EPR study of (η5-cyclopentadienyl)nickel(I) complexes with P-and N-Donor ligands and 1,5-cyclooctadiene

Mononuclear (η⁵-cyclopentadienyl)nickel(I) complexes with triphenylphosphine, triethylphosphite, 2,2’-bipyridyl, and 1,5-cyclooctadiene formed in the course of reduction of nickelocene were studied by EPR method. Monocyclopentadienyl Ni(I) complexes of the composition CpNiL₂ were shown to form during nickelocene reduction irrespective of the method applied (the use of organometallic compound, alkali metal, thermal conditions) in the presence of stabilizing ligands L (L = PPh₃, P(OEt)₃, Bipy/2, COD/2) and in the course of contradisproportionation reaction between nickelocene and the corresponding NiL₄ complex. It was found that in the structure of these CpNiL₂ complexes (L = PPh₃, P(OEt)₃, Bipy/2), the main molecular axis is perpendicular to the L-Ni-L plane and these complexes should be considered as derivatives of trigonal structures of D _3h symmetry distorted by Cp ligand. In CpNi(COD) complex, the main axis passes through the Cpring center and this complex should be treated as a derivative of pentagonal structure of C _5v symmetry distorted by COD ligand. Nonequivalence of ³¹P nuclei results from vibronic interaction effect in tricoordinate structures in pseudodegenerate electron state (Jahn-Teller effect).     

Effect of pH on the Behavior of a Random Copolymer of Acrylamide

A temperature- and pH-sensitive random copolymer of N-[3-(diethylamino)propyl]-N-methylacrylamide] and N,N-diethylacrylamide was obtained. The copolymer contained 20 mol % of amine units and had a molecular weight of 3.3 × 10⁴. Buffer solutions containing 0.0102 g/cm³ of the synthesized copolymer were studied in the pH range of 7–13.5 by light scattering and turbidimetry. At low temperatures, macromolecules and large aggregates coexist in the solutions. The copolymer is temperature- and pH-sensitive in the studied pH range. The temperature and the width of the phase separation interval increase with increasing acidity of the medium.