OOC CH Research Articles

Two new hexanuclear titanium oxo cluster types and their structural connection to known clusters

Ti6O6(OiPr)2(OOCR′)10 (R′ = C4H7, Et) and Ti6O3(OiPr)14(OOC–CHCH–COO)2 represent new structure types of carboxylate-substituted clusters with a Ti6Ox core (x = 3–6).

Structural variability in M2+ 2-hydroxyphosphonoacetate moderate proton conductors

Abstract The structural variability of two series of Mg2+- and Zn2+- 2-hydroxyphosphonoacetates have been studied in the range of 25–80°C and 95% relative humidity in order to correlate the structure with the proton conductivity properties. In addition to selected previously reported 1D, 2D and 3D materials, a new compound, KZn6(OOCCH(OH)PO3)4(OH)·5H2O (KZn6-HPAA-3D), has been prepared and thoroughly characterized. The crystal structure of this solid, solved ab initio from synchrotron X-ray powder diffraction data, consists of a negatively charged 3D framework with K+ ions, as compensating counterions. It also contains water molecules filling the cavities in contrast to the potassium-free 3D anhydrous NH4Zn(OOCCH(OH)PO3) (NH4Zn-HPAA-3D). In the range of temperature studied, the 1D materials exhibit a 1D→2D solid-state transition. At 80°C and 95% RH, the 2D solids show moderate proton conductivities, between 2.1×10−5 S·cm−1 and 6.7×10−5 S·cm−1. The proton conductivity is slightly increased by ammonia adsorption up to 2.6×10−4 S·cm−1, although no ammonia intercalation was observed. As synthesized KZn6-HPAA-3D exhibits a low proton conductivity, 1.6×10−6 S·cm−1, attributed to the basic character of the framework and a low mobility of water molecules. However, this solid transforms to the 2D phase, Zn(OOCCH(OH)PO3H)·2H2O, upon exposure to dry HCl(g), which enhances the proton conductivity with respect to the as-synthesized 2D material (4.5×10−4 S·cm−1). On the other hand, NH4Zn-HPAA-3D exhibited a higher proton conductivity, 1.4×10−4 S·cm−1, than the K+ analog.

Tuning Proton Conductivity in Alkali Metal Phosphonocarboxylates by Cation Size-Induced and Water-Facilitated Proton Transfer Pathways

The structural and functional chemistry of a family of alkali-metal ions with racemic R,S-hydroxyphosphonoacetate (M-HPAA; M = Li, Na, K, Cs) are reported. Crystal structures were determined by X-ray data (Li+, powder diffraction following an ab initio methodology; Na+, K+, Cs+, single crystal). A gradual increase in dimensionality directly proportional to the alkali ionic radius was observed. [Li3(OOCCH(OH)PO3)(H2O)4]·H2O (Li-HPAA) shows a 1D framework built up by Li-ligand “slabs” with Li+ in three different coordination environments (4-, 5-, and 6-coordinated). Na-HPAA, Na2(OOCCH(OH)PO3H)(H2O)4, exhibits a pillared layered “house of cards” structure, while K-HPAA, K2(OOCCH(OH)PO3H)(H2O)2, and Cs-HPAA, Cs(HOOCCH(OH)PO3H), typically present intricate 3D frameworks. Strong hydrogen-bonded networks are created even if no water is present, as is the case in Cs-HPAA. As a result, all compounds show proton conductivity in the range 3.5 × 10–5 S cm–1 (Cs-HPAA) to 5.6 × 10–3 S cm–1 (Na-HPAA) at 98% RH and T = 2...

Homochiral three-dimensional coordination polymer consisting of one-dimensional copper chain: Synthesis, structure and magnetic property

Abstract Novel chiral coordination polymers, l-1 and d-1, with the formula [Cu4(OOCCH(OH)CH2COO)2] were synthesized through a reaction of copper acetate with l-malic acid and d-malic acid, respectively, in the presence of base under solvothermal condition. The X-ray crystallography for l-1 revealed that the copper centers of the complex were alternatively linked by a bis(oxygen) bridge and mixed bridge composing of oxygen and 1,3-carboxylate to construct a one-dimensional (1D) chain structure. These 1D chains interdigitated with each other to give a 3D polymer structure as a result of the coordination interaction linking the neighboring 1-D chain. The magnetic property was studied to show strong antiferromagnetic coupling (J/k = − 596 K) within the chain and negligible one between the one-dimensional chain.

Syntheses, structures, and magnetic properties of one-dimensional coordination polymers based on N-succinopyridine ligand

A series of one-dimensional (1-D) N-succinopyridine-based complexes: [Cu(L−)(H2O)2]Cl·2H2O (1), [Pr(L−)(H2O)4]Cl2 (2), [Ln(L−)(H2O)5]Cl2·3H2O (Ln = Eu (3), Gd (4)), and [Er(L−)(H2O)4]Cl2·H2O (5) (HL = N-succinopyridine (−OOC–CH(N+C5H5)–CH2–COOH)) have been prepared and characterized by single-crystal X-ray diffraction. The frameworks of complexes 1, 2 and 5 constructed from dinuclear metal building blocks exhibit 1-D double-strand loop-like chains; these chains are further connected to each other by hydrogen bonds forming a 3-D supramolecular architecture. Whereas complexes 3 and 4 feature hydrogen bonding 2-D supramolecular networks assembled from 1-D chains that are constructed from mononuclear metal building blocks. The effects of different metal ions, steric hindrance and coordination diversities of HL on the polymeric architectures have been discussed. In addition, thermogravimetric and magnetic properties of these complexes were also investigated in this paper.

Modulated synthesis of Zr-fumarate MOF

We present the synthesis and characterization of a novel Zr-based metal–organic framework (MOF) which contains fumarate ( fum) dianions as linkers: −OOC–CH CH–COO −. The synthesis of this MOF is possible only via modulation, i.e. by the addition of a monocarboxylic acid to the synthesis mixture. We have used formic acid as a modulator and have investigated its influence on the synthesis of the Zr-fumarate MOF in detail. The modulator improves the crystallinity of the material; varying its amounts, the crystal size and the degree of aggregation can be influenced. The novel MOF probably has a topology which is similar to that of UiO-66, but has a primitive cubic lattice instead of a face-centered one. A structural model in line with the experimental data is proposed. The Zr- fum MOF is further characterized by thermogravimetric analysis (TGA) and Ar sorption, showing that it can be activated and exhibits microporosity. The linker fumarate as well as the modulator formic acid used in the synthesis of Zr- fum MOF are both naturally occurring molecules; possible applications of the MOF may thus lie in the field of biomaterials. Therefore, the stability of Zr- fum MOF was tested in water-based salt solutions commonly used in biomedical research.

PH-Specific synthetic chemistry, and spectroscopic, structural, electrochemical and magnetic susceptibility studies in binary Ni(II)-(carboxy)phosphonate systems

Nickel can play numerous roles in biological systems and in advanced abiotic materials. Supporting the diverse roles of Ni(II) in biological media are, among others, metal ion binding amino acids, their variably phosphorylated forms and/or exogenously administered organophosphonate drug substrates. In an effort to comprehend the aqueous chemistry of interactions between Ni(II) and organophosphonate substrates, research efforts were launched involving the ligands imino bis(methylenephosphonic acid) (H 4IDA2P), H 2O 3P–CH 2– NH 2 + –CH 2–PO 3H −, and N-(phosphonomethyl)glycine (glyphosate–H 3IDAP), HOOC–CH 2– NH 2 + –CH 2–PO 3H −. pH-Specific reactions of Ni(II) with H 4IDA2P and H 3IDAP led to the isolation of [Ni(C 2H 8O 6NP 2) 2(H 2O) 2] ( 1) and [Ni(OOC–CH 2–NH–CH 2–PO 3H) 2]·[Ni(H 2O) 6]·3.3H 2O ( 2), respectively. Compound 1 was characterized by analytical, spectroscopic techniques (UV–Vis, FT-IR), cyclic voltammetry, magnetic susceptibility measurements and X-ray crystallography. Compound 2 was characterized by elemental analysis, FT-IR spectroscopy, and X-ray crystallography. The structures of 1 and 2 reveal mononuclear octahedral Ni(II) assemblies bound by H 3IDA2P − and water ( 1), and glyphosate (HIDAP 2−) and water molecules ( 2), respectively. Magnetic susceptibility studies on 1 support the presence of high-spin octahedral Ni(II) in an oxygen environment, consistent with X-ray crystallography. The collective physicochemical features of the discrete Ni(II) assemblies in both species (a) shed light on aqueous binary Ni(II)–phosphoderivative interactions potentially influencing cellular physiology or toxicity, and (b) define the fundamental properties essential for the employment of such species in advanced materials synthesis and applications.

Copper(II) chlorofumarate trihydrate

Blue crystals of the title compound, poly[[[diaquacopper(II)]-μ3-chlorofumarato] monohydrate], {[Cu(OOC–CH=CCl–COO)(H2O)2]·H2O} n , crystallized unexpectedly from an aqueous solution containing acetylenedicarboxylic acid and CuCl2. Each copper cation is coordinated by five O atoms – three from three fumarate anions and two from two water molecules – in the form of a distorted square pyramid. All atoms of the asymmetric unit, except a carboxylate oxygen and the coordinated water molecule, lie on a mirror plane. These units are connected by the bifunctional anions to form ribbons along [001]. These ribbons are held together by hydrogen bonds, which also involve the third water molecule.

Effect of the pH, the concentration and the nature of the buffer on the adsorption mechanism of an ionic compound in reversed-phase liquid chromatography: II. Analytical and overloaded band profiles on Symmetry-C 18 and Xterra-C 18

In a previous report, the influence of the pH, the concentration, and the nature of the buffer on the retention and overloading behavior of propranolol (p K a = 9.45) was studied on Kromasil-C 18 at 2.75 < pH < 6.75, using four buffers (phosphate, acetate, phthalate, and succinate), at three concentrations, 6, 20, and 60 mM. The results showed that the propranolol cation was eluted as an ion-pair with the buffer counter-anion. A similar study was carried out with Symmetry-C 18 and Xterra-C 18. Two additional buffers, formate and citrate, were also used. Propranolol elution band profiles were recorded for a small (less than 1 μg) and a large (375 μg) sample size. The results are similar to those obtained with Kromasil and confirm earlier conclusions. The buffer concentration, not its pH, controls the retention time of propranolol, in agreement with the chaotropic model. The retention factor depends also on the nature of the buffer, particularly on its valence, and on the hydrophobicity of the basic anion. With the monovalent anions HCOO − (pH 3.75), H 2PO 4 − (pH 2.75), HOOC–Ph–COO − (pH 2.75), HOOC–CH 2–CH 2–COO − (pH 4.16), CH 3COO − (pH 4.75) and HOOC–CHCOOH–COO − (pH 3.14), at moderate loadings, and for the two larger buffer concentrations, the band profiles are well accounted for by a simple bi-Langmuir isotherm model (no adsorbate–adsorbate interactions). By contrast, these profiles are accounted for by a bi-Moreau isotherm model (i.e., with significant adsorbate–adsorbate interactions) with the bivalent anions −OOC–Ph–COO − (pH 4.75), −OOC–CH 2–CH 2–COO − (pH 5.61), HPO 4 2− (pH 6.75), and HOOC–CHCOO −–COO − (pH 4.77) and with the trivalent anion −OOC–CHCOO −–COO − (pH 6.39). The best values of the isotherm parameters were determined using the inverse method. The saturation capacity and the equilibrium constant on the low-energy sites increase with increasing buffer concentration, a result consistent with the formation in the mobile phase of a hydrophobic complex between the propranolol cation and the buffer anion. With bivalent and trivalent anions, adsorbate–adsorbate interactions are strong on the low-energy sites but they remain negligible on the high-energy sites. The density of the high energy sites is lower and the equilibrium constant on the low-energy sites are both higher with the bivalent and the trivalent buffer anions than with the univalent buffer anions. These results are consistent with the formation of a 2:1 and a 3:1 propranolol–buffer complex with the bivalent and the trivalent anions, respectively.

Role of the buffer in retention and adsorption mechanism of ionic species in reversed-phase liquid chromatography: I. Analytical and overloaded band profiles on Kromasil-C 18

The influence of the pH, the concentration, and the nature of the buffer on the retention and overloading behavior of propranolol (p K a=9.25) on Kromasil-C 18 was studied at 2.75<pH<6.75, using four buffers (phosphate, acetate, phthalate, and succinate), at three concentrations, 6, 20, and 60 mM. The propranolol band profiles were recorded for three sample sizes, less than 1 μg and 375 μg (sample less concentrated than the buffer), and 7500 μg (band more concentrated than the buffer). Results showed that the buffer concentration, not its pH, controls the retention time of propranolol, in agreement with the chaotropic model. The retention factor depends also on the nature of the buffer, particularly the valence of the basic anion. At moderate loading, the band profiles are well accounted for by a simple bilangmuir model (no adsorbate–adsorbate interactions) with the monovalent anions H 2PO 4 − (pH 2.75), HOOCPhCOO − (pH 2.75), HOOCCH 2CH 2COO − (pH 4.16) and CH 3COO − (pH 4.75), and by a bimoreau model (significant adsorbate–adsorbate interactions) with the bivalent anions − OOCPhCOO − (pH 4.75), − OOCCH 2CH 2COO − (pH 5.61) and HPO 4 2− (pH 6.75). The isotherm were determined using the inverse method. The results show that both the saturation capacity and the equilibrium constant on the low-energy sites increase with increasing buffer concentration, a result similar to that observed with neutral salts. For bivalent anions, the adsorbate–adsorbate interactions are much stronger on the low than on the high energy sites. The density of high energy sites is lower and the equilibrium constant on the low energy sites are higher with bivalent than with univalent anions. These results are consistent with the formation of a propranolol–buffer (2:1) complex with bivalent anions.

Complexes of heteroscorpionate trispyrazolylborate ligands. Part VI. Carboxylate induced conversion of mono-ligand Tp′M(L) into bis-ligand Tp′ 2M complexes (M=Co(II) and Cu(II))

A series of homoleptic complexes of hexacoordinate cobalt(II) and copper(II) complexes with 3,5-disubstituted homo- and heteroscorpionate tris(pyrazolyl)borate anionic ligands (Tp′) were synthesized, i.e. bis[hydrotris(3-phenyl,5-methylpyrazol-1-yl)borato]cobalt(II), bis[hydrobis(3-phenyl,5-methylpyrazol-1-yl)(3-methyl,5-phenylpyrazol-1-yl)borato]cobalt(II) and bis[hydrobis(3-phenyl,5-methylpyrazol-1-yl)(3-methyl,5-phenylpyrazol-1-yl)borato]copper(II) and their structures were elucidated crystallographically. The complexes were also formed spontaneously during attempted metathesis of the corresponding Tp′M(NCS) complexes into Tp′M(OOCCH(OH)CH 3) complexes. In the case of the analogous conversion applied for the thiocyanato [hydrobis(3-phenyl,5-methylpyrazol-1-yl)(3,5-dimethylpyrazol-1-yl)boratocobalt(II) complex with sodium carboxylates (lactate, pyruvate and 2-hydroxybutyrate), the cross-transfer of pyrazolyl residues between starting anionic ligands was observed resulting in formation of bis-ligand homo- and heteroleptic Tp′CoTp″ complexes, where Tp′, Tp″ were tris(pyrazolyl)borates composed of n 3(5)-phenyl,5(3)-methylpyrazolyl and (3− n) 3,5-dimethylpyrazolyl residues (n=0–3) identified by mass spectrometry. Metathesis of thiocyanate in thiocyanato hydrotris(3-phenyl,5-methylpyrazol-1-yl)boratocobalt(II) into pyruvate led to the isolation of stable the pyruvato hydrotris(3-phenyl,5-methylpyrazol-1-yl)boratocobalt(II) complex, the structure of which was determined crystallographically. The Tp′ ligands are η 3 coordinated to metal ions in every case, whereas the pyruvate anion is coordinated through carboxylate and carbonyl oxygen atoms to the cobalt center. Two rotational isomers distinguishable by 1H NMR spectroscopy for the hexacoordinate bis[hydrobis(3-phenyl,5-methylpyrazol-1-yl)(3-methyl,5-phenylpyrazol-1-yl)borato]cobalt(II) complex were detected in solution.

N,O-Chelate complexes of Ru(II), Ir(III), Pd(II), Pt(II) and Cu(II) with tetrahydroisoquinolinic acid. Molecular structures of [(Et 3P)(Cl)M(OOCCHCH 2C 6H 4CH 2NH)], M=Pd, Pt

From (S)-tetrahydroisoquinolinic acid and the chloro-bridged complexes [( p-cymene)RuCl 2] 2, [Cp*IrCl 2] 2, [(R 3P)MCl 2] 2 (M=Pd: R=Et, Ph; M=Pt: R=Et) the corresponding N,O-chelate complexes [LM(OOCCHCH 2C 6H 4CH 2NH)(Cl)] 2– 5 were obtained in the presence of NaOMe. Bis-chelate complexes M(OOCCHCH 2C 6H 4CH 2NH) 2 (M=Cu: 6, Pd: 7) were prepared from the acid and the metal(II) acetates. Crystal structure determinations of the PEt 3 complexes of Pd and Pt showed both complexes to be isostructural, with the S CS N configuration at the junction of the chelate ring and the piperidine ring.

Iron(III)–phosphonate complexes

The Fe(III) complexes of methylphosphonic acid (MPA), Fe 2(CH 3PO 3) 3·3H 2O, and aminomethylphosphonic acid (AMPA), FeOH(NH 3CH 2PO 3) 2·H 2O, were prepared in solid state and obtained as fine powders. In aqueous solution, both ligands form a complex with a 1:1 Fe(III) to ligand ratio and the proposed structures for these complexes are the monodentate protonated [FeO–PO(OH)CH 3] 2+ and the deprotonated chelate [FeO 2–POCH 2NH 3] 2+, respectively. These results permit the evaluation of the chemical bonds involved in the complex of Fe(III) and glyphosate, ( N-phosphonomethylglycine, PMG) in solid state and the formula FeOH( −OOC–CH 2–NH 2 + –CH 2–PO 3 2− )·2.25H 2O is proposed. While the phosphonate moiety of these ligands always bonds to the metal ion, the amino group remains protonated and not coordinated. The carboxylic acid of PMG only coordinates the Fe(III) in solid state, not in aqueous solution. Infrared spectra of the PMG complexes of Al(III) and Co(III) in the solid state are also presented and compared with the Fe(III) complex. Elemental microanalysis, UV–Vis, atenuated total reflection–Fourier transformed infrared (ATR–FTIR) spectroscopy, inductively coupled plasma (ICP) emission spectrometry, AAS and X-ray powder diffraction were used for the characterization of the complexes.

Complexes of heteroscorpionate trispyrazolylborate anionic ligands: Part II. The X-ray crystallographic and 1H NMR studies on thiocyanato[hydrobis(3-phenylpyrazolyl)(3,5-di- tert-butylpyrazolyl)borato]cobalt(II) and thiocyanato[hydrobis(3-phenyl,5-methylpyrazolyl)(3-methyl,5-phenylylpyrazolyl)borato]cobalt(II) complexes

Synthesis of two heteroscorpionate tris(pyrazolyl)borate anionic ligands (Tp′) was described; the sterically demanding [hydrobis(3-phenylpyrazolyl)(3,5-di- tert-butylpyrazolyl)borate] − obtained by condensation of KBH 4 with 3-phenylpyrazole and 3,5-di- tert-butylpyrazole and [hydrobis(3-phenyl,5-methylpyrazolyl)(3-methyl, 5-phenylylpyrazolyl)borate] − formed in similar reaction between NaBH 4 and 3(5)-methyl,5(3)-phenylpyrazole. The ligands were converted into tetracoordinate [HB(3,5-di- tBupz)(3-Phpz) 2]Co(NCS) and pentacoordinate [HB(3-Me,5-Phpz)(3-Ph,5-Mepz) 2]Co(NCS)(THF)·THF complexes, which molecular structures were determined by X-ray crystallographic method. The reactivity of high-spin cobalt(II) complexes was studied by the 1H NMR spectroscopy in solution. The reactive [HB(3-Me,5-Phpz)(3-Ph,5-Mepz) 2]Co(NCS) complex readily underwent conversions into pentacoordinate [HB(3-Me,5-Phpz)(3-Ph,5-Mepz) 2]Co(OOCCH(OH)CH 3) and hexacoordinate [HB(3-Me,5-Phpz)(3-Ph,5-Mepz) 2]Co[HB(pz) 3] complexes.

Interaction of [Rh2(O2CCH3)4(H2O)2] and [Rh2(O2CCH(OH)Ph)2(phen)2(H2O)2](O2C‐CH(OH)Ph)2 With Sulfhydryl Compounds and Ceruloplasmin

The interaction of binuclear rhodium(II) complexes [Rh2(OOCCH3)4(H2O)2], [Rh2{OOCCH(OH)Ph}2(phen)2(H2O)2] {OOCCH(OH)Ph}2, [Rh2(OOCCH3)2(bpy)2(H2O)2](OOCCH3)2 and [Rh2Cl2(OOCMe)2(bpy)2](3H2O) with ceruloplasmin, cysteine, glutathione and coenzyme A have been investigated using. UV-Vis and CD spectroscopies. The complexes containing phen or bpy at pH = 7.4 and 4.0 are readily reduced with sulfhydryl compounds, while rhodium(II) acetate is relatively stable in these conditions. Complex [Rh2{OOCCH(OH)Ph}2(phen)2(H2O)2] strongly changes structure of ceruloplasmin leading to the decrease of of α-helix content and loss of oxidase activity.

Structure and dynamics of the symmetric hydrogen bond in potassium hydrogen maleate: a neutron scattering study

The crystal structure of potassium hydrogen maleate KH(OOC–CHCH–COO) has been studied at 300, 14 and 5 K using three-dimensional single-crystal neutron diffraction data. There is no evidence for any phase transition. The crystal structure is orthorhombic, P bcm (D 2h ll), with four entities in the unit cell ( Z=4), in accord with previous X-ray diffraction work. The ion is nearly planar and deviation from C 2v symmetry is negligible. The short internal hydrogen bond parallel to the c axis, R O⋯O=2.427(1) Å at 5 K, is symmetrical with the proton located at the center. Inelastic neutron scattering (INS) spectra, from 16 to 4000 cm −1, of the fully hydrogenated sample and partially deuterated analogues, KH(OOC–CDCD–COO) and KD(OOC–CHCH–COO), have been recorded for powdered samples and aligned single crystals at 20 K. Complex spectral profiles are observed for the stretching mode of the hydrogen bond, ν a OHO, and for the totally symmetric out-of-plane deformation of the maleate ion. An isotopic mixture of KH(OOC–CDCD–COO), 20%, and KD(OOC–CDCD–COO), 80%, reveals that intermolecular coupling is negligible. Frequencies and intensities are amenable to symmetrical potential functions with a central minimum between secondary minima at higher energy. The INS and infrared band profiles suggest that the planar conformation with C 2v symmetry of the maleate ring is unstable in excited vibrational states. The quantum nature of the hydrogen bond is emphasised with the concept of `hydrogen bonding/anti-bonding' states.

Synthesis through an in situ esterification process and characterization of oxo isopropoxo titanium clusters

Three titanium oxo-isopropoxo clusters Ti 6O 4(OOCCH 3) 4(OPr 1) 12 ( 1), Ti 12O 16(OPr 1) 16 ( 2) and Ti 12O 16(OPr 1) 16·1.4CH 2Cl 2 ( 3) are obtained by refluxing Ti(OPr 1) 4 with 1.2 equivalents of carboxylic acids over two days. The molecular structures of Ti 6O 4(OOCCH 3) 4(OPr 1) 12 ( 1) and Ti 12O 16(OPr 1) 16· 1.4CH 2Cl 2 ( 3) have been resolved by single crystal X-ray diffraction. The titanium oxo organo cores of these clusters are also characterized in solution by 17O NMR spectroscopy and in solid-state by 13C CP MAS NMR spectroscopy.

Hush theory in a copper mixed valence bioinorganic model generated photochemically

In the present study a copper mixed valence (MV) compound has been generated photochemically from the (CH 3COO) 2Cu(II)Cu(II)(OOCCH 3) 2 dimeric species in 95/5% (vol./vol.) methanol/acetic acid mixture as solvent. The MV species shows two intervalence (IT) bands at 19.6 and 10.4 kK and seven complex lines in the EPR spectra at room temperature. Although the two bands are IT bands in character, only the second (960 nm) could be related through the Hush and Hopfield theories to a thermal electron transfer process between the copper centers with kinetic parameters Δ G #=21.6 kJ mol −1 and k th=1.2×10 9 s −1 (Hush) or 4.0×10 11 s −1 (Hopfield) at 298 K and related to the change from (d x 2− y 2 ) 2Cu(I)(d x 2− y 2 )Cu(II) to (d x 2− y 2 ) 1Cu(II)(d x 2− y 2 ) 2Cu(I) electronic configuration ( D 4 h symmetry for each copper center). The electronic assignation of the more energetic band is also discussed. The value obtained for k th is in the range measured by EPR spectroscopy for other Cu(II)Cu(I) dimeric systems and provides evidence for the validity of the essence of the theoretical approach in copper binuclear systems although the value for the electronic coupling parameter is relatively high. The complex studied in this work has some characteristics in common with those of the type III copper observed in copper oxidases in its MV state such as: dimeric structure with tetragonal environment for the coppers, with oxygen perhaps as bridging ligand, EPR signal related to one unpaired electron interacting with both coppers and with k th values which compare well with some biological systems; so we believe it is a good bioinorganic model for type III copper in multicopper oxidases.

Dimeric structure of the complex anion [(SnCitr) 4Pt(μ-SnCitr) 2Pt(SnCitr) 4] 6− (Citr 3− = −OOCCH 2C(OH)(COO) −CH 2COO −) with two bridging tin atoms obtained by the method of radial distribution functions of atoms in powder samples and in solution

Using the method of Radial Distribution Functions (RDF) of atoms it has been shown directly that a platinum-tin complex with tin coordinated by citrate ligands is the binuclear platinum anion [(SnCitr) 4Pt(μ-SnCitr) 2Pt(SnCitr) 4] 6−. The core of the complex is a platinum cluster wherein each platinum atom is bonded via metal-metal bonds (2.58 Å) with six tin atoms situated at the vertices of a slightly distorted octahedron. Two such quasi-octahedrons have a common edge (two of 10 tin atoms are bridges between two platinum atoms) so forming a dimer. The Pt···Pt separation is 3.92 Å, i.e. a direct PtPt bond is absent. A model simulation of RDF has allowed us to find the main geometric parameters of the platinum-tin cluster. Citrate ligands coordinate tin atoms in the periphery of the cluster. The structure of the complex anion is the same whether it appears in a potassium salt or in an acid. Solvation in water does not change the diplatinum anion structure.

Synthesis and X-ray, magnetic and spectroscopic investigations of tetrakis [μ-(β-alanine )- O, O′]bis(diphen ylphosphato)dicopper(II) di(diphenylphosphate) dihydrate

The crystal structure of the tetrakis [μ-(β-alanine)- O, O′]bis(diphenylphosphato)dicopper(II) di(di- phenylphosphate) dihydrate, [Cu 2(β-ala) 4(DPhP) 2]· 2DPhP·2H 2O (where β-ala= −OOCCH 2CH 2NH 3 + and DPhP = (C 6H 5O) 2PO 2 −, diphenylphosphate monoanion) was determined by single-crystal X-ray diffraction method. The compound crystallizes in the triclinic space group P 1 with orte formula weight in a unit cell of dimensions: a = 9.781(3), b = 14.247- (4), c = 13.809(4) Å, α = 94.59(5), β = 94.73(5) and γ = 114.67(5)°. The structure was solved by the heavy-atom technique and refined by full-matrix least-squares methods to a final R value of 0.050 based on 3540 non-zero, independent data with I > 3.8 σ( I). The crystal structure consists of centrosymmetric carboxylatobridged dimeric units, uncoordinated diphenylphosphate monoanions and water molecules of crystallization. The coordination geometry about each copper(II) center is squarepyramidal, with four oxygen atoms from zwitterionic β-alanine molecules in the basal plane and the oxygen diphenylphosphate atom at the apical position. The magnetic susceptibilitiy and ESR results are compared with those found in the copper(II) glycine polymeric complex.