Nickel Squarate Research Articles

AN X-RAY PHOTOELECTRON AND INFRARED SPECTROSCOPIC STUDY OF NICKEL SQUARATE DIHYDRATE AND BIS(2,4-PENTANEDIONATO)NICKEL(II)

Abstract The X-ray photoelectron spectra of nickel squarate dihydrate and of bis(2,4-pentanedionato)nickel(II) are interpreted in terms of the known crystal structures of these complexes. The comparative degree of pielectron delocalisation over metal and ligand for these complexes is also evaluated from the XPS data.

Thermal Decomposition of Copper(II) Squarate

AbstractA kinetic and thermochemical study has been made of the dehydration, decomposition and oxidation reactions of copper(II) squarate dihydrate, CuC4O4 · 2H2O. In contrast to results obtained for the nickel(II) salt, the copper salt undergoes preliminary dehydration in a temperature range (410–440 K) appreciably below that for decomposition (590–620 K). The anhydrous material is then more stable than nickel squarate (560–600 K). The major decomposition products in nitrogen are Cu and CO and the reaction may proceed further to CuO and CO2 in an oxyen atmosphere. Values for the enthalpies of dehydration, decomposition and oxidation are reported. Isothermal DSC was used to study the kinetics of dehydration and of decomposition and results were analyzed using relative‐rate reduced‐time (RRRT) curves. The dehydration conforms to the Avrami—Erofe'ev expression, whereas the decomposition approximates closely to the contracting area model. Apparent Arrhenius parameters are reported.

Thermal decomposition of nickel squarate dihydrate, NiC4O4· 2H2O

A kinetic and microscopic study has been made of the thermal decomposition of nickel squarate dihydrate in the solid state. Kinetic characteristics are sensitive to the availability of water vapour and behaviour varies with changes in reactant disposition within the reaction vessel. Reproducible data were obtained by standardization of technique and decomposition rates increased as the reactant mass was reduced. The activation energy for the reaction, found by extrapolation of decomposition rate coefficients to zero mass, was 163 ± 10 kJ mol–1. Kinetic measurements did not, however, permit characterization of the geometry of interface development within individual reactant particles. Microscopic observations provided crucial evidence for the interpretation of rate data. Such evidence revealed that decomposition was accompanied by cracking of the approximately cubic crystallites of reactant and that preferential two-dimensional growth of superficial nuclei preceded penetration of the reaction interface into the separated reactant blocklets.It is concluded that reaction involved two consecutive steps, dehydration followed by decomposition. A novel mechanism is proposed for the breakdown of the organic anion. It is suggested that nickel bonds to the four-membered unsaturated ring and bonds are then redistributed with the transitory intervention of nickel carbonyl, which rapidly disintegrates at reaction temperature (ca. 500 K) to give the predominant products, metallic nickel and carbon monoxide.

Thermal studies of some divalent metal chelates of croconic acid

The thermal properties of chelates of croconic acid and squaric acid with divalent copper, cobalt, nickel and zinc have been investigated by TG and DTA. The decreasing order of thermal stability for the decomposition of the croconate chelates was Ni > > Zn > Co=Cu and for the squarate complexes, Zn > Co=Cu > Ni. The copper croconate TG showed water loss in two distinct steps. This was rationalized on the basis of the already known Jahn-Teller effect for this molecule. The nickel squarate was thought to have a different structure than the other squarate chelates. Activation energies were calculated for the croconate chelates from their DTA curves.

An x-ray, spectroscopic, and magnetic study of the structure of nickel squarate dihydrate, NiC4O4 · 2H2O

The structure of nickel squarate dihydrate, NiC4O4 · 2H2O, has been investigated by initial susceptibility measurements, infrared spectroscopy, and single crystal x-ray diffraction techniques. The results indicate that the structure consists of Ni ions situated at the centers of the edges of a cube, with squarate ions in the cube faces. Each nickel is roughly octahedrally coordinated by four squarate oxygens, and by two water oxygens. The lattice constants were found to be a = b = c =8.0685A, with α = β = γ = 90° within experimental accuracy. The structure was found to be noncubic. A spin-orbit coupling parameter of −280 (30) cm−1, which is 86% of the free ion value, is obtained from the magnetic and spectroscopic results. The structure of this compound, which is isostructural with the Mn(II), Fe(II), and CO(II) squarates, is different than that proposed by two other sets of workers. All crystals investigated were found to be macroscopically twinned, and a reason for such twinning is proposed.

Magnetic transitions in the insulator nickel squarate dihydrate, NiC4O4·2H2O

The real and imaginary initial susceptibilities of two samples of nickel squarate dihydrate, NiC4O4·2H2O have been measured in the range 1.2–4°K. Both samples exhibited deviations from Curie-Weiss behavior and magnetic losses characteristic of ferromagnetic ordering. Magnetic transitions were found in both samples in the neighborhood of 1.6 and 1.9°K, the higher temperature transition occuring at 1.8°K in a sample grown from an alcohol-water solution, and at 2.1°K in a sample grown from a pure water solution. The difference in magnetic behavior of the two samples is thought to be related to the type of solvent molecule clathrated by the open NiC4O4·2H2O structure.