Preparation and mössbauer studies of tetraaquabis[maleato(1-)]-iron(II)

Summary Tetraaquabis[maleato(1-)]iron(II), Fe(C₄H₃O₄)₂ · 4H₂O has been synthesised. The compound is monomeric and is isomorphous with the manganese(II) analogue. The temperature dependence of quadrupole splitting and optical spectral data giveca. 10000 cm^–1,ca. 650 cm^–1,ca. 190 cm^–1 andca. 1400 cm^–1 for the 10 Dq, tetragonal field, rhombic field and the splitting of the E_g level, respectively. The quadrupole splitting data indicate that distortion from cubic symmetry increases in the order oxalate < malonate < maleate. DTA, TGA and Mössbauer studies indicate elimination of one molecule of maleic acid at 235 °C. The resulting product shows a less distorted structure and this is attributed to the formation of maleato(2-)iron(II).     

X-ray diffraction and IR spectral characteristics of zinc(II)tetra-tert-butylphthalocyanine

According to well-known procedures, alpha- and beta-crystal polymorphic modifications of zinc(II)tetra-tert-butylphthalocianine (Zn(t-Bu)4Pc) were prepared and X-ray analysis of their powders was carried out. It was found that four tert-butyl groups in Zn(t-Bu)4Pc molecule do not prevent the formation of the alpha- and beta-polymorphs. The alpha- and beta-polymorphs differ from each other mainly by a mutual arrangement of neighboring metallophthalocyenine molecules in pi-stacking. Comparison of IR spectra of the alpha- and beta-polymorphs of ZnPc and Zn(t-Bu)4Pc was carried out. It was indicated that new bands appear at 670-690, 1256 and 1362 cm(-1) in the spectrum of Zn(t-Bu)4Pc in comparison with that of ZnPc. The appearance of new band at 1256 cm(-1) is assigned to rocking C-CH(3) vibrations and the band at 1362 cm(-1) to symmetrical deformational C-H vibrations of methyl groups of the peripheral substitutes. The main spectral characteristics for identification of the polymorphic modifications of Zn(t-Bu)4Pc are listed.     

N-acetyl-DL-leucinate cobalt(II), nickel(II) and zinc(II) complexes

Summary Complexes of the type M(AcLeu)₂ · B₂ (M = Co^II, Ni^II or Zn^II; B = H₂O, py, 3-pic, 4-pic; AcLeu =N-acetyl-DL-leucinate ion) and M(AcLeu)₂ B (M = Co^II or Zn^II and B = o-phen) were prepared and investigated by means of magnetic and spectroscopic measurements. The i.r. spectra of all the complexes are consistent with bidentate coordination of the amino acid to the metal ion. The room temperature solid state electronic spectra indicate that the symmetry of this species is closer toD _4h and that MO₆ and MO₄N₂ chromophores are present in the M(AcLeu)₂ · 2 H₂O and M(AcLeu)₂B_n · x H₂O (B = py, 3-pic, 4-pic, n=2 and x=0 for M = Ni^II; B = o-phen, n=1 and x=0 for M = Co^II; B = py, 3-pic, 4-pic, n=1 and x=1 for M = Co^II) complexes, respectively. By comparing the Dq values of the amino acid and those of other N-substituted amino acids previously studied, a spectrochemical series of the the cobalt(II) and nickel(II) complexes is proposed. The¹ H n.m.r. spectra of the zinc(II) complexes confirm the proposed stereochemistry.     

Crystal structure and hydrogen bonding system in cellulose I(alpha) from synchrotron X-ray and neutron fiber diffraction

The crystal and molecular structure, together with the hydrogen-bonding system in cellulose I(alpha), has been determined using atomic-resolution synchrotron and neutron diffraction data recorded from oriented fibrous samples prepared by aligning cellulose microcrystals from the cell wall of the freshwater alga Glaucocystis nostochinearum. The X-ray data were used to determine the C and O atom positions. The resulting structure is a one-chain triclinic unit cell with all glucosyl linkages and hydroxymethyl groups (tg) identical. However, adjacent sugar rings alternate in conformation giving the chain a cellobiosyl repeat. The chains organize in sheets packed in a "parallel-up" fashion. The positions of hydrogen atoms involved in hydrogen-bonding were determined from a Fourier-difference analysis using neutron diffraction data collected from hydrogenated and deuterated samples. The differences between the structure and hydrogen-bonding reported here for cellulose I(alpha) and previously for cellulose I(beta) provide potential explanations for the solid-state conversion of I(alpha) --> I(beta) and for the occurrence of two crystal phases in naturally occurring cellulose.     

Chemisorption of copper(II) at zinc and cadmium dialkyldithiocarbamates: EPR and X-ray diffraction studies

Chemisorption of Cu²⁺ cations at zinc and cadmium dialkyldithiocarbamates was studied. According to EPR data, in the first step, the zinc and cadmium atoms are partially replaced by copper in the starting molecular structure to form heterobinuclear and heteropolynuclear complexes. In the second step, copper replaces up to 90 to 97% of the total number of the metal atoms, yielding binuclear and polynuclear copper(II) complexes. The possibility of the existence of heterobinuclear complexes in the individual state was demonstrated with [CuCd{S₂CN(C₂H₅)₂}₄] as an example. Its molecular and crystal structures were determined from X-ray diffraction data.     

X-ray K-absorption spectrum of nickel in some nickel (II) complexes

X-ray K-absorption edge of nickel in some nickel (II) complexes has been investigated using a 400-mm bent crystal spectrometer. The structure associated with the absorption edge has been used to deduce information regarding the bond lengths, the mode of bonding and the co-ordination of Ni(II) in the complexes. On the basis of the results obtained, it has been concluded that in the two forms of Ni(INAP)₂ (green and brown) the Ni(II) ions are surrounded by distorted octahedra whereas Ni(II) ions in Ni(C₆H₉N₂O₃)₂ has a square planar structure. Ni(αBMO)₂ appears to have NiNi type metallic interaction.     

Substituted alkylamine adducts of cobalt (II), nickel(II) and zinc(II) acetylacetonate

Thirty-seven adducts of cobalt(II), nickel(II) and zinc(II) acetylacetonate of formula [M(AA)₂(RNH₂)_n] (M = Co, Ni, Zn; AA = acetylacetonate ion; R = H, alkyl, aralkyl or phenyl substituent; n = 1 or 2) have been synthesized. With one exception the cobalt and nickel adducts are 6-co-ordinate but mono(amine) adducts are fairly common in the zinc series. Adduct formation induces a considerable shift of νM-O to lower frequencies in all three series (relative to the parent acetylacetonate) and a downfield shift of amino proton NMR signal in the zinc series (relative to the free amine). Correlations between the Taft polar substituent constants of the amine substituents and the i.r. and NMR data show that electron releasing substituents decrease the M-O bond order and increase the shielding of the amino protons.