Bis-bidentate Schiff-base Ligands Research Articles

Self-assembly of one Ag(I) 2D metallacrown polymer with bis-bidentate Schiff-base ligand N, N′-bis(furan-2-ylmethylene)hydrazine: Synthesis, crystal structures and luminescent properties

One new coordination polymer, [{Ag 2L 3(BF 4) 2}H 2O] n ( 1), has been generated via self-assembly from the ligand L N, N′-bis(furan-2-ylmethylene)hydrazine and AgBF 4. The complex 1 and ligand L are characterized by single-crystal X-ray diffraction analysis. Crystal structure analyses show that the complex 1 belongs to the rhombohedral space group R 3 ¯ with a = 9.8999(6) Å, b = 9.8999(6) Å, c = 34.208(4) Å, V = 2903.5(4) Å 3 and the ligand L belongs to the orthorhombic space group Pbca with a = 6.9014(12) Å, b = 9.0215(16) Å, c = 15.235(3) Å, V = 948.5(3) Å 3. The structure of 1 exhibits a 2D layer hexagonal network with 18-Mc-6 [Ag 6L 6] metallacrowns as building blocks and every two adjacent silver atoms are bridged through the two nitrogen atoms of N–N bridge of a ligand. Luminescence studies revealed that L and complex 1 exhibit fluorescent emissions in the solid state at room temperature at λ max = 348 and 506 nm, respectively.

Doubly Pyridazine-bridged Dicobalt(II) and Dinickel(II) Side-by-side Complexes of Variously Substituted Conjugated Bis-bidentate Ligands

A family of six acyclic bis-bidentate Schiff base ligands, Lx (prepared by condensation of 3,6-diformylpyridazine with a range of anilines: 2,4-dimethylaniline Lo,p-Me; 3,5-dichloroaniline Lm,m-Cl; 3,5-difluoroaniline Lm,m-F; p-toluidine Lp-Me; 4-aminophenol Lp-OH; 2,4,6-trimethylaniline Lo,o,p-Me), was complexed, 1:1, with cobalt(ii) or nickel(ii) perchlorate or tetrafluoroborate in refluxing dry acetonitrile. A family of dinuclear, doubly pyridazine-bridged complexes, M2II(Lx)2(solvent)n(ClO4)4 and [Ni2(Lo,o,p-Me)2(2H2O)4](BF4)4, resulted. An X-ray crystal structure determination on [Co2II(Lo,o,p)2(H2O)2(MeCN)2](ClO4)4·MeCN confirmed that it has the expected side-by-side architecture with axial solvent molecules completing the octahedral coordination sphere of the two cobalt(ii) ions. Magnetic analysis showed that the pyridazine bridges mediate weak-to-medium antiferromagnetic interactions between the metal ions. Specifically, for the cobalt(ii) complexes J was in the range –12 to –6 cm–1, while for the nickel(ii) complexes J was in the range –22 to –17 cm–1. There is no clear cut correlation of J values with electron-donating or -attracting properties of ligand substituent peripheral groups, although it is noted that the smallest J occurs in both the NiNi and CoCo families for the ligand Lo,o,p-Me.

The syntheses, characterizations, X-ray crystal structures and properties of Cu(I) complexes of a bis-bidentate schiff base ligand

Bis-bidentate Schiff base ligand L and its two mononuclear complexes [CuL(CH3CN)(2)]ClO4 (1)and [CuL(PPh3)(2)]ClO4 (2)have been prepared and thoroughly characterized by elemental analyses, IR, UV-Vis, NMR spectroscopy and X-ray diffraction analysis. In both the complexes the metal ion auxiliaries adopt tetrahedral coordination environment. Their reactivity, electrochemical and photophysical behavior have been studied. Complex 1 shows reversible Cu-II/I couple with potential 0.74 V versus Ag/AgCl in CH2Cl2. At room temperature L is weakly fluorescent in CH2Cl2, however in Cu(I)complexes 1 and 2 the emission in quenched. (C) 2009 Elsevier B. V. All rights reserved.

Synthesis, Characterization and Crystal Structure Determination of a Hepta-coordinated Cadmium(II) Complex with Thiocyanato-bridges

A new cadmium(II) complex [(C28H24N6)Cd(SCN)2]2(CH3OH)2 (1) has been synthesized and characterized by IR, UV spectra, TG-DTA technique and single crystal X-ray diffraction analysis. The crystallographic data for compound 1: triclinic P1¯, a = 9.630(2) A, b = 11.123(3) A, c = 15.396(4) A, α = 106.93(1)°, β = 91.60(1)°, γ = 99.99(1)°, V = 1,548.5(6) A3, Z = 1, Dc = 1.512 mg/m3, F(000) = 716, R 1 = 0.0332, wR 2 = 0.0907. The molecule contains a symmetrical dinuclear unit in which two Cd(II) ions are double bridged by two di-μ-1,3-SCN− anoins with a cadmium–cadmium separation of 6.48 A. Each Cd(II) ion is seven-coordinated with six nitrogen atoms and a sulfur atom to form a monocapped trigonal prism coordination geometry. In addition, the molecule is further connected by multiform intermolecular C–H···π, π···π interactions and hydrogen bonds to form a three-dimensional supramolecular structure. A hepta-coordinated Cd(II) complex which exhibits a distorted a monocapped trigonal prism coordination geometry has been achieved by using bisbidentate Schiff-base ligand and thiocyanate anion.

Factors Influencing Tetranuclear [2 × 2] Grid vs Dinuclear Side-by-Side Structures for Silver(I) Complexes of Pyridazine-Based Bis-Bidentate Ligands

Silver(I) complexes of five bis-bidentate Schiff-base ligands, derived from 3,6-diformylpyridazine and substituted anilines (2,4-dimethylaniline L ( o,p - Me ); 3,5-dichloroaniline L ( m,m - Cl ); 2-aminobiphenyl L ( o - Ph ); p-toluidine L ( p - Me ); 4-aminophenol L ( p - OH ); p-anisidine L ( p - OMe )), have been prepared. The ligands have a wide range of steric and electronic properties due to variation in the extent and nature of the substitution of the aniline rings. Four of the resulting complexes were structurally characterized by X-ray crystallography: three of the four, [Ag 2( L ( o,p - Me )) 2](BF 4) 2, [Ag 2( L ( m,m - Cl )) 2](BF 4) 2 and [Ag 2( L ( o - Ph )) 2](BF 4) 2 formed dinuclear side-by-side complexes, while [Ag 4( L ( p - Me )) 4](BF 4) 4 gave a tetranuclear [2 x 2] grid. The previously reported tetranuclear [2 x 2] grid [Ag 4( L ( p - OMe )) 4](BF 4) 4 was recrystallized in the presence of benzene to see if this would alter the architecture of this complex. It did not: the [2 x 2] grid architecture was retained despite the benzene molecules of solvation. Given the flexibility of silver(I) with regard to coordination geometry, the molecular structure of these complexes is influenced mostly by the ligand rather than the metal ion. In each case, the factors which influence the molecular architecture are presented and discussed. Substituent effects on the electrostatics of the intramolecular ligand-ligand pi-pi interactions (XED2.8) account for some of the differences observed in the structures.

Crystal Structure and Magnetic Properties of a Novel Octa-coordinated Manganese(II) Complex

The self-assembly and structural characterization of the new manganese(II) [MnL 2](ClO4)2(CH3OH)0.5 (1) complex has been achieved. The crystallographic data for the complex 1: Orthorhombic Pbca , a = 16.287(2) A, b = 21.293(2)A, c = 32.718(3) A, V = 11,347(2) A3, Z = 8. The two polydentate ligands strand intertwined each other and around the manganese(II) ions forming a mononuclear complex. The Mn(II) ion is eight-coordinated with the eight donor nitrogen atoms of two ligands to form a distorted square antiprismatic coordination geometry. The magnetic properties investigation indicates that there is a weak antiferromagnetic exchange coupling between the Mn(II) ions of the complex. An octa-coordinated Mn(II) complex which exhibits a distorted square antiprismatic coordination geometry has been achieved by using a bisbidentate Schiff-base ligand.

Pyridazine-bridged copper(i) complexes of bis-bidentate ligands: tetranuclear [2 ? 2] grid versus dinuclear side-by-side architectures as a function of ligand substituents

Eight bis-bidentate Schiff-base ligands, derived from 3,6-diformylpyridazine and substituted amino-benzenes, have been prepared. A variety of electron donating/withdrawing and/or sterically demanding/undemanding substituents were employed. Two ligands and five of the six pure copper(I) complexes have been structurally characterised. The sterically unhindered ligand derived from 3,5-difluoroaniline, (m,m-F), was almost completely flat whereas the very sterically hindered ligand derived from trimethylaniline, (o,o,p-Me), was severely twisted. The only dinuclear side-by-side complex obtained, [Cu(I)(2)((o-Ph))(2)](PF(6))(2), was of the ligand derived from 2-aminobiphenyl. All five of the other complexes are believed to be [2 x 2] tetranuclear grid complexes, and this was unequivocally shown to be the case for four of these complexes, [Cu(I)(4)((p-Me))(4)](PF(6))(4), [Cu(I)(4)((o,p-Me))(4)](PF(6))(4), [Cu(I)(4)((m,m-F))(4)](PF(6))(4) and [Cu(I)(4)((m,m-Cl))(4)](PF(6))(4). In all cases the copper(I) centres are substantially distorted from tetrahedral, with the most severe distortion present in the side-by-side complex. In the absence of any special effects, tetracopper(I) [2 x 2] grid architectures are observed to be the favored outcome for 1 : 1 reactions of these bis-bidentate ligands with copper(I) ions. Only when the aromaticity of the ligand was extended by employing a phenyl substituent on the phenyl rings, (o-Ph), did a dicopper(I) side-by-side architecture result. Cyclic voltammetry in acetone revealed that the free ligands did not undergo reduction until potentials below -0.8 V, whereas between three and four reversible one electron reductions were observed, between +0.16 and -0.71 vs. AgCl/Ag, for the tetranuclear copper(I) [2 x 2] grid complexes. The redox potentials observed for these complexes are highly dependent on the nature of the ligand phenyl ring substituent(s). The side-by-side complex had one irreversible reduction process, E(pc)ca.-0.5 V.

The synthesis and characterization of a series of bis-bidentate Schiff base ligands and their coordination complexes with silver(i), copper(i) and zinc(ii) d10 metal ionsElectronic supplementary information (ESI) available: Views of the crystal structures of ligands of 1, 2 and 3. See http://www.rsc.org/suppdata/nj/b3/b301632c/

Three bis-bidentate Schiff base ligands 1, 2 and 3 have been prepared and thoroughly characterized, and their complexation behavior with d10 silver, copper and zinc ions was studied. The coordination assembly of Cu(I) and Ag(I) with ligands 1 and 2, afforded di-nuclear dimeric complexes [Ag2(1)2](ClO4)2 (1a), [Cu2(1)2](ClO4)2 (1b), [Ag2(2)2](ClO4)2 (2a) and [Cu2(2)2](ClO4)2 (2b), in which the metal ion auxiliaries adopted a pseudo-tetrahedral coordination environment. In these compounds the two ligands wrap around the metal ions in a twisted manner, forming box-like structures. Within these complexes each metal ion binds to two nitrogen sites of one ligand and two N-sites of the other ligand. The metal assisted self-assembly process is complemented by supportive π–π overlap interactions between the aromatic fragments of the assembly. In 1a and 2a the two silver ions lie close to one another at 3.1 A. On the other hand, zinc(II) yields a monomeric crystalline complex with 2, [Zn(2)(H2O)(CH3CN)](ClO4)2 (2c), interacting with four N-donors of the same ligand and complementing its octahedral coordination sphere with molecules of water and acetonitrile. The materials were characterized by UV-VIS, IR, MS, NMR, and X-ray diffraction analysis. Electrochemical behavior of the copper(I) compounds was also examined.

Syntheses and Structural Characterization of Ferrocene-Containing Double-Helicate and Mononuclear Copper(II) and Silver(I) Complexes

The self-assembly and structural characterization of the new ferrocene-containing dicopper(II) double helicate [Cu2L12] (1) and related copper(II) complex [CuL2(CH3CN)][ClO4]2 (2) and silver(I) complexes [AgL2(CH3CN)][BF4] (3) and [AgL2][BF4] (4) have been achieved. These complexes are derived from inexpensive and easy-to-prepare ferrocene-containing bisbidentate Schiff-base ligands H2L1, [(C6H4)(OH)CHNNC(CH3)(C5H4)]2Fe, and L2, [(C5H4N)CHNNC(CH3)(C5H4)]2Fe. The neutral double-helical dicopper(II) complex 1 crystallizes in a polar space group. The two ferrocene-containing ligands strand interwined about each other and around the two tetrahedral copper ions in a double-helical fashion, with the Cu···Cu separation being 9.45 Å. The four metal centers are coplanar and form a slightly distorted rhombus with sides of ca. 5.8 Å. Reaction of the ligand L2 and copper(II) constructed a mononuclear copper complex, 2. X-ray structural analysis reveals that the copper(II) atom is coordinated in a distorted square pyramidal geometry, with four nitrogen atoms from the two bidentate bind sites forming the basal plane; the acetonitrile nitrogen atom occupies the apical position. The molecular structure of the silver(I) complex 3 is quite similar to that of copper complex 2, with the silver(I) surprisingly coordinated in a square pyramidal geometry. The silver(I) atom in mononuclear silver complex 4 is coordinated in a new square planar fashion. The result presented here shows that while the ligand (L1)2- can bridge two metal ions to give a double helicate with Cu(II), the ligand L2 acts as a tetradentate ligand chelate to a single metal center in its structurally characterized complexes with Cu(II) and Ag(I). Crystal structures of the free ligand H2L1 and L2 are also reported for comparison.

Bis[4-(2-pyridylmethyleneamino)-phenyl] ether.

The title compound, C(24)H(18)N(4)O, is a bis-bidentate Schiff base ligand exhibiting pseudo-C(2) symmetry. The molecule is twisted about the central ether linkage and exhibits an imine E configuration. In the crystal, the molecules are linked by weak intermolecular C-H.N hydrogen bonds.

Self-assembled dinuclear molecular box [Ag2L2]2+ and triple helicates [Co2L3]4+, [Ni2L3]4+ {L = bis[4-(2-pyridylmethyleneamino)phenyl] ether}

The self-assembly and structural characterization of the new silver(I) molecular box [Ag2L2]2+ and cobalt(II), and nickel(II) molecular helices [Co2L3]4+ and [Ni2L3]4+ have been achieved. These complexes are derived from an inexpensive and easy-to-prepare bis-bidentate Schiff base ligand bis[4-(2-pyridylmethyleneamino)phenyl] ether (L). The cage-like cation [Ag2L2]2+ is located at an inversion center with two tetrahedrally co-ordinated silver(I) atoms and two ether oxygen atoms in the corner of a box. The edge length Ag⋯O is ca. 7.1 A. Each silver(I) center is bound to two pyridylimine units, one from each ligand. One ligand passes above the silver(I)–silver(I) axis, while the other passes beneath, giving a non-helical metallo-cyclophane with Ag⋯Ag separation ca. 12.3 A. Both triple helical [Co2L3]4+ and [Ni2L3]4+ cations contain two metal atoms and three ligands. Each metal center is bound to three pyridylimine units to attain a pseudo-octahedral co-ordination geometry. The ligand wraps in a helical arrangement around the two metal ions. Edge-to-face and face-to-face π–π interactions play important roles in the metal-assisted self-assembling process.

Syntheses and molecular structures of three Cu(II) complexes with tetradentate imine-phenols

Three Cu(II) complexes of N,N′-bis-(salicylidene)-1,3-diiminopropane ( 1), N,N′-bis-(salicylidene)-1,3-diimino-2,2-dimethylpropane ( 2), and N,N′-bis-(salicylidene)-1,5-diiminopentane ( 3) have been prepared and characterized by X-ray diffraction. All of the three complexes are four coordinated with Cu(II) in a tetrahedrally distorted square-planar geometry to two imine N atoms and two phenolate O atoms. Both 1 and 2 are monomeric with a 6-6-6 chelate ring structure and display the 2N2O donor atoms in a normal, tetradentate “ cis” configuration. However, in 3 two Cu(II) ions coordinate with bis-bidentate Schiff-base ligands, such that the Cu atoms are bridged by the two ligands; about each Cu atom, the arrangement of the iminophenolate groups is trans. The CuN1O1 and CuN2O2 planes intersect to form dihedral angles of 24.7° and 34.8° for 1 and 2, respectively, while the dihedral angle of two bidentate chelate planes of 3 is 40.5°.