2 Homometallic Alkoxides

96 Alkoxo and Aryloxo Derivatives of Metals
thus interpreted in terms of an octahedrally coordinated cobalt(II) configuration in
cobalt dimethoxide. The diffuse reflectance spectrum of cobalt chloride methoxide595 showed bands at 7300 cm 1 assigned to the 4 4 T1⊲F⊳ A2g transition and at 15 200,
17 600, and 18 900, all being assigned to split 4 4 T1⊲P⊳ A2 transitions. Taking the
value of 17 200 cm 1 , the average energy in this complex band gave the calculated
values of 10 Dq D 4250 cm 1 and the Racah parameter B D 785 cm 1 which are
comparable with the values observed for the CoCl4 2 ion (10 Dq D 3200 cm 1 and B D
715 cm 1 ). 596 The higher values obtained for the chloride methoxide as compared with
the CoCl4 2 ion may be attributed to the positions of methoxide ion and chloride ion in
the spectrochemical series since the methoxide is at higher energy than the chloride. The
above spectral data were consistent with the tetrahedral coordination of the Co(II) ion.
The spectrum of cobalt bromide methoxide was also consistent with the tetrahedral
configuration; however, on solvation with methanol to form CoBr(OMe).2MeOH
a change from intense blue to pink with corresponding changes in the reflectance
spectrum revealed a change in structure from tetrahedral to octahedral. 595
The diffuse reflectance spectrum of cobalt iodide methoxide was rather complex and
showed a large charge transfer band in the visible region. However, some discontinuity
was observed around 16 000 and 18 000 cm 1 4 whichwasassignedtoa4T1⊲P⊳ A2
transition superimposed on the charge transfer edge.
The reflectance spectrum of the d8 nickel dimethoxide showed bands at 8700,
14 500, and 25 000 cm 1 whichwereassignedto2 2 T2g⊲F⊳ A2g⊲F⊳, 3 3 T1g⊲F⊳ A2g,
and 3 3 TIg⊲P⊳ A2g transitions, respectively. 219 The bands are in good agreement
with the octahedral nickel(II) involving MO6 configuration. Nickel monochloride
monomethoxide also exhibits three bands at 7900, 12 900 and 22 100 cm 1 with the
ligand field parameter Dq D 790 and Racah parameter B D 870 in its reflectance
spectrum which are consistent with octahedral geometry for the nickel(II) ion
corresponding to 3 3
T2g A2g, 3 3 T1g⊲F⊳ A2g, and 3 3 T1g⊲P⊳ A2g transitions,
respectively. 541 The reflectance spectra of various halide alkoxides have also been
measured, and show three bands at about the above positions. It was observed that
in the series NiCl(OMe), NiCl(OMe).MeOH, Ni3Cl2⊲OMe⊳4, andNi3Cl⊲OMe⊳5 the
3 3
T2g A2g transition bands appear at 7900, 8100, 8200, and 8300 cm 1 , respectively
which are consistent with the values 7200 and 8500 cm 1 observed for nickel dichloride
and nickel dimethoxide, respectively. These observations indicate that the 10 Dq values
increased steadily as chloride was replaced by methoxide in the above series.
The diffuse reflectance spectrum of d9 copper dimethoxide showed broad asymmetric
bands with a maximum in the range 13 800–16 000 cm 1 and these bands were assumed
to be due to the 2 2
T2g Eg transition. 542
Karraker597 measured the electronic absorption spectrum of dimeric uranium pentaethoxide
and the weak narrow bands observed at 5405, 5680, 6622, 6934, 10 200,
11 690, and 14 490 cm 1 have been assigned to f–f transitions for a distorted octahedral
f1 system with a spin–orbit coupling constant of 1905 cm 1 .
3.6 Magnetic Susceptibility Measurements
The magnetic properties of metal alkoxides have been studied in some detail for the
first row transition metal alkoxides. Basi and Bradley 334 in 1963 measured the magnetic