Luminescence properties of europium (III) cryptates trapped in sol-gel glass

The Lanthanide complexes Eu-2.2.1 and Eu-2.2.2 were synthesized and then incorporated into silica based transparent organic-inorganic hybrid material by the sol-gel method as an example of how doped xerogel materials are emerging as an important means of producing new materials. The produced gels were diagnosed to monitor emission spectra of the luminescent trivalent europium (Eu³⁺) complexes; emissions were compared to those for gels containing uncomplexed Eu³⁺. Results of the experiments (emission and lifetimes) concerning the coordination sphere composition showed that a cryptand ligand with aromatic groups (short range effect) and the hydrophobic gel host (long range effect) settle efficient action in the antenna effect and isolate the central ion from efficient quenchers, as e.g. water molecules. Each ligand imposed a distinct splitting pattern on the europium emission bands that helps identify them.     

Conductance study of the thermodynamics of some transition and heavy metal cryptates in binary acetonitrile-dimethylsulfoxide mixtures

A conductance study of the interaction between Co²⁺, Ni²⁺, Cu²⁺, Cd²⁺, Zn²⁺ and Pb²⁺ ions with cryptands C211, C221 and C222 in different acetonitrile-dimethylsulfoxide mixtures has been carried out at various temperatures. The formation constants of the resulting metal cryptates were determined from the molar conductance-mole ratio data. It was found that the stability of Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ cryptates vary in the order C211>C221>C222, while for Cd²⁺ cryptates the stability order is C221>C222>C211. A linear relationship is observed between logK _f of different metal cryptates and the mole fraction of acetonitrile in the solvent mixture. The enthalpy and entropy of cryptate formation reactions were determined from the temperature dependence of the formation constants. The enthalpy and entropy changes are quite sensitive to the solvent composition and the resultingTS ⁰–H ⁰ plot shows a fairly good linear correlation, indicating the existence of an entropy-enthalpy compensation in the cryptate formation reactions. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82181 (30 pages).     

Synthesis and Crystal Structure of Two New Molydenum(V) Pyrophosphate Complexes

Two new reduced molybdenum pyrophosphates, Na₂₈[Na₂{(Mo₂O₄)₁₀(P₂O₇)₁₀(HCOO)₁₀}]·108H₂O ( 1 ) and Na₂₂(H₃O)₂[Na₄{(Mo₂O₄)₁₀(P₂O₇)₁₀(CH₃COO)₈(H₂O)₄}]·91H₂O ( 2 ) have been synthesized and characterized by single‐crystal X‐ray diffraction. Red crystals of 1 are triclinic, space group , with a = 17.946(4) Å, b = 18.118(4) Å, c = 21.579(4) Å, α = 114.47(3)°, β = 93.54(3)°, γ = 114.39(3)° and V = 5581.8(19) ų, and orange crystals of 2 are monoclinic, space group P2₁/n, with a = 21.467(4) Å, b = 23.146(5) Å, c = 24.069(5) Å, β = 101.76(3)° and V = 11708(4) ų. They are both constructed by Mo^V dimers ({Mo₂O₄(O_P)₄(HCOO)} in 1 , {Mo₂O₄(O_P)₄(CH₃COO)} and {Mo₂O₄(O_P)₄(H₂O)₂} in 2 ) and pyrophosphoric groups. Their structures can be described as two interconnected nonequivalent wheels which are approximately perpendicular, delimiting a large cavity. The larger wheel contains six Mo^V dimers, while the smaller one has four dimers.     

An Unusual Mixed‐Anionic Iodine‐Rich Polyiodide: [Rb(crypt‐2,2,2)]4(I5)2(I8)

Black crystals of [Rb(crypt‐2,2,2)]₄(I₅)₂(I₈) were obtained from a dichloromethane/ethanol solution of RbI, I₂ and Kryptofix‐2,2,2®. The crystal structure (monoclinic, P2₁/c (no. 14), a = 1250.1(1), b = 2555.2(2), c = 2313.4(3) pm, β = 121.45(1)°, V = 6309.9(11)·10⁶ pm³, Z = 2) consists of [Rb(crypt‐2,2,2)]⁺ cations leaving three‐dimensional channels for the V‐shaped (I₅)^? and Z‐shaped (I₈)^2? anions which are isolated from each other.     

Utilisation of Silver Cryptate [222] /Silver System as a Potential Reference for the Determination of the Solvation Transfer Coefficients of Ions. Stability of Cryptates in a Solvent Medium

Abstract

The formal potential of Ag [222] /Ag(s) system is supposed to be independent of the solvent, taking in account the [222] ligand structure and the corresponding cryptate. This extrathermodynamic hypothesis is confronted to the one usually considered, water, methanol, D. M. S. O., acetonitrile and tetramethylurea being the used solvents. It seems possible to generalize this hypothesis to other cations and cryptands. The stability constants of cryptate [222] of the evaluation of p^K _Ag[222]⁺ constants, Nernst's law being respected. The argentometric titration of ligand [222] in presence of Na⁺, Li⁺, Tl⁺, Cd²⁺, Ni²⁺ ions allows to evaluate the p^K of corresponding cryptates in D. M. S. O. and methanol. Tl [222]⁺/Tl system follows Nernst's law in methanol and D. M. S. O. The dissociation constants have been evaluated from polarographic measurements in acetonitrile. The electrochemical systems are not rigorously fast, which does not allow an accurate determination of those constants by that method. Still it gives an order of magnitude.     

The Proton Cryptate of Hexaethylenetetramine

The next higher homologue of hexamethylenetetramine was synthesized as the proton cryptate H⁺@ 1 ⋅Br⁻ (shown schematically), and its X-ray structure determined. The proton trapped by the lone pairs accumulated at the center of the T-symmetric tetraaza cage could not be exchanged or removed, even after heating for three days in 3 M NaOD.