Synthesis and coordination properties of new macrocyclic ligands: equilibrium studies and crystal structures

The synthesis and characterization of two new macrocyclic ligands, the bis-macrocyclic compound 2,6-bis(1,4,13-triaza-7,10-dioxacyclopentadec-1-ylmethyl)phenol (L) and 38-methoxy-1,4,13,16,19,28-hexaaza-7,10,22,25-tetraoxatricyclo[14.14.7.1(32,36)]octatriconta-32,34,Delta(36,38)-triene (L1) are reported. Equilibrium studies of basicity and coordination properties toward metal ions such as Cu(II), Zn(II), Cd(II) and Pb(II) were performed for ligand by potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I= 0.15 mol dm(-3)). L behaves as a hexaprotic base (logK(1)= 10.93, logK(2)= 9.70, logK(3)= 8.79, logK(4)= 8.05, logK(5)= 6.83, logK(6)= 2.55). All metal ions form stable mono- and dinuclear complexes: logK(MLH(-1))= 25.61 for Cu(II), 15.37 for Zn(II), 12.58 for Cd(II) and 13.79 for Pb(II); logK(M(2)LH(-1))= 31.61 for Cu(II), 23.38 for Zn(II), 24.49 for Cd(II) and 23.68 for Pb(II). All these dinuclear species show a great tendency to add the OH(-) group: the equilibrium constant for the addition reaction was found to be logK(M(2)LH(-1)OH)= 4.77 for Cu(II), 5.66 for Zn(II), 2.8 for Cd(II) and 3.18 for Pb(II). In the case of Ni(II), kinetic inertness prevents the possibility of solution studies. The dinuclear solid adducts [Ni(2)H(-1)L(N(3))(3)].EtOH and [Cu(2)H(-1)L(N(3))](ClO(4))(2) were characterized by X-ray analysis.     

Conformational investigation of some macrobicyclic compounds and of their monoprotonated cations through a comparison between X-ray crystal structures and molecular dynamics simulations

Abstract

In preceding works, which have dealt with the synthesis and characterisation of a series of macrobicyclic compounds with five donor atoms, the unusually high basicity constants of these polyaminic cage-like molecules have been ascribed to the inclusion of the proton inside the macrobicyclic cavity which results in a very efficient hydrogen-bond network. The present paper, based on previously reported X-ray crystal structures regarding five-atoms bridging units and on molecular modelling studies shows that the disposition of the five donor atoms in the monoprotonated species is related to the protonation site. Precisely, if the protonation occurs on a bridge-head nitrogen the resulting geometry of the donors is a trigonal bipyramid, whereas it is square pyramidal when the proton is bound to a nitrogen belonging to a macrobicyclic chain. For what concerns the geometrical array of the donor atoms in the free amines, the favoured array seems to be the trigonal bipyramidal.     

Synthesis, characterization and application of Ni(tta)2.tmeda to MOCVD of nickel oxide thin films

A novel nickel beta-diketonate adduct, Ni(tta)2.tmeda, has been synthesized using 2-thenoyltrifluoroacetone as the beta-diketonate and N,N,N,'N'-tetramethylethylendiamine as the Lewis base. It has been characterized by elemental analyses, IR, 1H NMR, 13C NMR spectroscopy and single-crystal X-ray diffraction studies. Physical and thermal properties of Ni(tta)2.tmeda precursor have been also extensively investigated. Its efficacy as a metal-organic chemical vapour deposition (MOCVD) precursor for the growth of nickel oxide films has been fully tested by applying it to the deposition of NiO films on quartz substrate. NiO thin films have been characterized by X-ray diffraction (XRD), scanning electron microscopy and UV spectroscopy.     

Cation and anion coordination chemistry of palladium(II) with polyazacycloalkanes. Thermodynamic and structural studies

The interaction of PdCl ₄ ^2– with the macrocyclic ligands of the series [3k]aneN _k has been studied both in solution and in the solid state. [18]aneN₆ and [21]aneN₇ form both mono- and binuclear Pd²⁺ complexes, whose stability constants have been determined in 0.5 mol dm^–3 NaCl at 298.15 K. [21]aneN₇ also forms, in solution, a trinuclear species in which an amino group deprotonates to bridge two Pd²⁺ ions, as observed in the solid state. The crystal structure of the complexes [Pd₂([18]aneN₆)Cl₂][ClO₄]₂ and [Pd₃([21]aneN₇)Cl₃][ClO₄]₂ · H₂O have been solved by single crystal X-ray analysis. C₁₂H₃₀N₆Cl₄O₈Pd₂: monoclinic, space group C2/m,a = 10.876(2),b = 18.117(2),c = 7.043(2) Å, = 113.78(2)°,V = 1270(12) ų,Z = 2,D _calc = 1.92 g cm^-3, = 16.94 cm^–1.R = 0.063,R _w = 0.059. C₁₄H₃₆N₇CI₅O₉Pd₃: orthorhombic, space groupPcab,a = 13.125(7),b = 13.213(3),c = 33.570(5) Å,V = 5822(3) ų,Z = 8,D _calc = 2.15 g cm^–3, = 21.20 cm^–1.R = 0.074,R _w = 0.061. In very acidic solutions the polyammonium cations (H _k [3k]aneN _k ) ^k+ interact with PdCl ₄ ^2– forming second sphere coordinated species. These reactions have been followed by a microcalorimetric technique in 2 mol dm^–3 HCl solutions. The slowness of the reactions of (H₁₀[30]aneN₁₀)¹⁰⁺ with PdCl ₄ ^2– has been interpreted in terms of inclusion of the anion into the receptor's cavity as shown by the crystal structure of [(PdCl₄)(H₁₀[30]aneN₁₀)][PdCl₄]₂Cl₄: triclinic, space group PT,a = 7.760(3),b = 11.448(4),c = 13.399(11) Å, = 96.31(8)°, = 104.50(6)°, = 92.30(3)°,Z = 1.R = 0.046 andR _w = 0.039.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Conformational and Database Study on the Intramolecular CH...π Aromatic Bond and Its Possible Influence on the Stereochemistry of Polypeptide Chains

The presence of intramolecular CH... aromatic bonds in organic molecules has been analyzed by means of CSD searches. In particular, molecules containing aromatic and methyl groups have been examined as a function of the length of the chain separating the interacting groups. The type of bonds in the chain and its geometry have also been taken into account. The maximum number of CH... interactions have been found for five-membered chains joining the aromatic and methyl moieties. In addition, this interaction seems favored when the chain contains two sp ² hybridized atoms. The interactions involving polypeptides have been carefully examined. Interest has focused on compounds containing both aromatic and methylic residues, i.e., a combination of phenylalanine (phe), tyrosine (tyr), and tryptophan (trp) with alanine (ala), valine (val), leucine (leu), and isoleucine (ile). The maximum number of CH... interactions have been found when five atoms constituted the chain, i.e., in the sequences phe–ala and ala–phe.     

Manganese(III) Formate: A Three-Dimensional Framework That Traps Carbon Dioxide Molecules

Carbon dioxide, formic acid, and water molecules are trapped in the crystal lattice of manganese(III ) formate (see 1 ), which was obtained by reducing permanganate with formic acid. Each CO₂ guest molecule exhibits four C−H⋅⋅⋅O−C−O interactions with the three-dimensional host framework of Mn(HCOO)₃ units. Compound 1 undergoes an antiferromagnetic phase transition at 27 K.