Mixed-ligand complexes of tetracyanonickelate(III) and dynamic Jahn-Teller distortions of hexacyanonickelate(III)
Oxidation of Ni/sup II/(CN)/sub 4//sup 2/minus// in aqueous solution gives trans-Ni/sup III/(CN)/sub 4/(H/sub 2/O)/sub 2//sup /minus//, which has labile axial water molecules that are readily replaced by other ligands. Electron paramagnetic resonance (EPR) spectra of frozen aqueous solutions indicate a variety of tetragonally elongated complexes with two equivalent axial donors, where an increase in g/sub av/ values (CN/sup /minus// < NH/sub 3/ < imidazole < N/sub 3//sup /minus// < pyridine < CH/sub 3/CN < Cl/sup /minus// < NCO/sup /minus// < H/sub 2/O) reflects a decrease in axial donor strength. Not all these complexes form in aqueous solution at room temperature, but five-line EPR spectra are seen for bis complexes of NH/sub 3/, imidazole, and pyridine. At 25/degree/C the values for the stepwise stability constants with pyridine are K/sub 1/ /approx equal/ 1 /times/ 10/sup 5/ M/sup /minus/1/ and K/sub 2/ /approx equal/ 4 /times/ 10/sup 2/ M/sup /minus/1/. Excess cyanide gives Ni/sup III/(CN)/sub 6//sup 3/minus//, which has temperature-dependent EPR spectra in frozen aqueous solutions (/minus/220 to /minus/35/degree/C) due to dynamic Jahn-Teller distortions. Studies with /sup 13/CN/sup /minus// confirm the presence of six cyanides around Ni(III). The reduction potential for Ni/sup III/(CN)/sub 4/(H/sub 2/O)/sub 2//sup /minus// is 1.15 V (vs NHE). The complex decomposes with a first-order rate constant of 4.0 /times/ 10/sup /minus/4/ s/sup /minus/1/ (pH 1-3, 25.0/degree/C, /mu/ = 0.1, /Delta/H/double dagger/ = 108 kJ mol/sup /minus/1/, /Delta/S/double dagger/ = 51 J mol/sup /minus/1/ K/sup /minus/1/). Base greatly accelerates this redox decomposition (k/sub obsd/ = 0.45 s/sup /minus/1/, /minus/log (H/sup +/) = 11.5, 25.0/degree/C, /mu/ = 0.1, /Delta/H/double dagger/ = 95 kJ mol/sup /minus/1/, /Delta/S/double dagger/ = 69 J mol/sup /minus/1/ K/sup /minus/1/). 38 refs., 7 figs., 9 tabs.
- Research Organization:
- Purdue Univ., West Lafayette, IN (USA)
- OSTI ID:
- 5852818
- Journal Information:
- Inorg. Chem.; (United States), Vol. 27:24
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CYANIDES
OXIDATION
NICKEL COMPLEXES
AQUEOUS SOLUTIONS
CARBON 13
EXPERIMENTAL DATA
JAHN-TELLER EFFECT
LABELLED COMPOUNDS
NICKEL 61
TRACER TECHNIQUES
CARBON ISOTOPES
CHEMICAL REACTIONS
COMPLEXES
DATA
DISPERSIONS
EVEN-ODD NUCLEI
INFORMATION
INTERMEDIATE MASS NUCLEI
ISOTOPE APPLICATIONS
ISOTOPES
LIGHT NUCLEI
MIXTURES
NICKEL ISOTOPES
NUCLEI
NUMERICAL DATA
SOLUTIONS
STABLE ISOTOPES
TRANSITION ELEMENT COMPLEXES
400201* - Chemical & Physicochemical Properties
400202 - Isotope Effects
Isotope Exchange
& Isotope Separation