Nick Choi

Syntheses and structural characterisation of the compounds [Pd(dba)L2] (where L=PBz3 and PPh2Np) and the novel dimer [Pd2(μ-dba)(μ-SO2)(PBz3)2]

Abstract In this paper we report the synthesis and structural characterisation (when L=PBz3 and PPh2Np) of the compounds [Pd(dba)L2] (where L, PPh2Np 1, PPh2An 2, PPhNp2 3 and PBz3 4; Np, 1-naphthyl; An, anthracenyl; Bz, benzyl; and dba, dibenzylideneacetone) from [Pd2(dba)3] and the corresponding phosphine. All these complexes with the exception of 4 retain their structures in solution. The 31P-NMR spectrum of 4 is both solvent and temperature dependent. Under an SO2 atmosphere the reaction between [Pd2(dba)3] and PBz3 gave the novel dimer [Pd2(μ-dba)(μ-SO2)(PBz3)2], 5, which has been structurally characterised. In this dimer both the dba and SO2 ligands bridge the two metal centres.

Transition metal complexes of dialkyl α-hydroxyiminophosphonates, a novel class of metal complexes

A new range of dialkyl α-hydroxyiminophosphonates has been prepared and the first examples of metal complexes of this class of compound have been obtained; X-ray crystal structure analysis of the dichlorobis(diethyl E-(α)-hydroxyiminopropanephosphonate)nickel(II) complex shows a distorted octahedral coordination at the nickel atom giving two symmetry related diethyl-(E)-α-hydroxyiminopropanephosphonate ligands and two chlorine donors.

Syntheses and crystal structures of piperazine-1,4-diylbis(methylene)bis(phosphonic acid)hydrochloride, [H5L]Cl, and its complex with cadmium(II), [Cd(OH)(H3L)(H2O)3]n·nH2O

Abstract Synthesis of the polymeric complex [Cd(OH)(H3L)(H2O)n·nH2O (I) [H4L = piperazine-1,4-diylbis(methylene)bis(phosphonic acid), (II)] and X-ray crystal structures of I and II·HCl are reported. In I, the phosphonic acid coordinates as a monoanionic zwitterion through one oxygen atom of each phosphonate group to give polymeric chains of Cd atoms bridged through the organic function of the ligands. Three water molecules and one hydroxo ligand complete the approximately octahedral coordination sphere around cadmium. The piperazine ring has the chair conformation in both I and II · HCl, and II can be regarded as doubly zwitterionic.

Synthesis and crystal structure of a gadolinium(III) complex of a tetraimine schiff-base macrocycle: a potential contrast agent for magnetic resonance imaging

A gadolinium(III) complex of an 18-membered hexa-aza macrocycle, with relaxivities higher than [Gd(DTPA)(H2O)]2− and [Gd(DOTA)(H2O)]−, has been synthesized and its crystal structure indicates a nine-coordinate gadolinium ion bound to three water oxygen atoms and six nitrogen donors from the macrocyclic ligand.

The crystal and molecular structures of the blood cell labelling agents tris(2-hydroxy-2,4,6-cycloheptatrien-1-onato-O,O')indium(III) and trans-{tris(4-iso-propyl-2-hydroxy-2,4,6-cycloheptatrien-1-onato-O,O')indium(III)}

Abstract X-ray crystal structure analyses of tris chelate complexes of In(III) with tropolone [InT 3 ] and 4- iso -propyltropoloe [In(4iT) 3 ] show them to be monomeric with, in each case, three bidentate ligands bonded to a central metal atom. The coordination polyhedra are intermediate between trigonal prismatic and trigonal antiprismatic; mean twist angles: InT 3 , 36.4°; In(4iT) 3 , 36.6°. The structural features of InT 3 (which is routinely used as a blood cell labelling agent) and In(4iT) 3 (which has been investigated for labelling properties) are discussed in terms of their solution chemistry.

Dimeric yttrium(III) and neodymium(III) macrocyclic complexes: potential catalysts for hydrolysis of double-stranded DNA

Dimeric complexes of macrocycle L, [{ML(OH)(H2O)}2](NO3)4 where M = Y and Nd, have been prepared via template synthesis. X-Ray structural analysis of [{YL(OH)(H2O)}2]4+ showed each yttrium atom to be coordinated to six nitrogens in the macrocycle, two hydroxide bridging units and one water molecule; the two macrocycles within the dimer have virtually identical conformations. Both dimeric complexes have the remarkable ability to degrade dsDNA, while the corresponding monomers have no activity. Cleavage likely involves random attack at single strands, in which closed circular plasmid DNA is initially converted to a nicked DNA intermediate before final cleavage.

The First Bismuth Phosphide Complex: [Li(thf)4]+[{(tBuP)3}2Bi]−

Thermally unstable crystals of the title compound-the first bismuth phosphide complex to be structurally characterized (see picture)-are obtained by the reaction of [Bi(NMe(2))(3)] with [tBuPHLi] (1:3) in THF/hexane. Berry pseudorotation of the pseudo-trigonal-bipyramidal [{(tBuP)(3)}(2)Bi](-) ion is prevented for steric reasons.

A novel hexaaza macrocycle with methylenephosphonate pendant arms: a potential useful chelate for biomedical applications†

A new 18-membered hexaaza macrocyclic ligand with four pendant methylenephosphonates has been synthesized via the Mannich reaction. The protonation behaviour of this macrocycle has been followed by 31P and 1H NMR spectroscopy. The initial protonation pattern of the N-functionalised macrocycle is rather like its corresponding macrocyclic amine. The proton NMR spectrum of its lanthanum(III) complex in aqueous solution indicates that the complex adopts only one of the five possible conformations, either SSSS or RRRR. The crystal structure of the novel macrocyclic ligand shows an extended hydrogen-bonded structure in its solid state. The macrocycle has an unusual conformation with the pendants alternating ‘up’ and ‘down’ round the ring. The LaIII complex has a unique ten-co-ordinate geometry with all pendant arms co-ordinated to the LaIII ion which is in the plane of the six macrocyclic nitrogen donors.

Comparative study of the interaction of ‘lop-sided’ 14- to 17-membered tetraaza macrocycles containing fused dibenzo substituents with nickel(II)

The effect of macrocyclic and chelate-ring size on the complexation behaviour of a series of dibenzo tetraaza macrocycles incorporating 14- to 17-membered inner rings has been investigated. Change in ring size along this ‘lop-sided%’ series has been achieved solely by varying the number of methylene carbons that link adjacent benzyl nitrogen atoms. Several solid complexes of type NiLX2·xH2O (L = macrocyclic ligand; x= 0 or 1; X = Cl, NCS or NO3) with these rings have been isolated. The results of five X-ray crystallographic analyses, as well as molecular mechanics studies, have allowed comparison of the effect of change of ring size on the structures of the 14- to 17-membered ring complexes with X = NCS. All complexes have similar six-co-ordinate trans-isothiocyanato geometries in which the four donors of the macrocycle occupy the equatorial plane. For this series an inverse correlation between in-plane and axial bond lengths around the nickel atoms occurs for the 14- to 16-membered ring complexes; the correlation is less apparent in the case of the 17-membered species. The X-ray and molecular mechanics studies indicate that, as the number of methylene carbons linking adjacent benzylamino nitrogens increases, the corresponding bite angle at the metal increases, with the opposite bite angle decreasing in a (partial) compensatory manner. As a consequence, there is only a minor variation in the planarity of the macrocyclic donor plane along the series. The crystal structure of the 16-membered ring complex of nickel(II) nitrate is also reported, as is that of the 17-membered ring complex of nickel(II) chloride. The former contains an equal mixture of two (trans-octahedral) complexes of type [NiL(NO3)2] and [NiL(NO3)(H2O)]NO3. Cyclic voltammetry indicates that formation of the respective nickel(III) species is facilitated by the smaller-ring ligands; the oxidation of the 17-membered ring complex is non-reversible and probably ligand based.

Yttrium(III) and lanthanide(III) metal complexes of an 18-membered hexaaza tetraimine macrocycle. Crystal structure of the gadolinium(III) complex

Complexes of YIII, LaIII, GdIII and DyIII with an 18-membered hexaaza tetraimine macrocyclic ligand (L1) containing backbone cyclohexyl units have been prepared and characterized. The crystal structure of [GdL1(H2O)3]Cl3·3H2O shows a nine-co-ordinate gadolinium ion bound to three water oxygens and six nitrogen donors from the macrocyclic ligand. Solution studies with radiolabelled 90Y indicated that, in competition with the very strong chelator diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (H5dtpa), a 90YIIIL1 macrocyclic unit is maintained for 1 h. The relaxivity of the gadolinium(III) complex, [GdL1(H2O)3]3+, is higher than those of [Gd(dtpa)(H2O)]2– and [GdL(H2O)]–(H4L = 1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid), both of which are currently used as contrast agents in magnetic resonance imaging. A tetramethyl analogue of L1, i.e. L2, has been synthesized for the first time and a crystal structure determination showed that it adopts a stepped conformation, the direction of folding being dictated by the racemic conformation of the cyclohexane.