Ethylenedibiguanide-a particularly interesting ligand in relation with the crystal structure of metal complexes
01 Jun 1990-Journal of Chemical Crystallography (Kluwer Academic Publishers-Plenum Publishers)-Vol. 20, Iss: 3, pp 279-284
TL;DR: In this article, the structure of ethylenedibiguanide Mn(III) nitrate monohydrate has been determined using MoKα radiation, and the structure was solved by the heavy-atom method, and refined by full-matrix least-squares to anR value of 0.024 for 3369 observed reflections.
Abstract: The structure of ethylenedibiguanide Mn(III) nitrate monohydrate has been determined using MoKα radiation. The complex is triclinic:P¯1,a=9.412(2),b=11.452(3),c=8.635(1) A,α= 101.10(2)°,β=102.45(2)° andγ=102.13(2)°. The structure was solved by the heavy-atom method, and refined by full-matrix least-squares to anR value of 0.024 for 3369 observed reflections. The disposition and nature of the metal-ligand bond in this and related compounds have been discussed. The crystal structure of the present compound is not in agreement with that proposed from chemical evidence.
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TL;DR: The present contribution represents a unique investigation of the effect of the coordinated metal (M) on the M(n+)-disulfide/M((n+1)+)-thiolate switch properties and can be rationalized by considering the different electrochemical properties of the involved Co and Mn complexes and the DFT-calculated driving force of the disulfides/thiolates conversion.
Abstract: It has recently been proposed that disulfide/thiolate interconversion supported by transition-metal ions is involved in several relevant biological processes. In this context, the present contribution represents a unique investigation of the effect of the coordinated metal (M) on the Mn+¢
disulfide/M(n+1)+¢thiolate switch properties. Like its isostructural CoII-based parent compound, CoII 2SS (Angew. Chem. Int. Ed. 2014, 53, 5318), the new dinuclear disulfide-bridged MnII complex MnII 2SS can undergo an MII¢disulfide/MIII¢thiolate interconversion, which leads to the first disulfide/thiolate
switch based on Mn. The coordination of iodide to the metal ion stabilizes the oxidized form, as the disulfide is reduced to the thiolate. The reverse process, which involves the reduction of MIII to MII with the concomitant oxidation of the thiolates, requires the release of iodide. The MnII 2SS
complex slowly reacts with Bu4NI in CH2Cl2 to afford the mononuclear MnIII¢thiolate complex MnIIII....
15 citations
TL;DR: The potential for the complexes to act as tectons for the rational assembly of hydrogen bonded metallosupramolecules is discussed and the X-ray structure of such an assembly, between [Ni(L3)2] and 1,8-naphthalimide, is presented.
Abstract: 1,5-Diarylbiguanides, where the aryl groups are phenyl (HL1), 3,5-dimethylphenyl (HL2), 3,5-dimethoxyphenyl (HL3), 4-t-butylphenyl (HL4) or 4-bromophenyl (HL5), have been prepared and characterised. HL3 and HL5 have been structurally characterised by X-ray crystallography, which shows them to adopt the expected tautomeric form for biguanides. They have extensive hydrogen-bonding interactions in the solid state, involving the biguanide NH groups supported by, in the case of HL3, the OCH3 aryl substituents or, in the case of HL5, Br⋯Br interactions. Reactions of HL1–HL4 with Ni(BF4)2 gives complexes of the type [Ni(HL)2](BF4)2, while reactions of HL1–HL4 with Ni(BF4)2 and triethylamine give neutral complexes of the type [Ni(L)2], where the biguanide ligand has been deprotonated at the Nring nitrogen. Both series of complexes were characterised in solution and the solid state. Cyclic voltammetry shows a largely irreversible Ni(II)/Ni(III) oxidation which becomes easier by ca. 70 mV upon ligand deprotonation, with more subtle variations resulting from the changes in aryl ring substituents. Infrared and 1H NMR spectroscopies both provide evidence for ligand deprotonation leading to the chelate ring becoming increasingly aromatised. X-ray crystallographic analyses of five of the complexes also show changes in bond lengths and angles within the chelate ring, consistent with increased electron delocalisation. A variety of hydrogen bonding motifs involving the complex ions, counterions and solvent molecules are found. The results of DFT calculations on both cationic and neutral complexes provide calculated structures consistent with the experimental ones and these, along with the results of vibrational spectroscopic studies, provide further evidence for increased aromatisation upon deprotonation. The potential for the complexes to act as tectons for the rational assembly of hydrogen bonded metallosupramolecules is discussed and the X-ray structure of such an assembly, between [Ni(L3)2] and 1,8-naphthalimide, is presented.
8 citations
TL;DR: The crystal structure of C6H16N8O2·CuCl2, a biguanide metal complex, has been determined by X-ray diffraction data using MoKα radiation.
Abstract: The crystal structure of C6H16N8O2·CuCl2, a biguanide metal complex, has been determined by X-ray diffraction data using MoKα radiation. The compound crystallizes in the monoclinic space groupP21/a, witha=11.074(4),b=12.061(4),c=5.312(3)A andβ=102.8(1)°.
5 citations
References
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TL;DR: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations as mentioned in this paper.
Abstract: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations. Revisions are based on new structural data, empirical bond strength-bond length relationships, and plots of (1) radii vs volume, (2) radii vs coordination number, and (3) radii vs oxidation state. Factors which affect radii additivity are polyhedral distortion, partial occupancy of cation sites, covalence, and metallic character. Mean Nb5+-O and Mo6+-O octahedral distances are linearly dependent on distortion. A decrease in cation occupancy increases mean Li+-O, Na+-O, and Ag+-O distances in a predictable manner. Covalence strongly shortens Fe2+-X, Co2+-X, Ni2+-X, Mn2+-X, Cu+-X, Ag+-X, and M-H- bonds as the electronegativity of X or M decreases. Smaller effects are seen for Zn2+-X, Cd2+-X, In2+-X, pb2+-X, and TI+-X. Bonds with delocalized electrons and therefore metallic character, e.g. Sm-S, V-S, and Re-O, are significantly shorter than similar bonds with localized electrons.
51,997 citations
TL;DR: Given a set of atomic positional and thermal parameters in a crystal defined by the unit cell constants and the space group symmetry operations, the estimated standard deviations of the derived quantities are calculated from the e.s.d.'s of the atomic parameters and unit cell constant.
Abstract: Given a set of atomic positional and thermal parameters in a crystal defined by the unit cell constants and the space group symmetry operations, the ti The estimated standard deviations of the derived quantities are calculated from the e.s.d.'s of the atomic parameters and unit cell constants, neglecti
1,584 citations
TL;DR: In this paper, a square-planer configuration was proposed for the trivalency of a trivalent silver compound in the presence of four nitrogen atoms of the ligand.
Abstract: WHILE trying to prepare co-ordination compounds of ethylenebidiguanine with bivalent silver analogous to Cu(II) and Ni(II) by oxidation of a silver salt by sodium persulphate, Ray and Ghosh1 found that a complex compound was formed in which silver exhibited an oxidation state of three instead of the expected two. Tervalent silver is isoelectronic with Pd(II). Ray and Ghosh proved the trivalency of silver by showing experimentally the diamagnetic character of silver (III) ethylenebidiguanide complex salts, and on the basis of this evidence they proposed a square–planer configuration (dsp2 hybridization) for silver in these compounds, with the silver coordinated to four nitrogen atoms of the ligand. I have analysed the crystal structure of silver ethylenebidiguanide nitrate to confirm this proposal, and also because complete crystallographic work on a trivalent silver compound has not yet been reported.
20 citations
TL;DR: The crystal structure of ethylenebis(biguanidine)nickel(II) dichloride monohydrate, Ni(C_6H_(16)N_(10))Cl_2.H_2O, has been determined and refined on the basis of three-dimensional intensity data collected on an automated diffractometer.
Abstract: The crystal structure of ethylenebis(biguanidine)nickel(II) dichloride monohydrate, Ni(C_6H_(16)N_(10))Cl_2.H_2O, has been determined and refined on the basis of three-dimensional intensity data collected on an automated diffractometer. The crystals are monoclinic, space group P2_1/c, with cell dimensions ɑ = 6-911, b = 11·678, c = 18·055 A, β = 101·39°; there are four molecules in the cell. The structure was determined by Patterson methods and refined by least-squares to an R index of 0·048 and a goodness-of-fit of 1·11 for 2879 reflections of non-zero weight. The resulting standard deviations in the atomic positions are about 0·002-0·003 A for the C, N and 0 atoms, 0·02-0·03 A for the H atoms and less than 0·001 A for Ni and CI-. The organic ligand is tetradentate and forms a square-planar array about the central nickel atom; the average Ni-N distance is 1 ·865 A. Chemically equivalent bonds are equal in length within experimental
error, and the bond distances have been satisfactorily correlated with molecular-orbital and valencebond descriptions of the cation. All available hydrogen atoms are involved in hydrogen bonds to chloride ions or water molecules. An interesting feature is that, in spite of considerable double-bond character in the C-N bonds, many of the hydrogen atoms are displaced appreciably from the plane of the cation toward the hydrogen-bond acceptors; the bonding about the nitrogen atoms thus becomes pyramidal.
11 citations