Metal Coordination Polyhedron Research Articles

Synthesis and crystal structure of diisothiocyanatotetrakis(4-methylpyridine N-oxide)cobalt(II) and diisothiocyanatotris(4-methylpyridine N-oxide)cobalt(II) showing two different metal coordination polyhedra

The reaction of Co(NCS)2 with 4-methylpyridine N-oxide (C6H7NO) leads to the formation of two compounds, namely, tetrakis(4-methylpyridine N-oxide-κO)bis(thiocyanato-κN)cobalt(II), [Co(NCS)2(C6H7NO)4] (1), and tris(4-methylpyridine N-oxide-κO)bis(thiocyanato-κN)cobalt(II), [Co(NCS)2(C6H7NO)3] (2). The asymmetric unit of 1 consists of one CoII cation located on a centre of inversion, as well as one thiocyanate anion and two 4-methylpyridine N-oxide coligands in general positions. The CoII cations are octahedrally coordinated by two terminal N-bonding thiocyanate anions in trans positions and four 4-methylpyridine N-oxide ligands. In the extended structure, these complexes are linked by C—H...O and C—H...S interactions. In compound 2, two crystallographically independent complexes are present, which occupy general positions. In each of these complexes, the CoII cations are coordinated in a trigonal–bipyramidal manner by two terminal N-bonding thiocyanate anions in axial positions and by three 4-methylpyridine N-oxide ligands in equatorial positions. In the crystal, these complex molecules are linked by C—H...S interactions. For compound 2, a nonmerohedral twin refinement was performed. Powder X-ray diffraction (PXRD) reveals that 2 was nearly obtained as a pure phase, which is not possible for compound 1. Differential thermoanalysis and thermogravimetry data (DTA–TG) show that compound 2 start to decompose at about 518 K.

Binding of N8-Acetylspermidine Analogues to Histone Deacetylase 10 Reveals Molecular Strategies for Blocking Polyamine Deacetylation.

Eukaryotic histone deacetylase 10 (HDAC10) is a Zn2+-dependent hydrolase that exhibits catalytic specificity for the hydrolysis of the polyamine N8-acetylspermidine. The recently determined crystal structure of HDAC10 from Danio rerio (zebrafish) reveals a narrow active site cleft and a negatively charged "gatekeeper" (E274) that favors the binding of the slender cationic substrate. Because HDAC10 expression is upregulated in advanced-stage neuroblastoma and induces autophagy, the selective inhibition of HDAC10 suppresses the autophagic response and renders cancer cells more susceptible to cytotoxic chemotherapeutic drugs. Here, we describe X-ray crystal structures of zebrafish HDAC10 complexed with eight different analogues of N8-acetylspermidine. These analogues contain different Zn2+-binding groups, such as hydroxamate, thiolate, and the tetrahedral gem-diolate resulting from the addition of a Zn2+-bound water molecule to a ketone carbonyl group. Notably, the chemistry that accompanies the binding of ketonic substrate analogues is identical to the chemistry involved in the first step of catalysis, i.e., nucleophilic attack of a Zn2+-bound water molecule at the scissile carbonyl group of N8-acetylspermidine. The most potent inhibitor studied contains a thiolate Zn2+-binding group. These structures reveal interesting geometric changes in the metal coordination polyhedron that accommodate inhibitor binding. Additional interactions in the active site highlight features contributing to substrate specificity. These interactions are likely to contribute to inhibitor binding selectivity and will inform the future design of compounds selective for HDAC10 inhibition.

Synthesis and crystal structure of mixed halide Cu(I) complexes with 1,3-benzimdazolone

By a direct reaction of 1,3-allylbenzimidazolone in ethanol medium with copper(II) halogenides under alternate current technique conditions with copper wire electrodes were obtained and X-ray single crystal method structurally characterized ( Agilent Gemini A diffractometer) three new isostructural pi-complexes of [C 7 H 4 N 2 O(C 3 H 5 ) 2 Cu 2 X 2 ] composition: space group , Z = 2, X= 0,77Cl/0,33Br ( I ) – a = 8.358(3), b = 9.683(3), c = 9.749(3) A, α = 85.04(3), β = 75.96(3), γ = 70.39(3)°, V = 721.1(4) A 3 , r calc. = 1.99 g/cm 3 , m( MoK a ) = 4.48 mm −1 , q max. = 36.8°, 9089 measured, 4927 used reflections, R ( F 2 ) = 0.057, S = 1.12; X= 0.25Cl/0,75Br ( II ) – a = 8.3294(8), b = 9.8050(11), c = 9.8368(5) A, α = 85.572(6), β = 76.528(6), γ = 70.931(9)°, V = 738.39(12) A 3 , r calc. = 2.16 g/cm 3 , m( CuK a ) = 9.10 mm −1 , q max. = 73.4°, 10408 measured, 2879 used reflections, R ( F 2 ) = 0.040, S = 1.03; X= Br ( III ) – a = 8.3086(3), b = 9.8417(3), c = 9.8642(4) A, α = 85.739(3), β = 76.780(3), γ = 71.049(3)°, V = 742.66(5) A 3 , r calc. = 2.24 g/cm 3 , m( MoK a ) = 8,24 mm −1 , q max. = 29.9°, 11904 measured, 3692 used reflections, R(F 2 ) = 0.020, S = 1.06. Structures were solved by direct methods and refined by full matrix least-squares method on F 2 by SHELXT and SHELXL-2014 with following graphical user interfaces of OLEX 2 . In a crystal structure of the compounds I–III two structurally independent copper atoms possesses trigonal-pyramidal coordination environment consisted of C=C bonds of both allylic groups of organic ligands and halide or oxygen atoms. Due to bridging function of halogenides anions metal coordination polyhedra connected into tetrameric topological units. Last due to coordination of allylic groups of 1,3-dyallylbenzimidazolone with crystallographically non equivalent copper(I) center metal coordination polyhedron linked to infinite chains {L 2 Cu 4 Х 4 } connected by very week C–H…Hal(O) bonds. Keywords : benzimidazolon, copper(І), pi-complexes, crystal structure.

Iron(II) Bis-α-Benzyldioximate Complexes with 3- and 4-Pyridine Hemiacetals as Axial Ligands: Synthesis, Structure, and Physicochemical Properties

The coordination compounds [Fe(DfgH)2(HL1)2] and [Fe(DfgH)2(HL2)2], where DfgH = is the α-benzyldioxime monoanion, HL1 = 3-pyridine hemiacetals: methoxy(pyridin-3-yl)methanol (I), ethoxy(pyridin-3-yl)methanol (II); HL2 = 4-pyridine hemiacetal: methoxy(pyridin-4-yl)methanol (III), ethoxy(pyridin-4-yl)methanol (IV), and propoxy(pyridin-4-yl)methanol (V), were synthesized and studied by X-ray diffraction and IR and Mossbayer spectrosopy. According to X-ray diffration data (CIF files CCDC 1578217–1578221 for I–V, respectively), all of these Fe(II) complexes are molecular. The metal coordination polyhedron is an octahedron formed by four equatorial nitrogen atoms of two monodeprotonated α-benzyldioxime residues coordinated in the bidentate chelating fashion and by two axial nitrogen atoms of two neutral 3- or 4-pyridine hemiacetal molecules coordinated in the monodentate fashion. The DfgH– ligands in complexes I–V are joined by intramolecular O–H···O hydrogen bonds to form a pseudomacrocyclic system. The ligands HL1 and HL2 are generated in the reaction of the corresponding alcohols with 3- or 4-pyridinecarboxaldehyde. The IR and Mossbauer spectra of the products were studied. The Mossbauer spectral parameters of compounds I–V correspond to low-spin iron(II) ions.

Synthesis and crystal structure of copper (I) sulfamate π-complex with 5-methyl-N-(Allyl)-1,3,4-thiadiazol-2-amine of [Cu2(C6H10N3S2)2(NH2SO3)2] composition

[Cu 2 ( Mepeta ) 2 (NH 2 SO 3 ) 2 ] compound has been obtained by means of alternating current electrochemical technique starting from the mixture of propanolic solution of 5-methyl- N -(allyl)-1,3,4-thiadiazol-2-amine ( Mepeta ) and water solution of Cu(NH 2 SO 3 ) 2 ·xH 2 Oand later X-ray structurally characterized by single crystal method. High-quality crystals of the compound appeared in three days. The compound crystallizes in the triclinic system: Sp. gr. – P -1, a = 7.799(2), b = 8.054(3), c = 10.165(2) Å, α = 96.003(7), β = 109.17 (3), γ = 112.95(3)°, V = 535.2 (3) Å 3 ,Z = 1, D х = 1.954(3) g/sm 3 , R ( F ) = 0.056 for 2052 independent reflections with F ≥ 4 σ ( F ). In the structure 1 , organic molecule Mepeta acts as chelate-bridging tridentate ligand being connected to copper (I) by two N atoms of thiadiazo leringand (C=C)-bond fromallyl-group, resulting in a formation of stable cationic dimers [Cu 2 ( Mepeta ) 2 ] 2+ . In the structure 1 , N atom from sulfamate-anion occupies an apical position of the metal coordination polyhedron. The efficiency of Cu(I)-(C=C) interaction is confirmed by the fact that allylic C=C bond is slightly elongated to 1.355(7) Å. Selected bond length (in Å) and angle (in deg) values: Cu1–N3 2.092(3), Cu1–N4 i 1.998(4), Cu1–N1 2.267(4), Cu–m 1.965(4) (m –middle point of C7=C8 bond), C8–C9 1.355(7), N4 i –Cu1–N3 112.8(3), N4 i –Cu1–N1 95.5(4), N4 i –Cu1– m 130.5(2), N3–Cu1–N1 86.5(3), N3–Cu1– m 109.6(3). Despite the presence of sulfamate anion NH 2 SO 3 – N-atom, thiadiazole ligand participates in the formation of stable tectone [Cu 2 ( L ) 2 ] 2+ previously found in the structures of other Сu(I) π-complexes with allyl derivatives of 1,3,4-thiadiazole. Hydrogen bonds N-H···O play an additional stabilizing role in the formation of hydrogen-bonded chains. Keywords : copper (I), sulfamate anion, π-complex, 1,3,4-thiadiazole, crystal structure.

Two New Series of Coordination Polymers and Evaluation of Their Properties by Density Functional Theory

Five new coordination polymers (CPs), CPO-68-M (M = Zn, Mn, and Co) and CPO-69-M (M = Ca and Cd), were synthesized by solvothermal methods using 4,4′-dimethoxy-3,3′-biphenyldicarboxylic acid as the organic linker. The three-dimensional frameworks are formed by metal carboxylate chains that are separated by the linker. Structural analysis reveals dense networks with narrow rhombic channels and sra topologies for both CPO-68-M and CPO-69-M. The major structural difference between the two series of CPs is in the metal coordination polyhedra, which are four- and eight-coordinated in CPO-68-M and CPO-69-M, respectively. The CPs are highly crystalline, robust, and have good thermal stability (> 350 °C). On the basis of the topological similarities with MIL-53, we tested whether the CPs would exhibit a similar flexible structure response to gas stimulus. Density functional theory (DFT) modeling was used to evaluate the CPs’ potential as gas adsorption materials over a large range of pressures. The DFT analysis concluded that the CPs are ill-suited for gas adsorption due to their structural rigidity. However, electronic structure calculations reveal that CPO-68-M and CPO-69-M are indirect band gap semiconductors with an estimated band gap between 2.49 and 2.98 eV.

Crystal structure of bis(4-benzoyl-3-methyl-1-phenyl-4,5-dihydro-1H-pyrazol-5-onato)-(ethanol)-dioxourane(VI) ethanol solvate

The crystal structure of bis(4-benzoyl-3-methyl-1-phenyl-4,5-dihydro-1H-pyrazol-5-onato)-(ethanol)-dioxourane(VI) ethanol solvate [UO2L2(C2H5OH)]·C2H5OH (I), where HL is 4-benzoyl-3-methyl-1-phenyl-4,5-dihydro-1H-pyrazol-5-one, is determined. The asymmetric part on the unit cell of the crystal structure of I contains the complex of uranyl ion with two bidentately coordinated L− ions and coordinated molecule of ethanol. In the outer coordination sphere of the central atom, the solvated ethanol molecule is located. The coordination polyhedron of the uranium atom in complex I is a pentagonal bipyramid. Its equatorial plane is composed of oxygen atoms of HL and ethanol. In the axial positions of the metal coordination polyhedron the oxygen atoms are located. In the crystal, the complexes of the studied compound are linked together via hydrogen bonds of the outer-sphere ethanol molecule in chains along the [100] direction. Between the chains in the crystal, the van der Waals interaction occurs.

Synthesis and structure of new copper(II) coordination compounds with 8-quinoline aldehyde semicarbazones and thiosemicarbazones

Copper(II) salts were reacted with various quinoline aldehyde chalcogensemicarbazones to yield compounds formulated as Cu(HL)X2 · nH2O (I: HL = quinoline aldehyde thiosemicarbazone (HL1), X = ClO4, n = 2; II: HL = quinoline aldehyde 4-C2H5-thiosemicarbazone (HL1a), X = NO3, n = 0; III: HL = quinoline aldehyde semicarbazone (HL2), X = ClO4, n = 3 and IV: HL = quinoline aldehyde 4-Ph-semicarbazone (HL2a), X = NO3, n = 1). Regardless of the reagent ratio, the products were compounds having the metal: ligand ratio of 1: 1, where the organic ligand was coordinated tridentate in a molecular form. Single-crystal X-ray diffraction showed that, depending on the chalcogen atom in the organic ligand (S or O), the substituent in the 4th position (at the terminal nitrogen atom), and the specifics of the acido ligand, complexes I–IV had appreciably differing molecular structure organizations. The structures of I and III are formed by a 1D charged coordination polymer, ClO4− anions, and water molecules and may be described by the formula [Cu(HL)(H2O)(ClO4)]n(ClO4)n · nH2O. Copper(II) coordination polyhedra in I and II are (4 + 2) and (4 + 1 + 1) tetragonal bipyramids, respectively. In II and IV, the structures are monomeric and can be described as [Cu(HL1a)(NO3)2] with the metal coordination polyhedron shaped as a (4 + 1) tetragonal pyramid in II and as [Cu(HL2a)(H2O)(NO3)](NO3) with the metal coordination polyhedron shaped as a (3 + 2) trigonal bipyramid in IV. The structure of II is built of molecular complexes, each comprising, apart from ligand HL1a, two monodentate coordinated NO3− groups. The oxygen atom of one anion together with the NNS donor atom set of ligand HL1a form the base, and the oxygen atom of the other anion is in the apex of the coordination polyhedron. In IV, the structure is ionic and built of NO3− anions and [Cu(HL2a)(H2O)(NO3)]+ complex cations, where a cationic coordination polyhedron has a trigonal-bipyramidal configuration with organic ligand HL2a positioned along the long edge. The bipyramidal base is made up by the oxygen atoms of the coordinated water molecule and monodentate nitrato group and the nitrogen atom N2 of the azomethyne group.

Synthesis and crystal structure of [La(NO3)3(H2O)2(BiPy)]·1.5(BiPy)

The molecular and crystal structure of the [La(NO3)3(H2O)2(2.2′-BiPy)]·1.5(2.2′-BiPy) compound is determined. The metal coordination polyhedron in the La(III) complex is formed from 10 donor atoms of O8N2: 6 oxygen atoms belong to three chelate-coordinated NO 3 − anions, 2 oxygen atoms belong to two water molecules, and 2 nitrogen atoms belong to a bidentate bipyridine molecule coordinated in the neutral form. The structure is based on the metal complexes linked together in chains through the O(W)-H...O hydrogen bonds, in which oxygen atoms of the coordinated NO 3 − anions act as acceptors. It is a framework structure, further stabilized by a system of O(W)-H...N and C-H...N hydrogen bonds, in which nitrogen atoms of the uncoordinated bipyridine molecules act as proton acceptors.

The copper(II) acetate complex with 2-(2-Hydroxyphenyl)-4,4-diphenyl-1,2-dihydro-4H-3,1-benzoxazine

The Cu(II) acetate complex with 2-(2-hydroxyphenyl)-4,4-diphenyl-1,2-dihydro-4H-3,1-benzoxazine (L) was synthesized for the first time and structurally studied by X-ray diffraction. The complex crystallizes as two crystallographically independent centrosymmetric binuclear molecules [Cu2(μ-L)2Ac2] of similar structure, where L occurs as azomethin tautomeric form. The ligand performs tridentate chelate-bridging function. Each Cu atom exhibits extended tetragonal-pyramidal coordination by two O atoms and the N atom of one ligand L in the equatorial plane and by the O atom of the second ligand L in the axial position. The fourth equatorial position in the metal coordination polyhedron is occupied by the O atom of monodentate terminal acetate group.

Redetermination oftrans-diaquatetramethanolcobalt(II) bis(rac-1,1′-binaphthalene-2,2′-diylphosphate) methanol disolvate monohydrate: a two-dimensional supramolecular hydrogen-bonded network

In the title compound, trans-[Co(CH3OH)4(H2O)2](C20H12PO4)2·2CH3OH·H2O, the crystal packing shows a separation of the hydro­phobic naphthyl ring systems from the hydro­philic part of the structure, viz. the (RO)2PO2− phosphate anion, the cobalt complex cation and the solvent mol­ecules. The binaphthyl tail-to-tail packing in the hydro­phobic layer is governed by weak C—H⋯π inter­actions. The present study performed at 203 K confirms the previous room-temperature study [McCann, Murphy, Cardin & Convery (1991), Polyhedron, 10, 2771–2777], but with improved precision. The centro­symmetric cobalt complex has very similar Co—O bond lengths and is isostructural with the trans-[Cu(H2O)2(CH3OH)4]2+ cation (which features a tetra­gonally compressed instead of the typical Jahn–Teller distorted elongated copper octa­hedron) in the isotypic copper(II) compound. The high degree of similarity in the Co and Cu structures shows the dominating effect of the hydrogen-bonding network on the metal coordination polyhedra. All H atoms of the Co and Cu aqua and methanol ligands are engaged in typical strong hydrogen-bonding inter­actions.

Synthesis, structure, and properties of [Re2(HPO4)2(H2PO4)2(H2O)2] · 4H2O

The complex [Re2(HPO4)2(H2PO4)2(H2O)2] · 4H2O (I) was synthesized and investigated by conductometric, potentiometric, electronic and vibration spectroscopic methods. Thermal behavior of the title compound was studied and its molecular structure was determined from X-ray diffraction data. In the dimeric neutral complex, the bridging pairs of the hydrophosphate and dihydrophosphate groups close four five-membered Re-O-P-O-Re chelate rings. The O atom of water molecule occupies the axial position in the metal coordination polyhedron. The Re-Re distance 2.2168(8) A corresponds to quadruple bond.

Tetrachloridobis{(E)-1-[(E)-(1R,4R)-1,7,7-trimethylbicyclo[2.2.1]hept-2-ylideneaminooxy]propylideneamine}platinum(IV)

The metal coordination polyhedron of the title complex, [PtCl4(C13H22N2O)2], is a slightly distorted PtN2Cl4 octa­hedron. The E configurations of the trans imino ligands are stabilized by intra­molecular N—H⋯N hydrogen bonds.

Supramolecular architectures assembled by the interaction of purine nucleobases with metal-oxalato frameworks. Non-covalent stabilization of the 7H-adenine tautomer in the solid-state

The synthesis, crystal structure and variable-temperature magnetic measurements of the compounds [Mn(mu-ox)(H2O)(7H-pur-kappaN9)]n (1), {[Mn(mu-ox)(H2O)2].(7H-ade).(H2O)}n (2) and {[Cu(mu-ox)(H2O)(7H-ade-kappaN9)][Cu(mu-ox)(mu-H2O)(7H-ade-kappaN9)]. approximately 10/3H2O}n (3), (where ox: oxalato dianion, pur: purine, and ade: adenine) are reported. Compounds 1and 2 contain one-dimensional chains in which manganese(II) atoms are bridged by bis-bidentate oxalato ligands. The distorted octahedral geometry around each metal centre is completed in compound 1 by one water molecule and the imidazole N9 donor site of the purine ligand, which is a rare example of direct binding between the Mn(II) ion and the N donor site of an isolated nucleobase. Unlike 1, the adenine moiety in compound 2 is not bonded to manganese atoms and the metal coordination polyhedron is filled by two water molecules in a cis-arrangement. Its crystal building is constructed from pi-stacked layers of Watson-Crick hydrogen-bonded adenine...(H2O2)...adenine aggregates and zig-zag Mn(II)-oxalato chains held together by means of a strong network of hydrogen bonding interactions. The nucleobase exists in the lattice as the 7H-adenine tautomer which represents an unprecedented solid-state characterization of this minor tautomer as free molecule (without metal coordination) stabilized through non-covalent interactions. Compound consists of two slightly different [Cu(ox)(H2O)(7H-ade-kappaN9)] units in which the nucleobase coordinates through the imidazole N9 atom. The planar complex entities are parallel stacked and joined by means of long Cu-O bonds involving oxygen atoms from the oxalato and the aqua ligands, giving one-dimensional chains with a [4 + 1] square-planar pyramidal and a [4 + 2] octahedral coordination around the metal centre, respectively. Self-assembled process of compound 3 is further driven by an in-plane network of hydrogen bonding interactions to generate a porous 3D structure containing parallel channels filled by guest water molecules. Variable-temperature magnetic susceptibility measurements of all the complexes show the occurrence of antiferromagnetic interactions between the paramagnetic centres. DFT calculations have been performed to check the influence of packing in the stability of the 7H-amino tautomer of 2 and in the complex geometry of 3.

Inhibitor coordination interactions in the binuclear manganese cluster of arginase.

Arginase is a manganese metalloenzyme that catalyzes the hydrolysis of L-arginine to form L-ornithine and urea. The structure and stability of the binuclear manganese cluster are critical for catalytic activity as it activates the catalytic nucleophile, metal-bridging hydroxide ion, and stabilizes the tetrahedral intermediate and its flanking states. Here, we report X-ray structures of a series of inhibitors bound to the active site of arginase, and each inhibitor exploits a different mode of coordination with the Mn(2+)(2) cluster. Specifically, we have studied the binding of fluoride ion (F(-); an uncompetitive inhibitor) and L-arginine, L-valine, dinor-N(omega)-hydroxy-L-arginine, descarboxy-nor-N(omega)-hydroxy-L-arginine, and dehydro-2(S)-amino-6-boronohexanoic acid. Some inhibitors, such as fluoride ion, dinor-N(omega)-hydroxy-L-arginine, and dehydro-2(S)-amino-6-boronohexanoic acid, cause the net addition of one ligand to the Mn(2+)(2) cluster. Other inhibitors, such as descarboxy-nor-N(omega)-hydroxy-L-arginine, simply displace the metal-bridging hydroxide ion of the native enzyme and do not cause any net change in the metal coordination polyhedra. The highest affinity inhibitors displace the metal-bridging hydroxide ion (and sometimes occupy a Mn(2+)(A) site found vacant in the native enzyme) and maintain a conserved array of hydrogen bonds with their alpha-amino and -carboxylate groups.

Protonation state of Asp120 in the binuclear active site of the metallo-beta-lactamase from Bacteroides fragilis.

The determination of the protonation state of enzyme active sites may be crucial for the investigation of their mechanism of action. In the bizinc beta-lactamase family of enzymes, no consensus has been reached on the protonation state of a fully conserved amino acid present in the active site, Asp120. To address this issue, we carry out here density functional theory (DFT) calculations on large models (based on Bacteroides fragilis X-ray structure) which include the metal coordination polyhedron and groups interacting with it. Our calculations suggest that Asp120 is ionized. The relevance of this finding for site-directed mutagenesis experiments on the 120 position and on the mechanism of action is discussed.

Modeling anhydrous and aqua copper(II) amino acid complexes: a new molecular mechanics force field parametrization based on quantum chemical studies and experimental crystal data.

This paper presents the vacuum structures of aquacopper(II) bis(amino acid) complexes with glycine, sarcosine, N,N-dimethylglycine, and N-tert-butyl-N-methylglycine estimated using the B3LYP method. The differences between the B3LYP vacuum structures and experimental crystal structures suggested considerable influence of crystal lattice packing effects on the changes in the complexes' geometries. A previously developed molecular mechanics force field for modeling anhydrous copper(II) amino acidates was reoptimized to simulate these changes and predict the properties of both trans and cis anhydrous and aqua copper(II) amino acid complexes. The modeling included experimental molecular and crystal structures of 13 anhydrous and 10 aqua copper(II) amino acidates with the same atom types (Cu(II), C, H, N, and O) but various copper(II) coordination polyhedron geometries, crystal symmetries, and intermolecular interactions. The empirical parameters of the selected potential energy functions were optimized on the B3LYP vacuum copper(II) coordination geometries of three anhydrous copper(II) amino acidates and on experimental crystalline internal coordinates and unit cell dimensions of six anhydrous and six aqua copper(II) amino acid complexes. The respective equilibrium structures were calculated in vacuo and in simulated crystalline environment. The efficacy of the final force field, FFW, was examined. The total root-mean-square deviations between the experimental and theoretical crystal values were 0.018 A in the bond lengths, 2.2 degrees in the valence angles, 5.5 degrees in the torsion angles, and 0.395 A in the unit cell lengths. FFW reproduced the unit cell volumes in the range from -8.1 to 9.6%. The means of Cu to axial water oxygen distances were 2.4 +/- 0.1 A (experiment) and 2.6 +/- 0.1 A (FFW). This paper describes the ability of the molecular mechanics model and FFW force field to simulate the flexibility of the metal coordination polyhedron. The new force field proved effective in predicting the most stable molecular conformation of copper(II) amino acidato systems in vacuo.

Inframolecular acid–base studies of the tris and tetrakis myo-inositol phosphates including the 1,2,3-trisphosphate motif

The intrinsic acid–base properties of the phosphate groups of three myo-inositol derivatives which display the 1,2,3-trisphosphate motif, i.e. (±)- myo-inositol 1,2,3-trisphosphate (Ins(1,2,3)P 3), (±)- myo-inositol 1,2,3,6-tetrakisphosphate (Ins(1,2,3,6)P 4), and (±)- myo-inositol 1,2,3,5-tetrakisphosphate (Ins(1,2,3,5)P 4) are reported. The studies were performed in 0.2 M KCl solution at 37 °C, near physiological ionic strength and temperature. In addition, in order to shed light on the transition metal complexation properties of Ins(1,2,3)P 3, the influence of the Zn 2+ cations on its 31P NMR titration curves was investigated. From the titration curves as well as from the determined protonation microconstants, it appears that for Ins(1,2,3)P 3, the two lateral P1 and P3 phosphates strongly contribute to stabilise a proton on the central P2 phosphate. However, in the fully deprotonated form of Ins(1,2,3)P 3, P1 and P3 repulse each other so that they establish hydrogen bonds with, respectively, their neighbouring OH6 and OH4 hydroxyls. The 1,2,3-trisphosphate motif of Ins(1,2,3,5)P 4 behaves very similarly to that of Ins(1,2,3)P 3 indicating a poor interaction with the distant P5 phosphate. By contrast, moving a phosphate group from position 5 to position 6 on the myo-inositol ring as in Ins(1,2,3,6)P 4, leads to major changes in the basicity and cooperativity of the phosphate groups. Finally, the presence of Zn 2+ cations has a marked influence on the 31P NMR titration curves of Ins(1,2,3)P 3, leading to the conclusion that two equatorial phosphates, assisted by a middle axial one, afford an optimal chelating moiety that is able to occupy all sites of the metal coordination polyhedron which could be the reason for its antioxidant properties.

The interaction of 5-fluoroorotic acid with transition metals: synthesis and characterisation of Ni(II), Cu(II) and Zn(II) complexes

5-Fluoroorotic acid (H 3FOro) is a potent inhibitor for some metalloproteins such as dihydroorotase and dihydroorotate dehydrogenase and for thymidylate synthase (nonmetalloprotein) in the human malaria parasite Plasmodium falciparum. To study the coordination chemistry of H 3Foro, the ammonium salt [NH 4 +][H 2FOro −].1H 2O ( 1) and the first coordination compounds of H 3FOro with transition metals [Ni(HFOro 2−)(H 2O) 4].1H 2O ( 2), [Cu(HFOro 2−)(NH 3)(H 2O)] n ( 3) and [Cu 3(FOro 3−) 2(NH 3) 6(H 2O) 2] ( 4) have been synthesised and characterised by single-crystal X-ray diffraction, IR spectroscopy and by thermogravimetry. Three different coordination modes of 5-fluoroorotic acid have been established. In all cases the ligand is chelated to the metal via an amido-nitrogen and a carboxylate-oxygen but for ( 3), there is also a carboxylate oxygen from another HFOro 2− ligand resulting in a polymeric structure and for ( 4), the second amido-nitrogen in the ororotic acid ring coordinates to give a trinuclear complex. The metal coordination polyhedra are octahedral in ( 2), square-pyramidal in ( 3) and square-planar and approximately square-pyramidal in ( 4). An octahedral coordination geometry including a N(1)/O(61)-chelating HFOro 2− ligand with four aqua ligands is proposed for the Zn complex [Zn(HFOro 2−) (H 2O) 4].0.5H 2O ( 5), based on IR and thermogravimetric data. Extensive hydrogen bonded networks and some ring–ring stacking interactions are observed in each of the structures.

Dimensional Reduction: A Practical Formalism for Manipulating Solid Structures

Conceptually, it is not difficult to imagine reaching into a solid structure and carving out just that portion of the framework we desire. Solid-state reactions incorporating an ionic component into a covalent structure have long been recognized as experimental means for accomplishing just such feats. However, the method does not always succeed, and so, in an effort to extend its use in more logical approaches to solid synthesis, we herein provide an assessment of the scope and limitations of the reaction type. Dimensional reduction is set forth as a general formalism describing how the metal−anion (M−X) framework of a parent compound, MXx, is dismantled upon reaction with an ionic reagent AaX to form a child compound AnaMXx+n. The added anions serve to terminate M−X−M bridges, yielding a less tightly connected framework that retains the metal coordination geometry and polyhedron connectivity mode of the original parent structure. In most instances, the connectedness of the ensuing framework can also be p...