Self-assembly of the octanuclear cluster [Cu8(OH)10(NH2(CH2)2CH3)12]6+ and the one-dimensional N-propylcarbamate-linked coordination polymer {[Cu(O2CNH(CH2)2CH3)(NH2(CH2)2CH3)3](ClO4)}n

The reaction of Cu(ClO4)2.6-H2O and n-propylamine in methanol gives two high-nuclearity products of well-defined compositions. At amine concentrations greater than seven equivalents compared to copper ion concentration, the system fixes carbon dioxide from air to form the one-dimensional carbamate-bridged coordination polymer, {[Cu(mu2-O,O'-O2CNH(CH2)2CH3)(NH2(CH2)2CH3)3](ClO4)}n ({1-ClO4}n). Lower relative amine concentrations lead to the self-assembly of an octanuclear copper-amine-hydroxide cluster [Cu8(OH)10(NH2(CH2)2CH3)12]6+ (2). Both compounds exhibit unique structures: {1-ClO4}n is the first mu2-O,O'-mono-N-alkylcarbamate-linked coordination polymer and 2 is the largest copper-hydroxide-monodentate amine cluster identified to date. The crystal structures indicate that the size of the n-propyl group is probably crucial for directing the formation of these compounds. Magnetic susceptibility studies indicate very weak antiferromagnetic coupling for 1. The octanuclear cluster 2 displays slightly stronger net antiferromagnetic coupling, despite the presence of a number of Cu-O(H)-Cu angles below the value of about 97 degrees that would normally be expected to yield ferromagnetic coupling.     

CHROMOTROPIC CHANGES OF Cu(II) AND Ni(II) COMPLEXES WITH N2O2 AND N3O2 SCHIFF-BASE LIGANDS IN THE SOLID PHASE

Abstract

Four new Schiff-base ligands have been prepared from the condensation of 3-formyl-4-hy-droxy-1,8-naphthyridin-2-one with different diamines and a triamine, H₂L_a-H₂L_d. Two series of Ni(II) and Cu(II) complexes with the four ligands were also prepared. The ligands and their metal complexes were characterized by chemical analyses, IR, Far-IR, electronic, ESR and mass spectra as well as magnetic measurements and X-ray diffraction patterns.

Different products for Ni(II) and Cu(II) were obtained in similar reactions with the same metal salt, depending on the nature of the ligand. Different geometries were also obtained depending on the counter anion of metal salt. Thus, violet square-planar Cu(II) complexes were obtained with Cu(OAc)₂. H₂O and green octahedral ones with CuCl₂. 2H₂O, except the reaction with ligand H₂L_d which gave only an octahedral product whether the anion was acetate, chloride or perchlorate. Electronic and ESR spectra were used to differentiate between the two geometries of the Cu(II) complexes. The green octahedral Cu(II) complexes undergo irreversible thermochromism to the violet square-planar complexes except the copper complex of the ligand H₂L_d which did not not show any color change and retained its octahedral geometry. Based on the magnetic moments and thermal analyses, only one Ni(II) complex of the Schiffbase ligand H₂L_c undergoes reversible thermochromism from green (octahedral) to red (squareplanar). The reverse change of the thermal product (red) to the parent complex (green) proceeded on exposure to atmospheric air for a few minutes. On the other hand, Ni(II) complexes of ligands H₂L_a and H₂L_b have stable square-planar geometry and all efforts to add other ligands such as H₂O or pyridine to these complexes failed to yield other products. The corresponding Cu(II) complexes were easily transformed to their octahedral geometry by adding H₂O or pyridine and heating.     

Hydrothermal Synthesis and Structure of a Copper(II) Complex, [Cu(4,4''''bpy)(H_2O)_3]SO_42H_2O

1 INTRODUCTION Recently, there has been increasing interest in crystal engineering of supramolecular architectures by means of covalent bonding, hydrogen bonding or other weak intermolecular interactions[1, 2], which reflect their potential applications in host-guest che- mistry, catalysis and function materials[3～5]. The construction of such materials is mainly provided by geometry of transition metal extending through rigid ligands. The oxidation state and coordination predisposition …     

A High‐Valent Iron(IV) Peroxo Core Derived from O2

Dioxygen‐tolerant [NiFe] hydrogenases catalyze not only the conversion of H₂ into 2 H⁺ and 2 e^? but also the reduction of O₂ to H₂O. Chemists have sought to mimic such bifunctional catalysts with structurally simpler compounds to facilitate analysis and improvement. Herein, we report a new [NiFe]‐based catalyst for O₂ reduction via an O₂ adduct. Structural investigations reveal the first example of a side‐on iron(IV) peroxo complex.     

Dioxygen Activation by a Macrocyclic Copper Complex Leads to a Cu2O2 Core with Unexpected Structure and Reactivity

We report the Cu^I/O₂ chemistry of complexes derived from the macrocylic ligands 14‐TMC (1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane) and 12‐TMC (1,4,7,10‐tetramethyl‐1,4,7,10‐tetraazacyclododecane). While [(14‐TMC)Cu^I]⁺ is unreactive towards dioxygen, the smaller analog [(12‐TMC)Cu^I(CH₃CN)]⁺ reacts with O₂ to give a side‐on bound peroxo‐dicopper(II) species (^SP), confirmed by spectroscopic and computational methods. Intriguingly, 12‐TMC as a N4 donor ligand generates ^SP species, thus in contrast with the previous observation that such species are generated by N2 and N3 ligands. In addition, the reactivity of this macrocyclic side‐on peroxo‐dicopper(II) differs from typical ^SP species, because it reacts only with acid to release H₂O₂, in contrast with the classic reactivity of Cu₂O₂ cores. Kinetics and computations are consistent with a protonation mechanism whereby the TMC acts as a hemilabile ligand and shuttles H⁺ to an isomerized peroxo core.     

ACID DISSOCIATION BEHAVIOR OF 2, 3- AND 2, 3, 9,lO-METHYL- OR CYCLOHEXYL-SUBSTITUTED CYCLAMS,THEIR COMPLEXATION BEHAVIOR WITH COPPER@) AND THE AXIAL SOLVENT SPECTRUM OF THEIR COMPLEXESINTERACTION EFFECT ON THE LIGAND-FIELD

Abstract

Stability constants of Cu(Il)-complexes for 1, 4, 8, 11-tetra-azacyclotetradecane (cyclam) analogs with periphery substituted [14]aneN₄-ring, 2, 3-tetramethyl-, 2, 3, 9, 10-octamethyl-, 2, 3-cyclohexyl, and 2, 3, 9, 10-dicyclohexyl-cyclams have been determined at 25°C in aqueous solution. The UV-Vis absorption spectra of their complexes, ([Cu(L)] (C1O₄)₂), were measured in water and some typical organic solvents (methanol, acetone, propylene carbonate, formamide, N, N-dimethylformamide, and dimethylsulfoxide). A good linear relationship was found between the stability constant logK_CuL) and the difference between the wavenumber of maximum absorption in water and in the organic solvents (δλ_max ^?1 (W-S)). The value of logK_CuL at δλ_max ^?1(W-S) = 0 not only shows a linear relation to solvent parameters, donor number and dielectric constant, but also to the enthalpy of transfer of ClO₄ ^? from water to the organic solvents. The value is proposed as a new solvent parameter ‘Kλlue’ to be used as an index for solvent-effects on Cu(II)-complexes of cyclam analogs. The increasing order of the new parameter (log scale) is as follows; DMF(27.24)>DMSO(27.14)>FA(26.82)>MeOH(26.27)>PC(25.75)>AC(24.71). Another meaning of the new parameter is assumed from connection of the potentiometric data with spectrometric data. The solvent effects on stability and the UV-Vis spectra are assumed to be caused by perturbation of the D_{4 h} or axially-elongated ligand field through axial approach of solvent to the Cu(II)-complexes and by formation of a solvent-separated ion pair between a solvated Cu(lI)-complex cation and counter anion (ClO₄)     

Multistep oligometal complexation of the macrocyclic tris(N2O2) hexaoxime ligand

A macrocyclic oxime ligand H₆L, which has an O₆ cavity surrounded by three N₂O₂ chelate sites, was synthesized and the multistep oligometal complexation behavior was investigated. Upon complexation with zinc(II), the H₆L ligand afforded two kinds of hexanuclear complexes, L₂Zn₆ then LZn₆. Each of the complexation steps proceeded highly efficiently. In the latter complex, a Zn₃(μ₃‐OH) unit was incorporated into the trimetalated ligand, LZn₃. The integrated N₂O₂ chelate coordination sites provide a unique environment for a homometallic complex. The different nature of the peripheral N₂O₂ sites and the central O₆ site is particularly suitable for the selective formation of heterometallic complexes. Complexation with the zinc(II) ion in the presence of alkaline earth (Ca and Ba) or rare earth (La, Eu, Lu) metal ions afforded the heterotetranuclear complexes LZn₃M (M=Ca, Ba, La, Eu, Lu), in which zinc(II) and ion M occupied the N₂O₂ and O₆ sites, respectively. Titration experiments showed that the heterometallic complexes LZn₃Ca and LZn₃Ba were converted into the homometallic complex LZn₆ whereas LZn₃La was not. As a result, the binding affinity in the central O₆ site of the LZn₃ unit is apparently in the order of Ca²⁺, Ba²⁺3(μ₃‐OH)3+. This difference in the affinities of metal ions as well as the ionic sizes makes the novel conversion efficient, particularly in the case of the three‐step conversion from H₆L to H₂LZn₂Ba, LZn₃Ba, then LZn₆.     

Organic-inorganic hybrids based on novel bimolecular [Si2W22Cu2O78(H2O)]12- polyoxometalates and the polynuclear complex cations [Cu(ac)(phen)(H2O)]n n+ (n=2, 3)

The reaction of a monosubstituted Keggin polyoxometalate (POM) generated in situ with copper-phenanthroline complexes in excess ammonium or rubidium acetate led to the formation of the hybrid metal organic-inorganic compounds A7[Cu2(ac)2(phen)2(H2O)2][Cu3(ac)3(phen)3(H2O)3][Si2W22Cu2O78(H2O)].approximately 18 H2O (A=NH4+ (1), Rb+ (2); ac=acetate; phen=1,10-phenanthroline). These compounds are constructed from inorganic and metalorganic interpenetrated sublattices containing the novel bimolecular Keggin POM, [Si2W22Cu2O78(H2O)]12-, and Cu-ac-phen complexes, [Cu(ac)(phen)(H2O)]n n+ (n=2, 3). The packing of compound 1 can be viewed as a stacking of open-framework layers parallel to the xy plane built of hydrogen-bonded POMs, and zigzag columns of pi-stacked Cu-ac-phen complex cations running along the [111] direction. Magnetic and EPR results are discussed with respect to the crystal structure of the compounds. DFT calculations on [Cu(ac)(phen)(H2O)]n n+ cationic complexes have been performed, to check the influence of packing in the complex geometry and determine the magnetic exchange pathways.