M. Mitewa

Chromium(V) coordination chemistry

Mecanisme de formation des complexes de Cr(V). Structure et liaison. Photochimie de la reduction de Cr(VI)

Au(III) interaction with Methionine- and Histidine-containing peptides

Mononuclear Au(III) complexes of the peptides H-His-Met-OH (D) and H-Gly-Gly-Met-OH (T) and their N-protected forms Ac-His-Met-OH (Ac-D) and Ac-Gly-Gly-Met-OH (Ac-T) were structurally characterized by means of IR, MS and NMR. In the complexes with dipeptides [AuLCl2]Cl (L = D or Ac-D), Au(III) is coordinated through S and imidazole N atoms from methionine and histidine fragments of the ligands forming macrochelate rings at mol ratio Au : L = 1 : 1. Additionally, Au(III) is coordinated by two terminal chloride ions in a square-planar arrangement. In complexes with the tripeptides [AuL′Cl] (L′ = T or Ac-T), however, the metal ion is coordinated in a tridentate fashion, through S and two N atoms, also at mol ratio M : L = 1 : 1. The fourth position of Au(III) is occupied by a Cl− ligand.

Pulsed laser photolysis of the PtCl62−—creatinine system in methanol

Abstract The pulsed laser photolysis (excimer laser, XeCl; 308 nm) of the PtCl 6 2− —creatinine—methanol system was studied. The formation of an intermediate Pt III species (PtCl 5 2− cr, where cr = creatinine) was demonstrated and its decay kinetics were examined. Some kinetic and thermodynamic data of the photoinduced reaction were determined. The photolysis of the same system using stationary irradiation was also investigated allowing the end product of the reaction to be determined.

Monomeric Pt(II) and Pd(II) complexes with Creatinine. Crystal structure of tetrakis-(Creatinine) platinum(II) diperchlorate

Abstract Pt(II) and Pd(II) complexes with creatinine, C3H2N2(O)(CH3)NH2, were synthesized. Potentiometric and IR spectroscopic analyses were carried out. A model for the coordination of the ligands to the central atoms was confirmed by X-ray structural investigation of Pt(creat)4(ClO4)2. The compound [Pt(C4H7N3O)(ClO4)2] crystallizes in the monoclinic crystal system, space group C2/c, a = 15.748(5), b = 15.763(7), c = 24.843(8) A, β = 106.84(4)°, V = 5902 A3, Z = 8. The refinement of the structure by the least-squares method gave R = 0.051 and Rw = 0.054 for 1527 observed reflections with I > 2σ(I). The structure consists of Pt(creat)42+ complex cations, possessing approximate D2 symmetry and rotationally disordered perchlorate anions. The Pt atom is square-planarly coordinated by the endocyclic N atoms of four creatinine ligands. The PtN bond lengths range from 2.00(2) to 2.03(1) A and the NPtN angles from 88.4(9) to 91.8(8)°. The ligands are almost planar and tilted towards the PtN4-plane by 82.1(8)–93.5(9)°.

Coordination chemistry of N6 macrocycles

Abstract The complexation ability of saturated and unsaturated N 6 macrocycles towards different metal ions, synthesis, thermodynamics and structure of the metal complexes (mono- and dinuclear) formed are discussed. The data concerning protonation processes of the saturated azamacrocycles, i.e. cyclic polyamines and their ability to react selectively with some anions (host-guest chemistry) are also reviewed.

Intermediate chromium(V) complex species and their role in the process of chromium(VI) reduction by ethylene glycol

Abstract The interaction of ethylene glycol with potassium dichromate is studied at 80° in pseudo first-order conditions by ESR method, monitoring the formation of CrV and CrIII. The formation of CrV complex with ethylene glycol was observed and its kinetics studied. The kinetic data show, that CrV is produced as a result of the reaction CrIV+CrVI→2CrV. Water has a strong influence on the reaction as in its presence the process 3CrV→2CrVI+CrIII takes place. If the reaction is carried out at a low pressure and water formed in the reaction course removed, the current CrV concentration i srelatively high and the CrV complex with ethylene glycol stabilized for several days at room temperature. The final products of ethylene glycol oxidation are water and glycol aldehyde, no cleavage reaction being found to proceed in these conditions.

Crystal structure and properties of the copper(II) complex of sodium monensin A

The preparation and structural characterization of a new copper(II) complex of the polyether ionophorous antibiotic sodium monensin A (MonNa) are described. Sodium monensin A binds Cu(II) to produce a heterometallic complex of composition [Cu(MonNa)(2)Cl(2)].H(2)O, 1. The crystallographic data of 1 show that the complex crystallizes in monoclinic space group C2 with Cu(II) ion adopting a distorted square-planar geometry. Copper(II) coordinates two anionic sodium monensin ligands and two chloride anions producing a neutral compound. The sodium ion remains in the inner cavity of the ligand retaining its sixfold coordination with oxygen atoms. Replacement of crystallization water by acetonitrile is observed in the crystal structure of the complex 1. Copper(I) salt of the methyl ester of MonNa, 2, was identified by X-ray crystallography as a side product of the reaction of MonNa with Cu(II). Compound 2, [Me-MonNa][H-MonNa][CuCl(2)]Cl, crystallizes in monoclinic space group C2 with the same coordination pattern of the sodium cation but contains a chlorocuprate(I) counter [CuCl(2)](-), which is linear and not coordinated by sodium monensin A. The antibacterial and antioxidant properties as two independent activities of 1 were studied. Compound 1 is effective against aerobic Gram(+)-microorganisms Bacillus subtilis, Bacillus mycoides and Sarcina lutea. Complex 1 shows SOD-like activity comparable with that of the copper(II) ion.

Coordination properties of the bioligands creatinine and creatine in various reaction media

Abstract Data on the ability of the important bioligands creatinine and creatine to form various types of complexes with different metal ions are summarized. The crucial role of the nature of the reaction medium in complex formation with these ligands is emphasized. The conditions for obtaining paramagnetic oligomeric platinum complexes of the “platinum blue” type (resulting from multistep redox and coordination processes) are presented.

ESR study on chromium(V) complexes formed in the process of photochemical oxidation of diethylene glycol by dichromate

Abstract The oxidation of diethylene glycol with K 2 Cr 2 O 7 was studied in pseudo first-order conditions, the diol being in a large excess. The first stage of the reaction is the formation of non-cyclic monoester of Cr 2 O 7 2− with the diol, in which a photochemical redox process takes place leading to a complex of Cr (V) , denoted as Cr v) (1). This complex can be stabilized only at low temperatures; at room temperature it changes into another Cr (V) complex, denoted as Cr v (2). The ESR parameters of the complexes Cr v (1) and Cr v (2) permit some information to be obtained about their composition and structure. The last stage of the reaction which is also a photosensitive one, proceeds on in the complex Cr v (2), leading to the final reaction products - Cr (III) and a carboxylic acid. The spectral sensitivity of the photochemical processes was studied and compared with the absorption spectra of the initial and transition species. The quantum yield of the first photochemical reaction - the formation of Cr (V) - was found to be 0.46. The consecutive stages of the reaction are discussed in detail, some of them being experimentally studied in separation. A scheme for the reaction mechanism is proposed.

New platinum(II) and platinum(III) complexes of creatinine

A b s t r a c t The i n t e r a c t i o n of P t ( I 1 ) with c r e a t i n i n e i s s t u d i e d i n d i f f e r e n t r e a c t i o n c o n d i t i o n s . A t L:M r a t i o from 4 t o 10 s e v e r a l new complexes of P t ( I 1 ) a r e o b t a i n e d , s t u d i e d by s p e c t r o s c o p i c methods and X-ray d i f f r a c t i o n . I n these monomer i c s p e c i e s the l i g a n d i s coord ina ted only through the endogenic n i t r o g e n . A t L:M = 1 a slow redox process t a k e s p l a c e leat i ing t o the format ion of s e v e r a l ( n e u t r a l , a n i o n i c and cat i o n i c ) b l u e t o green paramacne t i c s p e c i e s . The process proceeds on with a marked decrease of plI and i s s e n s i t i v e t o t h e a c i d i t y , t o t h e n a t u r e of t h e s o l v e n t (1120, D,O or organic s o l v e n t ) and t o t h e presence of O2 as wel l . A-green monomeric s p e c i e s was i s o l a t e d and s t u d i e d by X-ray s t r u c t u r a l a n a l y s i s .