O. Angelova

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)°.

Abstract: Bis(diethyldithiophosphinato)nickel(II), [(C2H5)2PS2]2Ni and bis(di-n-propyl dithiophosphinato)nickel(II), [(n-C3H7)2PS2]2Ni, single crystals doped with the corresponding copper(II) complexes have been prepared and studied by EPR spectroscopy. The components of the g-tensor, 63Cu hyperfine coupling tensor and 63Cu nuclear quadrupole coupling tensor have been determined. An X-ray crystal structure determination of bis(di-n-propyldithiophosphinato)nickel(II) shows the nickel atom to lie at a centre of symmetry, coordinated by four sulphur atoms at 2.220(4) and 2.230(3) A.

Abstract: Abstract In this paper, guanidine copper compounds are reviewed with an emphasis on structural characteristics and their application in bioinorganic chemistry and catalysis. The literature survey includes the copper coordination chemistry of biological guanidine derivatives, peralkylated guanidines including bicyclic ones and of further nitrogen-rich guanidine-type systems such as azoimidazoles, triazolopyrimidines and triaminoguanidines. From a sporadic interest dating back to the 1960s, research on this ligand class and its use in copper coordination chemistry has gained new impetus since 2000. With the synthesis of examples with sophisticated substitution at the characteristic CN3 framework, complex problems can be addressed in several fields of chemistry. This paper analyses the different types of guanidines for their special donor properties and highlights the specific advantages of guanidines as neutral donor ligands in copper coordination chemistry where a great variety of coordination modes was found. These compounds offer the ability to distribute the formal positive charge of the metal throughout the guanidine unit and represent more than simple σ-donating ligands.

Abstract: The 1:1 proton transfer compound LH2, (creatH)+ (pydcH)−, has been prepared from the reaction of creatinine, creat, and dipicolinic acid, pydcH2, (2, 6- pyridinedicarboxylic acid) and characterized using IR, 1H and 13C NMR spectroscopy. The first coordination complex (creatH)[Zn(pydc)(pydcH)]·4H2O, was prepared using LH2 and zinc(II) nitrate, and characterized using IR, 1H and 13C NMR spectroscopy and single crystal X-ray crystallography. The crystal system is triclinic with space group with two molecules per unit cell. The unit cell dimensions are a = 8.085(2) A, b = 10.802(4) A, c = 13.632(4) A, α = 104.98(2)°, β = 90.31(2)° and γ = 92.55(3)°. The structure has been refined to a final value for the crystallographic R factor of 0.0381 based on 3003 reflections. The zinc atom is six-coordinated with a distorted octahedral geometry. The (pydc)2− and (pydcH)− units are almost perpendicular to each other. Extensive hydrogen bondings between carboxylate groups, (creatH)+ and water molecules throughout the zinc(II) complex as well as π–π stacking and ion pairing play important roles in stabilizing the corresponding lattices. The protonation constants of the building blocks of the pydcH2-creat adduct, the equilibrium constants for the reaction of (pydc)2− with creat and the stoichiometry and stability of the ZnII complex with LH2 in aqueous solution were accomplished by potentiometric pH titration. The solution studies support a self-associated (creatH)+(pydcH)− as the most abundant species at pH = 3.4. The stoichiometry of the crystalline complex (i.e. (creatH) [Zn(pydc)(pydcH)])and that of the most abundant species detected in solution were found the same.

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.