Laura Gasque

Coexistence of Intramolecular Ligand-Mediated and Through Hydrogen-Bond Magnetic Interactions in a Chain of Dicopper(II) Units

The reaction of 2,8-dimethyl-5,11-bis(pyridin-2-ylmethyl)-1,4,5,6,7,10,11,12-octahydroimidazo[4,5-h]imidazo[4,5-c][1,6]-diazecine (dimp) with copper(II) nitrate in water produces the compound [Cu(2)(dimp)(H(2)O)(2)(NO(3))(2)](NO(3))(2). The single-crystal X-ray structure shows the formation of hydrogen-bonded chains in the lattice that are formed by dicopper(II) units doubly connected by nitrate/water bridges. Within the one-dimensional chains, the Cu ions are separated by either intramolecular or intermolecular distances of 7.309(2) Å or 6.255(2) Å, respectively. The magnetic susceptibility data revealing weak antiferromagnetic exchange interactions between the copper(II) ions were interpreted by considering two possible models, namely, an isolated dinuclear and a 1-D chain picture. The latter leads to an alternation J(1) = -11.6 and J(2) = -3.0 cm(-1) along the chain. In order to clarify the relative strengths of the exchange couplings through hydrogen bonds and via the bridging dimp ligand, solution EPR studies and quantum chemical calculations were carried out. EPR studies unambiguously conclude on the existence of an exchange interaction J(a) mediated by the dinucleating dimp ligand, while the through-H coupling J(b) is physically absent in solution. On the basis of dinuclear units extracted from the X-ray data, J(a) was estimated around -5.0 cm(-1) from DFT-based calculations (M06 functional), whereas J(b) is negligible. In contrast, wave function configuration interaction calculations (DDCI) support a description where both inter- and intramolecular pathways coexist with a preeminent role of H bonds with J(a) = -2.8 and J(b) = -10.4 cm(-1). Not only are these values very consistent with the extracted set of parameters (J(1), J(2) = -11.6, -3.0 cm(-1)) but the possibility to generate leading exchange coupling through weak bonds is evidenced by means of wave function-based calculations.

A dicopper complex with distant metal centers. Structure, magnetic properties, electrochemistry and catecholase activity.

The crystal structure and magnetic properties of a dinuclear copper(II) complex of the ligand [2,8-dimethyl-5,11-di-(dimethylethyleneamine) 1,4,5,6,7,10,11,12-octahydroimidazo [4,5-h] imidazo [4,5-c] [1,6]diazecine] dimeim have been investigated. Also, its catecholase activity has been explored in different solvent mixtures: MeCN/H2O and OH/H2O, each at several pH values. In CH3OH/H2O, where the activity was superior, the optimal pH value for the catalytic activity was found to be lower than in CH3CN/H2O. The study of the complexs electrochemical behavior (cyclic voltammetry) which was also investigated in these various media, revealed that although an increase in pH in both solvent mixtures results in an increase both in Me oxidizing power (E(1/2)) and reversibility (ipa/ipc) the change of solvent system seems to be a more influencing factor. The superior catalytic activity found in MeOH/H2O pH=8.0, is associated with a significantly more reversible behavior displayed in this medium. Potentiometric determination of the overall formation constant and three successive pKas for the complex, suggest the formation of stable hydroxo complexes which could be the catalytically active species.

CU-O STRETCHING FREQUENCY CORRELATION WITH PHENANTHROLINE PKA VALUES IN MIXED COPPER COMPLEXES

Abstract A study of Cu–O vibration frequencies in 32 isostructural mixed copper complexes containing eight differently substituted phenanthrolines and four different oxygen donor bidentate ligands, is presented. In all cases linear correlation was found between phenanthroline p K a values and the studied vibration frequencies, suggesting that an increase in phenanthroline basicity weakens Cu–O bonds in this type of compound.

Synthesis, characterization and X-ray structures of the new dinucleating ligand 2,8-dimethyl-1,4,5,6,7,10,11,12-octahydroimidazo[4,5-h] imidazo[4,5-c][1,6]diazecine-5,11-diethanoic acid and its Cu(II) complex; an alternating chain of Cu(II) ions, coupled both intramolecularly and intermolecularly

Abstract The design and synthesis of a new, rigid dinucleating ligand 2,8-dimethyl-1,4,5,6,7,10,11,12-octahydroimidazo[4,5-h] imidazo[4,5-c][1,6]diazecine-5,11-diethanoic acid (H2glymeim) is reported together with its molecular and crystal structure. The rigid ligand structure is confirmed by the structure and magnetic properties of its bis Cu(II) complex, [Cu2(C16H22N6O6)(H2O)4](ClO4)2(H2O)2, (Cu2glymeim). Crystals of free glymeim are composed of units of C16H22N6O4 and eight water molecules linked by a two dimensional network of hydrogen bonds. Six of them contribute to a one-dimensional network that links the organic molecules. The 1,6-diazecine ring shows a chair conformation, with expected angles and bond distance values. A stretched conformation of the glycine residue is observed in the free ligand. When this residue is coordinated, it produces significant stress over the diazecine ring caused by the closure of the glycine residue around the metal ion. The copper complex has a dinuclear structure with a square pyramidal environment around both metal ions. The apical position in the two pyramids point to opposite directions in the molecule and they are related by an inversion center. The pyramidal bases of both copper atoms are in the same plane. The intramolecular metal–metal distance in the complex is 7.445(3) A. However, the shortest distance is of intermolecular nature, with a value of 5.378(2) A. The crystal structure of the complex consists of a chain of dinuclear units, with an alternating chain arrangement. Low temperature magnetic susceptibility and EPR are in agreement with an antiferromagnetic dinuclear behavior in solution and like a linear chain uniformly spaced, with J=−8.54 cm−1 and α=1. The magnetic behavior of this compound can be explained as the result of an intramolecular magnetic exchange (long distance), and a superexchange path through the hydrogen bond network between adjacent dinuclear molecules.

Interaction between Glyglu and Ca2+, Pb2+, Cd2+ and Zn2+ in solid state and aqueous solution.: Crystal structures of poly[aqua-1,2-κ-O-di[lead(gly-gluH)]bis(perchlorate)] and poly[bisglycylglutamic-cadmium(II) tetrahydrate]

Abstract Glycylglutamic acid (GE H 2 ) is a peptide usually present in calcium binding sites. The interaction between the peptide and the cations Ca 2+ , Pb 2+ , Cd 2+ , and Zn 2+ in aqueous solution and in the solid state is described. Six compounds were isolated with different protonation states of the ligand. Potentiometric equilibrium studies, 13 C and 111 Cd solid state CP MAS NMR and IR spectroscopy were performed. Two crystal structures are reported: [Pb(GE H )(H 2 O) 1/2 ]ClO 4 and [Cd(GE H ) 2 ]·3H 2 O. Both constitute 3D polymers, where only carboxylate groups are coordinated to the cations. The crystalline lead compound shows a hemidirected coordination sphere due to its stereochemically active lone pair. In deprotonated derivatives, it is possible to assign a metal-amino interaction to a far IR signal (340–370 cm −1 ).

Solvent and pH effects on the redox behavior and catecholase activity of a dicopper complex with distant metal centers

A dicopper complex is described for which significant catecholase activity was found, particularly for a compound in which the two metal ions are more than 7A apart. Variations on the catecholase activity of this complex were explored in a range of pH values from 5.5 to 9.0 in two solvent mixtures, MeCN/H(2)O and MeOH/H(2)O. The catalytic performance of the complex was found to be substantially better in the second, where the maximum activity was achieved at a pH value one unit lower than in the first. Electrochemical studies of the complex in the absence and presence of dioxygen revealed a very different behavior in each of the two solvent mixtures, which may account for the correspondingly distinct catalytic activity.

Complexation of lead(II) by l-aspartate: crystal structure of polymeric Pb(aspH)(NO3)

Abstract Two lead compounds containing the aspartate ligand are described, with compositions Pb(aspH)NO3 and Pb(asp). The crystal structure of the first shows it is a three-dimensional polymer in which each lead atom is coordinated to six oxygen atoms, five from carboxyl groups and one from a nitrate ion. For Pb(asp), spectroscopic data suggest the presence of Pb–NH2 interaction.

Cadmium complexation by aspartate. NMR studies and crystal structure of polymeric Cd(AspH)NO3

Abstract Two cadmium compounds containing the aspartate ligand are described, with compositions Cd(AspH)NO 3 and Cd(Asp). The crystal structure of the first shows it is a two dimensional polymer in which each cadmium is coordinated to seven oxygen atoms, four from carboxylates and three from the nitrate moiety which acts both as a chelate and as a bridging ligand. For Cd(Asp), 111 Cd NMR studies suggests the presence of CdNH 2 interaction.

Mixed chelate complexes. II. Structures of l-alaninato(aqua)(4,7-diphenyl-1,10-phenanthroline)copper(II) nitrite monohydrate and aqua(4,7-dimethyl-1,10-phenanthroline)(glycinato)(nitrato)copper(II) monohydrate

[Cu(C 3 H 6 NO 2 )(C 24 H 16 N 2 )(H 2 O)]NO 2 .H 2 O (1), M r =566.1, monoclinic, P2 1 , a=11.864 (3), b=7.726 (2), c=14.832 (3) A, β=102.17 (2) o , V=1329.0 (9) A 3 , Z=2, D x =1.414 Mg m -3 , λ(Mo Kα)=0.71069 A, μ=0.868 mm -1 , T=288 K, R=0.064 for 2061 reflections. [Cu(C 2 H 4 NO 2 )(NO 3 )(C 14 H 12 N 2 )(H 2 O)].H 2 O (II), M r =443.9, triclinic, P1, a=14.138 (3), b=10.016 (2), c=7.565 (2) A, α=104.83 (2), β=83.47 (2), γ=119.93 (2) o , V=897.3 (6) A 3 , Z=2, D x =1.642 Mg m -3 , λ(Mo Kα)=0.71069 A, μ=1.265 mm -1 , T=288 K, R=0.046 for 1322 reflections

Dinuclear copper complexes with imidazole derivative ligands: a theoretical study related to catechol oxidase activity.

Catechol oxidase is a very important and interesting metalloprotein. In spite of the efforts to understand the reaction mechanism of this protein, there are important questions that remain unanswered concerning the catalytic mechanism of this enzyme. In this article, dinuclear copper compounds are used as biomimetic models of catechol oxidase to study plausible reaction paths. These dinuclear copper(II) complexes have distant metal centers (of 7.5 Å approximately) and superior catalytic activity to that of many dicopper complexes with shorter Cu-Cu distances. One mononuclear copper(II) complex is also analyzed in this investigation in order to see the influence of the two metal centers in the catalytic activity. Density functional theory calculations were performed to obtain optimized structures, vertical ionization energies, vertical electron affinities, the electrodonating power (ω(-)), the electroaccepting power (ω(+)) and the energy difference of several reaction paths. The K(M) experimental results that were previously reported compare well with the electroaccepting power (ω(+)) of the copper compounds that are included in this article, indicating that this index is useful for the interpretation of the electron transfer capacity and therefore the catalytic activity. The catechol moiety coordinates to only one Cu ion, but two metal atoms are needed in order to have a good electron acceptor capacity of the biomimetic models.