Specfrochimica
Ado,
0584-8539/81/
[email protected]/0 @ 1981Pergamon PressLtd.
Vol. 37A. No. 9. pp. 71 l-719, 1981.
Printedin GreatBritain
Vibrational spectral study of ZrCL and HfCL complexes with acetonitrile and acetonitrile4 YOSHIYUKI HASE and OSWALDO L. ALVES Instituto de Quimica, Universidade Estadual de Campinas, C.P. 1170, 13100 Campinas, SP, Brasil (Received
20 January
1981)
Abstract-The Raman and i.r. spectral data of the addition compounds of ZrCI, and HICI, with acetonitrile and acetonitrile-dx have been investigated for the polycrystalline samples. A detailed vibrational assignment of the observed bands above 2OOcm-’ has suggested to these complexes a cis-configuration with two non-equivalent ligands. The normal coordinate calculations have been performed using modified Urey-Bradley force field to obtain the force constants and potential energy distribution.
INTRODUCTION
The CrN bond stretching vibration for acetonitrile molecule is known to be in Fermi resonance with the combination band between the CH, symmetric bending and C-C stretching vibrations and this Fermi interaction is, of course, absent in acetonitrile-&[1,2]. In spite of the characteristic fundamental band shifts due to coordination effects, the CH3CN complexes showed also a Fermi resonating satellite band, which may be attributed to the above combination, to the side of the CrN stretching band[3-101. In the cases of the addition compounds with Tic& and SnC14[7], a new CEN band splitting of about 5 cm-’ was found for both the CHXN and CDXN complexes. A slight ligand fundamental band splitting was further observed for the C-C stretching and CCN linear bending vibrations. On the other hand, only two characteristic bands due to Fermi resonance of about 25 cm-’ were found in the CzN stretching band region of the addition compounds of CH,CN with BF,, BCl,, BBr,, SbFS, SbCI,, NbQ, TaC&, ZnCl,, ZnBr, and ZnI,[3-6,8-101. In the present study, the vibrational analyses are investigated on the Raman and i.r. spectral data found for ZrC1,.2CD,CN, ZrCl.+.2CH,CN, HfC14.2CH,CN and HfC14.2CD3CN and the normal coordinate calculations are performed using the modified Urey-Bradley force field. The molecular structure is discussed by comparing the vibrational spectral data with the selection rules. EXPERIMENTAL The investigated compounds were prepared according to the method described in the literatureIll] and the purities were examined by elemental analyses for Zr, Hf and Cl. The Raman spectra were obtained in the region from 4000 to IOcm- with a Cary 82 spectrometer equipped with an argon ion laser in which the 488.0 and 514.5 nm lines were used for excitation. The samples were in the form of polycrystalline powder in capillary cells. SAA Vol. 37A. No. 9-A
The i.r. spectra of the polycrystalline samples were recorded in the 4000-180cm-’ region for nujol and fluorolube mulls between two CsI or polyethylene plates, on a Perkin-Elmer IR 180 spectrophotometer. All sample manipulations were carried out in a dry box.
RESULTSAND DISCUSSION
The vibrational spectral data experimentally observed for ZrCl+2CHaCN and ZrC1+2CD,CN with the aid of Raman and i.r. spectroscopy are summarized in Table 1, together with the band assignment, and those for HfC14.2CH,CN and HfC14.2CDSCN in Table 2. An octahedral coordination compound of the formula MC&L2 exhibits cis-trans isomerism. Since the truns-isomer possesses a center of inversion on the central metal atom and belongs to DAh point group on a point mass assumption for the methyl groups, the Raman-i.r. mutual exclusion rule is expected to be effective. On the other hand, the &-isomer belongs to C,, point group which gives the coincident Raman and i.r. bands for most of the fundamentals and the ligand vibrations may show band splittings in this force field. To facilitate the vibrational analyses, the band assignment is carried out separately to the ligand vibrations and to the skeletal vibrations. Among the ligand fundamentals, the CH, stretching, bending and rocking bands are considerably affected by deuteration. Indeed, the bands observed at about 2995,2930,1395,1355 and 1020cm-’ are attributable to the CH, fundamentals and the corresponding CD3 bands are found at about 2225,2105, 1020, 1090 and 843 cm-‘, respectively. This band assignment can be supported by comparing with that for free CH,CN and CD,CN[l, 21. To explain the irregular isotope effect on the CH, and CD, symmetric bending bands, a mechanical coupling between the CD, symmetric bending and C-C stretching modes must be taken into consideration. This mode mix711
Y. HASE and 0. L. ALVES
712 Table
1. Vibrational
spectral
data (cm-‘)
for ZrCl,.2CH$ZN and ZrC1,.2CD&N
ZrCl4.2CD3CN
ZrClq.2CH3CN
Assignment
I. r.
Raman
Raman
1.r.
2997 w
2994 w
CH3
asym.
2933
2933 w,sh
CH3
sym.
5
2920“3 2312
s
2305
s
2928
s
2313 2306
5 s
s
2277
s
2286 2278
1393 m
1358 In
1360
m
1356 m
1356
5
VW
412 w
1022
s
947 937
5
405 w 396
395 m
CSN
stretch asym.
2107 s 2104 5
2108 2104
s s
CD3
sym.
CHj
asym.
CH3
sym.
bend
CDg
sym.
bend
CH3
rock
1093
VW
1018 m
asym. stretch
C-C
stretch
844
m
CD3
rock
CCN
bend
CCN
bend
383 w,sh 378 w,sh
357 S
352
vs,br
337 w
Zr-Cl'
asym.stretch
Zr-Cl'
sym.
zr-CI"
asym.
Zr-cl"
sym.
314 w 238
242 w
236 w
236 w
Zr-N
sym.
214
Zr-N
asym.
220 VW
215 VW 179 VW
145 m
145 m
121 s
121 S
96 m,br
97 m,br
67
67 VW
VW
52 w
S
VW
stretch stretch stretch
stretch stretch
185 m
196 m VW
bend
s s
311
180
bend
CD3
314 w
VW
stretch
C-C
312 s
220
stretch
857 851
375 w 353 vs,br
336 w
w
(Fr)
CD3
m m
375 w s
stretch
m m
385 w,sh 380 w
357
C%N
5
411 402
w
s
2249 2200
1020 VW 948 w 937w
s
2293
(Fr)
2249 m 2200 m
1093 w 1020
2301
5 s
1397 w
stretch
combination
2300 s 2292 “S 2284
stretch
ZrCl,,N? bend
ZrNC
bend
53 w
38 5
39 S
24 s
24 s
16 s
16 s
lattice
vibrations
The following abbreviations have been used: s, strong; m, medium; w, weak; v, very; br, broad; sh, shoulder; Fr, Fermi resonance. ing results also a slight isotope wavenumber shift on the C-C stretching band. The observed band position is about 94Ocm-’ for the CH,CN complexes and about 855cm-’ for the CD,C!N complexes. On the other hand, the CCN linear bending is mechanically coupled with the CDS rocking mode and the fundamental band at about 400 cm-’ is shifted to about 380 cm-’ upon deuteration. The CnN stretching band is undoubtedly found at about 23OOcm-’ for the CD&N complexes, while that for the CH3CN complexes is in Fermi
resonance with the combination between the CH, symmetric bending and C-C stretching modes. The resulting bands are found at about 2310 and 2280cm-‘. The Fermi resonance corrected C=N bond stretching wavenumbers are quite comparable with the fundamental wavenumbers observed on the CD,CN complexes. As easily seen in Tables 1 and 2, the most of the ligand fundamentals give slight band splittings due to intramolecular or intermolecular interaction between two ligand molecules or due to two non-equivalent ligand molecules. Taking into
Study of ZrCld and HfC1, complexes with acetonitrile and acetonitrile-d3
71:
Table 2. Vibrational spectral data (cm-‘) for HfCIe2CH3CN and HfC1,.2CQCN HfCl4.2CH3CN
HfCl4.2CD3CN Assignment
Raman
I.r.
Raman
2998 w
2996 w
2933 5
2933 s
2928
ys
29285
2314
s
2307
s
2315 2307
5 s
5
2279
s
2287 2280
f vs
VW
1398 m
1358
m
1359
5
1356 m
1355
5
VW
1021
s
943 940
s 5
415 w 408 m
413 m 405 m
398
396 m
VW
s
" m
2248
m
2197
m
2107 2103
s s
2108 2104
5 s
1020 351 w 342 w
s
2295
2249 2198
1030 w 1020
2302
5 s
1398
CH3
asym.
CH3
sym.
stretch stretch
combination 2304 2235
2285
1.r.
VW
lo89
VW
lole m
::z
m
a57 851
842
VW
844 m,sh
385 w,sh 375 w
s 5
384 w 373 w
(Fr)
CcN
stretch
EN
stretch
CO3
asym.
CO3
sym.
CH3
asym.
(FF) stretch
stretch bend
CHx
sym.
bend
CD3
sym.
bend
CH3
rock
CD3
asym.
C-C
stretch
bend
C-C
stretch
CD3
rock
CCN
bend
CCN
bend
363
VW
351
s
j51
vs
350
s
350
vs,br
Hf-Cl'
asym.stretch sym.stretch
330
w,sh
w,sh
Hf-Cl'
365 VW
332
vs,br
330
330 vs,br
Hf-Cl"
asym.
310 w
310
vs,br
311 w
310
Hf-Cl"
sym.
233
VW
241
w
238
VW
235 w
Hf-N
sym.
221
VW
223
VW
220
VW
219 w
Hf-N
asym.
203
m
stretch stretch
stretch stretch
194 m
130 VW
lea VW
142 m
144 m
125 s
125 s
101 m,br
102 m,br
70 WJ
70 VW
52 w
54 w
37 s
37 5
21 5
21 s
14 s
14 s
For abbreviations,
"S
HfCl,,Na bend
HfNC
bend
lattice
vibrations
see footnote to Table I.
account the vibrational spectral data for the zinc halide complexes with CH,CN and CD,CN[8,9], the latter term seems to be more reasonable to explain the band separations of about 5cm-‘. The symmetry lowering of the ligand by coordination can not be accepted as the first factor because the non-degenerate fundamentals of ligand vibration also show the band splittings. The typical band splitting in the CEN stretching region is illustrated in Fig. 1. According to the selection rules derived on MC&L, skeletal vibrations, two Raman and one i.r.
active M-Cl stretching fundamentals are expected for the trnns-isomer, while the &-isomer should have four M-Cl stretching fundamentals active in both the Raman and i.r. spectra. A recent study for TiCl+2CH,CN, TiC14.2CD3CN, SnC14.2CH3CN and SnC1+2CD,CN showed that the M-Cl stretching bands for these complexes were easily distinguished from other skeletal vibrations and were found in the same wavenumber region with those for MCI, and MC&‘[7]. Consequently, taking into account the fundamentals for ZrC14, ZrCl;‘, HfC& and HfCl;z[12-15], the Zr-Cl and Hf-Cl stretching
Y. HASE and 0. L. ALVES
714
2310
2270cm-' 2310 I
2270 I
I
2310
I
I
2270
I
~
-(b)-
I
I
2310
I
I
1
2270
2310
-(c)--
I
I
b I
2270
cm-1
Fig. 1. The Raman
and i.r. spectra
-kO--
2310
in the region
2270
I
2310
of the C=N stretching
I
2270
vibration
for (a)
ZrC14.2CHSCN,(b) ZrCl,.2CD,CN, (c) HfCI,.ZCH,CN and (d) HfCl+2CD,CN. bands of the investigating complexes are expected in the 410-240cm-’ and 390-260 cm-’ regions, respectively. As seen in Tables 1 and 2 and also in Fig. 2, the four bands of the ZrCl, complexes at about 375, 355,336 and 312 cm-’ are attributable to the Zr-Cl stretching modes and the four bands of the HfCl., complexes at about 364, 350, 330 and 310cm-’ to the Hf-Cl stretching ones. The fact that four M-Cl stretching bands are found for each complex results a &-configuration for ZrC14.2CH&N, ZrCl.,.2CD,CN, HfCL2CHXN and HfC1.+2CD,CN. The molecular structure is given in Fig. 3. Since the i.r. intense bands at about 312 and 310cm-’ are found to be less sensitive to the central metal elements, these can be assigned to the M-Cl” symmetric stretching mode. The bands at about 355 and 350cm-’ are assigned to the M-Cl’ symmetric stretching mode because of their Raman intensities. On the other hand, the bands at about 375 and 336cm-’ and at about 364 and 330 cm-’ are assigned to the M-Cl’ and M-Cl” asymmetric stretching modes by considering the Pans-influence by CH,CN/CD,CN and Clligands. From the vibrational spectral data previously reported for the metal halide complexes with CH3CN and CDsCN[5-101, the M-N stretching
bands should be weak in both the Raman and i.r. spectra and expected in the 2OOcm-’ region. Therefore, the bands at about 240 and 220 cm-’ are reasonably assigned to the symmetric and asymmetric stretching modes, respectively. The skeletal bending and MNC linear bending bands are found in the region below 220cm-’ and are assigned rather tentatively by comparing with the corresponding fundamental bands of the TiCI., and SnCI, complexes[7] and by taking the results of the normal coordinate calculations into consideration. Below 90cm-‘, there are five Raman bands for each complex. The observed wavenumbers are about 67,52,38,24 and 16 cm-’ for,ZrCl,.2CHXN and ZrC14.2CD3CN and about 70, 53, 37, 21 and 14 cm-’ for HfC1.+2CH,CN and HfCL2CDJJN. Since no bands show characteristic wavenumber shifts upon deuteration, these bands are attributed to the fundamental and combination modes of the lattice vibrations.
NORMAL COORDINATE
ANALYSIS
The normal coordinate calculations were performed on the basis of &-configuration by application of Wilson’s GF matrix method 1161. In the
Study of ZrCL and HfCh complexes with acetonitrile and acetonitrile-d, 360 I
I
320 I
366 I
320 lrn-' 360 I
1
I60
320
320
I
I
I
360 I
I
;‘,. L -09
t
I
-
I
320 I
-_(d)-
1
1
360
I
I
I
320
360
8
Fig. 2. The Raman and i.r. spectra in the region of the M-Cl stretching ZrCl,.2CH,CN,
715
(b) ZrCl,.2CDJ!N,
I
320
vibration (c) HfC&.2CH&N and (d) HfC&.2CD$N.
Fig. 3. The structure of MCl,.2CXpCN (M = Zr and Hf; X=HandD).
absence of structural data, the molecular parameters were assumed to be the same as for SnC1,.2CH3CN[17], except for r(Zr-N) = r(HfN) = 2.33 A and r(Zr-Cl) = r(Hf-Cl) = 2.34 A. A modified Urey-Bradley force field with two stretch-stretch truns-interaction force constants, I(M-N, M-Cl’) and I(M-Cl”, M-Cl”), was assumed in this study and the defined force constants were refined by the least squares procedure[lS, 191 to reproduce the observed fundamental wavenumbers.
for (a)
The numerical calculations were carried out for the internal symmetry coordinates, whose numbering and approximate description are summarized in Table 3, with a set of computer programs [20], using an electronic computer PDP10 at the Centro de Computacao Eletronica of the Universidade Estadual de Campinas. The final set of force constants listed in Table 4 gives satisfactory agreements between the observed and calculated fundamental wavenumbers and the calculated potential energy distribution gave support, as a whole, to the vibrational band assignment. The calculated wavenumbers and potential energy distribution for ZrC1.,.2CH,CN and ZrC14.2CD3CN are listed in Table 5 and those for HfC14.2CH3CN and HfC14.2CD3CN in Table 6. According to the donor-number defined by Gutmann[21], the basicity of acetonitrile as a solvent is found to be weak in spite of its high polarity. The metal-ligand force constants obtained, K(Zr-N) = 0.890 mdynlk’ and K(HfN) = 0.961 mdyn/k’, are comparable with K(TiN) = 0.794 mdyn/A-’ and K(Sn-N) = 0.668 mdyn/& [7] and these values seem to be reasonable to the coordination bonds[22]. From the results, it is found that the order of increasing
Y. HASE and 0. L. ALVES
716 Table 3. Approximate
CHs/CDs
asymmetric
CH3/CD3
symmetric
C-N
and numbering for symmetry coordinates
stretch stretch
al
a2
bl
b2
Sl
516
526
535 536
S2
stretch
537
S3
CH3/CD3
asymmetric
CH3/CD3
symmetric
CH3/CD3
rock
C-C
description
bend
S4
bend
bend
stretch
s9
M-Cl"
stretch
SIO
S6
stretch
CH3/CD3
bend
skeletal
bend
bend
internal
543 s30 SW!
s13.s14
s22
s31
s451s46
515,516
$23
532
s47
s17
524
533
548
s25
534
rotation
Table 4. Urey-Bradley
542
512
bend
skeletal linear
s29
Sll
skeletal
M-NSC
s21
S40 S41
M-Cl'
Cl-M-Cl
S28
s7
linear
N-M-Cl
SZO
536 $39
s6
stretch
N-H-N
527
55
C-CEN
M-N
s19
force constants (mdyn A-‘) ZrCl4.2CH3CN
HfCl4.2CH3CN
ZrCl4.2CD3CN
HfCl4.2CD3CN
K(M-Cl')
1.726
K(H-Cl")
1.427
1.564
K(H-N)
0.890
0.961
K(ClN)
17.975
17.951
K(C-C)
3.941
3.944
K(C-H/C-D)
4.469
4.465
H(NMN)
0.004
0.003
F(N..N)
D.ZOOt
0.200t
H(NMCI)
0.035
0.054
F(N..Cl)
D.ZOOt
D.ZODt
H(CIMCI)
0.094
0.107
F(CI..Cl)
0.100t
0.1oot
H(CCH/CCD)
0.189
0.183
F(C..H/C..D)
0.618
0.635
H(HCH/D~D)
0.386
0.389
F(H..H/D..D)
0.060
0.057
H(CCN)
D.lOl*
0.103*
H(HNC)
0.101*
0.103*
I (N-N,M-cl')
0.009
0.046
I (H-CI",M-Cl")
0.249
0.104
1.980
*Assumed to be HKCN) = H(MNC). tFrom reference [7]. covalent character is Sn-N < Ti-N < Zr-N < HfN and is contrary with that of increasing electronegativity of the central metal. This fact is explicable by considering the effective positive charge on the metal atom in the MCI, moiety. The weak M-N bond also reflects directly on the values of H(NMN), H(NMCI) and I(M-N. M-W. Since the M-Cl bond of the MCI, complex may be expected, on the basis of electron distribution, to be weaker than that for MCI, free molecule and stronger than that for MCl;’ complex ion, the
M-Cl force constant for the complex molecule should be between the values for MC& and MCI;* as already found for the TiCL and SnCX complexes[7]. Indeed, K(Zr-Cl) = 1.726 and 1.427 mdyn A-’ are smaller than 2.296 mdyn A-’ for ZrCl,[lZ] and larger than 1.023 mdyn A-’ for ZrCla2[23]. The same is also true among K(HfCl) = 1.980 and 1.564 mdyn A-’ for the CH,CN and CDXN complexes, 2.373 mdyn A-’ for HfCI,[12] and l.O57mdynW-’ for HfCl;*[23]. The force constant difference between K(M-Cl’) and K(M-
Study of Z&l, and HfCl, complexes with acetonitrile and acetonitrile-d3
Table 5. Calculated fundamental
wavenumbers and potential energy distribution for ZrC&.2CH,CN and ZrC14.2CD3CN
ZrCl4.2CH3CN ir calcd.
=1
a2
bl
b2
ZrCl4.2CD3CN PED
(%I*
D
PED
calcd.
(%)*
2996
loos,
2296
88S,,lOS,
2931
99s2
2219
YYSl
2292
8753,115~
2099
96s~
1395
YDSS
1086
6255.3557
1350
9255
1001
94s4
1021
8956
858
5457.3055
944
84~
802
94s6
404
49s17,43se
401
5os17,42ss
357
84sg,10s11
357
8559
312
91s10
311
93s10
244
74s11,14510
238
75s11.11s10
220
49512.33s13,11sl3
220
4Ys12,33s13,1ls8
160
46s15,26514S10513.10s16
159
46sl5,26slr,1osl3,1os16
126
34s1~,26s16,23s15
126
35514r27516r23515
106
47517,4osfj
105
47517.4lSz3
2996
!OOSl~
2219
99s1e
1395
9os19
1001
94s19
1021
8Yszo
802
94s20
401
5oszt+r45sz1
398
51sw+,44sz.1
204
8OS22.11%3
204
80522.11523
143
86523
143
86523
107
47s2br4lszl
106
47b,.41s21
2996
100526
2219
YYs26
1395
Y"s27
1001
94527
1021
8%23
802
94528
402
50s,,,~~s,,
399
5os3,.43s,g
336
94s30
336
94s30
215
88S3,
215
84531
162
98~32 4YS,,,44S,,
162
98s,z
107
4YS,,,45S,,
108
717
2996
1oos35
2295
87s,,,los,,
2931
YYs36
2219
99s35
2290
87537,11541
2099
96S36
1395
9os3e
1086
62s,g,34s,, 94s3,
1358
92539
1001
1021
89s40
854
6os41.31sgg
940
85s4,
802
94s40
397
5ls4,,46s,,
394
51s,8,45s,,
373
86S43
372
87s43
216
855,4,10543
210
84544
179
72s4,,14s,7
179
73s,5,14s,7
135
45s47,33s46,11s45
135
45s47,34s4,,11s,,
107
44s4,,38s4,,14s,,
106
44s,,,3Ys,,,13s,,
*Potential energy distribution. Terms below 10% are omitted.
Y. HASEand 0. L.
718
Table
6. Calculated
fundamental
wavenumbers
ALVES
and potential
energy distribution for HfC1,.2CH$N
and HfCl,.2CD3CN HfCl4.2CD3CN
HfCl4.2CH3CN 3
=1
a2
bl
b2
PED
calcd.
(%I*
iJ calcd.
PED
(%)*
2997
loos1
2297
aas3,10s7
2931
99s2
2219
YYS,
2292
875311157
2099
9652
1398
90%
1085
6255,3657
1357
9256
1003
9454
1021
89s6
862
54
948
a4s7
802
94j6
407
49S17.4356
405
5OS17,42S6
353
9659
353
96s9
310
9'510
309
93SlO
243
76s11,12slo
236
69s11
223
43s12,3as13.13s11
222
36s12,3Os13,2Os11
155
46515,25514
154
46515.25514
131
37S11+,27516,2ls16
131
38514,28516,21515
106
4as,,,41s,
105
48S17.4256
7,3055
2997
lOOS1a
2219
99S16
1398
9OS19
1003
94519
1021
89S20
802
94szo
405
5osz1+,45sz1
402
s~sz~,43%1
215
8lszz,lOs23
214
81s
149
87sz3
149
87s23
107
48szk,42s21
106
48szk,43sz1
2Z.:Os23
2997
loos26
2219
99s26
1398
9os27
1003
94%~
1021
89%
802
406
%,,,44s,g
403
5os33,43sz9
331
97s30
331
97s30
222
86S31
222
86S31
160
9as32
160
98s32
108
49s33r44S29
lo7
49s33,45sz9 8753?,lOS41
94s~
2997
100536
2295
2931
99S36
2219
99535
2290
87s37111541
2098
96s~
1398
90538
1084
62539.35541
1357
92s 39
1003
94S38
1021
90540
859
6Os41r3ls39
944
8ss41
802
94540
401
5ls~,46s42
397
5ls48,4%2
362
94s43
361
94s43
220
87sh4
212
87s44
178
76% s
178
77545
139
52sti7,38Sb6
138
52s47,38s46
108
46s~r41s~r1ls,+6
107
46546,42~42,11~4~
*See footnote to Table 5.
Study of Z&l,
and HfCl, complexes with acetonitrile and acetonitrile-dl
Cl”) is attributable to trans-influence by CH&N/CD$N and Cl. The ratios K(MCl’)/K(M-Cl”) are found to be almost constant and the values are 1.14, 1.16, 1.21 and 1.27 for the SnCl.+ TiCl,, ZrCL and HfCl, complexes, respectively. The ligand force constants obtained for the ZrCl, and HfCl, complexes are not essentially different by comparison with those for the TiCL and SnCI, complexes 171. Acknowledgements-The authors would like to thank Prof. K. KAWAI of the Toyama University for donating ZrC& and HfCl,. Y. H. wishes to acknowledge the Conselho National de Desenvolvimento Cientifico e Tecnol6gico (CNPq) for his research fellowship. REFERENCES [l]
[2] [3] [4] [5]
E. L. PACE and L. J. NOE, J. Chem. Phys. 49, 5317 (1968). M. P. MARZ~CCHI and M. G. MIGLIORINI, Spectrochim. Acta 29A, 1643 (1973). B. SWANSON and D. F. SHRIVER, Znorg. Chem. 9, 1406 (1970). D. F. SHRIVER and B. SWANSON, Znorg. Chem. 10, 1354 (1971). D. M. BYLER and D. F. SHRIVER, Znorg. Chem. 12,
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HASE, C. AIROLDI, Y. GUSHIKEM and Y. KAWANO, Spectrosc. Lett. 9, 105 (1976). [9] Y. HASE, C. AIROLDI, Y. GUSHIKEM and Y. KAWANO, Spectrosc. Lett. 9, 177 (1976). 1101 Y. HASE, 0. L. ALVES and I. V. P. YOSHIDA, An.
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