Trans/cis isomerization of [RuCl2(diphosphine)(diamine)] complexes: synthesis, X-ray structure and catalytic activity in hydrogenation.

The diamine (N-N) co-ligand 2,2-dimethyl-1,3-propanediamine and 2,3-diaminophathalene react individually with [RuCl(2)(dppb)(2)(µ-dppb)] to afford complexes with kinetically stable trans-[Cl(2)Ru(dppb)(N-N)] as the favoured isomer. The thermodynamically stable cis-[Cl(2)Ru(dppb)(N-N)] isomer of complex 1 was formed from the trans-1 isomer. The trans to cis isomerization reaction was conducted in CHCl(3) at RT and monitored by (31)P{(1)H} NMR. The structures of the desired complexes were characterized via elemental analyses, IR and, UV-visible spectroscopy, FAB-MS and NMR. The structure of the cis-1 isomer was determined by single crystal X-ray measurements. Both the trans-1 and cis-1 isomers were shown to have a significant catalytic role in selective hydrogenation reactions under mild conditions using cinnamic aldehyde as typical model reaction.

2,6-Dimethyl-pyridinium bromide.

The asymmetric unit of the title salt, C(7)H(10)N(+)·Br(-), comprises two 2,6-dimethyl-pyridinium cations and two bromide anions. One cation and one anion are situated in general positions, while the other cation and the other anion lie on a crystallographic mirror plane parallel to (010). Each pair of ions inter-act via N-H⋯Br and C-H⋯Br hydrogen bonding, generating motifs depending on the cation and anion involved. Thus, the cation and the anion on the mirror plane generate infinite chains along the c axis, while the other ionic pair leads to sheets parallel to the ac plane. In the overall crystal packing, both motifs alternate along the b axis, with a single layer of the chain motif sandwiched between two double layers of the sheet motif. The sheets and chains are further connected via aryl π-π inter-actions [centroid-centroid distances = 3.690 (2) and 3.714 (2) Å], giving a three-dimensional network.

Redetermination of 2,2'-bipyridine-1,1'-diium dibromide.

In the title mol-ecular salt, C(10)H(10)N(2) (2+)·2Br(-), the dihedral angle between the aromatic rings is 20.83 (14)° and the N-H groups have a transoid conformaton [N-C-C-N = 158.5 (3)°]. In the crystal, the cations are linked to the anions by two N-H⋯Br and five C-H⋯Br hydrogen bonds, generating corrugated sheets incorporating R(2) (1)(7), R(4) (2)(10), R(4) (2)(11) and two different R(4) (2)(12) loops. This structure was originally reported by Nakatsu et al. [Acta Cryst (1972), A28, S24], but no atomic coordinates are available.

Bis(2,6-dimethyl-pyridinium) dibromo-iodate bromide.

In the title salt, 2C(7)H(10)N(+)·IBr(2) (-)·Br(-), each of the anions, viz. [IBr(2)](-) and Br(-), lie on a twofold axis. The IBr(2) (-) anion is almost linear, with a Br-I-Br angle of 178.25 (3)°. The cation is essentially planar (r.m.s. deviation = 0.0067 Å). In the crystal, each Br(-) anion links two cations via N-H⋯Br⋯H-N hydrogen-bonding inter-actions.

2-Amino-5-methyl-pyridinium dibromo-iodate.

In the title salt, C(6)H(9)N(2) (+)·Br(2)I(-), the cation is essentially planar (r.m.s. deviation = 0.0062 Šfor the non-H atoms) while the anion is almost linear with a Br-I-Br angle of 177.67 (2)°. The crystal packing shows two anions and two cations connected via N-H⋯Br and (pyridine)N-H⋯Br hydrogen-bonding inter-actions, forming centrosymmetric tetra-mers with R(4) (4)(16) ring motifs. Very weak offset aromatic π-π stacking interactions [centroid-centroid separation = 4.038 (4), slippage = 1.773 Å] also occur.

Synthesis, spectral, thermal, X-ray single crystal of new RuCl2(dppb)diamine complexes and their application in hydrogenation of Cinnamic aldehyde.

The preparation of new three trans-[RuCl(2)(dppb)(N-N)] with mixed diamine (N-N) and 1,4-bis-(diphenylphosphino)butane (dppb) ligands, starting from RuCl(2)(PPh(3))(3) as precursor is presented. The complexes are characterized on the basis of elemental analysis, IR, (1)H, (13)C and (31)P{(1)H}NMR, FAB-MS, TG/DTA and single crystal X-ray diffraction studies. Complex (2L(1)) crystallizes in the monoclinic unit cells with the space group P2(1). The catalysts are evaluated for their Cinnamic aldehyde hydrogenation. The catalysts show excellent activity and selectivity for the unsaturated carbonyl compound under mild conditions.

Bis(2,4-dimethyl-pyridinium) tetra-bromido-mercurate(II).

The asymmetric unit of the title compound, (C7H10N)2[HgBr4], consists of one cation and one half-anion, bis-ected by a twofold rotation axis passing through the metal atom. The anion exhibits a distorted tetra-hedral arrangement about the Hg(II) atom. In the crystal, the cations and anions are linked by N-H⋯Br hydrogen-bonding inter-actions along [010]. Cation-cation π-π stacking and Br⋯Br inter-molecular inter-actions are absent.

Bis(2,4,6-trimethyl-pyridinium) tetra-bromidozincate.

In the title compound, (C(8)H(12)N)(2)[ZnBr(4)], the coordination geometry of the anion is approximately tetra-hedral. The Zn-Br bond lengths range from 2.3901 (19) to 2.449 (2) Šand the Br-Zn-Br angles range from 107.09 (8) to 112.48 (8)°. In the crystal, each [ZnBr(4)](2-) anion is connected to four cations through two N-H⋯Br and two C-H⋯Br hydrogen bonds, forming two-dimensional ⋯(cation)(2)⋯anion⋯(cation(2))⋯ sheets parallel to the bc plane. Within each sheet, the anions are arranged in stacks with no significant inter-anion Br⋯Br inter-actions [the shortest being > 4.3 Å], while the cations are in chains, with weak π-π stacking inter-actions [centroid-centroid distance = 3.991 Å] between cations inter-acting with the same anion.

3-(Ammonio-meth-yl)pyridinium dibromide.

In the title salt, C(6)H(10)N(2) (2+)·2Br(-), the non-H atoms of the 3-methyl-pyridinium unit of the cation are almost coplanar (r.m.s. deviation = 0.0052 Å). In the crystal, the dications and Br anions are linked by a combination of six hydrogen bonds, viz. one N(py)-H⋯Br, two C-H⋯Br and three H(2)N-H⋯Br, into supra-molecular layers, parallel to the bc plane, composed of alternating R(2) (4)(10) and R(2) (4)(8) loops. Weak π-π inter-actions between cationic rings with centroid-centroid distances of 3.891 (2) Šare also observed.

Three isomorphous 2,6-dibromopyridinium tetrabromidometallates: (C(5)H(4)Br(2)N)(2)[MBr(4)].2H(2)O (M = Cu, Cd and Hg).

The structures of three isomorphous compounds, namely bis(2,6-dibromopyridinium) tetrabromidocuprate(II) dihydrate, (C(5)H(4)Br(2)N)(2)[CuBr(4)].2H(2)O, bis(2,6-dibromopyridinium) tetrabromidocadmate(II) dihydrate, (C(5)H(4)Br(2)N)(2)[CdBr(4)].2H(2)O, and bis(2,6-dibromopyridinium) tetrabromidomercurate(II) dihydrate, (C(5)H(4)Br(2)N)(2)[HgBr(4)].2H(2)O, show a crystal supramolecularity represented by M-Br...H-O-H...Br-M intermolecular interactions along with (pi)N-H...OH(2) hydrogen-bonding interactions forming layers connected via aryl-aryl face-to-face stacking of cations, leading to a three-dimensional network. The anions have significantly distorted tetrahedral geometry and crystallographic C(2) symmetry. The stability of this crystal lattice is evidenced by the crystallization of a whole series of isomorphous compounds.

Three-dimensional framework structures: isomorphous bis(2,6-diamino-3,5-dibromopyridinium) tetrabromidometallate(II) salts with Cd(II) and Mn(II).

In the structural motifs of two isomorphous triclinic salts, (C5H6Br2N3)2[MBr4] (M = Cd(II) and Mn(II)), each [MBr4]2- anion interacts with eight surrounding 2,6-diamino-3,5-dibromopyridinium cations through intermolecular C/N-H...Br and Br...Br interactions, leading to a three-dimensional framework structure. The cations show a minor degree of pi-pi stacking, adding extra stability to the three-dimensional architecture.

Biotransformation of methyl cholate by Aspergillus niger.

Biotransformation of methyl cholate using Aspergillus niger was investigated. This led to the isolation of two derivatives: methyl 3alpha,7alpha,12alpha,15beta-tetrahydroxy-5beta-cholan-24-oate identified as a new compound, and a known compound methyl 3alpha,12alpha-dihydroxy-7-oxo-5beta-cholan-24-oate. The structure elucidation of the new compound was achieved using 1D and 2D NMR, MS and X-ray diffraction.

2,5-Dibromo-pyridine.

In the title compound, C(5)H(3)Br(2)N, C-H⋯N hydrogen-bonding inter-actions and Br⋯Br inter-actions [3.9418 (3) and 3.8986 (3) Å] connect the mol-ecules into planar sheets stacked perpendicular to the b axis. In addition, pyrid-yl-pyridyl inter-sheet π-π stacking inter-actions [centroid-centroid distance = 4.12 (1) Å] result in a three-dimensional network.

Bis(2,6-dimethyl-pyridinium) tetra-bromido-zincate(II).

In the crystal structure of the title compound, (C(7)H(10)N)(2)[ZnBr(4)], the coordination geometry of the anion is approximately tetra-hedral and a twofold rotation axis passes through the Zn atom. The Zn-Br bond lengths range from 2.400 (2) to 2.408 (3) Šand the Br-Zn-Br angles range from 108.14 (6) to 115.15 (15)°. In the crystal structure, the [ZnBr(4)](2-) anion is connected to two cations through N-H⋯Br and H(2)C-H⋯Br hydrogen bonds, forming two-dimensional cation-anion-cation layers normal to the b axis. No significant Br⋯Br inter-actions [the shortest being 4.423 (4) Å] are observed in the structure.

Bis(2,6-diamino-3,5-dibromo-pyridinium) hexa-bromidostannate(IV).

The asymmetric unit of the title compound, (C(5)H(6)Br(2)N(3))(2)[SnBr(6)], contains one cation and one half-anion in which the Sn atom is located on a crystallographic centre of inversion and is in a quasi-octa-hedral geometry. The crystal structure is assembled via hydrogen-bonding inter-actions of two kinds, N(pyridine/amine)-H⋯Br-Sn, along with C-Br⋯Br-Sn interactions [3.4925 (19) Å]. The cations are involved in π-π stacking, which adds an extra supra-molecularity as it presents a strong case of offset-face-to-face motifs [centroid-centroid distance = 3.577 (3) Å]. The inter-molecular hydrogen bonds, short Br⋯Br inter-actions and π-π stacking result in the formation of a three-dimensional supra-molecular architecture.

Bis(2,6-dimethyl-pyridinium) tetra-bromido-cobaltate(II).

In the crystal structure of the title compound, (C(7)H(10)N)(2)[CoBr(4)], the [CoBr(4)](2-) anion is connected to two cations through N-H⋯Br and H(2)C-H⋯Br hydrogen bonds to form two-dimensional cation-anion-cation layers normal to the crystallographic b axis. Inter-actions of the π-π type are absent between cations in the stacks [centroid-centroid separation = 5.01 (5) Å]. Significant inter-molecular Br-aryl inter-actions are present in the structure, especially an unusually short Br-ring centroid inter-action of 3.78 (1) Å. The coordination geometry of the anion is approximately tetrahedral and a twofold rotation axis passes through the Co atom.

Bis(2-bromo-pyridinium) hexa-chlorido-stannate(IV).

The asymmetric unit of the title compound, (C(5)H(5)BrN)(2)[SnCl(6)], contains one cation and one half-anion. The [SnCl(6)](2-) anion is located on an inversion center and forms a quasi-regular octa-hedral arrangement. Hydrogen-bonding inter-actions of two kinds, viz. N-H⋯Cl-Sn and C-H⋯Cl-Sn, along with Cl⋯Br inter-actions [3.4393 (15) Å], connect the ions in the crystal structure into two-dimensional supra-molecular arrays. These supra-molecular arrays are arranged in layers approximately parallel to (110) built up from anions inter-acting with six symmetry-related surrounding cations.

Bis-(2-amino-6-methyl-pyridinium) tetra-bromido-cuprate(II).

In the crystal structure of the title compound, (C(6)H(9)N(2))(2)[CuBr(4)], the geometry around the Cu atom is inter-mediate between tetra-hedral (T(d)) and square planar (D(4h)). Each [CuBr(4)](2-) anion is connected non-symmetrically to four surrounding cations through N-H⋯X (pyridine and amine proton) hydrogen bonds, forming chains of the ladder-type running parallel to the crystallographic b axis. These layers are further connected by means of offset face-to-face inter-actions (parallel to the a axis), giving a three-dimensional network. Cation π-π stacking [centroid separations of 3.69 (9) and 3.71 (1) Å] and Br⋯aryl inter-actions [3.72 (2) and 4.04 (6) Å] are present in the crystal structure. There are no inter-molecular Br⋯Br inter-actions.

Bis(2-bromo-pyridinium) hexa-bromido-stannate(IV).

The asymmetric unit of the title compound, (C(5)H(5)BrN)(2)[SnBr(6)], contains one cation and one half-anion. The [SnBr(6)](2-) anion is located on an inversion center and forms a quasi-regular octa-hedral arrangement. The crystal structure consists of two-dimensional supra-molecular layers assembled via hydrogen-bonding inter-actions of N-H⋯Br-Sn [D⋯A = 3.375 (13)-3.562 (13) Šand D-H⋯A = 127-142°, along with C-Br⋯Br synthons [3.667 (2) and 3.778 (3) Å]. These layers are parallel to the bc plane and built up from anions inter-acting extensively with the six surrounding cations.

3-Ammonio-pyridinium tetra-bromido-mercurate(II) monohydrate.

The asymmetric unit of the title compound, (C(5)H(8)N(2))[HgBr(4)]·H(2)O, consists of one cation, one anion and one water mol-ecule. The anion exhibits a distorted tetra-hedral arrangement about the Hg atom. The crystal structure contains alternating sheets of cations (in the ac plane) and stacks of anions. Several strong hydrogen-bonding inter-actions (pyN-H⋯Br and C-H⋯Br; py is pyridine), along with O-H⋯Br inter-actions, connect the sheets of cations to the stacks of anions. Cation-cation π-π stacking is also present (C⋯C distances in the range 3.424-3.865 Å). The shortest Br⋯Br distance is 3.9527 (9) Å.