Pavel Vojtíšek

Complexes of tetraazacycles bearing methylphosphinic/phosphonic acid pendant arms with copper(II), zinc(II) and lanthanides(III). A comparison with their acetic acid analogues

Abstract A comparison of complexing properties of cyclen and cyclam derivatives containing acetic acid pendant arms on one hand and their methylphosphonic or methylphosphinic acid analogues on the other is made mainly with complexes of copper and lanthanides due to their applications in medicine. The stability constant values of Cu(II) complexes are determined mainly by the basicity of amine groups. The influence of other possible effects, such as the macrocyclic effect in tetraazacycle in contrast to linear amines or the number of additional donor atoms in or outside of pendant arms and their basicity, seems to be very small. The stability constants for Gd(III), in addition to the basicity of amines, are also influenced by the basicity of the pendants and their number. The values of cyclam derivatives are lower than those of cyclen and it corresponds to the ring size effect as was found for zinc(II) complexes. In contrast to Cu(II), the Gd(III) stability constants of the phosphonic acid ligands are also lower than those with H4dota derivatives. A comparison of co-ordination polyhedra of the carboxylic and phosphonic or phosphinic derivatives shows similar motifs that are more determined by the macrocyclic effect than by the kind of donor groups in pendant arms. The differences between the polyhedra observed result from longer C–P(O) bond in the phosphorus derivatives than that C–C(O) in the acetate pendants. Consequently, the lanthanide(III) complexes with phosphorus acid derivatives are more sterically hindered; oxygen atoms in the O4 plane are close to one another and there is insufficient room for co-ordination of a water molecule, which is crucial in MRI applications.

Synthesis, crystal structures and magnetic properties of 1D polymeric [MnIII(salen)N3] and [MnIII(salen)Ag(CN)2] complexes

The syntheses, crystal structures and variable temperature (5–300 K) magnetic susceptibility measurements of two salen complexes of manganese(III) [where H2salen = N,N′-bis(salicylidene)-1,2-diaminoethane] having azido and dicyano argentate(I) as bridging ligands are reported. Both complexes belong to one-dimensional systems in which the azido functions as μ-(1,3) and Ag(CN)2− as ⋯NC– Ag–CN⋯ bridging ligands. The azido-bridged compound is antiferromagnetic with an intrachain interaction constant J = −4.52(4) cm−1 (Weng model) or J = −5.19(8) cm−1 (Fisher model), and it is a candidate to observe the Haldane gap in a S = 2 system. The silver cyanide bridged complex shows single ion behaviour of the Mn(III) ion, perhaps in combination with a very weak antiferromagnetic interaction.

Synthesis, Crystal Structures, and Solution Properties ofN-Methylene(phenyl)phosphinic Acid Derivatives of Cyclen and Cyclam

Two phenylphosphinic acid derivatives of tetraaza surprisingly high. The complexes of Zn2+ and Cd2+ with (L1)4– and (L2)4– are less stable than those with other similar macrocycles, (1,4,7,10-tetraazacyclododecanetetrayl)tetrakis(methylene)tetrakis(phenylphosphinic acid)] (H4L) and ligands, which is in accordance with lower overall basicity of H4L and H4L. A pronounced drop in the stability of the (1,4,8,11-tetraazacyclotetradecanetetrayl)tetrakis(methylene)tetrakis(phenylphosphinic acid)] (H4L), were complexes of H4L can be explained by partial coordination of the ligand to the metal ions. The solution properties of the synthesised and the crystal structures of H4L and its bis(1adamantylammonium) salt were determined. In both the ligands were also investigated by 31P-NMR spectroscopy. The spectra observed suggest stable (on the NMR time scale) structures, the ring conformation is virtually the same and is stabilised by hydrogen bonds. Protonation constants of the conformations of the protonated ligands in solution. A comparison of NMR spectra in solution and CP/MAS-NMR acids and stability constants of their Zn2+ and Cd2+ complexes were determined pH-metrically at 25 °C and at spectra indicates that the structures of the conformers roughly correspond to the structures observed in the solid an ionic strength of 0.1 mol dm–3 (KNO3). The pKA values found for both the compounds are lower than those for their state. The conformations are stabilised by intramolecular hydrogen bonds and by hydrophobic interactions of carboxylic analogues and correspond to the expected electron-withdrawing ability of the –P(Ph)O2H moiety. The phenylphosphinic moieties. The conformers are stable even at 90 °C, but not in the presence of complexing metal ions. value pK1 of the last dissociation constant of H4L is

Complexes of divalent transition metal ions with bis(aminomethyl)phosphinic acid in aqueous solution and in the solid state

Bis(aminomethyl)phosphinic acid, (NH2CH2)2PO2H (HL), was synthesized using a new procedure. Its coordination ability towards Co(II)/(III), Ni(II), Cu(II) and Zn(II) was studied both in solution and in the solid state. Because of the presence of two nitrogen atoms the ligand exhibits a higher overall basicity than common (aminoalkyl)phosphinic acids. Consequently, the values of the determined stability constants are comparable with those found for (aminoalkyl)phosphonic acids. NMR titrations of Zn(II) point to the interaction of phosphinate with the metal ion in a strong acid solution. The X-ray structures show several coordination modes in the solid state. All-trans-[MCl2(H2L-O)2(H2O)2]Cl2, where M(II) are Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Ca(II), and Cd(II), crystallized from acid solutions. The central ion is octahedrally coordinated with two phosphinate oxygen atoms, two molecules of water and two chlorides in all-trans arrangement. Amine groups are protonated and non-coordinated. Participation of the donor groups in crystals isolated from neutral solutions depends on the metal ion. All donor atoms are coordinated in monomeric fac-N,N,O-trans-O,O′-[Co(L-N,N,O)2]+. On the other hand, in the zinc(II) complex, two phosphinate oxygen atoms and two amine nitrogen atoms (trans to each other) of two different ligand molecules are coordinated in an equatorial plane and two amino groups of the two other ligand molecules are bound in axial positions. Thus, each molecule of the amino acid forms a five-membered N,O-chelate to one zinc(II) ion and the other amino group is bound to the neighbouring ion creating an infinite chain. Nickel(II) forms a trans-O,O′-[Ni(H2O)2(L-N,N)2] complex in which the metal ion is chelated by four amine nitrogen atoms forming two six-membered chelates in an equatorial plane and the octahedron is completed with two water molecules at the apical positions. The phosphinate group is not coordinated. The above results point to a relatively low coordination ability of the phosphinate group; however, due to its low pKA, it is able to bind metal ions at lower pH than other coordinating groups do.

Preparation, resolution and absolute configuration of 2,2′-bipyridine-3,3′-dicarboxylic acid 1,1′-dioxide and its ester

Abstract The title racemic acid (±)- 1 , prepared by hydrogen peroxide oxidation of 2,2′-bipyridine-3,3′-dicarboxylic acid, was resolved via the brucine salts. The absolute configuration of acid (+)- 1 was determined by X-ray diffraction study of its barium salt using the Bijvoets anomalous dispersion method. The activation energy ΔG # for interconversion of enantiomers of the dimethyl ester 2 was found to be −106.5 kJ/mol at 50 °C.

Complexing properties of phosphinic analogues of glycine

A series of aminomethylphosphinic acids H2NCH2PRO2H (R = H, Me, But or Ph) was synthesized and the acid–base and complexing properties with CoII, NiII and CuII were determined pH-metrically (25 °C, 0.1 mol dm–3 KNO3). The pKa values were found to increase from R = H to Ph, Me and But, as the –I effect decreases. The complex stability constants lie in the same order, except for R = H. The compound H2NCH2PHO2H (HL1) exhibits higher values than the ligands with methyl or phenyl substituents, probably due to better deformability of the PHO2– group and its better ability to form chelate rings. The complexes of H2NCH2P(Ph)O2H (HL4), H2NCH2P(Me)O2H (HL2) and H2NCH2P(But)O2H (HL3) with several transition metals were prepared and the crystal structures of [CuL42]1 and [Cu3L24][ClO4]22 were determined. The formation of chelate rings was observed in both structures; 1 forms dimers and 2 polymeric layers via the phosphinates.

Activation of a coordinated alkyne by electron transfer: crystal structures of [Ph2}{C(CO2Me)CH(CO2Me)}] and [PPh2}{C(CO2Me)C(CO2Me)}]

Abstract A new zerovalent complex [ Pd{PPh 2 CH 2 C(Bu t )NNC(Bu t )CH 2 P Ph2}{C(CO2Me)C(CO2Me)}] (1) was prepared and its crystal structure was determined by X-ray diffraction analysis, which shows it crystallises in the C2/C monoclinic space group with a=10.940(1) A, b=22.086(1) A, c=19.042(2) A and β=92.692(9)°. The azine diphosphine ligand chelates the metal in a (Z,Z) configuration with a PPdP bite angle of 114.63(4)°. The alkyne carbon atoms lie essentially in the PPdP plane. The electrochemical reduction of 1 promoted the conversion of the alkyne ligand to a vinyl species, and of the azine diphosphine to ene-hydrazone diphosphine, with formation of [ Pd{PPh 2 CHC(Bu t )NNC(Bu t )CH 2 P Ph2}{C(CO2Me)CH(CO2Me)}] (2). X-ray diffraction analysis of complex 2 shows it crystallises in the triclinic space group P1 with a=11.302(1) A, b=12.528(1) A, c=16.028(2) A, α=107.64(2)°, β=92.27(1)° and γ=111.79(2)°. It displays a square-planar geometry with the two phosphorus atoms in trans position. Extended Huckel MO calculations were performed in order to elucidate the redox process.A new zerovalent complex [Ph2}{C(CO2Me)C(CO2Me)}] (1) was prepared and its crystal structure was determined by X-ray diffraction analysis, which shows it crystallises in the C2/C monoclinic space group with a=10.940(1) A, b=22.086(1) A, c=19.042(2) A and β=92.692(9)°. The azine diphosphine ligand chelates the metal in a (Z,Z) configuration with a PPdP bite angle of 114.63(4)°. The alkyne carbon atoms lie essentially in the PPdP plane. The electrochemical reduction of 1 promoted the conversion of the alkyne ligand to a vinyl species, and of the azine diphosphine to ene-hydrazone diphosphine, with formation of [Ph2}{C(CO2Me)CH(CO2Me)}] (2). X-ray diffraction analysis of complex 2 shows it crystallises in the triclinic space group P1 with a=11.302(1) A, b=12.528(1) A, c=16.028(2) A, α=107.64(2)°, β=92.27(1)° and γ=111.79(2)°. It displays a square-planar geometry with the two phosphorus atoms in trans position. Extended Huckel MO calculations were performed in order to elucidate the redox process.

Synthesis, characterisation and extraction behaviour of calix[4]arene-based phosphonic acids

Three new bis(phosphonic) acids were prepared by derivatization of p-tert-butylcalix[4]arene on the lower rim by –(CH2)xPO3H2 groups and were fully characterized by NMR spectroscopy; some of them were further investigated by X-ray analysis. The compounds obtained were tested as extractants for La3+, Eu3+, Yb3+ and Th4+ in 0.1–1 M HNO3. Structural details of the complex HLn(H2L1)2 where Ln = Y, La, Eu were elucidated by NMR techniques in solution. The extraction efficiencies decrease with increasing length of the CH2 spacer; the dependence is not monotonic, and an extraordinary selectivity was observed for Yb. The extraction efficiency of Ln3+ for all of the ligands studied increased significantly with decreasing ionic radius.

Aminomethylenephosphinic acids and their complexing properties

A study of the dependence of the 1H, 31P and 13C NMR spectra of D2O solutions of piperidinomethylphosphinic acid (HL1) and piperazine-1,4-diylbis(methylene)bis(phosphinic acid)(H2L2) on the pH has indicated a strong acidity of the phosphinic groups and a low basicity of the nitrogen atoms. It is confirmed that the acids from zwitterions in aqueous solution and that the HL1 ring behaves similarly to the N-methylpiperidine ring. The stability constants of complexes formed with Mg2+, Ca2+, Pb2+, Co2+, Ni2+, Cu2+, Cd2+ and Zn2+ are lower than those of their acetic or phosphonic acid analogues. In the solid state, HL1·H2O exists as a zwitterion, monoclinic, space group P21/n, a= 6.884(2), b= 11.485(2), c= 11.994(2)A and β= 97.87(2)°. Two molecules are linked by hydrogen bonds into dimers which are connected by water molecules to form endless chains.

Complexes of nitrilotrimethylphosphonic acid with cobalt, nickel, copper and zinc

Abstract Substances of the types MH4ntmp, Mg3[M(Hntmp)]2, M2H2ntmp and Mg[M2(Hntmp)]2, where M = Co, Ni, Cu, Zn and H6ntmp = N[CH2PO(OH)2]3 were prepared. The sodium and cesium salts of the [Co(Hntmp)]3− complexes were also prepared. The IR and electronic spectra and the experimental magnetic susceptibilities indicate that these are high-spin complexes. The coordination surroundings of the central atom consist of a highly distorted octahedron of the ligand oxygen atoms. The nitrogen atom is not coordinated to the central atom.