Mononuclear oxovanadium complexes of tris(2-pyridylmethyl)amine

Mononuclear oxovanadium(IV) and dioxovanadium(V) complexes of tris(2-pyridylmethyl)amine (tpa) have been prepared for the first time. Crystal structure determinations of three oxovanadium(IV) complexes, [VO(SO4)(tpa)], [VOCl(tpa)]PF6, or [VOBr(tpa)]PF6, and a dioxovanadium(v) complex [V(O)2(tpa)]PF6 disclosed that the tertiary nitrogen of the tpa ligand always occupies the trans-to-oxo site. The structures of an oxo-peroxo complex [VO(O2)(tpa)]Cl that was prepared previously and of a mu-oxo vanadium(III) complex [{VCl(tpa)}2(mu-O)](PF6)2 have also been determined. The tertiary nitrogen is located at a trans site to the peroxo and chloride ligands, respectively. The total sums of the four V-N bond lengths from the tpa ligand are remarkably similar among the six complexes, indicating that the vanadium oxidation states become less influential in tpa bonding due primarily to the coordination of electron-donating oxo ligand(s). Absorption spectra of [VOCl(tpa)]+ in acetonitrile showed a significant change upon addition of p-toluenesulfonic acid and HClO4, but not on addition of benzoic acid. Protonation at the oxo ligand by the former two acids is suggested. Cyclic voltammetric studies in acetonitrile verified the proton-coupled redox behavior of the V(III)/V(IV) process involving the oxo ligand for the first time. From the dependence of the added p-toluenesulfonic acid to the CV, redox potentials for the following species have been estimated: [V(IV)OCl(tpa)]+/[V(III)OCl(tpa)](E1/2=-1.59 V vs. Fc+/Fc), [V(IV)(OH)Cl(tpa)]2+/[V(III)(OH)Cl(tpa)]+(Epc=-1.34 V), [V(IV)(OH2)Cl(tpa)]3+/[V(III)(OH2)Cl(tpa)]2+(Epa=-0.49 V), and [V(IV)Cl2(tpa)]2+/[V(III)Cl2(tpa)]+(E1/2=-0.89 V). The reduction of [V(V)(O)2(tpa)]+ in 0.05 M [(n-Bu)4N]PF6 acetonitrile showed a major irreversible reduction wave V(V)/(IV) at -1.48 V. The metal reduction potentials of the oxovanadium(IV) and dioxovanadium(V) species are very close, reinforcing the significant influence of the oxo ligand(s).     

Luminescent lanthanide complexes with stereocontrolled tris(2-pyridylmethyl)amine ligands: chirality effects on lanthanide complexation and luminescence properties

A series of tris(2-pyridylmethyl)amines including one and two asymmetric centers were synthesized in a stereo-controlled fashion as potential ligands of lanthanide cations. The reaction of chiral pyridylethyl methanesulfonates and bis(pyridylmethyl)amines occurred via an S(N)2 mechanism with complete inversion of asymmetric centers and gave the stereocontrolled tris(2-pyridylmethyl)amines, the stereochemical purity of which was ascertained by GPC, NMR, X-ray, and polarimetry experiments. They formed stable Tb(3+) and Eu(3+) complexes having 1:1, 1:2, and 1:3 stoichiometry (metal:ligand) in CH(3)CN solutions. NMR and UV titration experiments revealed that their complexation behaviors were rarely influenced by ligand chirality but significantly affected by the nature of the counteranion and the concentration ratio of metal to ligand. The Tb(3+) and Eu(3+) complexes with these tripodal ligands exhibited characteristic luminescence spectra upon excitation for pyridine chromophores (260 nm), the intensities of which were largely dependent on the ligand chirality. The meso isomer of the disubstituted tripods particularly exhibited the enhanced terbium luminescence ca. three times more than its diastereomer and un- and monosubstituted tripods. Direct excitation at the lanthanide center had similar chirality effects on the luminescence profiles, indicating that the stereochemistry of the employed ligand largely influenced the lanthanide emitting processes. Since the ligand chirality finely modified the local coordination environments around the lanthanide center, the use of stereocontrolled ligands is applicable in design of the luminescent lanthanide complexes.     

Nonheme oxoiron(IV) complexes of tris(2-pyridylmethyl)amine with cis-monoanionic ligands

Treatment of [Fe(IV)(O)(TPA)(NCMe)](CF3SO3)2 [TPA, N,N,N-tris(2-pyridylmethyl)amine] with 3 equiv of NR4X (X = CF3CO2, Cl, or Br) in MeCN at -40 degrees C affords a series of metastable [Fe(IV)(O)(TPA)(X)]+ complexes. Some characteristic features of the S = 1 oxoiron(IV) unit are quite insensitive to the ligand substitution in the equatorial plane, namely, the Fe-O distances (1.65-1.66 A), the energy ( approximately 7114.5 eV) and intensity [25(2) units] of the 1s-to-3d transition in the X-ray absorption spectra, and the M?ssbauer isomer shifts (0.01-0.06 mm.s(-1)) and quadrupole splittings (0.92-0.95 mm.s(-1)). The coordination of the anionic X ligand, however, is evidenced by red shifts of the characteristic near-IR ligand-field bands (720-800 nm) and spectroscopic observation of the bound anion by (19)F NMR for X = CF3CO2 and by EXAFS analysis for X = Cl (r(Fe-Cl) = 2.29 A) and Br (r(Fe-Br) = 2.43 A). Density functional theory calculations yield M?ssbauer parameters and bond lengths in good agreement with the experimental data and produce excited-state energies that follow the trend observed in the ligand-field bands. Despite mitigating the high effective charge of the iron(IV) center, the substitution of the MeCN ligand with monoanionic ligands X- decreases the thermal stability of [Fe(IV)(O)(TPA)]2+ complexes. These anion-substituted complexes model the cis-X-Fe(IV)=O units proposed in the mechanisms of oxygen-activating nonheme iron enzymes.     

Synthesis and properties of oxo-carboxylato- and dioxo-bridged diosmium complexes of tris(2-pyridylmethyl)amine

A series of oxo-bridged diosmium complexes with tpa ligand (tpa = tris(2-pyridylmethyl)amine) are synthesized. The hydrolytic reaction of the mononuclear osmium complex [Os(III)Cl(2)(tpa)]PF(6) in aqueous solution containing a sodium carboxylate yields a μ-oxo-μ-carboxylato-diosmium(III) complex, [Os(III)(2)(μ-O)(μ-RCOO)(tpa)(2)](PF(6))(3) (R = C(3)H(7) (1), CH(3) (2), or C(6)H(5) (3)). One-electron oxidation of 1 with (NH(4))(2)Ce(IV)(NO(3))(6) gives a mixed-valent [Os(III)Os(IV)(μ-O)(μ-C(3)H(7)COO)(tpa)(2)](PF(6))(4) complex (4). A mixed-valent di-μ-oxo-diosmium complex, [Os(III)Os(IV)(μ-O)(2)(tpa)(2)](PF(6))(3) (5), is also synthesized from 1 in an aerobic alkaline solution (pH 13.5). All the complexes exhibit strong absorption bands in a visible-near-infrared region based on interactions of the osmium dπ and oxygen pπ orbitals of the Os-O-Os moiety. The X-ray crystallographic analysis of 1, 3, and 4 shows that the osmium centers take a pseudo-octahedral geometry in the μ-oxo-μ-carboxylato-diosmium core. The mixed-valent osmium(III)osmium(IV) complex 4 has a shorter osmium-oxo bond and a larger osmium-oxo-osmium angle as compared with those of the diosmium(III) complex 1 having the same bridging carboxylate. Crystal structure of 5 reveals that the two osmium ions are bridged by two oxo groups to give an Os(2)(μ-O)(2) core with the significantly short osmium-osmium distance (2.51784(7) ?), which is indicative of a direct osmium-osmium bond formation with the bond order of 1.5 (σ(2)π(2)δ(2)δ*(2)π*(1) configuration). In the electrochemical studies, the μ-oxo-μ-carboxylato-diosmium(III) complexes exhibit two reversible Os(III)Os(III)/Os(III)Os(IV) and Os(III)Os(IV)/Os(IV)Os(IV) oxidation couples and one irreversible redox wave for the Os(III)Os(III)/Os(II)Os(III) couple in CH(3)CN. The irreversible reductive process becomes reversible in CH(3)CN/H(2)O (1:1 Britton-Robinson buffer; pH 5-11), where the {1H(+)/2e(-)} transfer process is indicated by the plot of the redox potentials against the pH values of the solution of 1. Thus, the μ-oxo-μ-butyrato-diosmium(III) center undergoes proton-coupled electron transfer to yield a μ-hydroxo-μ-butyrato-diosmisum(II) species. The di(μ-oxo) complex 5 exhibits one reversible Os(III)Os(IV)/Os(IV)Os(IV) oxidation process and one reversible Os(III)Os(IV)/Os(III)Os(III) reduction process in CH(3)CN. The comproportionation constants K(com) of the Os(III)Os(IV) states for the present diosmium complexes are on the order of 10(19). The values are significantly larger when compared with those of similar oxo-bridged dimetal complexes of ruthenium and rhenium.     

Synthesis and structural characterisation of cobalt(II) and iron(II) chloride complexes containing bis(2-pyridylmethyl)amine and tris(2-pyridylmethyl)amine ligands

Treatment of (2-C₅H₄N)CH_{2 3}N (TPA) with one equivalent of MCl₂ in n-BuOH at elevated temperatures affords the six-coordinate complexes [(TPA)MCl₂] (M = Co (1), Fe (2)) and, in the case of CoCl₂, the five-coordinate chloride salt [(TPA)CoCl]Cl (3). Conversely, addition of an excess of CoCl₂ in the latter reaction leads to [(TPA)CoCl]₂[CoCl₄] (4) as the only isolable product. Interaction of one equivalent of (2-C₅H₄N)CH_{2 2}NH (DPA) and MCl₂ under similar reaction conditions to that described above affords the dimeric species [(fac-DPA)MCl(μ-Cl)]₂ (M = Co (5), Fe (6)), while the bis(ligand) halide salts [(fac-DPA)₂M]Cl₂ (M = Co (7), Fe (8)) are accessible on addition of two equivalents of DPA. In the presence of air, 6 undergoes oxidation to give [ (fac-DPA)FeCl_{2 2}(μ-O)] (9). Single-crystal X-ray diffraction studies are reported for 1, 2 · MeCN, 3, , 7 · 3MeCN, 8 · 3MeCN and 9.     

Structural comparison of copper(I) and copper(II) complexes with tris(2-pyridylmethyl)amine ligand

Copper(I) complexes with the tris(2-pyridylmethyl)amine (TPMA) ligand were synthesized and characterized to examine the effect of counteranions (Br(-), ClO(4)(-), and BPh(4)(-)), as well as auxiliary ligands (CH(3)CN, 4,4'-dipyridyl, and PPh(3)) on the molecular structures in both solid state and solution. Partial dissociation of one of the pyridyl arms in TPMA was not observed when small auxiliary ligands such as CH(3)CN or Br(-) were coordinated to copper(I), but was found to occur with larger ones such as PPh(3) or 4,4'-dipyridyl. All complexes were found to adopt a distorted tetrahedral geometry, with the exception of [Cu(I)(TPMA)][BPh(4)], which was found to be trigonal pyramidal because of stabilization via a long cuprophilic interaction with a bond length of 2.8323(12) ?. Copper(II) complexes with the general formula [Cu(II)(TPMA)X][Y] (X = Cl(-), Br(-) and Y = ClO(4)(-), BPh(4)(-)) were also synthesized to examine the effect of different counterions on the geometry of [Cu(II)(TPMA)X](+) cation, and were found to be isostructural with previously reported [Cu(II)(TPMA)X][X] (X = Cl(-) or Br(-)) complexes.     

Trigonal bipyramidal geometry and tridentate coordination mode of the tripod in FeCl(2) complexes with tris(2-pyridylmethyl)amine derivatives bis-alpha-substituted with bulky groups. structures and spectroscopic comparative studies

A series of dichloroferrous complexes with ligands derived from the tris(2-pyridylmethyl)amine tripod has been prepared and characterized. The X-ray crystal structures of the complexes [bis(2-bromo-6-pyridylmethyl)(2-pyridylmethyl)amine]Fe(II)Cl(2) ((Br(2)TPA)Fe(II)Cl(2)) and [bis(2-phenyl-6-pyridylmethyl)(2-pyridylmethyl)amine]Fe(II)Cl(2), ((Ph(2)TPA)Fe(II)Cl(2)) are reported. In these complexes, the tripod coordinates in the tridentate mode, with a substituted pyridyl arm dangling away from the metal. Both complexes have a trigonal bipyramidal iron center with two equatorial chloride ions. Their crystal structures are compared with those of the [tris(2-pyridylmethyl)amine]Fe(II)Cl(2) and [(2-bromo-6-pyridylmethyl)bis(2-pyridylmethyl)amine]Fe(II)Cl(2) complexes ((TPA)Fe(II)Cl(2) and (BrTPA)Fe(II)Cl(2), respectively) in which the ligand coordinates in the tetradentate mode. For all complexes, the metal to ligand distances are systematically above the value of 2.0 A, and (1)H NMR displays paramagnetically shifted resonances with short relaxation times. This indicates that the iron is in a high-spin state. Electric conductivity measurements show that, for all complexes, the measured values lie within the same range, significantly below those expected for ionic complexes. Together with the analysis of the UV-visible and NMR data, this strongly suggests that the coordination mode of the tripod is retained in solution.     

Structures of Mn(II) complexes of bis(2-pyridylmethyl)amine (bpa) and (2-pyridylmethyl)(6-methyl-2-pyridylmethyl)amine (Mebpa): geometric isomerism in the solid state

The crystal structures of [Mn(bpa)₂](ClO₄)₂ (1), [bpa?=?bis(2-pyridylmethyl)amine], and Mn(6-Mebpa)₂(ClO₄)₂ (2), [6-Mebpa?=?(6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine] have been determined. In 1, two facial [Mn(bpa)₂]²⁺ isomers are observed in the same unit cell, one with C _i (1a) and the other with C₂ (1b) symmetries. In 2, only the isomer with C₂ symmetry is observed. The structure of [Mn(bpa)₂]²⁺ with only C₂ symmetry has been reported previously (Inorg. Chem., 31, 4611 (1992)). The bond length order Mn–N_amine?>?Mn–N_pyridyl, observed in the C₂ and the C _i isomers in the crystals of 1, is the reverse of the order observed in the structure of [Mn(bpa)₂](ClO₄)₂ which contains only the C₂ isomer in the unit cell. The structure of 2 in which only the C₂ isomer is found, also shows the bond length order Mn–N_pyridyl?>?Mn–N_amine. In cyclic voltammetric experiments in acetonitrile solutions, 1 and 2 show irreversible anodic peaks at E _p?=?1.60 and 1.90?V respectively, (vs. Ag/AgCl), assigned to the oxidation of Mn(II) to Mn(III). The substantially higher oxidation potential of 2 is attributable to a higher rearrangement energy in complex 2 due to the steric effect of the methyl substituent.     

Synthesis, magnetism and crystal structure of a chloride-bridged binuclear nickel(II) complex of tris(2-pyridylmethyl)amine

Summary A new binuclear Ni^II complex, [{(TPA)Ni(-Cl)}₂]-(ClO₄)₂·H₂O (1), where TPA = tris(2-pyridyl-methyl) amine, has been prepared and characterized. The X-ray crystal structure and variable temperature magnetic susceptibility (4–300 K) of the complex have been determined. The two Ni^II atoms of (1) are in a distorted octahedral environment and are bridged by Cl atoms. Ni-Cl distances are 2.363(6) and 2.503(7) Å, and the Ni-Cl-Ni angle is 92.7(2)°. The metal atoms are separated by a non-bonding distance of 3.523 Å.The effective magnetic moment of (1) increases slightly with decreasing temperature and appears to reach a maximum before decreasing. The observed data were fitted to the Heisenberg model and the results indicate that there is a ferromagnetic interaction (positive J) and weak antiferromagnetic intermolecular interaction (negative ).     

Efficient and specific strand scission of DNA by a dinuclear copper complex: comparative reactivity of complexes with linked tris(2-pyridylmethyl)amine moieties

The compound [Cu(II)(2)(D(1))(H(2)O)(2)](ClO(4))(4) (D(1) = dinucleating ligand with two tris(2-pyridylmethyl)amine units covalently linked in their 5-pyridyl positions by a -CH(2)CH(2)- bridge) selectively promotes cleavage of DNA on oligonucleotide strands that extend from the 3' side of frayed duplex structures at a site two residues displaced from the junction. The minimal requirements for reaction include a guanine in the n (i.e. first unpaired) position of the 3' overhang adjacent to the cleavage site and an adenine in the n position on the 5' overhang. Recognition and strand scission are independent of the nucleobase at the cleavage site. The necessary presence of both a reductant and dioxygen indicates that the intermediate responsible for cleavage is produced by the activation of dioxygen by a copper(I) form of the dinuclear complex. The lack of sensitivity to radical quenching agents and the high level of site selectivity in scission suggest a mechanism that does not involve a diffusible radical species. The multiple metal center exhibits a synergy to promote efficient cleavage as compared to the action of a mononuclear analogue [Cu(II)(TMPA)(H(2)O)](ClO(4))(2) (TMPA = tris(2-pyridylmethyl)amine) and [Cu(OP)(2)](2+) (OP = 1,10-phenanthroline) at equivalent copper ion concentrations. The dinuclear complex, [Cu(II)(2)(D(1))(H(2)O)(2)](ClO(4))(4), is even capable of mediating efficient specific strand scission at concentrations where [Cu(OP)(2)](2+) does not detectably modify DNA. The unique coordination and reactivity properties of [Cu(II)(2)(D(1))(H(2)O)(2)](ClO(4))(4) are critical for its efficiency and site selectivity since an analogue, [Cu(II)(2)(DO)(Cl(2))](ClO(4))(2), where DO is a dinucleating ligand very similar to D(1), but with a -CH(2)OCH(2)- bridge, exhibits only nonselective cleavage of DNA. The differences in the reactivity of these two complexes with DNA and their previously established interaction with dioxygen suggest that specific strand scission is a function of the orientation of a reactive intermediate.     

Studies of artificial hydrolytic metalloenzymes: The catalyzed carboxyester hydrolysis by copper(II), zinc(II) and cobalt(II) complexes of the tripod ligand tris(2-benzimidazylmethyl)amine

The hydrolysis kinetics of p-nitrophenyl acetate (NA) catalyzed by Cu^II, Zn^II and Co^II complexes of tris(2-benzimidazylmethyl)amine (NBT) have been studied. The hydrolysis rate is first-order in both metal(II) complex and NA. The second-order rate constants, k_cat are 0.083, 0.241 and 0.285mol^–1Ls^–1 (298K, I = 0.10molL^–1 KNO₃, 0.02molL^–1 tris buffer, 40% MeCN aqueous solution) for Zn–NBT, Co–NBT and Cu–NBT complexes, respectively. The result indicates that the hydrolytic metalloenzyme activity of different metal complexes increases with the electrophilicity of the metal ions and that the complexes, in this paper, constitute that most efficient hydrolytic metalloenzyme models reported to date. An increase in MeCN content in the solution greatly reduces the hydrolytic activity of the nucleophiles.     

Atom transfer radical addition in the presence of catalytic amounts of copper(I/II) complexes with tris(2-pyridylmethyl)amine

Highly efficient atom transfer radical addition of polyhalogenated compounds to alkenes catalyzed by copper(I/II) complexes with tris(2-pyridylmethyl)amine in the presence of a radical initiator [2,2'-azobis(2-methylpropionitrile)] was reported.     

Chromium(II) and chromium(III) complexes supported by tris(2-pyridylmethyl)amine: synthesis, structures, and reactivity

This report describes the synthesis, structural characterization, and polymerization behavior of a series of chromium(II) and chromium(III) complexes ligated by tris(2-pyridylmethyl)amine (TPA), including chromium(III) organometallic derivatives. For instance, the combination of TPA with CrCl(2) yields monomeric (TPA)CrCl(2) (1). A similar reaction of CrCl(2) with TPA, followed by chloride abstraction with NaBPh(4) or NaBAr(F)(4) (Ar(F) = 3,5-(CF(3))(2)C(6)H(3)), provides the weakly associated cationic dimers [(TPA)CrCl](2)[BPh(4)](2) (2A) and [(TPA)CrCl](2)[BAr(F)(4)](2) (2B), respectively. X-ray crystallographic analysis reveals that each chromium(II) center in 1, 2A, and 2B is a tetragonally elongated octahedron; such Jahn-Teller distortions are consistent with the observed high spin (S = 2) electronic configurations for these chromium(II) complexes. Likewise, reaction of CrCl(3)(THF)(3) with TPA, followed by anion metathesis with NaBPh(4) or NaBAr(F)(4), yields the monomeric, cationic chromium(III) complexes [(TPA)CrCl(2)][BPh(4)] (4A) and [(TPA)CrCl(2)][BAr(F)(4)] (4B), respectively. Treatment of 4A with methyl and phenyl Grignard reagents produces the cationic chromium(III) organometallic derivatives [(TPA)Cr(CH(3))(2)][BPh(4)] (5) and [(TPA)CrPh(2)][BPh(4)] (6), respectively. Similar reactions of 4A with organolithium reagents leads to intractable solids, presumably due to overreduction of the chromium(III) center. X-ray crystallographic analysis of 4A, 5, and 6 confirms that each possesses a largely undistorted octahedral chromium center, consistent with the observed S = (3)/(2) electronic ground states. Compounds 1, 2A, 2B, 4A, 4B, 5, and 6 are all active polymerization catalysts in the presence of methylalumoxane, producing low to moderate molecular weight high-density polyethylene.     

Anion sensing with luminescent lanthanide complexes of tris(2-pyridylmethyl)amines: pronounced effects of lanthanide center and ligand chirality on anion selectivity and sensitivity

Luminescent lanthanide complexes with tris(2-pyridylmethyl)amine ligands exhibited anion-specific sensory functions, and their anion selectivity and response sensitivity were modulated by a combination of lanthanide center and chiral ligand.     

Energy-level tailoring in a series of redox-rich quinonoid-bridged diruthenium complexes containing tris2-pyridylmethyl)amine as a co-ligand

Reactions of [{Ru(tmpa)}₂(μ‐Cl)₂][ClO₄]₂, ( 2 [ClO₄]₂, tmpa=tris(2‐pyridylmethyl)amine) with 2,5‐dihydroxy‐1,4‐benzoquinone ( L¹ ), 2,5‐di‐[2,6‐(dimethyl)‐anilino]‐1,4‐benzoquinone ( L² ), or 2,5‐di‐[2,4,6‐(trimethyl)‐anilino)]‐1,4‐benzoquinone ( L³ ) in the presence of a base led to the formation of the dinuclear complexes [{Ru(tmpa)}₂(μ‐ L¹ _{?2 H})][ClO₄]₂ ( 3 [ClO₄]₂), [{Ru(tmpa)}₂(μ‐ L² _{?2 H})][ClO₄]₂ ( 4 [ClO₄]₂), and [{Ru(tmpa)}₂(μ‐ L³ _{?2 H})][ClO₄]₂ ( 5 [ClO₄]₂). Structural characterization of 5 [ClO₄]₂ showed the localization of the double bonds within the quinonoid ring and a twisting of the mesityl substituents with respect to the quinonoid plane. Cyclic voltammetry of the complexes show two reversible oxidation and quinonoid‐based reduction processes. Results obtained from UV/Vis/NIR and EPR spectroelectrochemistry are invoked to discuss ruthenium‐ versus quinonoid‐ligand‐centered redox activity. The complex 3 [ClO₄]₂ is compared to the reported complex [{Ru(bpy)}₂(μ‐ L¹ _{?2 H})]²⁺ ( 1²⁺ , bpy=2,2′‐bipyridine). The effects of substituting the bidentate and better π‐accepting bpy co‐ligands with tetradentate tmpa ligands [pure σ‐donating (amine) as well as σ‐donating and π‐accepting (pyridines)] on the redox and electronic properties of the complexes are discussed. Comparisons are also made between complexes containing the dianionic forms of the all‐oxygen‐donating L¹ ligand with the L² and L³ ligands containing an [O,N,O,N] donor set. The one‐electron oxidized forms of the complexes show absorption in the NIR region. The position as well as the intensity of this band can be tuned by the substituents on the quinonoid bridge. In addition, this band can be switched on and off by using tunable redox potentials, making such systems attractive candidates for NIR electrochromism.     

Synthesis,crystal structure and properties of a novel copper(II) complex with tripod ligand tris(1H-benzimidazol- 2-ylmethyl)amine

A five-coordinate copper complex with the tripod ligand tris(1H-benzimidazol-2-ylmethyl)amine (ntb), of composition [Cu(ntb)(H₂O)] (C1O₄)₂?·?C₅H₄N₂O₃?·?H₂O (C₅H₄N₂O₃?=?4-nitropyridine-N-oxide), was synthesized and characterized by means of elemental analyses, electrical conductivities, thermal analyses, IR, and U.V. The crystal structure of the copper complex has been determined by single-crystal X-ray diffraction, and shows that the Cu^II is bonded to a tris(1H-benzimidazol-2-ylmethyl)amine (ntb) ligand and a water molecule through four N atoms and one O atom, giving a distorted trigonal–bipyramidal coordination geometry with approximate C ₃ molecular symmetry. Cyclic voltammograms of the copper complex indicate a quasi-reversible Cu⁺²/Cu⁺ couple. Electron spin resonance data confirm a trigonal-bipyramidal structure and with g ₂?<?g _ζ and a very small value of A ₂ (20?×?10^?4?cm^?1).     

Synthesis and complex formation of 2-ammoethylthioacet(N-2-pyridylmethyl)amide

Summary A new ligand, 2-aminoethylthioacet(N-2-pyridylmethyl)amide was synthesized. The complex formation of the ligand with Cu^II, Co^II and Co^III ions and that of the carbobenzoxy derivative of the ligand with Cu^II ions has been investigated. Structures are proposed for all complexes isolated and the factors influencing metal-sulphur bond formation in the complexes discussed.     

Synthesis,crystal structure and properties of a copper(II) complex with the tripod ligand tris ( N -methylbenzimidazol-2-ylmethyl)amine and 4-hydroxycinnamate

A five-coordinate copper complex with the tripod ligand tris(N-methylbenzimidazol-2-ylmethyl)amine (Mentb) and 4-hydroxycinnamate, with the composition [Cu(Mentb)(4-hydroxycinnamate)](ClO₄)?·?0.5DMF, was synthesized and characterized by means of elemental analyses, electrical conductivities, thermal analyses, IR, and UV. The crystal structure of the copper complex has been determined by single-crystal X-ray diffraction, and shows that the Cu^II atom is bonded to a tris(N-methylbenzimidazol-2-ylmethyl)amine (Mentb) ligand and a 4-hydroxycinnamate through four N atoms and one O atom, giving a distorted trigonal-bipyramidal coordination geometry (τ?=?0.78), with approximate C₃ molecular symmetry. Cyclic voltammograms of the copper complex indicate a quasireversible Cu⁺²/Cu⁺ couple. Electron spin resonance data confirm the trigonal–bipyramidal structure and indicate g _∥?<?g _⊥ with a very small value of A _∥ (57?×?10^?4?cm^?1).