Publications (6)0 Total impact
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ABSTRACT: The crystal and molecular structure of s- fac -[Co((S)-Asp)(medien)]ClO<sub>4</sub> . H<sub>2</sub>O . HClO<sub>4</sub> was elucidated by the heavy atom method. The positional parameters of the nonhydrogen atoms and their anisotropic temperature parameters were refined based on 2 474 observed reflection with final values of R = 0.0603 and wR = 0.0616. The substance crystallized in the orthorhombic system in the space group P2 <sub>1</sub> 2 <sub>1</sub> 2 <sub>1</sub>, Z = 4, a = 8.536(1), b = 13.378(1), c = 16.899(2) Å. The structure comprises layers of the complex cation which alternate with layers containing two perchlorate anions and one hydroxonium cation. The five-membered chelate ring of 4-methyl-1,4,7-triazaheptane exist in the asymmetric λ, δ envelope conformations and the N-CH<sub>3</sub> group of the triamine has the exo orientation. The five-membered ring of ( S )-aspartic acid assumes the symmetric envelope conformation, the six-membered chelate ring, the skew boat conformation.
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ABSTRACT: The crystal and molecular structure of s- fac -[Co(( S )-Asp)(dien)]ClO<sub>4</sub> . HClO<sub>4</sub> .2 H<sub>2</sub>O (dien = 1,4,7-triazaheptane) was solved by the heavy atom method. The position parameters of the non-hydrogen atoms and their anisotropic temperature parameters were refined based on 1 726 observed reflections with a final value of R = 0.073. The substance crystallizes in the orthorhombic system in the space group P2 <sub>1</sub> 2 <sub>1</sub> 2 <sub>1</sub>, Z = 4, a = 8.506(1), b = 17.171(2), c = 13.277(1) Å. The structure involves hydrogen bonds between the O2, O4 and HN2 atoms of aspartic acid and the two molecules of water. The five-membered dien chelate rings take the asymmetric envelope conformations. The five-membered ring of ( S )-aspartic acid possesses the symmetric envelope conformation whereas the six-membered ring exhibits the skew boat conformation.
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ABSTRACT: Reaction of [CoXY(en)(AB)]<sup>n+</sup> (AB = glycinato or (S)-α-alaninato anion, X = H<sub>2</sub>O, Y = Cl; AB = (S)-valinato anion, X = Y = Cl) with HCO<sup>-</sup><sub>3</sub>) or Ag(<sub>2</sub>CO)<sub>3</sub> gives mixture of mer- and fac- [CoCO(<sub>3</sub>(en)(AB)] isomers, ratio of which is temperature dependent. Both isomers undergo in aqueous solution to spontaneous isomerization which does not occur when carbonato group is replaced by oxalato or malonato one. This suggests that the source of stereolability in these complexes is a strain imposed by the four-membered carbonato chelate ring. The equilibrium constants (K = fac/mer ) increase in the order KGly < KVal < KAla. The total rate constants obtained at 45 °C and 55 °C increase in the order kAla < kVal < kGly. λ- mer- [CoCO<sub>3</sub>(en)(S)-Val)] isomer undergoes at 22 °C racemization at the octahedral centre yielding the mixture of 59% δ and 41% λ isomers.
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ABSTRACT: [Co(NH<sub>3</sub>)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>]OH . [Co(ohb-( S )-Leu)<sub>2</sub>] . 2 H<sub>2</sub>O (ohb, o -hydroxybenzyl) was characterized by single-crystal X-ray diffraction which shows that both ligands in the [Co(ohb-( S )-Leu)<sub>2</sub>]<sup>-</sup> anion assume facial coordination mode with all donor atoms trans to each other, proposed on the basis of UV-VIS and <sup>13</sup>C NMR spectroscopy, with R,S configuration of secondary N atoms. Compound crystallizes in the tetragonal space group I4 <sub>1</sub> with unit cell dimensions a = 22.173(7), c = 13.270(2) Å, V = 6 524 Å<sup>3</sup>, Z = 4. Structural data show that both ligands are not equivalent. Bond angles and bond lengths depend on whether secondary N atoms adopt R or S configuration. The average bond lengths are shorter when the ohb-( S )-Leu ligand coordinates with (N) R configuration.
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ABSTRACT: The crystal and molecular structure of the Ag[Co(ohb-( S )-Ala)<sub>2</sub>] . 5 H<sub>2</sub>O have been determined by X-ray diffraction method. The crystals are hexagonal with a = b = 9.039(0.002) Å, c = 24.896(0.006) Å, space group P3<sub>2</sub>21 , and Z = 3. Each Ag<sup>+</sup> counterion coordinated by one water molecule which is a part of hydrogen bond network, is bonded to aromatic rings. The anion adopts LAMBDA- mer absolute configuration. Mer geometry is in accord with the molecular mechanics calculations. Since CD spectroscopy does not reflect configurational chirality, the absolute configuration has been determined by the X-ray structure analysis and assigned using chirality descriptors. The arrangements at the chiral centers are R for both N atoms. The two five-membered rings each assume envelope conformation with C1 and C2 atoms exceptionally deviated (0.378(7) and 1.210(7) Å) from the N-Co-O plane. Both six-membered rings have delta twist boat conformations. The complex described has been also characterized by the electronic and <sup>13</sup>C NMR spectroscopies.
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ABSTRACT: Single-crystal X-ray diffraction study established the dimeric [Cu<sub>2</sub>(ohb-( S )-Ala)<sub>2</sub>] structure (ohb-( S )-Ala = N -(2-hydroxybenzyl-( S )-alaninate). The complex crystallizes in the tetragonal space group P4 <sub>3</sub> 2 <sub>1</sub> 2 with a = b = 8.849(1) Å, c = 24.913(2) Å, V = 1950.8(3) Å<sup>3</sup>, Z = 8. The Cu(II) ion has distorted square-pyramidal geometry with the equatorial positions occupied by three oxygen and one nitrogen atom. Each copper atom is weakly coordinated at the apical position by carbonyl oxygen atom of the neighbouring molecule at the distance 2.329(2) Å. The Cu-Cu separation 3.0204(7) Å and the Cu-O3-Cu angle 100.8(1)° lead to antiferromagnetic coupling (at room temperature μ<sub>eff</sub> = 1.35 μ<sub>B</sub>). The O1-Cu-O3 angle (154.9(1)°) indicates distortion of the square pyramid toward a trigonal bipyramid (t = 0.23).
