Choon Pyo Hong

A novel one-dimensional nickel(II) complex with a hydrogen-bond-link

Abstract A novel compound [Ni(L)(H2O)2]0.5[Ni(L)(WO4)2]0.5·4H2O (1) (L=3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,01.18,07.12]docosane) has been structurally and magnetically characterized. The nickel(II) ions are shown to be in distorted octahedral environments with secondary amines of macrocycles in which two trans water molecules and two trans tungstate ions are assembled around each metal center. Two nickel(II) complexes are connected into a one-dimensional chain via hydrogen bonds. The magnetic susceptibility measurement for 1 indicates weak antiferromagnetic interaction (J=−1.01(2) cm−1; H=−JΣSi·Si+1) between the S=1 nickel(II) paramagnetic centers.

KINETICS OF FORMATION AND DISSOCIATION OF TRIAZA-CROWN-ALKANOIC ACID COMPLEXES OF CERIUM(III) AND EUROPIUM(III)

The formation and dissociation rates of some lanthanide complexes of the 1,4,10-triaza-7,13-dioxacyclopentadecane-N,N′,N″-triacetic acid (1) and 1,4,10-triaza-7,13-dioxacyclopentadecane-N,N′,N″-tripropionic (2) have been measured by using stopped-flow and conventional spectrophotometry. Observations were made at 25.0±0.1°C and at an ionic strength of 0.1 M NaClO4. The complexation of Ce3+ and Eu3+ ions by ligand 1 proceeds through the formation of an intermediate complex in which the metal ion is incompletely coordinated. This may then proceed to a final product. Between pH 4.57 and 5.61, the monoprotonated (HL2−) form is the kinetically active species despite its low concentration. The dissociation reactions of Ln-1 and Ln-2 complexes were investigated with Cu2+ ions as scavenger in an acetate buffer. All complexes exhibit acid-independent and acid-catalysed contributions. The buffer and Cu2+ concentration dependent of the dissociation rate has also been investigated. The metal and ligand effects on the dissociation rate of some lanthanide complexes are discussed by comparing the rate constants with those of analogous linear and macrocyclic polyaminepolycarboxylate systems.

Synthesis, Crystal Structure, and Magnetic Properties of the Two-Dimensional Nickel(II) Complex via Covalent and Hydrogen Bonds: [Ni(L)(H2O)2][Ni2(L)(NTA)2]ċ6H2O (L = 3,14-di-methyl-2,6,13,17-tetra- azatricyclo[14,4,01.18,07.12]docosane, NTA = Nitrillotriacetate)

A new compound [Ni(L)(H2O)2][Ni2(L)(NTA)2]ċ6H2O (1) (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,01.18,07.12]- docosane, NTA = nitrillotriacetate) was prepared and its structure was determined by the X-ray diffraction method. Complex 1 crystallizes in the monoclinic space group P21/c with a = 11.217(2) Β, b = 18.048(5) Β, c = 15.393(3) Β, β = 90.78(2)°, V = 3115.9(12) Β3, and Z= 2, Each nickel atom in complex 1 has a distorted octahedral coordination geometry with an inversion center. Magnetic susceptibility measurement showed a weak intramolecular antiferromagnetic interaction between two Ni(1) and Ni(2) centers with a J value of -0.93(1) cm−1. The intermolecular hydrogen-bonding interaction gives rise to a two-dimensional network.

A novel four-coordinate zinc(II) complex of the di-N-hydroxypropylated tetraaza macrocycle

The compound [Zn(L2)Cl]ClO4·H2O (1) (L2 = 2,13,-bis(3-hydroxypropyl)-5,16-di-methyl-2,6,13,17-tetraazatricyclo[14,4,01.18,07.12]docosane) has been synthesized and structurally characterized. 1 crystallizes in the monoclinic system, space group P21/c with a = 8.932(2), b = 16.189(2), c = 22.492(4) Å β = 95.34(2)° V = 3238.3(11) Å3; and Z = 4. The zinc atom is placed in a highly distorted tetrahedral environment bonding with three nitrogen atoms of the macrocycle and one chlorine atom.

Formation kinetics of triaza-crown-alkanoic acid complexes of first-row transition metal(II) ions

Abstract The complex formation reactions of divalent metal ions of Co2+, Ni2+, Cu2+ and Zn2+ with the macrocyclic ligands 1,7-dioxa-4,10,13-triazacyclopentadecane-4,10,13-triacetic acid, 1, and 1,7-dioxa-4,10,13-triazacyclopentadecane-4,10,13-tripropionic acid, 2, have been studied by using stopped-flow and conventional spectrophotometry. The measurements were made at 25.0 ± 0.1°C in an aqueous solution of 0.1M (NaClO4) ionic strength. The formation reaction takes place by rapid formation of an intermediate complex (MH2L+∗) in which the metal ion is incompletely coordinated. This may then proceed to the final product in the rate-determining step. The stability constants (logK MH2L +∗) and the second-order rate constants (kOH ) for the rearrangement of the intermediate complex have been determined from the kinetic data. In the pH range examined, the monoprotonated (HL2−) form of ligands 1 and 2 is the kinetically active species despite of their low concentration. The structure of the intermediate is propos...