The spontaneous rate of nitrito to nitro isomerization of [(NH3),Co(ONO)]2+ spans two orders of
magnitude for 16 solvents studied. The volume of activation is small and negative (from - 3.5 to
-7 cm3 mol-1) for water, dimethyl sulfoxide, N-methylformamide and sulfolane. Combined with
the observation of negligible competitive solvolysis, and of an isokinetic plot of ΔH‡ against ΔS‡,
this indicates that isomerization is intramolecular in all solvents. The solvent dependence is interpreted
in terms of a dual-parameter equation involving terms for the Lewis basicities (DN) and
Lewis acidities and polarity (ET). By use of this approach both DN and ET of the solvents are shown
to be major contributing factors to reactivity. Further studies on base-catalysed nitrito to nitro
isomerizations reveal mild catalysis by F-, AcO- and Et3N in Me2SO. The metal ions HgZ+, Ag+
and Cd2+ also catalyse the isomerization in water [kHg 1.16 × dm3 mol-1 s-1, kAg 2.85 ×
dm3 mol-1 s-1, kCd 4.4 × 10-5 dm3 mol-1 s-1; ,μ 1.0 M (CIO4-), 25°C]. The lack of competition
by AcO-, NO3- and H2O in the Hg2+-catalysed isomerization reaction also implicates an intramolecular
process for this path. In acetone, the ions Hg2+, Ag+, Cd2+ and Zn2+ catalyse the
isomerization reaction with a rate law of the form
Kobs = Ks + Km[n+]
except for Ag+, where the rate law takes the form
Kobs = (ks + kK[Ag+])/(1 + K[Mn+])
with kAg = kK = 2.11 × dm3 mol-1 s-1, k = 1.74 × 10-4 s-1 and K = 12 ± 1 dm3 mol-1.
The limiting rate is ascribed to a high stability constant for the silver adduct intermediate. The
analogous RhIII and IrIII complexes also exhibit catalysis by Ag+ and Hg2+ in aqueous solution.
Die aus DMF und P‐oxychlorid gebildete Dimethyliminium‐Verbindung addiert sich an das Methylen‐C‐Atom des in dem p‐Co(III)‐Komplex (I) zweizähnig gebundenen Glycinats unter Bildung des als Tetrachlorozinkat‐cl?orid‐Monohydrat isolierten Komplexes (II).
for the two conformers. For 2,3-butanedione, where only the trans conformer was detected, it is possible to obtain only a value for V* (in the harmonic approximation V* = Vi + 4V2 + 9V¡ = 2RTjb2, where is the rms torsional amplitude) and thereby to calculate a value for the torsional frequency v = (2 )~1(&/µ/)1/'! = (2 ir)x( V* j 2µ )1''1 (here µ is the reduced moment of inertia). The results are V* = 11.4 kcal/mol ( = 2.5) and v = 53 cm-1 ( = 6). The latter is in excellent agreement with the reported values3,4 of 52 and 48 cm-1.
The addition of excess glycine ethyl ester to Co{(H2NCH2CH2)3N}(OSMe2)23+ in Me2SO leads to the symmetrical dimeric peroxo ion p,p - [Co( tren )(NH2CH2CO2Et)]2O24+ under mild conditions. The single-crystal X- ray structure of the perchlorate salt is described, and the mechanism for the dimer formation is considered.
A method for unambiguously assigning amine proton and carbon backbone signals, in 'H and "C NMR spectra respectively, is described. It is applied to multidentate amine complexes of cobalt(III), and the method relies upon different exchange rates for the inequivalent amine protons in the diamagnetic complex. Deuteration of the amines leads to both a and @ isotopic shifts in the I3C NMR spectrum, and it is the characteristic isotopomer patterns for an a-carbon which are mirrored in the @-carbon that permit the unequivocal assignments.
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