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The complexes of Cu(I), Cu(II), Ni(II), Zn(II) and Co(II) with a new polypyridyl ligand, 2,3-bis(2-pyridyl)-5,8-dimethoxyquinoxaline (L), have been synthesized and characterized. The crystal structures of these complexes have been elucidated by X-ray diffraction analyses and three types of coordination modes for L were found to exist in them. In the dinuclear complex [Cu(I)L(CH3CN)]2·(ClO4)2 (1), L acts as a tridentate ligand with two Cu(I) centers bridged by two L ligands to form a box-like dimeric structure, in which each Cu(I) ion is penta-coordinated with three nitrogen atoms and a methoxyl oxygen atom of two L ligands, and an acetonitrile. In [Cu(II)L(NO3)2]·CH3CN 2, the Cu(II) center is coordinated to the two nitrogen atoms of the two pyridine rings of L which acts as a bidentate ligand. The structures of [Ni(II)L(NO3)(H2O)2]·2CH3CN·NO3 (3), [Zn(II)L(NO3)2 (H2O)]·2CH3CN (4) and [Co(II)LCl2(H2O)] (5) are similar to each other in which L acts as a tridentate ligand by using its half side, and the metal centers are coordinated to a methoxyl oxygen atom and two bipyridine nitrogen atoms of L in the same side. The formation of infinite quasi-one-dimensional chains (1, 4 and 5) or a quasi-two-dimensional sheet (2) assisted by the intra- or intermolecular face-to-face aryl stacking interactions and hydrogen bonds may have stabilized the crystals of these complexes. Luminescence studies showed that 1 exhibits broad, structureless emissions at 420 nm in the solid state and at 450 nm in frozen alcohol frozen glasses at 77 K. Cyclic voltammetric studies of 1 show the presence of an irreversible metal-centered reduction wave at approximately −0.973 V versus Fc+/0 and a quasi-reversible ligand-centered reduction couple at approximately −1.996 V versus Fc+/0. The solution behaviors of these complexes have been further studied by UV–Vis and ESR techniques. [Copyright &y& Elsevier]

Abstract: In order to further understand the coordination chemistry of diazamesocyclic systems, a series of mononuclear NiII complexes with 1,4-diazacycloheptane (DACH) functionalized by additional imidazole or pyridine donor pendants, including [NiL1](ClO4)2·H2O (1), [NiL1Cl](ClO4) (2), [NiL2Cl](ClO4)·CH3OH (3), [NiL2Cl][NiL2](ClO4)3 (4) and [NiL3](ClO4)2 (5), where L1=1,4-bis(N-1-methylimidazol-2-yl-methyl)-1,4-diazacycloheptane, L2=1,4-bis(pyridyl-2-yl-methyl)-1,4-diazacycloheptane, and L3=1,4-bis-(imidazol-4-yl-methyl)-1,4-diazacycloheptane, have been prepared and characterized. A detailed study on the solid structures and solution spectra of these complexes indicates that tetradentate ligands L1, L2 and L3 would lead to new NiII complexes with different coordination environments in the solid states and solution. The N-methyl substituted imidazole functionalized ligand L1 forms green compound 2 and yellow product 1; while the pyridine functionalized ligand L2 affords red product 4 and green complex 3; the ligand L3 results in only one stable mononuclear NiII product 5. The solution behaviors of these interesting compounds were also investigated by UV–Vis technique. [Copyright &y& Elsevier]

The synthesis of a new oxalato-bridged dinuclear Cu(II) complex, [Cu2(DACO)2(μ-ox)Br2]·CH3OH (1), where DACO=1,5-diazacyclooctane, together with its spectral and magnetic characterization, are reported. Crystal structure of 1 has been determined by X-ray diffraction analysis, which is made up of centrosymmetric dinuclear [Cu2(DACO)2(μ-ox)Br2] unit and noncoordinated methanol molecule, assembling into a novel two-dimensional step-like extended network through hydrogen bonds. The magnetic susceptibility indicates that complex 1 is anti-ferromagnetic coupling with 2J=−242 cm−1. The strength of the exchange interaction is discussed on the basis of the structural feature. [Copyright &y& Elsevier]

Abstract: In our continuing efforts to explore the effects of substituent groups of ligands in the formation of supramolecular coordination structures, seven new CuII complexes formulated as [Cu2(L1 )4(DMF)2] (1), {[Cu2(L1 )4(Hmta)](H2O)0.75} ∞ (2), [Cu2(L2 )4(2,2′-bipy)2] (3), [Cu2(L3 )4(H2O)2] (4), [Cu2(L3 )4(Hmta)] ∞ (5), [Cu2(L3 )4(Dabco)] ∞ (6) and [Cu2(L3 )4(Pz)] ∞ (7) with three monocarboxylate ligands bearing different substituent groups HL1 –HL3 (HL1 =phenanthrene-9-carboxylic acid, HL2 =2-phenylquinoline-4-carboxylic acid, HL3 =adamantane-1-carboxylic acid, Hmta=hexamethylenetetramine, 2,2′-bipy = 2,2′-bipyridine, Dabco = 1,4-diazabicyclo[2.2.2] octane and Pz = pyrazine), have been prepared and characterized by X-ray diffraction. In 1, 2 and 4–7, each CuII ion is octahedrally coordinated, and carboxylate acid acts as a syn–syn bridging bidentate ligand. While each CuII ion in 3 is penta-coordinated in a distorted square-pyramidal geometry. 1 and 4 both show a dinuclear paddle-wheel block, while 2, 5, 6 and 7 all exhibit an alternated 1D chain structure between dinuclear paddle-wheel units of the tetracarboxylate type Cu2-(RCO2)4 and the bridging auxiliary ligands Hmta, Dabco and Pz. Furthermore, 3 has a carboxylic unidentate and μ1,1-oxo bridging dinuclear structure with the chelating auxiliary ligand 2,2′-bipy. Moreover, complexes 1–6 were characterized by electron paramagnetic resonance (EPR) spectroscopy. [Copyright &y& Elsevier]

Abstract: Five new complexes [Cu2(L1 )I2]∞ (1), [Cu(L2 )I]2 (2), {[Cu2(L2 )I2](CH3CN)3}∞ (3), [Cu2(L3 )I2]∞ (4) and {[Cu(L3 )I](CH3CN)}2 (5) have been obtained by reacting three structurally related ligands, 2,3-bis(n-propylthiomethyl)quinoxaline (L1 ), 2,3-bis(tert-butylthiomethyl)quinoxaline (L2 ) and 2,3-bis[(o-aminophenyl)thiomethyl]quinoxaline (L3 ) with CuI, respectively, at different temperatures. Single crystal X-ray analyses show that 1, 3, 4 possess 1D chain structures, while 2 and 5 are discrete dinuclear molecules. It is interesting that the reactions of CuI with L1 at room temperature and 0°C, respectively, only afforded same structure of 1 (1a and 1b), while using L2 (or L3 ) instead, two different frameworks 2 and 3 (or 4 and 5) have been obtained. The structural changes mainly resulted from the different conformations that L2 or L3 adopted at different temperatures. Our research indicates that terminal groups of ligands take an essential role in the framework formation, and the reaction temperature also has important effect on the construction of such Cu(I) coordination architectures. Furthermore, the influence of hydrogen bonds on the conformation of ligands and the supramolecular structures of these complexes have also been explored. The luminescence properties of complexes 1, 2, and 4 have been studied in solid state at room temperature. [Copyright &y& Elsevier]

Abstract: In our efforts to investigate the relationships between the structures of ligands and their complexes, two structurally related ligands, 1-(2-pyridylmethyl)-1H-benzimidazole (L1 ) and 1-(4-pyridylmethyl)-1H-benzimidazole (L2 ), and their four complexes, [Zn(L1 )2Cl2] (1), [Hg(L1 )Br2]∞ (2), {[Zn(L2 )Cl2](CH3CN)}∞ (3) and [Hg(L2 )Br2]2(CH3CN)2 (4) were synthesized and structurally characterized by elemental analyses, IR spectra and single-crystal X-ray diffraction analysis. Structural analyses show that 1 has a mononuclear structure, and 2 and 3 both take 1D structure. While 4 takes a dinuclear structure. 1, 2 and 4 were further linked into higher-dimensional supramolecular networks by weak interactions, such as C–H⋯Cl and C–H⋯Br H-bonding, C–H⋯π, and π⋯π stacking interactions. The structural differences of 1–4 may be attributed to the difference of the spatial positions of the terminal N donor atoms in the pendant pyridyl groups in L1 and L2 , in which the pyridine rings may act as the directing group for coordination and the benzimidazole rings act as the directing group for π⋯π stacking and C–H⋯π interactions. The luminescent properties of the corresponding complexes and ligands have been further investigated. [Copyright &y& Elsevier]

Abstract: In our efforts to investigate the factors that affect the formation of coordination architectures, such as secondary coordination donors and pendant skeletons of the carboxylic acid ligands, as well as H-bonding and other weak interactions, two kinds of ligands: (a) 3-(2-pyridyl)pyrazole (L 1 ) with a non-coordinated N atom as a H-bonding donor, a 2,2′-bipyridyl-like chelating ligand, and (b) four carboxylic ligands with different secondary coordination donors and/or pendant skeletons, 1,4-benzenedicarboxylic acid (H2 L 2 ), 4-sulfobenzoic acid (H2 L 3 ), quinoline-4-carboxylic acid (HL 4 ) and fumaric acid (H2 L 5 ), have been selected to react with Mn(II) salts, and five new complexes, [Mn(L 1 )2(SO4)]2 (1), [Mn(L 1 )2(L 2 )]∞ (2), [Mn(L 1 )(HL 3 )2]∞ (3), Mn(L 1 )2(L 4 )2 (4), and [Mn(L 1 )2(L 5 )]∞ (5), have been obtained and structurally characterized. The structural differences of 1–5 can be attributed to the introduction of the different carboxylic acid ligands (H2 L 2 , H2 L 3 , HL 4 , and H2 L 5 ) with different secondary coordination donors and pendant skeletons, respectively. This result also reveals that the typical H-bonding (i.e. N–H⋯O and O–H⋯O) and some other intra- or inter-molecular weak interactions, such as C–H⋯O weak H-bonding and π⋯π interactions, often play important roles in the formation of supramolecular aggregates, especially in the aspect of linking the multi-nuclear discrete subunits or low-dimensional entities into high-dimensional supramolecular networks. [Copyright &y& Elsevier]

Abstract: Two oxime-functionalized diazamesocyclic derivates, namely, N,N′-bis(acetophenoneoxime)-1,4-diazacycloheptane (H2 L 1) and N,N′-bis(acetophenonoxime)-1,5-diazacyclooctane (H2 L 2), have been prepared and characterized. Both ligands (obtained in the hydrochloride form) can form stable metal complexes with CuII and NiII salts, the crystal structures of which were determined by X-ray diffraction technique. The reactions of H2 L 1 with Cu(ClO4)2 and Ni(ClO4)2 afford a penta-coordinated mononuclear complex [Cu(H2 L 1)Cl]·ClO4 (1) and a four-coordinated monomeric [Ni(HL 1)]·ClO4 (2), in which the ligand is monodeprotonated. The ligand H2 L 2 also forms a quite similar mononuclear [Ni(HL 2)]·ClO4 complex with Ni(ClO4)2, according to our previous work. However, reactions of different CuII salts [Cu(ClO4)2, CuCl2 and Cu(NO3)2 for 3, and CuSO4 for 4] with H2 L 2 in the presence of NaClO4 yield two unusual mono-μ-Cl dinuclear CuII complexes [Cu2(HL 2)2Cl]·(ClO4) (3), and [Cu2(H2 L 2)(HL 2)Cl]·(ClO4)2 ·(H2O)(4). These results indicate that the resultant CuII complexes (1, 3 and 4) are sensitive to the backbones of diazamesocycles and even auxiliary anions. [Copyright &y& Elsevier]

Two CuII complexes with di-2-pyridylamine (dpa) and combined bridging ligands (azide or oxalato anions), [Cu(dpa)2(N3)2]·2H2O (1) and [Cu2(μ-ox)(dpa)2(CH3CN)2](ClO4)2 (2), have been synthesized and characterized by IR spectra, elemental analyses, TGA, UV–Vis spectra and ESR technique. The crystal structures of both complexes have been determined by single crystal X-ray diffraction analyses. In the mononuclear complex 1, the CuII center is coordinated to four N atoms of dpa and two N donors of azide (CuN6), taking an elongated octahedral geometry. The solvent water molecules interlink the neutral [Cu(dpa)2(N3)2] units through hydrogen bonds to form a two-dimensional (2D) layered structure with strong π–π stacking interactions between the adjacent pyridine rings. Complex 2 is made up of centro-symmetric dinuclear [Cu2(μ-ox)(dpa)2(CH3CN)2]2+ cation and non-coordinated perchlorate anions, assembling into a one-dimensional (1D) ladder structure through hydrogen bonding with π–π stacking co-effect. The magnetic properties of 2 have been investigated by variable-temperature magnetic susceptibility and magnetization measurements, indicating a very strong anti-ferromagnetic coupling between the intra-molecular CuII centers (having the perfect square-pyramidal geometry) with J=−382 cm−1. The strength of the exchange interaction is discussed in detail on the basis of the structural feature. [Copyright &y& Elsevier]