Nickel(II) and copper(II) complexes of 2-(2-pyridyl)benzimidazole: synthesis and structural characterization

2-(2-Pyridyl)benzimidazole (PBI) was synthesized by solvent-free aldol condensation and complexed with nickel(II) and copper(II) nitrate and perchlorate salts by simple reactions at room temperature. The transition metal complexes [Ni(PBI)2NO3](NO3) (1), [Ni(PBI)3](ClO4)2·1.5H2O (2), [Cu(PBI)2NO3](NO3) (3), and [Cu(PBI)3](ClO4)2·3H2O (4) (PBI=2-(2-pyridyl)benzimidazole) were synthesized in good yield and structurally characterized by X-ray crystallography, infrared absorption spectroscopy, and elemental analysis. Complexes 1 and 3 are isostructural, crystallizing in the same space group P21/c. Both the nickel(II) and copper(II) atoms have distorted square pyramidal geometries. The metal centers in these complexes are coordinated by two molecules of the bidentate ligand (PBI) and an O-atom of the coordinated nitrate anion. Complexes 2 and 4 are also isostructural but do not crystallize in the same space group: P-1 for 2 and Pccn for 4. The geometry around both the nickel(II) and the copper(II) centers is distorted octahedral. Here, the metal atoms are coordinated by three molecules of 2-(2-pyridyl)benzimidazole. The copper(II) complex 4 has 2-fold symmetry with one of the three PBI ligands being positionally disordered about the 2-fold axis. Intermolecular N-H···O hydrogen bonds, involving the NH H-atom and an O-atom of the coordinated nitrate anion, are observed in all four complexes. In 1 and 3, this gives rise to the formation of centrosymmetric dimer-like structures that are decorated by hydrogen-bonded nitrate anions. In 2 and 4 the perchlorate anions and the water molecules of crystallization are involved in N-H···O and O-H···O hydrogen bonds bridging two symmetry-related cations, thus forming cyclic arrangements. In the case of complex 4, this leads to the formation of two-dimensional hydrogen-bonded networks parallel to plane (011

The Crystal and Molecular Structures of 2,5-Bis(2'-pyridyl)-pyrazine (BPPZ) and Some 3d Transition-Metal Complexes

The symmetrical ligand 2,5-bis(2'-pyridyl)pyrazine (BPPZ) exists in the extended form with a dihedral angle between the pyrazine and the pyridine rings of 7.88°. BPPZ forms symmetrical bis(bidenate) complexes with MnII, FeII, and CuII. The dihedral angles between the best planes through the planar pyrazine ring and the pyridine ring are 2.6° in the MnII complex, 4° in the FeII complex, and 8.5° in the CuII complex. The metal-Npy bond distances are shorter than standard values and similar in length to the metal-Npz distances

AgI, CdII, and HgII complexes with 2,5-bis(pyridyl)pyrazine ligands: syntheses, spectral analyses, single crystal, and powder X-ray analyses

2,5-Bis(4-pyridyl)pyrazine (4-bppz) and 2,5-bis(3-pyridyl)pyrazine (3-bppz) have been synthesized and characterized spectroscopically and crystallographically. 4-bppz [unit cell: a = 7.319(1), b = 5.746(1), c = 12.756(2) Å, β = 93.16(1)° space group: P21/a] was characterized by X-ray single crystal diffraction methods while the structure of 3-bppz [unit cell: a = 10.9148(4), b = 4.5722(1), c = 11.4462(2) Å, β = 109.571(2)° space group: P21/c] was determined from laboratory X-ray powder diffraction data. In these compounds, the pyrazine ring contains two symmetrically attached pyridine substituents with the nitrogen atom in the para positions for 4-bppz and in the meta positions for 3-bppz. Both compounds possess Ci symmetry with the pyridine rings twisted by 17.7° (4-bppz) and 2.6° (3-bppz) with respect to the pyrazine ring. 4-bppz was used in the formation of coordination compounds with silver(I) and cadmium(II). The silver(I) complex [Ag(OAc)(4-bppz)] n (1) [unit cell: a = 8.472(1), b = 13.051(1), c = 19.063(2) Å, β = 109.96(1)° space group: P21/c] is characterized by the formation of a perfectly linear chain containing the silver ions bridged by the ligand molecule, the latter using its pyridine nitrogen donor atoms for coordination. A pair of chains is interconnected by silver-silver interactions, the silver coordination sphere being completed by acetate anions. A similar one-dimensional coordination polymer, [Cd(OAc)2(4-bppz)(MeOH)] n (2) [unit cell: a = 8.680(1), b = 10.035(1), c = 13.445(1) Å, α = 77.35(1), β = 71.17(1), γ = 80.14(1)° space group: $$P\bar 1$$ ], was obtained by the reaction of 4-bppz with Cd(OAc)2. Ligand 3-bppz forms an analogous cadmium(II) complex, [Cd(OAc)2(3-bppz)(MeOH)] n (3) [unit cell: a = 9.306(1), b = 9.733(1), c = 11.550(1) Å, α = 87.86(1), β = 76.73(1), γ = 85.91(1)° space group: $$P\bar 1$$ ], containing the molecules arranged in double zigzag chains. The reaction of 3-bppz with HgI2 leads surprisingly to a binuclear complex, [Hg2I4(3-bppz)2] (4) [unit cell: a = 17.555(1), b = 12.973(1), c = 16.195(1) Å, β = 115.32(1)° space group: C2/c]. Two ligand molecules are bridged by two mercury(II) ions forming a cyclic structure, the tetrahedral coordination sphere of the metal being completed by iodide anion

AgI, CdII, and HgII complexes with 2,5-bis(pyridyl)pyrazine ligands: syntheses, spectral analyses, single crystal, and powder X-ray analyses

2,5-Bis(4-pyridyl)pyrazine (4-bppz) and 2,5-bis(3-pyridyl)pyrazine (3-bppz) have been synthesized and characterized spectroscopically and crystallographically. 4-bppz [unit cell: a = 7.319(1), b = 5.746(1), c = 12.756(2) Å, β = 93.16(1)° space group: P21/a] was characterized by X-ray single crystal diffraction methods while the structure of 3-bppz [unit cell: a = 10.9148(4), b = 4.5722(1), c = 11.4462(2) Å, β = 109.571(2)° space group: P21/c] was determined from laboratory X-ray powder diffraction data. In these compounds, the pyrazine ring contains two symmetrically attached pyridine substituents with the nitrogen atom in the para positions for 4-bppz and in the meta positions for 3-bppz. Both compounds possess Ci symmetry with the pyridine rings twisted by 17.7° (4-bppz) and 2.6° (3-bppz) with respect to the pyrazine ring. 4-bppz was used in the formation of coordination compounds with silver(I) and cadmium(II). The silver(I) complex [Ag(OAc)(4-bppz)] n (1) [unit cell: a = 8.472(1), b = 13.051(1), c = 19.063(2) Å, β = 109.96(1)° space group: P21/c] is characterized by the formation of a perfectly linear chain containing the silver ions bridged by the ligand molecule, the latter using its pyridine nitrogen donor atoms for coordination. A pair of chains is interconnected by silver-silver interactions, the silver coordination sphere being completed by acetate anions. A similar one-dimensional coordination polymer, [Cd(OAc)2(4-bppz)(MeOH)] n (2) [unit cell: a = 8.680(1), b = 10.035(1), c = 13.445(1) Å, α = 77.35(1), β = 71.17(1), γ = 80.14(1)° space group: $$P\bar 1$$ ], was obtained by the reaction of 4-bppz with Cd(OAc)2. Ligand 3-bppz forms an analogous cadmium(II) complex, [Cd(OAc)2(3-bppz)(MeOH)] n (3) [unit cell: a = 9.306(1), b = 9.733(1), c = 11.550(1) Å, α = 87.86(1), β = 76.73(1), γ = 85.91(1)° space group: $$P\bar 1$$ ], containing the molecules arranged in double zigzag chains. The reaction of 3-bppz with HgI2 leads surprisingly to a binuclear complex, [Hg2I4(3-bppz)2] (4) [unit cell: a = 17.555(1), b = 12.973(1), c = 16.195(1) Å, β = 115.32(1)° space group: C2/c]. Two ligand molecules are bridged by two mercury(II) ions forming a cyclic structure, the tetrahedral coordination sphere of the metal being completed by iodide anion

Methanol{2-meth­oxy-6-[(2-oxidoprop­yl)imino­meth­yl]phenolato}dioxidomolyb­denum(VI)

In the structure of the title compound, [Mo(C11H13NO3)O2(CH3OH)], the MoVI ion is octahedrally coordinated by two oxide O atoms, the N atom and two deprotonated OH groups of the tridentate Schiff base ligand 2-meth­oxy-6-[(2-oxidoprop­yl)imino­meth­yl]phenolate and by a methanol O atom. In the crystal structure, two complexes are linked via O—H⋯O hydrogen bonds, yielding a centrosymmetric arrangement involving the methanol hydr­oxy group and one of the ligand O atoms coordinated to the MoVI ion

2,2′-[(2S*,6R*)-Piperidine-2,6-di­yl]­di­pro­pan-2-ol

In the title compound, C11H23NO2, the piperidine ring has a chair conformation. The two hy­droxy H atoms are disordered over two positions with fixed occupancy ratios of 0.57:0.43 and 0.63:0.37. In the mol­ecule, there are two short N—H⋯O inter­actions. In the crystal, four symmetry-related mol­ecules are linked by O—H⋯O hydrogen bonds to form a cage-like arrangement, centered about the point of inter­section of three twofold axes. These cages stack along the [100] direction

(RSS)-[N-Hydroxyethyloxy]-hexafluoroVal–MeLeu–Ala tert-butyl ester

The title compound [systematic name: (2S,5S,8R)-tert-butyl 8-(1,1,1,3,3,3-hexafluoropropan-2-yl)-12-hydroxy-5-isobutyl-2,6-dimethyl-4,7-dioxo-10-oxa-3,6,9-triazadodecanoate], C21H36F6N3O6, is a tripeptide crystallizing in the chiral ortho­rhom­bic spacegroup P212121. The absolute configuration (R) of the chiral center in the hexa­fluoro­valine unit is based on the known stereochemistry of MeLeu and Ala (SS). The N-hydroxy­ethyl­oxy substituent of hexa­fluoro­valine is positionally disordered [occupancy ratio 0.543 (9):0.457 (9)]. In the solid state structure there are N—H⋯F and N—H⋯O intra­molecular hydrogen bonds supporting the coiled structure of this tripeptide with the three hydro­phobic substituents on the outside

Axial versus equatorial coordination of thioether sulfur: mixed ligand copper(ii) complexes of 2-pyridyl-n-(2'-methylthiophenyl)-methyleneimine with bidentate diimine ligands

The synthesis, structure and spectral and redox properties of the copper(II) complexes [Cu(pmtpm)Cl2] (1) and [Cu(pmtpm)2](ClO4)2 (6), where pmtpm is the linear tridentate ligand 2-pyridyl-N-(2'-methylthiophenyl)methyleneimine containing a thioether and two pyridine donors, are described. Also, the mixed ligand complexes [Cu(pmtpm)(diimine)](ClO4)2 (2-5), where the diimine is 2,2'-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3), 2,9-dimethyl-1,10-phenanthroline (2,9-dmp) (4) or dipyrido-[3,2-d:2',3'-f]-quinoxaline (dpq) (5), have been isolated and studied. The X-ray crystal structures of the complexes 1, [Cu(pmtpm)(2,9-dmp)](ClO4)2 4 and 6 have been successfully determined. The complex 1 possesses a trigonal bipyramidal distorted square based pyramidal (TBDSBP) coordination geometry in which three corners of the square plane are occupied by two nitrogens and thioether s of pmtpm ligand and the remaining equatorial and the axial positions by two chloride ions. The complex 4 contains a CuN4S chromophore also with a TBDSBP coordination geometry in which two nitrogens and the thioether sulfur of pmtpm ligand occupy three corners of the square plane. One of the two nitrogens of 2,9-dmp ligand is equatorially coordinated and the other axially to copper. On the other hand, the complex 6 is found to possess a square based pyramidal distorted trigonal bipyramidal (SPDTBP) coordination geometry. The CuN2S trigonal plane in it is comprised of the pyridine and imine nitrogens and the thioether sulfur of the pmtpm ligand. The pyridine nitrogens of the ligand occupy the axial positions and the second thioether sulfur remains uncoordinated. On long standing in acetonitrile solution the mixed ligand complexes 2 and 3 undergo ligand disproportionation to provide the corresponding bis-complexes of bpy and phen, respectively, and 6. The electronic and EPR spectral parameters and the positive redox potential of complex 4 are consistent with the equatorial location of the thioether sulfur in the square-based coordination geometry around copper(II). On the other hand, the higher g|| and lower A|| values and lower E1/2 values for the complexes 2, 3 and 5 are consistent with the axial coordination of the thioether sulfur. Also, the Cu(II)/Cu(I) redox potentials increase with increase in number of aromatic rings of the diimine ligand. The steric and electronic effects of the bidentate diimine ligands in orienting the thioether coordination to axial or equatorial position are discussed