with the space group I4(1)/amd, although the R(int) values clearly indicate 4/m rather than 4/mmm Laue symmetry. Structure solution and refinement show that the pseudo a-glide results from the approximate m\bar 3m symmetry of the core (Si(8)O(12))O(8)(8-) unit. The positions of the molecules conform to a {110} d-glide that is broken by the small rotations of all the molecules in the same direction about [001]. Crystals grown from toluene give a diffraction pattern consisting of sharp peaks that can be indexed on the same ca 7200 A(3) unit cell, but with h + k even, and l even only. The l = odd layers contain no Bragg spots, but instead exhibit diffuse sheets of intensity. Within the sheets of diffuse scattering are streaks parallel to r* = 110* that cross at the h + k odd Bragg positions. This diffuse scattering pattern arises from well ordered rods of molecules parallel to c with frequent faults in the stacking sequence of molecules parallel to 110, with displacement vectors of [00(1/2)].

Structural diversity in 4,4'-trimethylenedipyridine-zinc phosphite hybrids: incorporation of neutral guest molecules in hybrid materials.

Six new zinc phosphite hybrids are prepared under a variety of reaction conditions from the primary building blocks, trimethylenedipyridine, zinc acetate, and phosphorous acid. Neutral guest molecules are incorporated into several of the structures. Under hydrothermal conditions at 130 degrees C, an anionic framework structure, 1, templated on trimethylenedipyridinium, is obtained while a neutral ladder structure, 2, is formed at room temperature. These reactions are done at an initial pH of 4.7-5.0. When the reaction is done at an initial pH of 7.8-8.0, a neutral layered motif is obtained with 1,3-dipyridylpropane pillars and neutral guests in the interstitial space. Structures with water, phenol, and catechol as the guests, compounds 3, 4, and 5, respectively, are reported. The use of catechol as a template results in the breakup of the ZnPO sheet structure common to both 3 and 4. When amino acids, including alanine, were added to the reaction medium, a neutral three-dimensional framework, 6, is obtained with no incorporation of the potential template. The syntheses and structures of these new materials are reported.

Syntheses, structures, and magnetic properties of inorganic-organic hybrid cobalt(II) phosphites containing bifunctional ligands.

Seven new cobalt(II) phosphites, [Co(HPO(3))(C(14)H(14)N(4))(H(2)O)(2)].2H(2)O (1), [Co(HPO(3))(C(22)H(18)N(4))].H(2)O (2), [Co(2)(HPO(3))(2)(C(22)H(18)N(4))(2)H(2)O].H(2)O (3), [Co(2)(HPO(3))(2)(C(12)H(10)N(4))(1.5)H(2)O].1.5H(2)O (4), [Co(HPO(3))(C(14)H(14)N(4))(0.5)].H(2)O (5), [Co(HPO(3))(C(18)H(16)N(4))(0.5)] (6), and [Co(HPO(3))(C(18)H(16)N(4))(0.5)] (7) were synthesized in the presence of 1,2-bis(imidazol-1-ylmethyl)benzene (L1), 1,4-bis(benzimidazol-1-ylmethyl)benzene (L2), 1,3-bis(benzimidazol-1-ylmethyl)benzene (L3), 1,4-bis(1-imidazolyl)benzene (L4), 1,4-bis(imidazol-1-ylmethyl)benzene (L5), 1,4-bis(imidazol-1-ylmethyl)naphthalene (L6), and 1,5-bis(imidazol-1-ylmethyl)naphthalene (L7), respectively, and their structures were determined by X-ray crystallography. Compound 1 is a molecular compound in which two cobalt(II) ions are held together by double mu-O linkages. The inorganic framework of compounds 2 and 3 are composed of vertex-shared CoO(2)N(2)/CoO(3)N(2) and HPO(3) polyhedra that form four rings; these are further linked by an organic ligand to generate 2D sheets. Compounds 4 and 5 both have 1D inorganic structures, with the bifunctional ligands connected to each side of the ladder by coordination bonds to give 2D hybrid sheets. A 3D organically pillared hybrid framework is observed in 6 and 7. In 6, the stacking of the interlayer pillars gives rise to a small hydrophobic channel that extends through the entire structure parallel to the sheets. The temperature-dependent magnetic susceptibility measurements of these compounds show weak interactions between the metal centers, mediated through the mu-O and/or O-P-O linkages.

Novel zinc phosphate topologies defined by organic ligands.

Six new zinc phosphates [C18H20N4][Zn4(HPO4)4(H2PO4)2(C18H18N4)3].2H2O (1), [Zn4(HPO4)4(C18H18N4)3].4H2O (2), [Zn3(HPO4)3(H2PO4)(C22H22N8)0.5(C22H24N8)0.5] (3), [Zn2(HPO4)2(C18H16N4)] (4), [Zn(HPO4)(C18H14N2)] (5), and [Zn2(HPO4)2(C12H10N4)] (6) have been synthesized under mild hydrothermal conditions in the presence of 1,4-bis(N-benzimidazolyl)butane (L1), 1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene (L2), 1,4-bis(imidazol-1-ylmethyl)naphthalene (L3), 9-(imidazol-1-ylmethyl)anthracene (L4), and 1,4-bis(1-imidazolyl)benzene (L5), respectively, and their structures were determined by X-ray crystallography. Compound 1 exhibits a unique inorganic motif of isolated 8-rings interconnected by L1. Compound 2, also formed from L1, contains a previously unobserved chain structure composed of edge-sharing 4-rings and 8-rings. Compound 3, prepared from L2, possesses an unusual one-dimensional framework, which is composed of vertex-sharing 4-rings and triple fused 4-rings. The inorganic portions of 4, 5, and 6 each adopt a layer structure. The sheets in 4 and 5 have a 4.8(2) topology, and in 6, a 6(3) topology is observed. The zinc atoms in compounds 1-6 are all tetrahedrally coordinated by a combination of phosphate groups and organic ligands. Potential relationships between the inorganic motifs reported in the present study are identified. These are indicative of a possible pattern of self-assembly of zinc and phosphorus tetrahedra and indicative of the role of the organic ligands in the formation of hybrid structures.

A two-dimensional cationic lattice built from [Zn6(HPO4)2(PO4)2]2+ clusters.

A unique cationic zinc phosphate cluster linked by neutral bifunctional rigid ligands to form a two dimensional framework was synthesized and structurally characterized.

Five new zinc phosphite structures: tertiary building blocks in the construction of hybrid materials.

The syntheses and structures of five new zinc phosphites [Zn(HPO(3))(C(4)H(6)N(2))] (1), [Zn(2)(HPO(3))(2)(C(10)H(10)N(2))(2)](2) (2), [Zn(HPO(3))(C(14)H(14)N(4))(0.5)] (3), [Zn(2)(HPO(3))(2)(C(14)H(14)N(4))].0.4H(2)O (4), and [Zn(2)(HPO(3))(2)(C(14)H(14)N(4))] (5) are reported. In compounds 1-3, the zinc atoms are ligated by 1-methylimidazole, 1-benzylimidazole, and 1,4-bis(imidazol-1-ylmethyl)benzene, respectively, while compounds 4 and 5 are synthesized in the presence of the same bifunctional ligand, 1,3-bis(imidazol-1-ylmethyl)benzene. The inorganic framework of compound 1 is composed of vertex-shared ZnO(3)N and HPO(3) tetrahedra that form 4-rings, which, in turn, are linked to generate a one-dimensional ladder structure. In 2, the inorganic framework is composed of 4-rings and 8-rings to form the well-known 4.8(2) 2D network. This is connected via C-H...pi interactions between 1-benzylimidazole ligand to generate a pseudo-pillared-layer structure. In 3, the inorganic framework again has the 4.8(2) topology pillared by the bis(imidazole) ligand, 1,3-bis(imidazol-1-ylmethyl)benzene. In 4, a new layer pattern is observed. Specifically, three edge-sharing 4-rings form triple-fused 4-rings. These tertiary building units are further connected to form 12-rings. The alternating triple 4-rings and 12-rings form a previously unknown 2D inorganic sheet. The sheets are joined together by the bis(imidazole) ligand, 1,3-bis(imidazol-1-ylmethyl)benzene, to generate a 3D pillared-layer structure. In 4, benzene rings and imidazole rings stack in a zigzag pattern in the interlayer space. A significant role for the triple 4-ring tertiary building unit in the formation of hybrid inorganic/organic metal phosphite structures is proposed for 4 and 5. In 5, the triple 4-rings fuse to give a 1D stair-step structure. Calculations show that the triple 4-ring pattern observed in the linear ladder structure of 1 is more stable than that in the stair step pattern of 5.

New zinc phosphates decorated by imidazole-containing ligands.

Four new zinc phosphates [Zn(HPO4)(C6H9N3O2)] (1), [Zn(HPO4)(C4H6N2)].H2O (2), [Zn2(HPO4)2(C14H14N4)].2H2O (3), and [Zn(HPO4)(C14H14N4)] (4) were synthesized in the presence of d-histidine, 1-methylimidazole, 1,4-bis(imidazol-1-ylmethyl)benzene (L1), and 1,2-bis(imidazol-1-ylmethyl)benzene (L2), respectively, and their structures were determined by X-ray crystallography. The inorganic framework of compounds 1, 2, and 3 is composed of vertex-shared ZnO3N and HPO4 tetrahedra that form four rings, which, in turn, are linked to generate a one-dimensional ladder structure. In 1 and 2 the organic groups (monoimidazole ligand) are located at each side of the ladders, while in 3 the bisimidazole ligand, 1,4-bis(imidazol-1-ylmethyl)benzene, links the ladders together to form a novel 2D structure. Compound 1 is the first zinc phosphate framework to be templated by an N-bonded chiral amino acid. In 4 the zero-dimensional four rings are joined together by the linear bridging ligand, 1,2-bis(imidazol-1-ylmethyl)benzene, to generate a one-dimensional framework with a new face-to-face structural motif. The 3D structure of compound 4 is stabilized by hydrogen-bonding, pi-pi interactions, and C-H...pi interactions. The approach of incorporating multifunctional ligands into zinc phosphate frameworks and linking the inorganic zinc phosphates subunits by an organic ligand provides opportunities for the design of new inorganic-organic open frameworks.

High pressure study of Ru3(CO)12 by X-ray diffraction, Raman, and infrared spectroscopy.

The single-crystal X-ray structure of Ru(3)(CO)(12) is reported at 8 pressures ranging from 1 atm (0.0 GPa) to 8.14(5) GPa. Although intramolecular bonding parameters remain relatively constant, intramolecular and intermolecular nonbonding contact distances decrease by an average of 4% and 15%, respectively. At 8.14 GPa, O...O, C...O, and C...C intermolecular distances as short as 2.54(4), 2.64(6), and 3.07(4) A, respectively, are observed, and the unit cell compresses to 75% of the ambient pressure volume. Raman and infrared spectroscopic measurements show that carbonyl stretching frequencies shift to higher wavenumber values by as much as 80 cm(-)(1), even though Ru-C and C-O distances stay roughly constant throughout the entire pressure range studied. Compression of the sample to above 18 GPa with laser radiation results in an irreversible transformation due to either decomposition or a total collapse of D(3)(h) molecular geometry accompanied by color darkening.