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Tetracarbonyl complexes of low-valent Group VI transition metals (Mo and W), containing diimine bidentate ligands, namely W(CO)4(4,6-diphenyl-2,2′-bipyridine) ( 1), W(CO)4(6-(2,6-dimethoxyphenyl)-4-phenyl-2,2′-bipyridine) ( 2), Mo(CO)4(2,2′-dipyridylamine) ( 3), and W(CO)4(2,2′-dipyridylamine) ( 4), were synthesized and tested as homogeneous catalysts for the electrochemical reduction of CO2 in nonaqueous media. Cyclic voltammetry performed under a CO2 atmosphere, revealed that these complexes have significant catalytic activity in acetonitrile, and gas chromatographic measurements together with exhaustive electrolysis showed that CO is the major reduction product. Mechanistic insights were obtained by IR-spectroelectrochemical measurements. The substantially different electrocatalytic performances obtained for the two classes of catalysts are compared and discussed. [ABSTRACT FROM AUTHOR]

The title compound, (Hdipya)(H3pyr), where Hdipya is protonated 2,2'-dipyridilamine and H3pyr is the monoanion of pyromellitic acid (H4pyr), was obtained from a reaction mixture containing Zn(II) ions, dipya, Na4pyr (in the mole ratio 2:2:1) and HNO3. The products (micro- and single-crystalline) were characterized by X-ray structure determination, FT-IR spectroscopy and TG/DSC analysis. The most striking structural feature of (Hdipya)(H3pyr) are short inter- and extremely short intramolecular hydrogen bonds. These bonds mutually connect cations and anions making thin layers parallel to the crys-tallographic (223) plane. In addition, quite unusual, linear proton-bound polymeric {H(H2pyr)-}n were identified in the structure. The results of crystal structure determination are compared with FT-IR and TG/DSC data. The low position of the νas (COO) vibration at 1660 cm-1 is in accordance with strong hydrogen bonding. This value could be used as a measure of the C=O bond order, which was calculated to be 1.81. [ABSTRACT FROM AUTHOR]

Abstract: Treatment of Cu2(OAc)4·2H2O with 2,2′-dipyridylamine (dpa) in 1:2 molar ratio in MeCN–H2O results neutral [Cu(OAc)2(dpa)]·2H2O (1) which on subsequent treatment with 1equiv of NaBF4 affords [Cu(OAc)(dpa)2]BF4 (2). The complexes are characterized using microanalytical, spectroscopic, magnetic, thermal, electrochemical, and other physicochemical results. Electrochemical electron transfer study of 1 and 2 in MeCN solutions show a reductive response presumably due to copper(II)–copper(I) couple. Thermal study (TG-DTA) of 1 reveals a weight loss of 9.21% at 70–85K corresponding to two crystalline water molecules. Structures of 1 and 2 are solved by X-ray diffraction study. Compound 1 adopts a distorted octahedral CuN2O4 environment coordinated through two N atoms of dpa and four O atoms of two chelating acetates with elongated axial bonds. In 2, copper(II) is ligated by four N atoms of two dpa units and two O atoms of an acetate in chelating fashion resulting a cationic core of [Cu(OAc)(dpa)2]+. Crystal packings show that mononuclear units of 1 self-assemble through cooperative hydrogen bonds and π…π interaction and of 2, through hydrogen bonds along with C–H…π interaction leading to 2D sheets. Both the complexes show high-energy intraligand 1(π…π∗) fluorescence and intraligand 3(π…π∗) phosphorescence in glassy solutions (DMF at 77K). [Copyright &y& Elsevier]

Abstract: One-pot reactions of metal acetate, 2,2′-dipyridylamine (dpa) and NaN3 in a 1:2:2 ratio in aqueous-acetonitrile solutions result in mononuclear complexes of the type [M(dpa)2(N3)2]·H2O [M=Ni (1), Zn (2)]. Structural analyses reveal that both the metal centres adopt distorted octahedral MN6 environments coordinated through four N atoms of two dpa units and two azide N atoms as terminal ligands – the latter occupying mutual cis positions. The crystal packing shows that the mononuclear units self-assemble through hydrogen bonds to afford infinite two-dimensional (2D) sheets. Additionally, the pyridyl planes of adjacent sheets are engaged in face-to-face π⋯π and C–H⋯π interactions leading to a 3D supramolecular continuum. Complexes 1 and 2 exhibit high-energy intraligand 1(π–π*) fluorescence and intraligand 3(π–π*) phosphorescence in glassy solutions (DMF at 77 K). A band (374 nm) observed in their solid-state emission spectra is an excimeric emission originating from an aromatic π⋯π interaction. The role of dpa is highlighted in controlling crystalline aggregation and in arousing luminescence characteristics. [Copyright &y& Elsevier]

Abstract: Oxygen-prebleached kraft pulp (OKP) was bleached with H2O2 activated with a copper complex coordinated with 2,2′-dipyridylamine (dpa) or 4-aminopyridine (4-ap) under alkaline conditions. Bleaching of OKP by H2O2 activated with the Cu(II)–dpa complex decreased the kappa number (k) and viscosity () of the pulp by 26 and 0.7%, respectively. In contrast pulp bleaching without the coordinator resulted in a decrease in k and values of 25 and 7.8%, respectively. Thus, selectivity for delignification, expressed by , was increased 12-fold by the coordination with dpa. ESR demonstrated that the coordination with dpa suppressed the production of . These results support the involvement of a hydroperoxo complex of Cu(II) formed by the reaction of −OOH with [Cu(II)(dpa)(H2O)3]2+. When the OKP was bleached with H2O2 activated with a Cu(II)–4-ap complex, selectivity () in pulp bleaching increased by 2.6-fold and production of sed by 47%. We conclude that Cu(II)–dpa is a catalyst potentially applicable to totally chlorine free (TCF) bleaching sequences due to its high selectivity for delignification. [Copyright &y& Elsevier]

Abstract: Four complexes of the type [Mn(dpa)2(X)2]·H2O (dpa=2,2′-dipyridylamine; ; X=NCO−, 2) and [Mn(dpa)2(X)(OH2)]ClO4 (; X=NCO−, 4) have been synthesized using single-pot reactions of manganese(II) salt, dpa and X in 1:2:2 and 1:2:1 molar ratios, respectively. The compounds have been characterized by microanalytical, physicochemical, spectroscopic and magnetic results. Room temperature magnetic moments (μ eff) are in the range 5.88–5.97 BM and are typical of high-spin manganese(II) complexes ( idealized, S =5/2). The complexes display a Mn(III)–Mn(II) couple at ∼0.6 V versus SCE in DMF solutions. X-ray structure determinations show that in 1–4 the manganese(II) centres are in a distorted octahedral environment. Compounds 1 and 2 contain the MnN6 chromophore, completed by two bidentatendpa units and two terminal azido groups in 1 or N-coordinated cyanato ligands in 2, along with a water of crystallization. In 3 and 4, one water molecule acts as a coordinating ligand replacing one of the terminal pseudohalides in 1 and 2, respectively, resulting in a MnN5O chromophore. The amine H, terminal azido N or cyanato O, O and H’s of the water molecule are engaged in extensive hydrogen bonding of the type N–H⋯N, O–H⋯N and N–H⋯O in 1 and 2. Additionally O–H⋯O bonding is observed in 3 and 4. Supramolecular 2D sheet structures are obtained arising from such weak intermolecular forces. All the complexes display high-energy intraligand 1(π–π*) fluroscence and intraligand 3(π–π*) phosphorescence in glassy solutions (DMF at 77 K). [Copyright &y& Elsevier]