Dimeric Moiety Research Articles

Crystal structures of seven gold(III) complexes of the form LAuX 3 (L = substituted pyridine, X = Cl or Br).

The structures of seven gold(III) halide derivatives of general formula LAuX 3 (L = methyl-pyridines or di-methyl-pyridines, X = Cl or Br) are presented: tri-chlorido-(2-methyl-pyridine)-gold(III), [AuCl3(C6H7N)], 1 (as two polymorphs 1a and 1b); tri-bromido-(2-methyl-pyridine)-gold(III), [AuBr3(C6H7N)], 2; tri-bromido-(3-methyl-pyridine)-gold(III), [AuBr3(C6H7N)], 3; tri-bromido-(2,4-di-meth-yl-pyridine)-gold(III), [AuBr3(C7H9N)], 4; tri-chlorido-(3,5-di-methylpyridine)-gold(III), [AuCl3(C7H9N)], 5; tri-bromido-(3,5-di-methyl-pyridine)-gold(III), [AuBr3(C7H9N)], 6, and tri-chlorido-(2,6-di-methyl-pyridine)-gold(III), [AuCl3(C7H9N)], 7. Additionally, the structure of 8, the 1:1 adduct of 2 and 6, [AuBr3(C6H7N)]·[AuBr3(C7H9N)], is included. All the structures crystallize solvent-free, and all have Z' = 1 except for 5 and 7, which display crystallographic twofold rotation symmetry, and 4, which has Z' = 2. 1a and 2 are isotypic. The coordination geometry at the gold(III) atoms is, as expected, square-planar. Four of the crystals (1a, 1b, 2 and 8) were non-merohedral twins, and these structures were refined using the 'HKLF 5' method. The largest inter-planar angles between the pyridine ring and the coordination plane are observed for those structures with a 2-methyl substituent of the pyridine ring. The Au-N bonds are consistently longer trans to Br (average 2.059 Å) than trans to Cl (average 2.036 Å). In the crystal packing, a frequent feature is the offset-stacked and approximately rectangular dimeric moiety (Au-X)2, with anti-parallel Au-X bonds linked by Au⋯X contacts at the vacant positions axial to the coordination plane. The dimers are connected by further secondary inter-actions (Au⋯X or X⋯X contacts, 'weak' C-H⋯X hydrogen bonds) to form chain, double chain ('ladder') or layer structures, and in several cases linked again in the third dimension. Only 1b and 7 contain no offset dimers; these structures instead involve C-H⋯Cl hydrogen bonds combined with Cl⋯Cl contacts (1b) or Cl⋯π contacts (7). The packing patterns of seven further complexes LAuX 3 involving simple pyridines (taken from the Cambridge Structural Database) are compared with those of 1-8.

Catena-Poly[[μ2-aqua-diaquabis(μ4-pyridazine-3,6-dicarboxylato)tetralithium] monohydrate

In the polymeric structure of the title compound {[Li2(C6H2N2O4)2Li(H2O)2Li(H2O)]·H2O}n, the coordination of two independent LiI ions is distorted trigonal–bipyramidal and that of the other two independent LiI ions is distorted tetra­hedral. The former two LiI ions are bridged by hetero-ring N atoms of two independent pyridazine-3,6-dicarboxyl­ate ligands, making a dimeric moiety. The carboxyl­ato-O atoms of both bidentate ligands bridge the dimers to adjacent independent aqua-coordinated LiI ions, forming mol­ecular ribbons. The latter are bridged by ligand carboxyl­ato and aqua O atoms, forming mol­ecular layers parallel to (100) which are held together by an extended system of O—H⋯O hydrogen bonds.

Poly[[(μ(2)-acetato-κO,O':O')aqua-bis-(μ(3)-isonicotinato-κO:O':N)samarium(III)silver(I)] perchlorate

The title compound, {[AgSm(C6H4NO2)2(CH3CO2)(H2O)]ClO4}n, is a three-dimensional heterobimetallic complex constructed from a repeating dimeric unit. Only half of the dimeric moiety is found in the asymmetric unit; the unit cell is completed by crystallographic inversion symmetry. The SmIII ion is eight-coordinated by four O atoms of four different isonicotinate ligands, three O atoms of two different acetate ligands, and one O atom of a water mol­ecule. The two-coordinate AgI ion is bonded to two N atoms of two different isonicotinate anions, thereby connecting the disamarium units. In addition, the isonicotinate ligands also act as bridging ligands, generating a three-dimensional network. The coordinated water mol­ecules link the carboxyl­ate group and acetate ligands by O—H⋯O hydrogen bonding. Another O—H⋯O hydrogen bond is observed in the crystal structure. The perchlorate ion is disordered over two sites with site-occupancy factors of 0.560 (11) and 0.440 (11), whereas the methyl group of the acetate ligand is disordered over two sites with site-occupancy factors of 0.53 (5) and 0.47 (5).

3D-QSAR CoMFA Study to Predict Orientation of Suprahistaprodifens and Phenoprodifens in the Binding-Pocket of Four Histamine H1 -Receptor Species.

Several phenylhistamines and histaprodifens were identified to act as (partial) agonists at the histamine H1 -receptor (H1 R). The large diversity of these compounds led to pKi values in a range between 4.5-7.5 at human, rat, bovine and guinea-pig histamine H1 R. Hybrid molecules, consisting of two different H1 R-agonist partial structures, like suprahistaprodifens or phenoprodifens for example, or compounds with a dimeric histamine moiety are able to bind in two different orientations into the binding-pocket of the H1 R. In order to predict the percentage of ligand bound in orientation 1 or in orientation 2, 3D-QSAR studies at four H1 R species were performed. The training set contains ligands which can only bind in one orientation and the test set all ligands with two possible orientations. In general, the predicted pKi values of the test compounds were in good correlation to the experimental ones. Additionally, the predicted pKi values for all ligands with two possible orientations were used to calculate the percentage of the hybrid ligands bound in orientation 1 and 2. Our models suggest that the preferred orientation of these hybrid molecules is dependent on ligand and H1 R species.

From Polyoxometalates to Polyoxoperoxometalates and Back Again; Potential Applications

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Energy Transfer in Hybrids Based on a Thiophene-Substituted Ethynylbipyridine Dimer Decorated with Re(I), Ru(II), and Os(II) Units

The preparation, structural features, electrochemical behavior, and optical properties (at room temperature and at 77 K) are reported for a series of thiophene-containing hybrids based on the bent conjugated backbone of a rigid ditopic ligand, the dimeric moiety 3,4-dibutyl-2,5-bis{5'-[(3,4-dibutylthien-2-ylethynyl)-2,2'-bipyridin-5-yl]ethynyl}thiophene (TBTBT). Within the dimer, the diethynyl-2,2'-bipyridine units (bpy, the coordination sites) alternate with three 3,4-dibuthylthiophene units and coordination of the [Re(CO)3Cl], [Ru(bpy)2]2+, and [Os(bpy)2]2+ centers results in the mononuclear species RuTBTBT and OsTBTBT and the binuclear species RuTBTBTRu, OsTBTBTOs, RuTBTBTOs, and ReTBTBTOs. At room temperature, the emitting states obtained by photoexcitation are of 3MLCT nature, and vibronic analysis of the emission spectra indicates that they are largely delocalized over the TBTBT ligand. In the binuclear species, the intermetal separation is ca. 17 A, and for RuTBTBTOs, an efficient Ru --> Os excitation transfer takes place, resulting solely in an Os-based emission. The process is ascribed to double-electron transfer (Dexter), as mediated by the TBTBT ligand; a similar conclusion holds for the case of ReTBTBTOs. For RuTBTBTOs, the process is discussed in some detail also with regard to the possibility of disentangling the constituent hole and electron-transfer events.

A novel mixed-ligand antimycobacterial dimeric copper complex of ciprofloxacin and phenanthroline

A novel mixed-ligand Cu(II) complex of ciprofloxacin (cfH) and phenanthroline, is found to crystallize as a dimeric moiety containing monocationic and dicationic species. Two such dimeric moieties are found in the same unit cell leading to a dicationic cluster. The higher negative redox potential for this cluster dampens its antimycobacterial activity against M. smegmatis.

A new μ 1,5-dicyanamide bridged cyclic tetranuclear copper (II) complex with 1,5,9-triazacycledodecane ligands: structure, ESR spectroscopic and magnetic properties

The tetranuclear complex [Cu 2L 2(dca) 2(ClO 4) 2] 2 ( 1) (L = 1,5,9-triazacyclododecane, dca = dicyanamide [N(CN) 2] −) has been synthesized and its crystal structure, ESR spectra and magnetic properties determined. The complex contains a tetranuclear copper (II) moiety in which two dimeric units are bridged by two dca ligands. In each dimeric moiety the two copper (II) ions are bridged by one μ 1,5-dicyanamide ligand. Magnetic susceptibilities for the complex in the solid state are measured over the temperature range 4–300 K. The complex shows a weak antiferromagnetic coupling with a best fit J value −0.436 cm −1. The μ 1,5-dicyanamide bridges are the principal pathway for the super-exchange interaction and the weak antiferromagnetic coupling of the complex is interpreted in term of the μ 1,5-dicyanamide ligand behavior as a poor magnetic mediator.

Magneto-structural characterization of tetranuclear copper(II) complex [Cu 4(pz) 4L 2]·(ClO 4) (LH=1,3-diamino-2-propanol, Hpz=pyrazole)

The title compound C 18H 30ClCu 4N 12O 6 has been synthesized and its crystal structure and magnetic properties determined. The compound contains a tetranuclear copper(II) complex in which two dimeric units are bridged by two pyrazolate ligands and a perchlorate anion which is bound to the tetrameric unit by hydrogen bonds in the asymmetric unit. In each dimeric moiety the two copper(II) ions are bridged by the alkoxo group of the ligand and an additional pyrazolate ligand, these dimers are then bridged by two pyrazolate ions to form the tetranuclear complex. Magnetic susceptibilities for the compound in the solid state are measured over the temperature range 4.5–306.8 K. The experimental magnetic susceptibilities were fitted to the Bleaney–Bowers equation for a spin-coupled S=1/2 system in which the singlet–triplet separation is 2 J. The title compound shows weak antiferromagnetic coupling with a best fit J value −98.5 cm −1. The alkoxo oxygen bridge is one of the principal pathways for the super-exchange interaction and the weak antiferromagnetic coupling of the complex is interpreted in terms of the countercomplementary effect of the different bridging ligands which participate in the super-exchange interactions. The ab initio restricted Hartree–Fock molecular orbital calculation has shown that the pyrazolate bridge contributes to magnetic interaction countercomplementarily to the alkoxide bridge.

Polymerized isomers of CuCl2(C8H12N2S2). The X-ray crystal structures of dichloro(5,5?-6,6?-tetrahydro-2,2?-bi-4H-1,3-thiazine-N 3, N 3?)copper(II) and di-?-chloro-bis[chloro(5,5?-6,6?-tetrahydro-2, 2?-bi-4H-1,3-thiazine-N 3,N 3?)copper(II)

The monomer in the title was obtained as a first crop and the dimer as a second crop from a 95% ethanolic solution of CuCl2 and 5,5′-6,6′-tetrahydro-2,2′-bi-4H-1,3-thiazine (2,2′-bi-2-thiazine) in the mole ratio 1∶1.1. The monomeric crystals are blue, dichloro(5,5′-6,6′-tetrahydro-2,2′-bi-4H-1, 3-thiazine- N 3,N 3′)copper(II). The crystal consists of monomeric molecules with no short contacts to neighbouring molecules. The Cu atoms occupy special positions on 2-fold axes. The bidentate 2,2′-bi-2-thiazine bonds via N as it assumes a cis configuration with a twist of 10.3° about the inter-ring C—C bond. The Cu—N distance is 2.013(5) A, and Cu—Cl is 2.231(2) A. Coordination around Cu is slightly distorted square planar with a dihedral angle of 5.8(2)° between the Cu, N, Cl plane and Cu, N′, Cl′ plane. The dimeric crystals are green, di-μ-chloro-bis[chloro(5,5′-6,6′-tetrahydro-2,2′-bi-4H-1, 3-thiazine-N 3,N 3′)copper(II)]. The structure consists of discrete centrosymmetric dimers [CuCl2(C8H12N2S2)]2. Coordination around Cu is distorted square pyramidal (τ = 0.32) with two N atoms from the bidentate 2,2′-bi-2-thiazine occupying adjacent basal sites, and two Cl atoms occupying the other two basal sites. The average Cu—N distance is 2.028(4) A, Cu—Cl(1) is 2.284(2) A, Cu—Cl(2) is 2.239(1) A. Dihedral angle between the CuN2 and CuCl2 planes is 23.7°. Cl(1)′ of the adjacent inversion-related monomer, CuCl2-(C8H12N2S2), occupies the apical position. Cu—Cl(1)′, r = 2.618(2) A. Dimensions in the chloride-bridged planar dimeric moiety, Cu2Cl2, are Cu ⋯ Cu′ 3.449(1) A; Cl(1) ⋯ Cl(1)′ 3.498(2) A; Cu—Cl(1)—Cu′, φ = 89.2(1)°, φ/r = 34.07°/A. The two saturated rings in C8H12N2S2 show a twist of 11.4° about the inter-ring C—C bond.

Flexibility in coordinative behavior of propane-1,3-diamine toward Zn(II) and Cd(II) halides: M(1,3pn) 2X 2 (M=Zn, Cd; X=Cl, Br, I)

A series of compounds of formula M(1,3pn) 2X 2 (M  Zn(II), Cd(II); 1,3pn=propane-1,3-diamine; X  Cl, Br, I) has been prepared; two of them (M  Zn, X  Cl) and (M  Cd, X  I) have been structurally characterized. The Zn(1,3pn) 2Cl 2 ( I) compound crystallizes in the P2 1/ c space group, with eight formula units in a cell of dimensions: a=12.833(4), b=16.753(9), c=13.010(4) Å, β=118.88(3) °. The Cd(1,3pn) 2I 2 ( II) compound crystallizes in the P2 1/ n space group with four formula units in a cell of dimensions: a=12.406(3), b=8.655(2), c=14.372- (4) Å, β=113.57(2) °. The structures were solved with the heavy-atom method and refined by full matrix least-squares to R and R w values of 0.029 and 0.038, 0.042 and 0.058 for I and II respectively. The asymmetric unit of I consists of a dimeric [Zn- (1,3pn) 2] 2 4+ moiety, where both Zn ions are tetrahedrally coordinated to four nitrogen atoms belonging to one chelating and two bridging 1,3pn ligands. The dimeric moiety generates an infinite chain upon translation of one cell in the direction of the diagonal (1,0,1). The structure of II shows a polymeric arrangement of octahedral Cd atoms sharing both iodine atoms and 1,3pn ligands. The MN stretching vibrations are discussed and assigned in the light of the known structures.