Circular dichroism of the tetracyanonickelate(II) ion

Abstract

When [Ni(CN),IZ-is dissolved in optically active 1,2-propanediol, two circular dichroism bands are observed which can be attributed to electronic transitions in the complex. Based on previous molecular orbital calculations, the relative energy levels of the d orbitals have been determined as d.T:, dy:Canadian Journal of Chemistry, 46, I444 (1968) In the last few years there has been considerable interest in the electronic structures of square planar metal complexes. Much of this interest has been due to the fact that the relative energies of the d orbitals in square planar complexes are not known with certainty, even in compounds of D,, symmetry. Information regarding the ordering of the energy levels of the d orbitals often may be obtained by examining the absorption spectra of the complexes. However, for many of the square planar complexes it has been difficult to observe the bands due to d-d transitions because of very strong overlapping with the charge transfer bands. This is particularly found to be the case when n-bonding ligands such as CN,-are present and as a consequence the d-d absorption bands usually occur only as shoulders in the region of the low energy charge transfer band or are completely hidden.Gray and other workers (1-4) have studied various square planar complexes with cyanide ions and have attempted to determine energy levels from the observed transitions. However, in most cases the peaks due to the d-d transitions were well hidden. We wish to report a study of the [~i(cN),]'-ion which gives further insight into the relative ordering of the energy levels of the molecular orbitals in this type of compound.The study was suggested by a recent paper (5) in which circular dichroism (c.d.) was reported for the [PtC1,I2-ion in optically active 2,3-butanediol. In the region of one of the d-d transitions, a c.d. band was observed and this was attributed to the concentration of the dissymmetric influences of the solvent to the tetragonal (f z and -z) positions of the ion.We have examined the [Ni(CN),I2-complex in a similar optically active solvent (cl-1,2-propanediol) and have found evidence for two c.d. bands. The observed spectra are shown in Fig. I . The bands are quite reproducible for a given set of conditions and remain relatively unchanged over a period of 1 to 2 weeks. Due to very strong absorption by both the solvent and solute, the c.d. maximum for the high energy band could not be obtained. However, it is unquestionable that a second negative c.d. peak does occur and some rounding of the curve at approximately 272 mp is indicated.For [PtCl4I2-, the observed c.d. was attributed to the ' A , , -> 'A,, transition (5). This assignment would correspond to an arrangement of the d-orbitals which is different from that given by Gray and Ballhausen (1). Recently new molecular orbital calculations have been made (6) and the ordering of energy levels in [~t C l , ]~-is now given as d22 < dxz, dyz < dxy < dX2-y2.

Electrochemistry of Mercuric Chloride in Molten Zinc Chloride‐Potassium Chloride Eutectic

“…Since a Hg(I) species is known to exist in molten salts (3)(4)(5), the reduction of mercurous chloride was also studied using chronopotentiometry. Mercurous chloride disproportionates upon dissolution in molten ZnC12-KC1 yielding a black precipitate and a solution which yields well-defined chronopotentiograms.…”

ZINDO Calculations of the Ground State and Electronic Transitions in the Tetracyanonickelate Ion, Ni(CN)42-

“…The tetracyanonickelate ion has generated a great deal of interest over several decades on its own − as well as from being a member of one-dimensional solid-state systems which are of interest with regard to one-dimensional conductivity. − Recent interest in this complex includes cocrystallization with tris(ethylenediamine)nickel(II) and Fe(methylpyridine), one-dimensional ladder structures, simple modeling for more complex systems such as substituted phthalocyanines which are used in photovoltaic devices, and applications as tumor imaging agents . The planar tetracyanometalates are most notable for the dramatic red-shifting and intensity increase of the prominent low-energy charge-transfer transitions, A 1g → A 2u (a 1g (d z 2 ) → a 2u (p z , π*)) and A 1g → E u (e g (d xz , d yz ) → a 2u (p z , π*)), when the planes are subjected to external pressure − or when cocrystallized with various cations to give closer planar stacking. ,− They also have interesting electrical properties. ,, Our eventual goal is to model the spectral perturbations in aggregates of these complexes.…”

Electrochemical Studies on Ag, Fe, and Cu Species in AlCl[sub 3]-NaCl Melts

“…Electrochemical studies of metal/metal ion systems in molten A1C13-a]kali halides have received considerable attention in recent years (1-10). These studies have been carried out almost exclusively in A1Cls-rich melts where, in several cases (11)(12)(13)(14), unusually low oxidation states are stabilized because of the high acidity of the solvent. To our knowledge studies of metal/metal ion systems in NaCl-rich or equimolar chloroaluminate melts, where the greatest change in acidity occurs, have gone unreported.…”