Vasilis Tangoulis

CuII-herbicide complexes: structure and bioactivity

Abstract Copper complexes with the commercial auxin herbicides 2,4-dichlorophenoxy-acetic acid (2,4-D), 3,4-dichlorophenoxy-acetic acid (3,4-D), 2,4,5-trichlorophenoxy-acetic acid (2,4,5-T), 2-methyl-4-chloro-phenoxy-acetic acid (MCPA), 2,3-dichlorophenoxy-acetic acid (2,3-D) and 2-(2,4-dichlorophenoxy)-propanoic acid (2,4-DP) in the presence or not of 2,2′-bipyridine (bipy), an antimicrobial agent, were prepared and characterized. The available evidence supports a dimeric structure for the 2,3-D complex, while the presence of bipy leads to monomeric forms. The solution behaviour of dinuclear complexes in dimethylformamide (DMF) has shown that the complexes are converted to monomeric compounds by the addition of more than 1:2 of bipy. The cyclic voltammograms of dimers in DMF suggest that the complexes retain the dimeric structure in solution. The electron spin resonance spectra of the compound (aqua)(2,2′-bipyridine)bis(2-methyl-4-chloro-phenoxyacetato) copper(II) (I) show features characteristic of the presence of an S = 1 triplet state. The crystal structure of 1 was determined and refined by least-squares methods using three-dimensional Mo Kα data. 1 crystallizes in the space group C2 c , in a cell of dimensions a=40.49(1), b=7.286(3), c=19.617(6) A , β=103.23(1)°, V=5634(3) A 3 , Z=8 . Study of the antimicrobial activity showed that the presence of bipy increases the efficiency 4–8 times.

Synthesis, spectroscopic, and structural characterization of the first aqueous cobalt(II)-citrate complex: toward a potentially bioavailable form of cobalt in biologically relevant fluids.

Abstract Citric acid represents a class of carboxylic acids present in biological fluids and playing key roles in biochemical processes in bacteria and humans. Its ability to promote diverse coordination chemistries in aqueous media, in the presence of metal ions known to act as trace elements in human metabolism, earmarks its involvement in a number of physiological functions. Cobalt is known to be a central element of metabolically important biomolecules, such as B12, and therefore its biospeciation in biological fluids constitutes a theme worthy of chemical and biological perusal. In an effort to unravel the aqueous chemistry of cobalt in the presence of a physiologically relevant ligand, citrate, the first aqueous, soluble, mononuclear complex has been synthesized and isolated from reaction mixtures containing Co(II) and citrate in a 1 :2 molar ratio at pH∼8. The crystalline compound (NH4)4[Co(C6H5O7)2] (1) has been characterized spectroscopically (UV/vis, EPR) and crystallographically. Its X-ray structure consists of a distorted octahedral anion with two citrate ligands fulfilling the coordination requirements of the Co(II) ion. The magnetic susceptibility measurements of 1 in the range from 6 to 295 K are consistent with a high-spin complex containing Co(II) with a ground state S=3/2. Corroborating this result is the EPR spectrum of 1, which shows a signal consistent with the presence of a Co(II) system. The spectroscopic and structural properties of the complex signify its potential biological relevance and participation in speciation patterns arising under conditions consistent with those employed for its synthesis and isolation.

Preparation, structural characterization and properties of malonamato(−1) complexes

Abstract The complexes trans-[M(LH)2(H2O)2] (M = Mn, Co, Ni, Cu, Zn; LH− = the monoanion of malonamic acid) have been synthesized and the X-ray crystal structures of the copper (II) and zinc (II) complexes show an octahedral geometry around the metal ion in both molecules. The ligand LH− acts as a bidentate chelate with ligated atoms being the amide and one of the carboxylate oxygens. Both structures are stabilized through similar, intermolecular 2D hydrogen bonds. The thermal decomposition data, magnetic susceptibilities, and electronic, variable-temperature ESR and FT-IR spectra of the complexes are discussed in terms of the nature of bonding and known structures.

The case of symmetry-dependent ground-state spin value in Ni(II) clusters of high-nuclearity. Crystal structure and magnetic properties of a pentanuclear and a nonanuclear Ni(II) clusters

Abstract The crystal structures and the magnetic properties of a pentanuclear (1) and a nonanuclear (2) Ni(II) clusters are described. In the former, crystallizing in the cubic I23 space group, the Ni(II) assembly is composed of a regular tetrahedral geometry of four metal ions centered on the fifth. The nonanuclear cluster crystallizes in the hexagonal crystallographic system -R3 space group - the Ni(II) assembly is composed of two regular tetrahedra, like that of the pentanuclear cluster, sharing a common apex. All metal ions in either cluster are six-coordinate. Variable-temperature magnetic susceptibility data show antiferromagnetic interactions for both clusters. Moreover, magnetization data are in line with uneven intermediate-spin ground states [S=1, S=2] and [S=2, S=3] for 1 and 2, respectively. A comparison of both the symmetry and the spin ground state of 1 to those of lower-symmetry pentanuclear Ni(II) clusters, reveals that the ground-state spin value increases with the cluster symmetry.

Preparation, structure and preliminary magnetic studies of an octanuclear alkoxo-bridged copper(II) cluster of the acetato-bridged dicubane type

A novel double-cubane copper complex [Cu8L8(O2CMe)4][ClO4]4 is prepared, and structurally and magnetically characterised (L = the monoanion of the hydrated, gem-diol form of di-2-pyridyl ketone).

Benzotriazolate-mediated assembly of the discrete asymmetric pentanuclear nickel complex [Ni5(OH)(bta)5(acac)4(H2O)4](Hbta = benzotriazole, Hacac = pentane-2,4-dione)

Reaction of [Ni(acac)2(H2O)2] with benzotriazole (Hbta) in acetone–n-hexane yields the pentanuclear nickel complex [Ni5(OH)(bta)5(acac)4(H2O)4]1; the novel structure of this compound is described, together with the results of magnetic susceptibility studies which indicate antiferromagnetic coupling between the nickel(II) ions within the complex.

Aromatic Chelator-Specific Lattice Architecture and Dimensionality in Binary and Ternary Cu(II)-Organophosphonate Materials

Synthetic efforts linked to the design of defined lattice dimensionality and architecture materials in the binary/ternary systems of Cu(II) with butylene diamine tetra(methylene phosphonic acid) (H8BDTMP) and heterocyclic organic chelators (pyridine and 1,10-phenanthroline) led to the isolation of new copper organophosphonate compounds, namely, Na6[Cu2(BDTMP)(H2O)4]·[Cu2(BDTMP)(H2O)4]0.5·26H2O (1), [Cu2(H4BDTMP)(py)4]·2H2O (2), and [Cu2(H4BDTMP)(phen)2]n·6.6nH2O·1.5nMeOH (3). 1-3 are the first compounds isolated from the Cu(II)-BDTMP family of species. They were characterized by elemental analysis, spectroscopic techniques (FT-IR, UV-vis), magnetic susceptibility, TGA-DTG, cyclic voltammetry, and X-ray crystallography. The lattice in 1 reveals the presence of discrete dinuclear Cu(II) units bound to BDTMP(8-) and water molecules in a square pyramidal geometry. The molecular lattice of 2 reveals the presence of ternary dinuclear assemblies of Cu(II) ions bound to H4BDTMP(4-) and pyridine in a square pyramidal environment. The molecular lattice of 3 reveals the presence of dinuclear assemblies of Cu(II) ions bound to H4BDTMP(4-) and 1,10-phenanthroline in a square pyramidal environment, with the organophosphonate ligand serving as the connecting link to abutting dinuclear Cu(II) assemblies in a ternary polymeric system. The magnetic susceptibility data on 1, 2, and 3 suggest that compounds 1 and 3 exhibit a stronger antiferromagnetic behavior than 2, which is also confirmed from magnetization measurements. The physicochemical profiles of 1-3 (a) earmark the influence of the versatile H8BDTMP ligand as a metal ion binder on the chemical reactivity in binary and ternary systems of Cu(II) in aqueous and nonaqueous media and (b) denote the correlation of ligand hydrophilicity, aromaticity, denticity, charge, and H-bonding interactions with emerging defined Cu(II)-H8BDTMP structures of distinct lattice identity and spectroscopic-magnetic properties. Collectively, such structural and chemical factors formulate the interplay and contribution of binary and ternary interactions to lattice architecture and specified properties of new Cu(II)-organophosphonate materials with defined 2D-3D dimensionality.

Heptanuclear antiferromagnetic Fe(III)-D-(-)-quinato assemblies with an S = 3/2 ground state-pH-specific synthetic chemistry, spectroscopic, structural, and magnetic susceptibility studies.

Iron is an essential metal ion with numerous roles in biological systems and advanced abiotic materials. D-(-)-quinic acid is a cellular metal ion chelator, capable of promoting reactions with metal M(II,III) ions under pH-specific conditions. In an effort to comprehend the chemical reactivity of well-defined forms of Fe(III)/Fe(II) toward α-hydroxycarboxylic acids, pH-specific reactions of: (a) [Fe3O(CH3COO)6(H2O)3]·(NO3)·4H2O with D-(-)-quinic acid in a molar ratio 1:3 at pH 2.5 and (b) Mohrs salt with D-(-)-quinic acid in a molar ratio 1:3 at pH 7.5, respectively, led to the isolation of the first two heptanuclear Fe(III)-quinato complexes, [Fe7O3(OH)3(C7H10O6)6]·20.5H2O (1) and (NH4)[Fe7(OH)6(C7H10O6)6]·(SO4)2·18H2O (2). Compounds 1 and 2 were characterized by analytical, spectroscopic (UV-vis, FT-IR, EPR, and Mössbauer) techniques, CV, TGA-DTG, and magnetic susceptibility measurements. The X-ray structures of 1 and 2 reveal heptanuclear assemblies of six Fe(III) ions bound by six doubly deprotonated quinates and one Fe(III) ion bound by oxido- and hydroxido-bridges (1), and hydroxido-bridges (2), all in an octahedral fashion. Mössbauer spectroscopy on 1 and 2 suggests the presence of Fe(III) ions in an all-oxygen environment. EPR measurements indicate that 1 and 2 retain their structure in solution, while magnetic measurements reveal an overall antiferromagnetic behavior with a ground state S = 3/2. The collective physicochemical properties of 1 and 2 suggest that the (a) nature of the ligand, (b) precursor form of iron, (c) pH, and (d) molecular stoichiometry are key factors influencing the chemical reactivity of the binary Fe(II,III)-hydroxycarboxylato systems, their aqueous speciation, and ultimately through variably emerging hydrogen bonding interactions, the assembly of multinuclear Fe(III)-hydroxycarboxylato clusters with distinct lattice architectures of specific dimensionality (2D-3D) and magnetic signature.

Structurally diverse copper(II) herbicide complexes: mono- and bi-nuclear neutral or cationic complexes

Copper complexes with the commerical auxin herbicides 2,3-dichlorophenoxyacetic acid and 2-(2,4-dichlorophenoxy)propanoic acid and 2,2′-bipyridine(bipy) were prepared and characterized: [Cu2(Cl2C6H3OCH2CO2)4(MeOH)2]1, [Cu{Cl2C6H3OCH(Me)CO2}2(bipy)(H2O)]2 and [Cu{Cl2C6H3OCH(Me)CO2}(bipy)2]Cl 3. The available evidence supports a dimeric structure for complexes 1 while the presence of bipy leads to monomeric forms. In dimethylformamide solution the binuclear complex is converted into a monomeric complexe upon addition of a > 1:2 ratio of bipy. The ESR powder spectrum of compound 2 exhibits features characteristic of the presence of a S= 1 triplet state which may be assigned to a hydrogen-bond network. The crystal structures of the three complexes have been determined.