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The molecular structure of bipyridinium tris(bipyridine)chromium(III) perchlorate
Pdyhedron Vol. 8, No. 12, pp. 1557-M+, F’rinted in Great Britain
1989 0
0277~5387/89 53.00+.00 1989 Fwgamon Rem plc
THE MOLECULAR STRUCTURE OF BIPYRIDINIUM TRIS(BIPYRIDINE)CHROMIUM(III) PERCHLORATE KY&WANG
LEE and PATRICK
E. HOGGARD*
Department of Chemistry, North Dakota State University, Fargo, ND 58105, U.S.A. (Received
17 January 1989 ; accepted 15 February 1989)
Ahstract-[Cr(bpy)3](C10J3 (bpy = 2,2’-bipyridine) cocrystallizes with bipyridinium perchlorate in the triclinic space group PI (No. 2), with a = 13.532(2), b = 16.596(3), c = 10.324(l) A, rx = 92.16(l), /? = 100.92(l), y = 102.76(l)“, Y= 2212.7 A’ and 2 = 2. The structure was refined to R = 0.073 and R, = 0.098. The cocrystallized HbpyC104 may also have been present in earlier preparations, but could have escaped detection because of the similarity in carbon, hydrogen, nitrogen and chlorine percentages, with and without the cocrystallite.
Hauser et al. recently published the crystal structure and low temperature polarized sharp-line absorption spectra for [Cr(bpy)3](PF6)3.’ The space group was reported to be R32, in which by necessity the enantiomers must occupy non-equivalent positions. The differences between the two sites, however, appeared extreme. The N-Cr-N bite angle, for example, was reported as 74.8“ in one site (equal by symmetry for all three rings) and 84.7” in the other. Large differences in other bond lengths and bond angles were also manifest. If this structure is correct it is unique among transition metal chelate complexes. Because the geometry of the tris(bipyridine) chromium(II1) complex is important to the ligand field analysis of the electronic spectra,’ we attempted to repeat the solution of the crystal structure of [Cr(bpy)3](PFs)3, but failed due to an apparent twinning of the crystals. 3 We therefore chose another salt, the perchlorate, for crystallographic work. It has been the most commonly used salt of [Cr(bpy),13+ for photochemical and spectroscopic studies. A problem surfaced in the course of the elemental analyses of this compound. The carbon, hydrogen and nitrogen analyses were as expected, and in one case so was the chromium analysis. However, another sample from the same batch sent to a different firm produced a chromium percentage about 25% lower
than expected. The latter analysis turned out to be correct, however, since refinement of the crystallographic data revealed the presence of cocrystallized bipyridinium perchlorate. This does, however, raise the question of what compound was actually used by previous investigators. RESULTS
AND DISCUSSION
Solution of the X-ray crystal structure showed there to be one chromium complex per asymmetric unit and revealed the presence of the cocrystallized HbpyCIOa. The enantiomeric complex is related by inversion symmetry in the PI space group. One enantiomer is shown in an ORTEP diagram in Fig. 1. Table 1 contains an abbreviated list of bond lengths and angles. Table 1 also includes a comparison with the data of Hauser et al. for the hexafluorophosphate salt. ’ Although the two sites in the latter compound are characterized by several disparate bond lengths and angles, when they are averaged they agree fairly well with an average of the same quantities from the three rings in the perchlorate salt. For example, the bipyridine bite angle (N-0-N) is 79.6, 79.7 and 80.4” in the three rings of [Cr(bpy),] (Clod), * HbpyC104, as opposed to the 74.8 and 84.7” angles mentioned above for the two sites in the [Cr(bpy),](PF,), structure. The inter-ring C-C distance, an important measure of the extent of delocalization, is between 1.46 and 1.49 8, in the * Author to whom correspondence should be addressed. perchlorate salt, but stated by Hauser to be 1.39 1557
1558
KYU-WANG LEE and P. E. HOGGARD Table 1. Comparison of selected bond lengths (A) and bond angles (“) for [Cr(bpy),](ClO,), - HbpyClO, and [Cr(hPY)3](PF&” (23)
ClO; salt
Fig. 1. ORTEP drawing of the [Cr(bpy),13+ molecular unit in [Cr(bpy),](ClO& - HbpyClO,, showing the atomlabelling scheme.
and 1.56 8, in the two sites of the PF; salt. The most likely explanation for the overlarge site differences is that the crystallographic data were refined in the wrong space group. There are numerous references in the literature to [Cr(bpy),](ClOJ,, and it is impossible to tell which of them are actually cocrystallized with bipyridinium perchlorate. The carbon, hydrogen, nitrogen and chlorine percentages are very similar in [Cr(bpy) 31W04)3 and [Cr@w)3lWOd 3HbpyC104. There are many reports of the synthesis of [Cr(bpy)3](C10,)3 without the inclusion of analytical data. 4-7 In some cases, one-half of a water of crystallization is included in the formula, either with a (C, H, N, Cl) analysis’ or without. 9 In one instance, two waters of crystallization are reported, lo but the supporting analyses were not published. The optimum coincidence in analytical percentages occurs with no additional water molecules, so it may be inferred that bipyridinium perchlorate has not cocrystallized when any water of crystallization is reported. The bipyridinium ion probably becomes available for cocrystallization through displacement of coordinated bipyridine by water in [Cr(bpy)3]2+. This in turn should be facilitated by higher acid concentrations, and it is likely that the perchloric acid concentration during oxidation is the critical factor in determining whether or not bipyridinium perchlorate is incorporated in the crystal. Porter and Van Houten have also discussed the method and order of addition during the oxidation procedure and how they affect the yield.6 They found that when [Cr(bpy)3]2+ was first dissolved in acid and then slowly oxidized, the yield was reduced through displacement of bipyridine.
PF; salt Site 1 Site 2
Cr-N( 1) Cr-N(2) Cr-N(3) Cr-N(4) Cr-N(5) Cr-N(6) C(1l)--c(25) C(3l)-C(45) C(51)--C(65) C(71)-C(85)
2.023(9) 2.034(8) 2.025(8) 2.035(7) 2.036(9) 2.037(9) 1.460(13) 1.490(14) 1.471(14) 1.441(13)
2.040 2.040 2.040 2.040 2.040 2.040 1.55 1.55 1.55
2.053 2.053 2.053 2.053 2.053 2.053 1.39 1.39 1.39
N(l)-Cr-N(2) N(l)-Cr-N(3) N( 1)-0-N(4) N(l)-Cr-N(5) N(l)-Cr-N(6) N(2)-Cr-N(3) N(2)---Cr-N(4) N(2)-Cr-N(5) N(2)-Cr-N(6) N(3)-Cr-N(4) N(3)-Cr-N(5) N(3)--C-N(6) N(4)---Cr-N(5) N(4)-Cr-N(6) N(S)-Cr-N(6)
79.7(3) 93.8(3) 94.3(3) 171.4(3) 92.6(3) 94.1(3) 171.6(4) 96.6(3) 89.7(8) 80.4(3) 94.2(3) 173.1(4) 90.2(3) 96.5(3) 79.6(3)
84.7 90.8 94.1 173.4
74.8 97.0 92.3 168.4
173.4 90.8 94.1 84.7
168.4 97.0 92.3 74.8
173.4 94.1 90.8 84.7
168.4 92.3 97.0 74.8
‘As reported in ref. 1.
In the procedure we followed, ii oxidation was not as rapid as in the method advised by Porter and Van Houten. Our “dilute” perchloric acid was approximately 1 M, whereas other workers have often used solutions 10-100 times more dilute. It thus seems that two different products may be formed depending on the perchloric acid concentration and/or the speed of oxidation. The solution characteristics would of course be identical. But without appropriate elemental analyses it is unclear how many of the literature references to this compound do and do not contain cocrystallized HbpyClO,. EXPERIMENTAL T&(2,2’-bipyridine)chromitmr(III) perchlorate ’ ’ was prepared by air-oxidizing [Cr(bpy)3]2+, made from CrC12 and bipyridine in stoichiometric ratio,‘* in dilute perchloric acid, and was recrystallized twice from dil. HC104 solution. Single crystals for
Bipyridinium
tris(bipyridine)chromium(III)
perchlorate
1559
Table 2. Experimental and data processing parameters (a) Crystal data 2,2’-Bipyridinium
tris(2,2’-bipyridine)chromium(III) perchlorate F, 1075.55
(C,~H,N2~(C3,H2~CrNdg,0,, F(OOO)= 834 Crystal dimensions (mm) Peak width at half height (“) Radiation Temperature (“C) Space group Lattice parameters
0.15 x0.25x 0.35 0.33 MO-& (1 = 0.71069 A) 23+1 Triclinic PI No. 2 a = 13.532(2) A b = 16.596(3) A c = 10.324(l) A CI= 92.16(l)’ /I = 100.92(l) y = 102.76(l)’ I’ = 2212.7(6) A’ 2 d= 1.614 5.09
Unit cell volume Z value Calculated density (g cm- ‘) Linear absorption coefficient (cm- ‘) (b) Intensity measurements
Rigaku AFC6R Graphite crystal, incident beam Zr foil, factor 20.7 6.0 6.0 horizontal 6.0 vertical 40 *28 16.0 (in omega), 2 re-scans (1.31+0.30tan0) 45.1 6123 total; 5827 unique Lorentz-polarization
Diffractometer Monochromator Attenuator Take-off angle (“) Detector aperture (mm) Crystal-detector distance (cm) Scan type Scan rate (” min- ‘) Scan width (“) Maximum 20 (“) Number of reflections measured Corrections (c) Structure solution and refinement Solution Minimization function Least-squares weight Anomalous dispersion Reflections included Parameters refined Unweighted agreement factor Weighted agreement factor ESD of obseyation of unit weight Maximum e/A’ from difference Fourier map
X-ray analysis were grown by slow evaporation in the dark from dil. HClO+ Solution of the crystal structure revealed the presence of cocrystallized (Hbpy)ClO,,. Found: Cr, 4.9; C, 44.5; N, 10.5; H, *Supplementary material. Tables of refined atomic coordinates, bond distances, bond angles and anisotropic temperature factors have been deposited at the Cambridge Crystallographic Data Centre.
Direct methods I: w(lFJ - IFCI)’ 4F,/a2 (F:) All non-hydrogen atoms 3624 with F,’ > 3a(Fz) 618 0.073 0.098 2.39 1.03
2.8. Calc. for Cr(C,0H8N2)~-HC10HsN2(C104)4: Cr, 4.8; C, 44.7; N, 10.4; H, 3.1%. (E & R Microanalytical Laboratories.) X-ray diffraction data were collected by the Molecular Structure Corporation on a Rigaku AFC6R diffractometer with graphite monochromated MO-& radiation.* Cell constants were determined from 25 centred reflections in the range of 35.90” < 28 < 41.29”. The data were collected at
KYU-WANG
1560
LEE and P. E. HOGGARD
23f 1°C using the w-28 scan technique to a maximum 20 value of 45.1”. Details are given in Table 2. The structure was refined at NDSU using direct methods” and full-matrix least-squares optimization14 for 5827 unique reflections to a final R value of 0.073 (I& = 0.098). Because of storage limitations, only the atoms in the [Cr(bpy),13+ unit were refined with anisotropic thermal parameters. material is based upon work supported in part by the National Science Foundation under Grant RI18610675 We also thank the donors of the Petroleum Research Fund, administered by the American Chemical Society, for their support of this research. Acknowle~ements-This
REFERENCES
5. B. Bnmschwig and N. Sutin, J. Am. Chem. Sot. 1978,100,7568. 6. G. B. Porter and J. Van Houten, Znorg. Chem. 1979, l&2053.
7. A. Bakac, K. Zahir and J. H. Espenson, Znorg. Chem. 1988,27, 315. 8 B. R. Baker and B. D. Mehta, Znorg. Chem. 1965,4, . 848.
g M. S. Henry and M. Z. Hoffman, Inorganic and . Organometallic Photochemistry (Edited by M. S. Wrighton), p. 91. American Chemical Society, Washington, DC (1978). 10. T. Ohno, S. Kato, S. Kaizaki and I. Hanazaki, Znorg. Chem. 1986,25,3853. 11. S. Herzog, Dissertation, University of Jena, G.D.R. (1952) as cited in Gmelins Handbuch der Anorganische Chemie, System 52 (Chromium), Part C, p. 106. Verlag Chemie, Weinheim, F.R.G. (1965). 12. F. Hein and S. Herzog, Z. Anorg. Allg. Chem. 1952, 267, 337.
A. Hauser, M. Mlder, W. T. Robinson, R. Murugesan and J. Ferguson, Znorg. Chem. 1987,26, 133 1. P. E. Hoggard, Coord. Chem. Rev. 1986,70,85. L. J. Radonovich, University of North Dakota, private communication. Y. Saito, J. Takemoto, B. Hutchinson and K. Nakamoto, Znorg. Chem. 1972,11,2003.
13. P. Main, S. E. Fiske, G. Germain, J. P. Declerq and M. M. Woolfson, MULTAN, a System of Computer Programs for CrystaI Structure Determination from X-ray Dzji-action Data. Universities of York, U.K.
and Louvain, Belgium (1980). Structure Determination 14. B. A. Frenz, SDP-PLUS Package. Enraf-No&s, Delft, Netherlands (1982).
1989 0
0277~5387/89 53.00+.00 1989 Fwgamon Rem plc
THE MOLECULAR STRUCTURE OF BIPYRIDINIUM TRIS(BIPYRIDINE)CHROMIUM(III) PERCHLORATE KY&WANG
LEE and PATRICK
E. HOGGARD*
Department of Chemistry, North Dakota State University, Fargo, ND 58105, U.S.A. (Received
17 January 1989 ; accepted 15 February 1989)
Ahstract-[Cr(bpy)3](C10J3 (bpy = 2,2’-bipyridine) cocrystallizes with bipyridinium perchlorate in the triclinic space group PI (No. 2), with a = 13.532(2), b = 16.596(3), c = 10.324(l) A, rx = 92.16(l), /? = 100.92(l), y = 102.76(l)“, Y= 2212.7 A’ and 2 = 2. The structure was refined to R = 0.073 and R, = 0.098. The cocrystallized HbpyC104 may also have been present in earlier preparations, but could have escaped detection because of the similarity in carbon, hydrogen, nitrogen and chlorine percentages, with and without the cocrystallite.
Hauser et al. recently published the crystal structure and low temperature polarized sharp-line absorption spectra for [Cr(bpy)3](PF6)3.’ The space group was reported to be R32, in which by necessity the enantiomers must occupy non-equivalent positions. The differences between the two sites, however, appeared extreme. The N-Cr-N bite angle, for example, was reported as 74.8“ in one site (equal by symmetry for all three rings) and 84.7” in the other. Large differences in other bond lengths and bond angles were also manifest. If this structure is correct it is unique among transition metal chelate complexes. Because the geometry of the tris(bipyridine) chromium(II1) complex is important to the ligand field analysis of the electronic spectra,’ we attempted to repeat the solution of the crystal structure of [Cr(bpy)3](PFs)3, but failed due to an apparent twinning of the crystals. 3 We therefore chose another salt, the perchlorate, for crystallographic work. It has been the most commonly used salt of [Cr(bpy),13+ for photochemical and spectroscopic studies. A problem surfaced in the course of the elemental analyses of this compound. The carbon, hydrogen and nitrogen analyses were as expected, and in one case so was the chromium analysis. However, another sample from the same batch sent to a different firm produced a chromium percentage about 25% lower
than expected. The latter analysis turned out to be correct, however, since refinement of the crystallographic data revealed the presence of cocrystallized bipyridinium perchlorate. This does, however, raise the question of what compound was actually used by previous investigators. RESULTS
AND DISCUSSION
Solution of the X-ray crystal structure showed there to be one chromium complex per asymmetric unit and revealed the presence of the cocrystallized HbpyCIOa. The enantiomeric complex is related by inversion symmetry in the PI space group. One enantiomer is shown in an ORTEP diagram in Fig. 1. Table 1 contains an abbreviated list of bond lengths and angles. Table 1 also includes a comparison with the data of Hauser et al. for the hexafluorophosphate salt. ’ Although the two sites in the latter compound are characterized by several disparate bond lengths and angles, when they are averaged they agree fairly well with an average of the same quantities from the three rings in the perchlorate salt. For example, the bipyridine bite angle (N-0-N) is 79.6, 79.7 and 80.4” in the three rings of [Cr(bpy),] (Clod), * HbpyC104, as opposed to the 74.8 and 84.7” angles mentioned above for the two sites in the [Cr(bpy),](PF,), structure. The inter-ring C-C distance, an important measure of the extent of delocalization, is between 1.46 and 1.49 8, in the * Author to whom correspondence should be addressed. perchlorate salt, but stated by Hauser to be 1.39 1557
1558
KYU-WANG LEE and P. E. HOGGARD Table 1. Comparison of selected bond lengths (A) and bond angles (“) for [Cr(bpy),](ClO,), - HbpyClO, and [Cr(hPY)3](PF&” (23)
ClO; salt
Fig. 1. ORTEP drawing of the [Cr(bpy),13+ molecular unit in [Cr(bpy),](ClO& - HbpyClO,, showing the atomlabelling scheme.
and 1.56 8, in the two sites of the PF; salt. The most likely explanation for the overlarge site differences is that the crystallographic data were refined in the wrong space group. There are numerous references in the literature to [Cr(bpy),](ClOJ,, and it is impossible to tell which of them are actually cocrystallized with bipyridinium perchlorate. The carbon, hydrogen, nitrogen and chlorine percentages are very similar in [Cr(bpy) 31W04)3 and [Cr@w)3lWOd 3HbpyC104. There are many reports of the synthesis of [Cr(bpy)3](C10,)3 without the inclusion of analytical data. 4-7 In some cases, one-half of a water of crystallization is included in the formula, either with a (C, H, N, Cl) analysis’ or without. 9 In one instance, two waters of crystallization are reported, lo but the supporting analyses were not published. The optimum coincidence in analytical percentages occurs with no additional water molecules, so it may be inferred that bipyridinium perchlorate has not cocrystallized when any water of crystallization is reported. The bipyridinium ion probably becomes available for cocrystallization through displacement of coordinated bipyridine by water in [Cr(bpy)3]2+. This in turn should be facilitated by higher acid concentrations, and it is likely that the perchloric acid concentration during oxidation is the critical factor in determining whether or not bipyridinium perchlorate is incorporated in the crystal. Porter and Van Houten have also discussed the method and order of addition during the oxidation procedure and how they affect the yield.6 They found that when [Cr(bpy)3]2+ was first dissolved in acid and then slowly oxidized, the yield was reduced through displacement of bipyridine.
PF; salt Site 1 Site 2
Cr-N( 1) Cr-N(2) Cr-N(3) Cr-N(4) Cr-N(5) Cr-N(6) C(1l)--c(25) C(3l)-C(45) C(51)--C(65) C(71)-C(85)
2.023(9) 2.034(8) 2.025(8) 2.035(7) 2.036(9) 2.037(9) 1.460(13) 1.490(14) 1.471(14) 1.441(13)
2.040 2.040 2.040 2.040 2.040 2.040 1.55 1.55 1.55
2.053 2.053 2.053 2.053 2.053 2.053 1.39 1.39 1.39
N(l)-Cr-N(2) N(l)-Cr-N(3) N( 1)-0-N(4) N(l)-Cr-N(5) N(l)-Cr-N(6) N(2)-Cr-N(3) N(2)---Cr-N(4) N(2)-Cr-N(5) N(2)-Cr-N(6) N(3)-Cr-N(4) N(3)-Cr-N(5) N(3)--C-N(6) N(4)---Cr-N(5) N(4)-Cr-N(6) N(S)-Cr-N(6)
79.7(3) 93.8(3) 94.3(3) 171.4(3) 92.6(3) 94.1(3) 171.6(4) 96.6(3) 89.7(8) 80.4(3) 94.2(3) 173.1(4) 90.2(3) 96.5(3) 79.6(3)
84.7 90.8 94.1 173.4
74.8 97.0 92.3 168.4
173.4 90.8 94.1 84.7
168.4 97.0 92.3 74.8
173.4 94.1 90.8 84.7
168.4 92.3 97.0 74.8
‘As reported in ref. 1.
In the procedure we followed, ii oxidation was not as rapid as in the method advised by Porter and Van Houten. Our “dilute” perchloric acid was approximately 1 M, whereas other workers have often used solutions 10-100 times more dilute. It thus seems that two different products may be formed depending on the perchloric acid concentration and/or the speed of oxidation. The solution characteristics would of course be identical. But without appropriate elemental analyses it is unclear how many of the literature references to this compound do and do not contain cocrystallized HbpyClO,. EXPERIMENTAL T&(2,2’-bipyridine)chromitmr(III) perchlorate ’ ’ was prepared by air-oxidizing [Cr(bpy)3]2+, made from CrC12 and bipyridine in stoichiometric ratio,‘* in dilute perchloric acid, and was recrystallized twice from dil. HC104 solution. Single crystals for
Bipyridinium
tris(bipyridine)chromium(III)
perchlorate
1559
Table 2. Experimental and data processing parameters (a) Crystal data 2,2’-Bipyridinium
tris(2,2’-bipyridine)chromium(III) perchlorate F, 1075.55
(C,~H,N2~(C3,H2~CrNdg,0,, F(OOO)= 834 Crystal dimensions (mm) Peak width at half height (“) Radiation Temperature (“C) Space group Lattice parameters
0.15 x0.25x 0.35 0.33 MO-& (1 = 0.71069 A) 23+1 Triclinic PI No. 2 a = 13.532(2) A b = 16.596(3) A c = 10.324(l) A CI= 92.16(l)’ /I = 100.92(l) y = 102.76(l)’ I’ = 2212.7(6) A’ 2 d= 1.614 5.09
Unit cell volume Z value Calculated density (g cm- ‘) Linear absorption coefficient (cm- ‘) (b) Intensity measurements
Rigaku AFC6R Graphite crystal, incident beam Zr foil, factor 20.7 6.0 6.0 horizontal 6.0 vertical 40 *28 16.0 (in omega), 2 re-scans (1.31+0.30tan0) 45.1 6123 total; 5827 unique Lorentz-polarization
Diffractometer Monochromator Attenuator Take-off angle (“) Detector aperture (mm) Crystal-detector distance (cm) Scan type Scan rate (” min- ‘) Scan width (“) Maximum 20 (“) Number of reflections measured Corrections (c) Structure solution and refinement Solution Minimization function Least-squares weight Anomalous dispersion Reflections included Parameters refined Unweighted agreement factor Weighted agreement factor ESD of obseyation of unit weight Maximum e/A’ from difference Fourier map
X-ray analysis were grown by slow evaporation in the dark from dil. HClO+ Solution of the crystal structure revealed the presence of cocrystallized (Hbpy)ClO,,. Found: Cr, 4.9; C, 44.5; N, 10.5; H, *Supplementary material. Tables of refined atomic coordinates, bond distances, bond angles and anisotropic temperature factors have been deposited at the Cambridge Crystallographic Data Centre.
Direct methods I: w(lFJ - IFCI)’ 4F,/a2 (F:) All non-hydrogen atoms 3624 with F,’ > 3a(Fz) 618 0.073 0.098 2.39 1.03
2.8. Calc. for Cr(C,0H8N2)~-HC10HsN2(C104)4: Cr, 4.8; C, 44.7; N, 10.4; H, 3.1%. (E & R Microanalytical Laboratories.) X-ray diffraction data were collected by the Molecular Structure Corporation on a Rigaku AFC6R diffractometer with graphite monochromated MO-& radiation.* Cell constants were determined from 25 centred reflections in the range of 35.90” < 28 < 41.29”. The data were collected at
KYU-WANG
1560
LEE and P. E. HOGGARD
23f 1°C using the w-28 scan technique to a maximum 20 value of 45.1”. Details are given in Table 2. The structure was refined at NDSU using direct methods” and full-matrix least-squares optimization14 for 5827 unique reflections to a final R value of 0.073 (I& = 0.098). Because of storage limitations, only the atoms in the [Cr(bpy),13+ unit were refined with anisotropic thermal parameters. material is based upon work supported in part by the National Science Foundation under Grant RI18610675 We also thank the donors of the Petroleum Research Fund, administered by the American Chemical Society, for their support of this research. Acknowle~ements-This
REFERENCES
5. B. Bnmschwig and N. Sutin, J. Am. Chem. Sot. 1978,100,7568. 6. G. B. Porter and J. Van Houten, Znorg. Chem. 1979, l&2053.
7. A. Bakac, K. Zahir and J. H. Espenson, Znorg. Chem. 1988,27, 315. 8 B. R. Baker and B. D. Mehta, Znorg. Chem. 1965,4, . 848.
g M. S. Henry and M. Z. Hoffman, Inorganic and . Organometallic Photochemistry (Edited by M. S. Wrighton), p. 91. American Chemical Society, Washington, DC (1978). 10. T. Ohno, S. Kato, S. Kaizaki and I. Hanazaki, Znorg. Chem. 1986,25,3853. 11. S. Herzog, Dissertation, University of Jena, G.D.R. (1952) as cited in Gmelins Handbuch der Anorganische Chemie, System 52 (Chromium), Part C, p. 106. Verlag Chemie, Weinheim, F.R.G. (1965). 12. F. Hein and S. Herzog, Z. Anorg. Allg. Chem. 1952, 267, 337.
A. Hauser, M. Mlder, W. T. Robinson, R. Murugesan and J. Ferguson, Znorg. Chem. 1987,26, 133 1. P. E. Hoggard, Coord. Chem. Rev. 1986,70,85. L. J. Radonovich, University of North Dakota, private communication. Y. Saito, J. Takemoto, B. Hutchinson and K. Nakamoto, Znorg. Chem. 1972,11,2003.
13. P. Main, S. E. Fiske, G. Germain, J. P. Declerq and M. M. Woolfson, MULTAN, a System of Computer Programs for CrystaI Structure Determination from X-ray Dzji-action Data. Universities of York, U.K.
and Louvain, Belgium (1980). Structure Determination 14. B. A. Frenz, SDP-PLUS Package. Enraf-No&s, Delft, Netherlands (1982).