The crystal and molecular
structures of the compounds [Ni(py)4(ONO)2],2py,
[Ni(γmpy),(ONO)2] and [Ni(prz)4(ONO)2]
are reported.�All three are trans nitrito complexes, the pyridine
(py) compound containing two pyridine molecules of solvation. The aromatic rings
in the first two complexes adopt 'paddle wheel' conformations with pitch angles
varying between 40 and 70�. The nitrite ions are positioned so as to minimize
repulsive interactions with the amines, and it seems likely that these groups
bond through oxygen rather than nitrogen because this allows a lesser degree of
interligand steric interference. The amine rings in [Ni(prz)4(ONO)2]
are orthogonal to the plane containing the nickel and coordinated pyrazole
nitrogen atoms; the nitrito groups are disordered between two inequivalent
positions, each of which involves hydrogen bonding with the pyrazole NH groups.
The nitrite infrared frequencies are similar to those observed for other
nickel(II) nitrito complexes except that the antisymmetric NO stretching mode
of one of the groups in the pyrazole complex is much lower in energy than
expected, being in the range normally associated with a nitrogen-bonded or
chelated nitrite group. It is suggested that this deviation may be caused by
the hydrogen bonding in the complex. The electronic spectra of the compounds
yield 10Dq values of 9100 and 8500 cm-1 for the nitrite ligands in
[Ni(py)4(ONO)2] and Ni(prz)4(ONO)2],
respectively, placing the nitrito group towards the weaker end of the spectro-chemical
series.
The Electronic Spectra and Electronic Structures of the Nitrobenzene and Nitrotoluene Anions
