- Email: [email protected]
Substituent effects on the resonance Raman spectra of bis(dithiobenzil)nickel
Spenrochimico Acre. Vol. Printed m Great Britam
44A.
No
2. pp
209-21
Substituent
05x4-8539 XX $3.00 + 0.00 Pergamon Press plc
I, 198X.
effects on the resonance Raman spectra of bis(dithiobenzil)nickel H. NAKAZUMI ,* H. SHIOZAKI 1-and T. KITAO *
*Department of Applied Chemistry, College of Engineering, University of Osaka Prefecture, Sakai, Osaka 591. Japan and fLaboratory of Leather Technology. Osaka Prefectural Industrial Research Institute, Suita, Osaka 564, Japan (Receired 12 March 1987; in final form 26 June 1987; accepted 27 June 1987) Abstract-The influence of substituents on the resonance Raman spectra of bis(p-substituted dithiobenzil)nickels has been examined. The assigned sulfur-nickel stretching vibrations in the complexes appeared in the range 39WlO cm-’ with a shift to higher frequency being observed for the electrondonating substituent. It was found that Raman intensities at vibrations of the benzene ring for ligands excited with a 457.9 nm laser line are about 1.553.0 times larger than with a 514.5 nm laser line. The assignments of electronic transitions in the visible region of the nickel complexes were made on the basis of observed resonance Raman intensity patterns.
INTRODUCTION The structure and chemical properties of the dithiolato nickel complex have been the subject of various investigations [ 141. The first electronic transition of these complexes having 10~ electrons occurs in the near-i.r. region [S]. These complexes are useful as organic functional dyes for optical data storages, due to their near-i.r. absorption characteristics [6, 71. The absorption maxima in the near-i.r. region of bis(dithiobenzil)nickels I are affected by the substituent on the phenyl group, as they involve molecular orbitals extending over the whole molecular system
PI.
spectrometer. Concentrations of approximately lo- 5 mol dm- 3 nickel complexes in dichloromethane were used. Raman spectra were recorded on a Jasco NR-1000 spectrometer. To obtain the resonance Raman spectra of the nickel complexes, the solution was prepared in spectroscopic grade dichloromethane. Concentrations of the nickel complexes were approximately 2.5 x lo-’ moldme3. Each prepared solution, held in a spinning capillary tube, was irradiated with a NEC GLS 3200 arson ion laser emittine a power of 100 mW at 514.5 nm an; helium-neon ion laser emitting a power of 50 mW at 632.8 nm. The 760 cm ’ peak of dichloromethane was used as an internal intensity reference at each excitation wavelength. It was assumed that the Raman scattering of dichloromethane did not undergo appreciable resonance enhancement. The experimental setup permitted the band positions in the Raman spectra to be estimated
The resonance Raman technique has been applied to copper-sulfur complexes [9, lo] and nickel-sulfur complexes [ 111. A metal-sulfur stretching frequency has been assigned to several of these complexes. In this paper, we have applied the resonance Raman technique to the nickel complexes 1 in order to elucidate the substituent effects on their nickel-sulfur stretching frequencies of 1. The resonance Raman evidence for electronic transitions involving sulfur or nickel atom will be described. EXPERIMENTAL The nickel complexes were prepared using previously described procedures [5]. Electronic absorption spectra in the visible region were recorded on a Shimazu UV-265FS
with an accuracy
of + 2 cm-‘.
RESULTS AND DISCUSSION The nickel complexes (1) show intense absorption bands in the visible region (Fig. 1). These include L(ligandkL*, L-M* (nickel), and M-L* transitions of both u and r~ types. Excitation at 514.5 nm of la gave resonance Raman bands at 390 and 138cm-‘. The band at 390 cm-’ is assignable to v(Ni-S) by analogy with the recent assignments available for related systems [ll, 121. The two bands at 283.3 and 335 cm-’ in the resonance Raman spectra of bis(maleonitriledithiolato) complexes of Ni(II) were assigned to the Ni-S stretching vibrations [12]. In the i.r. spectra, the nickel-sulfur stretching frequencies for
la
lb lc Id le
209
x’=X’=H x’=x’=ct x1=X’ =CH, x1=X’ =OCHs Xl-H. X7=N(CHs)r
210
H. NAKAZUMIet al.
the nickel complex appeared at 370 cm- ’ [ 131. The i.r. spectra of la have been reported and a normal coordinate analysis of the ErU and BJU fundamentals has been performed [14]. Low-frequency resonance Raman spectra for various bis(p-substituted dithiobenzilhrickels 1 observed with 514.5 nm laser excitation are summarized in Table 1. Absorption maxima in the near-i.r. region of 1 are sensitive to substitution in the 4-position of the phenyl group. A good linear relationship (I_ = - 42.5~; +861) exists between Hammett’s substituent constants, cr,’, and the 1, of nickel complexes, 1. A more powerfully electron-donating substituent appears at the longer wavelength [8]. The resonance Raman bands are also affected by the substituents. The high-frequency v(Ni-S) peaks of 1 with a more powerfully electron-donating substituent such as NJ-dimethyl amino groups appeared at the higher frequency. This reflects the increase in nickeld-ligand-n orbital overlap. The low-frequency v(Ni-S) peak of le, compared with lb and le, appeared at the slightly higher frequency. The lowest-frequency peaks of 1 are randomly varied by the substituent due to overlap with the solvent band. The observed depolarization ratios (p,) for these peaks with excitation at 514.5 nm were 0.26-0.37, 0.36-0.47 and 0.2CM.44, respectively. Thus, these bands are polarized and assigned to totally symmetric vibrations. The geometry of the nickel complex, la, taken from
a single crystal structure determination, was regularized to give Dlh symmetry [15]. However, the NiS4 component, whichconsisted of four sulfur atoms and a nickel atom, is approximately square-planar. In the square-planar molecules (D&, there are three vibrational modes (AI,, Bzg and Bt,) which are Raman active and the highest frequencies with high intensity belonging to the AI,-mode [16,17]. Thus, the normal mode at the high-frequency
1600
700
600
spectra of (a) dichloromethane.
la
and
1400
,200
(b)
le
,000
800
600
400
200
,000
800
600
400
200
(cm-l)
900
(nm)
Fig. 1. Absorption
,200
(cm-‘1
,600
600
500
1400
in
Fig. 2. Resonance Raman Spectra of la and le using excitation at (a) 514.5 nm and (b) 457.9 nm. The bands marked “s” are due to the dichloromethane solvent.
Table 1. Low-frequency resonance Raman spectra of bis(dithiobenzi1) nickel in dichloromethane at 514.5 nm laser line. Relative intensity in parentheses
Compound X No. la lb lc Id le
Raman frequencies (cm - ’ ) v (Ni-S) (high-frequency peak)
H Cl CH, OCH, N(CH,), *The band at 370cm-’
390 392 400 406 410
(1.24) (1.59) (1.56) (1.43) (1.29)
Y(Ni-S) (low-frequency
peak)
_* 358 (0.17) 370 (0.33) 368 (0.91) 378 (3.28)
was observed at an excitation of 457.9 nm.
138 114 126 120 118
(0.52) (0.58) (0.70) (0.86) (0.71)
211
Raman spectra of bis(dithiobenzil)nickel v(Ni-S) peak shown in Table 1 is assigned to the symmetric stretching vibration belonging to the Al,mode. The other fundamental modes are the BQ- and I?,,-mode which correspond to an out-of-plane stretching vibration and planar bending vibration, respectively. The low-frequency v (NIX) peak may be assigned to the stretching vibration belonging to the B,,-mode. However, the lowest frequency peaks are not assigned, substituted several unsymmetric since in bis(dithiobenzil)nickels this peak disappeared [IS]. In order to study the intensity behavior of a Ni-S vibration resonanced by a transition including sulfur and nickel, we have measured the Raman excitation profile of the 390 cm- ’ vibration in la. The Raman relative intensities of la at 390 cm- ’ excited with the 457.9,476.5,496.5and632.8nmare0.90,1.18,1.24and 1.67, respectively, compared to the value of 1.0 in resonance with the 514.5 nm. These results suggest that some transitions including a nickel or a sulfur were involved in the region of 45&650 nm. According to the EHMO calculation for NiS4C4H4 [S] in this region, two S-M* and two S-K* (from the lone pairs at sulfur atoms to the 7c*orbital) transitions are orbitally allowed or forbidden. Similar transitions are predicted by the INDO calculation [ 193. The bands near 1600,150O and 1400 cm-’ in la are assigned to vibrations of the benzene ring. The higher frequency of the benzene ring stretching (1620 cm- ‘) of le, compared with a corresponding value of 1600 cm- ’ in la was attributed to the greater electrondonating effect of the N,N-dimethyl amino group. These bands became the most intense bands with 457.9 nm irradiation, although in the case of la they barely appeared with excitation at 514.5 nm, as shown in Fig. 2. The enhancement of Raman intensities of le at 1620 and 1410 cm- I is pronounced. For example, the intensity at 1620 cm- ’ for le excited with the 457.9 nm laser line is about 3 times larger than with the 514.5 nm laser line. Similar enhancement of Raman intensities for la at 1600, 1425, and 1160 cm-’ was observed. However, the intensity at 1425 and 1160 cm- I excited with the 457.9 nm laser line is about 1.5 times larger than with the 514.5 laser line. This is caused by a shift to a remarkably longer wavelength of iIn,, in le than la, as shown in Fig. 1. Significant intensification benzene
of
resonance
ring stretching
a transition
including
moiety
contributes
signed
transitions
Raman
vibrations n-type below
or
in NiS4C4H4
spectra
suggests MOs near
in the 450 nm.
below
in
the
that at least benzene The
as-
450 nm
are
M-n*, n-n*, and S-n* transitions, which are orbitally allowed. Most of the allowed transitions involve excitation to the LUMO 3b2, (Lt) orbital. Assigned transitions in la can be made on the basis of the resonance Raman spectra for 1 and an analogy with the MO calculations available for NiS4C4H, [S, 193 and related compounds [20]. The strong absorption at 860nm is assigned to a ligand Z--R* transition, the broad band observed at 600 nm to a S-M* transition, and the band below 450 nm involves M-n*, n--71*, and S-R* transitions. Acknowledgements-This work was partially supported by a Grant-in-Aid for Developmental Scientific Research from the Ministry of Education in Japan. REFERENCES
Cl1 G. N. SCHRAUZER, Act. Chem. Res. 2, 72 (1969). PI A. ZWEIG and W. A. HENDERSON, J. Pol)?m. Sci., Polym. them. Ed. 13, 717 (1975). c31 N. KURAMOTO and T. KITAO, J. Sot. Dyers Colourisls 98, 334 (1982). M K. ENMANJI, K. TAKAHASHIand H. KUSAKAWA, Nippon Kagaku Kaishi 592 (1983). CSI G. N. SCHRAUZER and V. P. MAYWEG, J. Am. them. Sot. 87, 1483 (1965); ibid., 87, 3585 (1965).
C61 TDK carp., Japan Kokai Tokkyo Koho JP 59-83695 (1984). c71 Mitubishi Electronic Corp. Japan Kokai Tokkyo Koho, 55-39340
PI
(1980).
_
-
H. SHIOZAKI. H. NAKAZLIM~and T. KITAO, J. Sot. Dyers Colourists, sibmitted for publication.
c91 0. SIIMAN and J. FRESCO,~lnorg. Chem. 8, 1846 (1969). Cl01 N. S. FERRIS. W. H. WOODRUFF,D. B. RORABACHER.T. E. JONES~~~ L. A. OCHRYMOWYCZ, J. Am. them. Sot. 100, 5939 (1978).
Cl11 0. SIIMAN and R. CALLAHAN, Conf. Int. Spectrosc. Raman, 7th, Abstr., 328, 1980. Cl21 R. J. H. CLARK and P. C. TURTLE, J. them. Sot. Dalton 2142 (1977).
[I31 C. W. SCHLAPFER and K. NAKAMOTO, lnorg. Chem. 14, 1338 (1975).
Cl41 J. M. BURKE and J. P. FACKLER, Inorg. Chem. 11,3000 (1972).
1151 D. SARTAIN~~~ M. R. TRUTER, J. them. Sot. A 1264 (1967).
Cl61 K. NAKAMOTO, Infrared and Raman Spectra of Inorganic and Coordination Compounds, p. 147. Wiley, New York (1978).
Cl71 H. STAMMREICH and R. FORNERIS, Spectrochim. Acta 16, 363 (1960). data. Cl81 Unpublished Cl91 Z. S. HERMAN, R. F. KIRCHNER, G. H. LOEW, U. T. MULLER-WESTERHOFF, A. NAZZAL and M. C. ZERNER, Inorg. Chem. 21, 46 (1982). PO1 R. CZERNUSZEWICZ,D. STROMMEN and K. NAKAMOTO, Inorg. Chim. Acta 34, L211 (1979).
44A.
No
2. pp
209-21
Substituent
05x4-8539 XX $3.00 + 0.00 Pergamon Press plc
I, 198X.
effects on the resonance Raman spectra of bis(dithiobenzil)nickel H. NAKAZUMI ,* H. SHIOZAKI 1-and T. KITAO *
*Department of Applied Chemistry, College of Engineering, University of Osaka Prefecture, Sakai, Osaka 591. Japan and fLaboratory of Leather Technology. Osaka Prefectural Industrial Research Institute, Suita, Osaka 564, Japan (Receired 12 March 1987; in final form 26 June 1987; accepted 27 June 1987) Abstract-The influence of substituents on the resonance Raman spectra of bis(p-substituted dithiobenzil)nickels has been examined. The assigned sulfur-nickel stretching vibrations in the complexes appeared in the range 39WlO cm-’ with a shift to higher frequency being observed for the electrondonating substituent. It was found that Raman intensities at vibrations of the benzene ring for ligands excited with a 457.9 nm laser line are about 1.553.0 times larger than with a 514.5 nm laser line. The assignments of electronic transitions in the visible region of the nickel complexes were made on the basis of observed resonance Raman intensity patterns.
INTRODUCTION The structure and chemical properties of the dithiolato nickel complex have been the subject of various investigations [ 141. The first electronic transition of these complexes having 10~ electrons occurs in the near-i.r. region [S]. These complexes are useful as organic functional dyes for optical data storages, due to their near-i.r. absorption characteristics [6, 71. The absorption maxima in the near-i.r. region of bis(dithiobenzil)nickels I are affected by the substituent on the phenyl group, as they involve molecular orbitals extending over the whole molecular system
PI.
spectrometer. Concentrations of approximately lo- 5 mol dm- 3 nickel complexes in dichloromethane were used. Raman spectra were recorded on a Jasco NR-1000 spectrometer. To obtain the resonance Raman spectra of the nickel complexes, the solution was prepared in spectroscopic grade dichloromethane. Concentrations of the nickel complexes were approximately 2.5 x lo-’ moldme3. Each prepared solution, held in a spinning capillary tube, was irradiated with a NEC GLS 3200 arson ion laser emittine a power of 100 mW at 514.5 nm an; helium-neon ion laser emitting a power of 50 mW at 632.8 nm. The 760 cm ’ peak of dichloromethane was used as an internal intensity reference at each excitation wavelength. It was assumed that the Raman scattering of dichloromethane did not undergo appreciable resonance enhancement. The experimental setup permitted the band positions in the Raman spectra to be estimated
The resonance Raman technique has been applied to copper-sulfur complexes [9, lo] and nickel-sulfur complexes [ 111. A metal-sulfur stretching frequency has been assigned to several of these complexes. In this paper, we have applied the resonance Raman technique to the nickel complexes 1 in order to elucidate the substituent effects on their nickel-sulfur stretching frequencies of 1. The resonance Raman evidence for electronic transitions involving sulfur or nickel atom will be described. EXPERIMENTAL The nickel complexes were prepared using previously described procedures [5]. Electronic absorption spectra in the visible region were recorded on a Shimazu UV-265FS
with an accuracy
of + 2 cm-‘.
RESULTS AND DISCUSSION The nickel complexes (1) show intense absorption bands in the visible region (Fig. 1). These include L(ligandkL*, L-M* (nickel), and M-L* transitions of both u and r~ types. Excitation at 514.5 nm of la gave resonance Raman bands at 390 and 138cm-‘. The band at 390 cm-’ is assignable to v(Ni-S) by analogy with the recent assignments available for related systems [ll, 121. The two bands at 283.3 and 335 cm-’ in the resonance Raman spectra of bis(maleonitriledithiolato) complexes of Ni(II) were assigned to the Ni-S stretching vibrations [12]. In the i.r. spectra, the nickel-sulfur stretching frequencies for
la
lb lc Id le
209
x’=X’=H x’=x’=ct x1=X’ =CH, x1=X’ =OCHs Xl-H. X7=N(CHs)r
210
H. NAKAZUMIet al.
the nickel complex appeared at 370 cm- ’ [ 131. The i.r. spectra of la have been reported and a normal coordinate analysis of the ErU and BJU fundamentals has been performed [14]. Low-frequency resonance Raman spectra for various bis(p-substituted dithiobenzilhrickels 1 observed with 514.5 nm laser excitation are summarized in Table 1. Absorption maxima in the near-i.r. region of 1 are sensitive to substitution in the 4-position of the phenyl group. A good linear relationship (I_ = - 42.5~; +861) exists between Hammett’s substituent constants, cr,’, and the 1, of nickel complexes, 1. A more powerfully electron-donating substituent appears at the longer wavelength [8]. The resonance Raman bands are also affected by the substituents. The high-frequency v(Ni-S) peaks of 1 with a more powerfully electron-donating substituent such as NJ-dimethyl amino groups appeared at the higher frequency. This reflects the increase in nickeld-ligand-n orbital overlap. The low-frequency v(Ni-S) peak of le, compared with lb and le, appeared at the slightly higher frequency. The lowest-frequency peaks of 1 are randomly varied by the substituent due to overlap with the solvent band. The observed depolarization ratios (p,) for these peaks with excitation at 514.5 nm were 0.26-0.37, 0.36-0.47 and 0.2CM.44, respectively. Thus, these bands are polarized and assigned to totally symmetric vibrations. The geometry of the nickel complex, la, taken from
a single crystal structure determination, was regularized to give Dlh symmetry [15]. However, the NiS4 component, whichconsisted of four sulfur atoms and a nickel atom, is approximately square-planar. In the square-planar molecules (D&, there are three vibrational modes (AI,, Bzg and Bt,) which are Raman active and the highest frequencies with high intensity belonging to the AI,-mode [16,17]. Thus, the normal mode at the high-frequency
1600
700
600
spectra of (a) dichloromethane.
la
and
1400
,200
(b)
le
,000
800
600
400
200
,000
800
600
400
200
(cm-l)
900
(nm)
Fig. 1. Absorption
,200
(cm-‘1
,600
600
500
1400
in
Fig. 2. Resonance Raman Spectra of la and le using excitation at (a) 514.5 nm and (b) 457.9 nm. The bands marked “s” are due to the dichloromethane solvent.
Table 1. Low-frequency resonance Raman spectra of bis(dithiobenzi1) nickel in dichloromethane at 514.5 nm laser line. Relative intensity in parentheses
Compound X No. la lb lc Id le
Raman frequencies (cm - ’ ) v (Ni-S) (high-frequency peak)
H Cl CH, OCH, N(CH,), *The band at 370cm-’
390 392 400 406 410
(1.24) (1.59) (1.56) (1.43) (1.29)
Y(Ni-S) (low-frequency
peak)
_* 358 (0.17) 370 (0.33) 368 (0.91) 378 (3.28)
was observed at an excitation of 457.9 nm.
138 114 126 120 118
(0.52) (0.58) (0.70) (0.86) (0.71)
211
Raman spectra of bis(dithiobenzil)nickel v(Ni-S) peak shown in Table 1 is assigned to the symmetric stretching vibration belonging to the Al,mode. The other fundamental modes are the BQ- and I?,,-mode which correspond to an out-of-plane stretching vibration and planar bending vibration, respectively. The low-frequency v (NIX) peak may be assigned to the stretching vibration belonging to the B,,-mode. However, the lowest frequency peaks are not assigned, substituted several unsymmetric since in bis(dithiobenzil)nickels this peak disappeared [IS]. In order to study the intensity behavior of a Ni-S vibration resonanced by a transition including sulfur and nickel, we have measured the Raman excitation profile of the 390 cm- ’ vibration in la. The Raman relative intensities of la at 390 cm- ’ excited with the 457.9,476.5,496.5and632.8nmare0.90,1.18,1.24and 1.67, respectively, compared to the value of 1.0 in resonance with the 514.5 nm. These results suggest that some transitions including a nickel or a sulfur were involved in the region of 45&650 nm. According to the EHMO calculation for NiS4C4H4 [S] in this region, two S-M* and two S-K* (from the lone pairs at sulfur atoms to the 7c*orbital) transitions are orbitally allowed or forbidden. Similar transitions are predicted by the INDO calculation [ 193. The bands near 1600,150O and 1400 cm-’ in la are assigned to vibrations of the benzene ring. The higher frequency of the benzene ring stretching (1620 cm- ‘) of le, compared with a corresponding value of 1600 cm- ’ in la was attributed to the greater electrondonating effect of the N,N-dimethyl amino group. These bands became the most intense bands with 457.9 nm irradiation, although in the case of la they barely appeared with excitation at 514.5 nm, as shown in Fig. 2. The enhancement of Raman intensities of le at 1620 and 1410 cm- I is pronounced. For example, the intensity at 1620 cm- ’ for le excited with the 457.9 nm laser line is about 3 times larger than with the 514.5 nm laser line. Similar enhancement of Raman intensities for la at 1600, 1425, and 1160 cm-’ was observed. However, the intensity at 1425 and 1160 cm- I excited with the 457.9 nm laser line is about 1.5 times larger than with the 514.5 laser line. This is caused by a shift to a remarkably longer wavelength of iIn,, in le than la, as shown in Fig. 1. Significant intensification benzene
of
resonance
ring stretching
a transition
including
moiety
contributes
signed
transitions
Raman
vibrations n-type below
or
in NiS4C4H4
spectra
suggests MOs near
in the 450 nm.
below
in
the
that at least benzene The
as-
450 nm
are
M-n*, n-n*, and S-n* transitions, which are orbitally allowed. Most of the allowed transitions involve excitation to the LUMO 3b2, (Lt) orbital. Assigned transitions in la can be made on the basis of the resonance Raman spectra for 1 and an analogy with the MO calculations available for NiS4C4H, [S, 193 and related compounds [20]. The strong absorption at 860nm is assigned to a ligand Z--R* transition, the broad band observed at 600 nm to a S-M* transition, and the band below 450 nm involves M-n*, n--71*, and S-R* transitions. Acknowledgements-This work was partially supported by a Grant-in-Aid for Developmental Scientific Research from the Ministry of Education in Japan. REFERENCES
Cl1 G. N. SCHRAUZER, Act. Chem. Res. 2, 72 (1969). PI A. ZWEIG and W. A. HENDERSON, J. Pol)?m. Sci., Polym. them. Ed. 13, 717 (1975). c31 N. KURAMOTO and T. KITAO, J. Sot. Dyers Colourisls 98, 334 (1982). M K. ENMANJI, K. TAKAHASHIand H. KUSAKAWA, Nippon Kagaku Kaishi 592 (1983). CSI G. N. SCHRAUZER and V. P. MAYWEG, J. Am. them. Sot. 87, 1483 (1965); ibid., 87, 3585 (1965).
C61 TDK carp., Japan Kokai Tokkyo Koho JP 59-83695 (1984). c71 Mitubishi Electronic Corp. Japan Kokai Tokkyo Koho, 55-39340
PI
(1980).
_
-
H. SHIOZAKI. H. NAKAZLIM~and T. KITAO, J. Sot. Dyers Colourists, sibmitted for publication.
c91 0. SIIMAN and J. FRESCO,~lnorg. Chem. 8, 1846 (1969). Cl01 N. S. FERRIS. W. H. WOODRUFF,D. B. RORABACHER.T. E. JONES~~~ L. A. OCHRYMOWYCZ, J. Am. them. Sot. 100, 5939 (1978).
Cl11 0. SIIMAN and R. CALLAHAN, Conf. Int. Spectrosc. Raman, 7th, Abstr., 328, 1980. Cl21 R. J. H. CLARK and P. C. TURTLE, J. them. Sot. Dalton 2142 (1977).
[I31 C. W. SCHLAPFER and K. NAKAMOTO, lnorg. Chem. 14, 1338 (1975).
Cl41 J. M. BURKE and J. P. FACKLER, Inorg. Chem. 11,3000 (1972).
1151 D. SARTAIN~~~ M. R. TRUTER, J. them. Sot. A 1264 (1967).
Cl61 K. NAKAMOTO, Infrared and Raman Spectra of Inorganic and Coordination Compounds, p. 147. Wiley, New York (1978).
Cl71 H. STAMMREICH and R. FORNERIS, Spectrochim. Acta 16, 363 (1960). data. Cl81 Unpublished Cl91 Z. S. HERMAN, R. F. KIRCHNER, G. H. LOEW, U. T. MULLER-WESTERHOFF, A. NAZZAL and M. C. ZERNER, Inorg. Chem. 21, 46 (1982). PO1 R. CZERNUSZEWICZ,D. STROMMEN and K. NAKAMOTO, Inorg. Chim. Acta 34, L211 (1979).