13177
J. Phys. Chem. 1994, 98, 13177-13181
Theoretical Investigation of the Conformations, Tautomeric Forms, and Spectra of Donor-Acceptor (Pheny1azo)arenes John 0. Morley Chemistry Department, University College of Swansea, Singleton Park, Swansea, SA2 8PP U.K. Received: June 11, 1994; In Final Form: September 15, 1994@
Calculations are reported on the structure of a series of donor-acceptor azobenzenes, (phenylazo)naphthalenes, and phenylazo heterocycles using the AM1 method. The geometries obtained are compared with crystallographic data where available, and reasonable correlations are found between theory and experiment for the bond lengths of the azo and hydrazo tautomers of the (pheny1azo)naphthols and (phenylazo)naphthylamines. The calculated heats of formation suggest that the azo tautomers of the azobenzenes and (pheny1azo)naphthalenes are more stable than the hydrazo form, though the difference between the tautomers of 1-((4'-nitrophenyl)az0)-2-naphthol is only 1.6 kcal mol-'. The azo tautomer of the phenylazo heterocycles is favored when the donor consists of the NHMe group, but the hydrazo form is favored for 2-((4'-nitropheny1)azo)-5-hydroxyfuran and -pyrrole. The calculated transition energies of the (pheny1azo)naphthalenes reproduce the experimental bathochromic shift observed in moving from the azo tautomer to the hydrazo form.
Introduction There is little (or no) doubt that the vast majority of donoracceptor (pheny1azo)benzenes (I) are planar with the aromatic rings in a trans conformation to one another.lP3 In cases where the donor contains an acidic hydrogen atom, as found in the amino, methylamino, hydroxyl, or thiol derivatives, tautomerism is possible and the structure can represented, for example, either as the azobenzene (Ia,b) or the hydrazobenzene (IIa,b).
tautomer (IVc) dominates in acetic acid with characteristic absorption'bands at 414 and 480 nm, re~pectively.~ However,
III a: R = NOz; X = NMe b: R = NOz; X = 0 C: R = H ; X = O d: R = O M e ; X = O
R'
I '
a: R = NOz; R' = Rz = R3 = H; X = NHMe b: R = NOz; R' = R' = R3 = H; X = OH c: R = NOz; R' = Rz = R3 = H; X = NMez d: R = CN; R1 = Br; R2 = R3 = H; X = NEt2 e: R = NOz; R' = Br; Rz = CN; R3 = NHCOMe; X = NEtz f: R = SOZMe; R1 = CI; R2 = H; R3 = NHCOMe; X = NEtz
R
0
N
H
"
-O
N
'
N
B
X
rv R = NOz; X = NMe b: R = NOz; X = 0 C: R = H ; X = O d: R = O M e ; X = O
8:
X
n R = NOz; X = NMe b: R = N O z ; X = O
8:
However, both spectros~opic'-~and crystallographic data4 strongly suggest that the azo form predominates in the solid state and in solution. In contrast, (pheny1azo)naphthalenes containing donor and acceptor groups are also planar, with the aromatic rings again in a trans conformation, but here the molecules may exist either as the (phenylazo)naphthalene, for example (IIIa-d) and (Va-g), or as the (phenylhydraz0)naphthalene (Iva-d) and (VIa-g), both in the solid state4 and in solution5depending on the nature of the substituents and also the solvent in the latter case. Spectroscopic data shows that 4-(phenylazo)-l-naphtholexists mainly as the azo tautomer (IIIc) in pyridine, but the hydrazo @
O
Abstract published in Advance ACS Abstracts, November 15, 1994.
0022-365419412098-13177$04.50/0
while solutions of 4-((4'-nitrophenyl)azo)-l-naphthol contain both the hydrazo (Ivb) and azo tautomers (IIIb) in an approximate ratio of 4:l in both solvents, the reverse ratio is found for 4-((4'-methoxypheny1)azo)- 1-naphthol with the azo form (IIId) favored in this case.5 In the solid state, relevant crystallographic data4 is limited to the structures of 1-(phenylazo)-Zsubstituted naphthalenes only. Here, electron attractors present in the phenyl ring appear to stabilize the hydrazo tautomer (VI), while electron donors present in either the phenyl or naphthalene ring appear to stabilize the azo tautomer (V). Thus, both 1-((4'-nitrophenyl)azo)-2-naphthylamine ( V C ) and ~ 1-((4'-(N,N-dimethylamino)phenyl)azo)-2-naphthol (Vf),' exist only as the azo tautomer while 1-((4'-nitrophenyl)az0)-2-naphthol (VIb),a 1-((4'-methyl2'-nitrophenyl)azo)-2-naphthol (VId): and 1-((4'-chloro-2'nitrophenyl)azo)-2-naphthol(VIe)l0exist in the hydrazo form. In the corresponding donor-acceptor 4-(phenylazo)thiophenes (VII), -furans (IX),or -pyrroles (XI), the azo form is thought 0 1994 American Chemical Society
Morley
13178 J. Phys. Chem., Vol. 98, No. 50, 1994
the CNDOVS method13 which has been specifically parametrized to reproduce the transition energies and oscillator strengths of dyes and pigments. All the calculations were carried out using a Silicon Graphics Indigo workstation. Results and Discusion
to dominate but there is little crystallographic data available for confirmation or for deciding which of the two possible conformers is preferred. In these cases, the azo linkage can be
(VII, Z = S)(IX, Z = 0)(XI, Z = NH) a: R = N02; X = NHMe b: R = N O z ; X = O H C:
R = NOn; X = NMe2
R e N { + x
(VIII, Z = S)(X, Z = 0)(XII,Z = NH) a: R = NO2; X = NMe b: R = N 0 2 ; X = O
either cis or trans to the double bond of the heterocyclic ring and both structures appear to be equally valid. The present studies have been carried out to theoretically explore the relative stability of both the conformations and tautomeric preferences of the donor-acceptor (phenylazo)benzenes, -naphthalenes, and heterocycles. In addition, the spectroscopic properties have been calculated to assess the effects on the transition energy in moving from the azo-tautomer to the hydrazo-form.
Initial calculations were carried out on empirical structures for the (pheny1azo)benzenesI (pheny1azo)naphthalenes 111,and phenylazo heterocycles VII, IX, and XI using the AM1 method." However, many of the resulting structures were found to be nonplanar with one aromatic ring twisted by at least 20" relative to the other. Furthermore, a tetrahedral sp3 nitrogen atom results at both the methylamino and dimethylamino groups of the respective structures with the methyl groups below the donor ring plane. For example, 2-(N,N-dimethylamino)-5-((4'nitropheny1)azo)thiophene (VIIc) is predicted to be nonplanar with the torsion angle between the plane of the azo linkage and the carbons at the 1- and 2-positions of the phenyl ring (N=N-C1-) of -10.0" and a torsion angle between the methyl carbons and the thiophene ring (Sl-C2-N-C) of -26.2". Similar results have been reported for 4-(N,N-dimethylamino)4'-nitroazobenzene (IC) using the AM1 method where the ring containing the nitro group is twisted by 21"-37" relative to the azo linkage depending on the convergence criteria adopted.13 However, in contrast, the same calculation on the corresponding (pheny1azo)furan (IXc) and -pyrrole (XIc) gives structures in which the heterocyclic rings are now essentially coplanar with the other aromatic ring, though the donor group still adopts a tetrahedral conformation. The initial calculated results obtained do not conform with known crystallographic data from the Cambridge Structural Database4 for (pheny1azo)benzenes which clearly show that the nitrogen of the donor groups in most related structures adopts a trigonal sp2conformation with the two aromatic rings coplanar. For example, 2-bromo-4-cyano-4'-(diethylamino)azobenzene (Id),14 6'-acetamido-6-bromo-2-cyano-4'-(diethylamino)-4-nitroazobenzene (Ie),15 and 2'-acetamido-2-chloro-4'-(diethylamino)-4-mesylazobenzene (If)16 are essentially planar with torsion angles between the plane of the azo linkage and the carbons at the 1- and 2-positions of each of the aromatic rings (N=N-Cl-C2 and N=N-C1'-C2' in a cis arrangement) ranging from 1.2" to 4.8" with a trigonal sp2 conformation for the nitrogen of the diethylamino group (Table 1). However, it is possible that the presence of a heterocycle in place of a phenyl ring might change the hybridization of the dimethylamino group from sp2 in the (pheny1azo)benzenes to sp3 in the phenylazo heterocycles (VIb), (IXb), or (XIb). Crystallographic data on related stmctures such ethyl 5-amino-4-cyano-3-methylthiophene2-carboxylate (XIIIa)" and 3-amino-4-cyano-2-(dicyanovinyl)thiophene (XIIIb)'* are not supportive as the amino groups in both are coplanar with the heterocyclic ring and are clearly hybridized with C-NH2 bond lengths of 1.33 and 1.34 respectively.
Method of Calculation The AM1 method" of the MOPAC package1* was used to calculate the structures, heats of formation, and electronic properties of the molecules described here. Spectroscopic calculations were carried out on the resulting structures using
A series of further calculations were canied out on the same structures as before, but this time all the atoms were constrained to lie in the same plane with the exception of the hydrogens at the methyl groups. The resulting modified structures were found
J. Phys. Chem., Vol. 98, No. 50, 1994 13179
Donor-Acceptor (Pheny1azo)arenes
TABLE 1: Experimental Structural Data for Donor- Acceptor (Pheny1azo)arenes bond lengths (A) CSD ref“ structure N-N C-Xb C-NO2 N-Npc N”CCd BUBHIP vc 1.279 1.347 1.493 1.389 -0.4 JARPIBOl NBZANOll MNIPZN
NQNCPHOl BEDSEI CEMSPC10 ACLMSA
Vf
vn, VId VIe Id Ie
If
1.275 1.361 1.317 1.312 1.254 1.281 1.278
1.364 1.269 1.229 1.232 1.364 1.353 1.373
1.452 1.457 1.481 1.472
1.398 1.310 1.309 1.331
-1.7 -1.5 1.2 0.9 4.8 -1.3 0.5
torsion angles (deg) NNCC‘ CCNCf -1.2 3.2 3.8 0.03 0.8 -2.6 -1.2 -4.2
-2.0 3.3 5.3
CCNCf
ref
--6.7 3.2 3.5
6 7 8 9 10 14 15 16
The codenames are unique and taken from ref 4. Distance between the heteroatom and the naphthalene ring. Distance between the naphthalene ring and the azo nitrogen. Carbon@)of the donor ring. Carbon(s) of the acceptor ring both with cis conformation for torsions. f Carbons of the NMe2 group relative to the aromatic ring. to be only 0.5-2 kcal mol-’ higher in energy than those from the unconstrained structure optimization. For example, the heat of formation of 2-(NJV-dimethylamino)-5-((4’-nitrophenyl)azo)furan (IXc) changes from 94.5 to 95.3 kcal mol-’ when the planar constraints are applied. A slightly larger change in the energy from 125.5 to 126.9 kcal mol-’ is found for the constrained optimization of the (pheny1azo)pyrrole (XIc). It appears therefore that the planar conformations are equally valid for these molecules. All the other molecules considered here were optimized with the same planar constraints applied to ensure that the donor group was forced to adopt an sp2 conformation. The calculated geometries of the resulting structures were then compared with experimental data where available. Calculations were also carried out on a number of different conformations for the phenylazo heterocycles, and the relative stabilities of the azo tautomers versus the hydrazo forms were explored for all of the systems described here. Each aspect will be discussed in tum. 1. Calculated versus Experimental Structures. The calculated geometry for 4-(N,N-dimethylamino)-4’-nitroazobenzene (IC) shows a N=N bond length which is somewhat underestimated at the AM1 level relative to crystallographic data (Table l), while the Ar-NMe2 and Ar-NO2 distances are ~verestimated.’~ As expected, there are considerable differences between the calculated structures of the azo and hydrazo tautomers of N-methyl-4-((4’-nitrophenyl)azo)-1-naphthylamine (IIIa and IVa), N-methyl-l-((4’-nitrophenyl)azo)-2-naphthylamine (Va and VIa), 4-((4’-nitrophenyl)azo)-l-naphthol (IIIb and IVb), and 1-((4’-nitrophenyl)a0)-2-naphthol (Vb) and Vlb), with the AM1 method reproducing the expected trends in the bond lengths (Table 2). Thus the hydrazo tautomer of the (phenylazo)-2-naphthol (VJb) shows shows typical quininoid character with the NH-N, N-Ar, and C=O distances at 1.32, 1.33, and 1.25 8,, respectively (Table 2) compared with values of 1.36, 1.31, and 1.27 8, found in the crystal structure8 (VIb, Tables 1 and 2). In constrast, the azo tautomer of N-methyl1-((4’-nitrophenyl)az0)-2-naphthylamine (Va) shows similar bond lengths to those found in the azobenzene (IC)with N=N, A r N H M e , and Ar-NO2 distances of 1.24, 1.37, and 1.48 A, respectively, compared with values of 1.28, 1.35, and 1.49 8, found in the crystal structure of the related (phenylazo)-2naphthylamine6 (Vc, Table 1). 2. Molecular Conformations. In the azobenzenes (I), the trans conformation is generally preferred over the corresponding cis arrangement for most substituted derivatives because steric interactions between the ortho hydrogens on each phenyl ring in the latter distort the planarity and raise the molecular energy. This repulsion occurs in the cis phenylazo heterocycles also but to a lesser degree because the larger angle at the heterocyclic ring increases the distance between the two ring hydrogens. In the more stable trans phenylazo heterocycles, however, there
are two possible conformers where the double bond of the heterocyclic ring is either arranged cis or trans to the azo group. The heat of formation of the constrained cis-(pheny1azo)furan (IXc) at 97.6 kcal mo1-I is some 2.29 kcal mol-’ higher in energy than the all-trans conformation. In contrast, the all-trans conformation for the (pheny1azo)thiophene (VIIc) is preferred over the cis arrangement by 1.05 kcal mol-’. On balance, therefore there seems little to choose between the two conformations in these cases and both seem to be equally valid though this is likely to change if substituents are placed in the 4-position of the heterocyclic ring. In the (pheny1azo)naphthalenes (III), although there are again two possible trans conformations where the second fused ring of naphthalene occupies a cis or trans arrangement to the azo group, only the latter is important because of steric interactions between the hydrogen at the 8-position of the naphthalene ring and the lone pair of electrons at the azo nitrogen. 3. Azo versus Hydrazo Tautomerism. Previous calculations on (pheny1azo)naphthols have explored the conformations and energy differences between the azo and hydrazo tautomers using the PCILO m e t h ~ d . ’ ~ The * * ~results obtained for 4-(phenylaz~)-l-naphthol’~ using a number of fixed bond lengths and angles show that the azo tautomer (IIIc) is preferred over the hydrazo form (IVc) by 32.1 kcal mol-’ though experimental data suggests that the latter is favored by around 2 kcal mol-’ in methylcyclohexane.21 A similar result is calculated for 1-(phenylaz0)-2-naphthol~~ where the azo tautomer (Vg) is strongly favored by 54.1 kcal mol-’ over the hydrazo form (VIg), in contrast to experimental data in benzene which shows both tautomers present in approximately equal amounts5 and the solid state which shows only the hydrazo tautomer.22 The AM1 method adopted here is more versatile than the PCILO method as all the key geometric variables are optimized. Nevertheless, similar trends are found in the calculated heats of formation of N-methyl-4-((4’-nitrophenyl)azo)-1-naphthylamine (IIIa) and N-methyl- 1-((4’-nitrophenyl)azzo)-2-naphthylamine (Va) where the azo tautomers (IIIa) and (Va) are favored by 12.5 and 9.40 kcal mol-’, respectively over the hydrazo forms (IVa) and (VIa) in line with the crystallographic data on the closely related 1-((4’-nitrophenyl)az0)-2- naphthylamine (Vc) which shows only the azo form? Furthermore, in 44Nmethylamino)-4’-nitroazobenzene,the margin in favor of the azo tautomer (Ia) increases to 20.5 kcal mol-’ over the hydrazo form (IIa) to conform with the experimental The same trend emerges for the 2-((4’-nitrophenyl)azo)-5-(N-methy1amino)thiophene (VIIa), -furan (ma), and -pyrrole (Ma) where the azo tautomers are again favored, but now by much smaller margins of 7.63, 8.16, and 8.40 kcal mol-’ over the corresponding hydrazo forms (VIIIa), (Xa), and (XIIa), respectively (Table 2). The energy differences between the azo and hydrazo tau-
13180 J. Phys. Chem., Vol. 98, No. 50, 1994
Morley
TABLE 2: Selected Bond Lengths, Dipole Moments, and Heats of Formation Calculated by the AM1 Method and Transition Energies and Oscillator Strengths Calculated by the CNDOVS Method for the (Pheny1azo)arenesI-XI1 AM1 bond lengths (A) molecule N=N ArX“ *NO2 N-Cb N-C‘ fid Hf‘ K P Ih Ia Ib IC
IIa In,
IIIa IIIb IVa Ivb
Va vb VIa VIb VIIa VIIb VIIC VIIIa VIIIb Ma Mb MC Xa Xb XIa XIb XIC
1.421 1.425 1.440 1.321 1.322
9.30 6.33 9.42
1.439 1.425
9.63 6.72
1.406 1.409 1.432 1.432 1.405 1.412 1.442 1.442 1.396
1.321 1.322 1.408 1.414
6.56 3.20 7.79 5.99
1.325 1.326
8.21 6.7 1
1.445 1.445 1.435
9.58 6.84 8.89
1.402 1.408
1.313 1.312
8.25 5.59
1.432 1.428 1.436 1.401 1.412
1.440 1.407 1.388 1.321 1.320 1.417 1.440 1.399
9.22 7.62 9.29
1.234 1.233 1.233 1.321 1.317 1.234 1.233
1.377 1.371 1.386
1.484 1.487 1.485
1.439 1.442 1.425
1.299 1.239 1.377 1.371
1.481 1.482 1.484 1.486
1.406 1.409 1.421 1.442
1.321 1.317
1.299 1.239
1.481 1.482
1.236 1.235
1.370 1.365
1.483 1.481
1.308 1.315
1.300 1.245 1.300 1.330 1.368 1.286 1.219
1.479 1.481
1.300 1.330 1.366 1.301 1.200
1.487 1.486 1.486
1.233 1.233 1.237 1.329 1.325 1.236 1.240 1.237 1.330 1.316 1.237 1.236 1.239
1.300 1.330 1.408 1.313 1.200
1.487 1.487 1.486 1.479 1.482
1.480 1.482 1.486 1.488 1.485
1.432 1.436 1.433 1.412 1.412
6.56 2.95
9.44 7.30 9.63 7.10 9.70 8.48 5.73
105.5 59.6 112.1 126.0 75.8 127.3 80.6 139.8 88.1 126.1 80.9 135.5 82.5 107.8 65.8 113.1 115.5 68.6 93.7 46.9 95.3 101.8 39.8 126.3 80.7 126.9 134.7 77.7
43 1 408 444
1.12 1.11 1.13
485 384-450 444-508
494 464 500 487
1.02 0.95 1.32 1.16
482-53 1’ 432
513
0.66
496-5 14‘
503
0.70
494
518
0.96
546
529
1.05
538
534
1.08
465
1.482 1.320 XIIa 1.316 1.482 1.320 1.316 XIIb X is the electron donor, =NMe or =O group. Carbon of the ring containing the NO2 group. Carbon of the other ring. AM1 dipole moment (in Debves). e AM1 heat of formation (in kcal mol-’). f CNDOVS transition energy (in nm). 8 CNDOVS oscillator strength. Experimental transition energies (from ref 24). Data for the closely related amino derivative.
’
tomers of the hydroxy azoarenes (Ib-XIIIb), however, are somewhat different. Although the azo tautomer Ib of 4-hydroxy-4’-nitroazobenzene is favored over the hydrazo form IIb by 16.2 kcal mol-’, the margin between the corresponding tautomers of 4-((4’-nitrophenyl)azo)-l-naphthol (IIIb) and 1-((4’-nitrophenyl)azo)-2-naphthol (Vb) falls to 7.51 and 1.60 kcal mol-’, respectively, in favor of the azo tautomers IIIb and Vb. In the latter case, the very small energy gap between the tautomers suggests that both are almost equally favored and although crystallographic data shows only the hydrazo tautomer VIb8 this may be preferentially favored and stabilized by dispersive and electrostatic forces within the crystal. In the heterocyclic analogues, the azo tautomer of 2-((4’nitrophenyl)azo)-5-hydroxythiophene (VIIb) is calculated to be only 2.76 kcal mol-’ more stable than the hydrazo form VIIIb, but the reverse is true for the corresponding 2-((4’-nitropheny1)azo)-5-hydroxyfuran and -pyrrole where now the hydrazo tautomers Xb and XIIb are 7.08 and 2.99 kcal mol-’ more stable than the azo forms IXb and XIb, respectively. The replacement of one phenyl ring by a naphthalene or a heterocyclic ring has a profound effect, therefore, on the stability of the azo and hydrazo tautomers. 4. Spectroscopic Calculations. There is limited spectroscopic data available on the novel donor-acceptor azoarenes calculated in the present studies with the exception of some hydroxy and dimethylamino derivatives. Experimentally, there are significant differences found between the absorption maxima of the azo and hydrazo tautomers of the (pheny1azo)naphthols though the corresponding (pheny1azo)naphthylamines appear to exist in the azo form Spectroscopic calculations were
carried out on a number of the structures obtained by the AM1 method to determine whether the predicted structural differences between the azo and hydrazo tautomers of 1,4-disubstituted naphthalenes I11 and IV produced the known experimental trends in the spectra. The CNDOVS method13 was used in preference to the AM1 method” because the former has been specifically parametrized for dyes and pigments and the latter is known to overestimate the transition energies.23 The calculated transition energy of the hydrazo tautomer IVb of 4-((4’-nitrophenyl)azo)-l-naphthol is predicted to occur at a longer wavelength than that of the azo tautomer IIIb. The values obtained for both tautomers at 487 and 464 nm, respectively (Table 2), compare favorably with the experimental absorption maxima at 465 and 432 nm.23 A similar pattern emerges for the tautomers of N-methyl-4-((4’-nitrophenyl)azo)1-naphthylamine though the bathochromic shift found in moving from the azo IIIa to the hydrazo form IIIb at 5 nm is much smaller than that found in the (pheny1azo)naphthols (Table 2). The correlation between the calculated and experimental transition energies of the other structures in nonpolar solvents is generally good (Table 2). Furthermore, the large calculated bathochromic shift of 85 nm observed in moving from 4-(N,Ndimethylamino)-4’-nitroazobenzene (IC) to 2-(N,N-dimethylamino)-5-((4’-nitrophenyl)azo)furan (IXc) is very close to the experimental shift of 94 nm (Table 2).
Conclusions The AM1 method gives a reasonable account of structure for a series of donor-acceptor azobenzenes, (phenylazo)-
Donor- Acceptor (Pheny1azo)arenes naphthalenes, and phenylazo heterocycles provided the heavy atoms of each are constrained to lie in the same plane. Satisfactory correlations are found between the calculated bond lengths of the azo and hydrazo tautomers of the (phenylazo)naphthols and (pheny1azo)naphthylamines and crystallographic data. The calculated heats of formation suggest that the azo tautomers of the azobenzenes and (pheny1azo)naphthalenesare more stable than the hydrazo form, though the difference between the tautomers of 1-((4’-nitrophenyl)azo)-2-naphtholis very small. The azo tautomer of the phenylazo heterocycles is favored when the donor consists of the NHMe group, but the hydrazo form is favored for 2-((4’-nitrophenyl)ao)-5-hydroxyfuran and -pyrrole. The calculated transition energies of the (pheny1azo)naphthalenes using the CNDOVS method appears to reproduce the experimental bathochromic shift observed in moving from the azo tautomer to the hydrazo form.
References and Notes (1) Griftiths, J. Colour and Constitution of Organic Molecules; Academic Press: London, 1976. (2) Fabian, J., Hartman, H. Light Absorption of Organic Colourants; Springer-Verlag: Heidelberg, 1980. (3) Gordon, P. F.; Gregory, P. Organic Chemistry in Colour; Springer-Verlag: Heidelberg, 1983. (4) Cambridge Structural Database, Cambridge Crystallographic Data Centre, University Chemical Laboratory, Lensfield Road, Cambridge, CB2 2EW, UK 11.
J. Phys. Chem., Vol. 98,No. 50, 1994 13181 (5) Kishimoto, S., Kitahara, S.; Manabe, 0.; Hiyama, H. J. Org. Chem. 1978,43,3882. (6) Kelemen, J.; Kormany, G.; Rihs, G. Dyes Pigm. 1982, 2, 249. (7) Olivieri, A. C.; Wilson, R. B.; Paul, I. C.; Curtain, D. Y. J. Am. Chem. Soc. 1989, 111,5525. (8) Whitaker, A. Z. Kristallogr. 1980, 152, 227. (9) Whitabker, A. Z. Kristallogr. 1978, 147, 99. (10) Whitaker, A. Z. Kristallogr. 1977, 145, 271. (11) Dewar, M. J. S.; Zoebisch, E. G.; Healy, E. F.; Stewart, J. J . Am. Chem. Soc. 1985, 107,3902. (12) QCPE Program 455 Version 6.0, Department of Chemistry, Indiana University, Bloomington, IN 47405. (13) Charlton, M. H.; Docherty, R.; McGeein, D. J.; Morley, J. 0. J . Chem. Soc., Faraday Trans. 1993, 89, 1671. (14) Woode, K. A.; Bart, J. C. J.; Calcatecra, M. Dyes Pigm. 1981, 2, 271. (15) Handal.. J. G.:. Gruska. R. P.:. Shoia. . . M.:. White. J. G. Z. Krvstalloar. . 1982,161, 61. (16) Gruska. R. P.: Ardebil. M. H. P.: Baccio. D.: White. J. G. Acta C&tallogr. 1980, 36, 3203. (17) Apinitis, S. K.; Kemme, A. A.; Bleidelis, Ya. Ya.; Palitis, E. L.; Gudrinietse, E. Yu. Lam. PSR Zinat. Akad. Vestis, Khim. Ser. 1984, 737. (1 8) Marinuzzi-Brosemer,S. A.; Dittmer, D. C.; Chen, M. H. M.; Clardy, J. J . Org. Chem. 1985, 50, 799. (19) Goursot, A.; Jacques, P.; Faure, J. Chem. Phys. 1977, 20, 319. (20) Goursot, A.; Jacques, P.; Faure, J. Chem. Phys. 1977, 26, 301. (21) Fischer, E.; Fei, Y. F. J . Chem. Soc. 1959, 3159. (22) Salmen, R.; Malterud, K. E.; Pederson, B. F. Acta Chem. Scund. Ser. A 1988, 42, 493. (23) Morley, J. 0. J. Mol.Struct., in press. (24) Okawara, M.; Kitao, T.; Hirashima, T.; Matsuoka, M. Organic Colourunts; Kodansha Ltd.: Tokyo, 1988.
