Jaroslav Majer

Synthesis and characterization of cobalt(III) complexes with a stereospecific ligand derived from (S)-valine

Abstract Complexes of the type [CoLX 2 ] + and [CoLXY], where L is the quadridentate ligand ethylenediamine-N,N′-di-(S)-α-isovalerate (H 2 ven) and X = H 2 O or ethylenediamine (en) and Y = NO 3 have been prepared. Three geometrical isomers, cis-α, cis-β, and trans forms, may in principle be obtained. The complex [Co(ven)(NO 3 )H 2 O] exists only as the cis-α geometrical isomer, while in the case of [Co(ven)-(H 2 O) 2 ] + and [Co(ven)en] + complexes both cis-α and cis-β are found to exist. The yields of the cis-α isomers exceeded considerably those of the cis-β isomers. 13 C-NMR and absorption spectral measurements confirm these arrangements. In addition, the IR spectra of the complexes are discussed. The compounds exhibit a string negative CD bond under the 1 A 1g → 1 T 1g cubic absorption band, which is due to the 1 A 1g → 1 E g tetragonal component, consistent with the Δ absolute configuration imposed by the (S) configuration of the asymmetric carbon atom in the (S)-valine moiety.

Crystal and molecular structure of Δ-cis-α-ethylenebis-S-prolinato(1,2-diamino-ethane)cobalt(III) perchlorate dihydrate, Δ-cis-α-[Co(ss-EBP)(en)] ClO4·2H2O

Abstract The crystal and molecular structure of Δ- cis -α- ethylenebis-S-prolinato(1,2-diaminoethane)cobalt(III) perchlorate dihydrate, Δ- cis -α-[Co(SS-EBP)(en)] ClO 4 · 2H 2 O, was determined from three-dimensional X-ray diffractometer data. The complex crystallizes in the orthorhombic system, space group P 2 1 2 1 2 1 with a = 7.879(4) A, b = 13.738(9) A, c = 19.445(2) A, V = 2104(2) A 3 . With Z = 4, the observed and calculated densities are 1.60(2) and 1.605 g cm −3 , respectively. The structure was refined by the block- diagonal least-squares technique to a final R = 0.0560 for 1604 observed reflections. The geometry about the cobalt atom is roughly octahedral with the tetradentate SS-EBP (= ethylenebis-S-prolinate ion), assuming cis -α configuration in which the complex possesses two out-of-plane amino acidate (R) rings and the backbone ethylenediamine (E) ring. The E ring conformation is δ. On the other hand, the R rings have λ conformation as well as the en ring. Δ-R N R N− (δ E  λ R 1  λ R 2 )(λ en )- cis -α-[Co(SS-EBP)(en)] + is one of two possible isomers of this compound which have been isolated and whose absolute configurations have been tentatively assigned by spectroscopy. The crystal and molecular structure determination confirms these assignments.

Proton chemical shifts in NMR spectra of diamagnetic metal-aminopolycarboxylate complexes

Abstract The proton chemical shifts of2-hydroxy-1, 3-propanediamine-N, N, N′, N′ -tetraacetic acid and 1, 3- propanediamine-N,N,N′,N′-tetraacetic acid in 1:1 complexes with diamagnetic metal ions have been investigated as a function o f the metal ion charge Z and crystal ionic radius r. The chemical shifts correlate with Z/r linearly but separately in (II)A, (II)B, and lanthanide group. The inductive effects, long-range shielding and solvent ordering effects of metal ions are discussed as the posibble contributions to the proton chemical shifts.