Theoretical S t u d y of Charge-TransferComplexes
137
Theoretical Study of Charge-Transfer Complexes 0. Mb, M. Yaiier, and J. 1. Fernandez-Alonso” Department of Chemistry, Quantum Chemistry Section, Universidad Autonoma, Cantoblanco, Madrid-34, Spain
(Received May 28, f974)
Publication costs assisted by the’Univprsidad Autonoma
CNDOI2 calculations on the geometry and stabilization energies of 12 p -benzoquinone charge-transfer complexes with different donors are reported. Each complex is treated as a “supermolecule” where the donor and acceptor molecules are located meta > para, observed for their
Theoretical Study of Charge-TransferComplexes
141
TABLE 111: Transferred Charge in p -Benzoquinone Complexes Total charge transferred Donor
CNDO
INDO
Benzene Toluene o-Xylene m-Xylene p-Xylene Aniline o-Toluidine m-Toluidine p-Toluidine o-Phenylenediamine m-Phenylenediamine p-Phenylenediamine
0.3836 0.3978 0.4634 0 .4650 0 .4094 0.3908 0.4171 0.4286 0.4034
0.3588 0.3711 0.3958 0.3959 0.3812 0.3588 0 .3926 0.3931 0 .3802
0.4162
0.3794
0.4186
0.3849
0.3956
0.3754
1.0098
0.4670
1.0690 Rlng = 27.9255 -CH3= 6.9919 7.0697
Ring -CH3 -NHz
L1.9871
Total
Total
=
=
27.5773 6.9313 7.0366
Aqt=O.L L 19
41.5452
Figure la. Charge distribution for o-toluidine. A9t is the transferred
charge. Toluene and aniline transfer more charge than benzene indicating that both types of substituents, methyl and amine, favor this donation. The effect is more pronounced in the methyl group than in the amino group since it is clear that toluene gives up more charge than aniline, the xylenes more than the toluidines, and these, more than the phenylenediamines. In order to discuss which atoms carry the greatest weight of the donation we have represented in Figure 10 the charge distribution for one of the donors (a) when it is isolated and (b) when it forms part of the complex. The atoms which suffer the greatest decrease in their total charge are those which form the aromatic ring, while the atoms of the substituents hardly undergo any modification in their electronic distribution. This fact can be interpreted, in principle, as a confirmation of the a-a character of the complexes studied.
ntJ
L.0
3.0
2.(
1.c
, 2.0
2.25
2.5
RIA)
, 2.75
Figure 9. Variation of the dipole moment increment vs. interplanar distance for xylene family complexes.
stabilization energies (Table I); that is, the more intense the transfer, the greater the stability of the complex. Analysis of t h e Amount of Charge Transferred. The amount of charge transferred in the formation of the complex is calculated as the difference between the total charge of the isolated donor and the total charge of the donor when it forms part of the complex. The values obtained using CNDOIB and INDO are given in Table 111. In the formation of the complex, it is observed that there is a partial transfer of electrons from the donor to the acceptor. It is very probably that, due to the limitations in the methods used, the value of this charge is overestimated. The fact that the value calculated by the CND0/2 method is always greater than that obtained by the INDO method seems to confirm this. As expected, according to the preceding section, the amount of charge transferred is greatest for the most stable complex within each family. Moreover, the results obtained permit us to deduce the effect of the donor substituents on the intensity of the charge donation.
Conclusions The results described in this article lead us to the following conclusions. The stabilization energy for CTC’s formed by donors of a similar size and polarizability and a common acceptor is inversely proportional to the ionization potential of the donor, in accordance with the theories of Dewar and Flurry. Electronic transfer plays an important role in the stabilization of the complex and the substituent groups of the donors show a classic inductive effect relative to charge donation. Considering the complex as a “supermolecule” seems, at least from a qualitative point of view, to account for its spectroscopic behavior.
Acknowledgment. The authors wish to thank Dr. A. Mac;as for heJpful suggestions and advice. This work was supported in part by Foment0 Investigaci6n Universidad and J E N (Madrid). References and Notes (1) J. Rose, “Molecular Complexes,” Pergarnon Press, London, 1967. (2) A. C. Allison and T. Nash, Nature (London), 197, 758 (1959). (3) G. Karreman, I. Isenberg, and A. Szent-Gyorgyi, Science, 130, 1191 (1959). (4) S. E. Epstein, et a/., Nature (London),204, 750 (1964). (5) N. P. Bun-Hoi and P. Jacquignon, Experentia, 13, 375 (1957). (6)R. Beukers and A. Szent-Gyorgyi, R e d Trav. Chim. Pays-Bas, 81, 255 (1962). (7) A. Pardo, Ph.D. Thesis, Valencia, Spain, 1972. (8) A. Szent-Gyorgyi, “Introduction to Submolecular Biology,” Academic Press, New York, N.Y., 1960. (9) T. Nash and A. C. Allison, “Biochemical Pharmacology,” Pergarnon Press, Oxford, 1963. The Journal of Physical Chemistry, Voi. 79, No. 2, 1975
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(IO)B. Grabe, "Almquist and Wiksells Boktryckeri AB," Uppsala, 1960. (11)J. Fritzsche, J. Prakt. Chem., 73,288 (1958). (12)F. Geiss and S. Sandroni, Rapp. Euratom, Eur, 87 (1962). (13)P. D. Eley and H. Inokuchi, "Proceedings of the Third Biennial Conference on Carbon," Pergamon Press, New York, N.Y., 1959. (14)S. D. Ross and I. Kuntz, J. Amer. Chem. SOC., 76, 3000 (1954). (15) J. Higuchi and R. No, Theor. Chim. Acta, 22, 61 (1971). (16)R. S.Mulliken and W. B. Person, "Molecular Complexes," Wiley, New York, N.Y., 1969. (17)M. J. S. Dewar and A. R. Lepley, J. Amer. Chem. SOC., 83, 4560 (1961). (18) R. L. Flurry, Jr., J. Phys. Chem., 6S, 1927 (1965). (19)J. N. Murrell, M. Randic, and D. R. Williams, Proc. Roy SOC., Ser. A, 284, 1865 (1965). (20) D. B. Chesnut and R. W. Moseley, Theor. Chim. Acta, 13, 230 (1969). (21)0.B. Nagy and J. 8. Nagy, ind. Chim. Be@., 36, 829 (1971). (22)J. L. Lippert, M. W. Hanna, and P. J. Trotter, J. Amer. Chem. SOC., 91,
4035 (1969). (23)W. C. Herndon and J. Feuer, J. Amer. Chem. Soc., SO, 5914 (1968). (24)H. Tsuchiya, F. Marumo, and Y. Saito, Acta Crystalogr., Sect. 19, 29, 659 (1973). (25)J. C. A. Boeyerns and F. H.Herbstein, J. Phys. Chem., 6S, 2153 (1965). (26)I. Ikemoto, K. Chlkaishi, K. Yakushi, and H. Kuroda, Acta Crystalogr., Sect. B, 28, 3503 (1972). (27)Z.Yoshida and T. Kobayashi, Theor. Chim. Acta, 23,67(1971). (28)D. B. Chesnut and P. E. S. Wormer, Theor. Chim. Acta, 20, 250 (1971). (29)P. Markov, C. R. Acad. Bulg. Sci., 22, 419 (1969). (30) B. Nelander, Theor. Chim. Acta, 25, 382 (1972). (31)M. J. S. Dewar and C. C. Thompson, Tetrahedron Suppl., No. 7, 97 (1966). (32)R. G. Jesaitis and A. Streitwieser, Jr., Theor. Chim. Acta, 17, 165 (1970). (33)R. S.Mulliken, J. Chem. Phys., 61, 20 (1964). (34)R. S.Mulliken, J. Amer. Chem. Soc.. 74, 811 (1952).
Polarized Electronic Spectra and Electronic Energy Levels of Some Tetragonal Nickel(l1) Complexes',* Jay S. Merriam and Jayarama R. Perumareddi" Department of Chemistry, Fiorida Atlantic University, Boca Raton, Florida 33432 (Received April 11, 7974)
Single crystal electronic spectra of quadrate nickel(I1) complexes, [Ni(py)cBrz], [Ni(py)&12], and [Ni(py)4(H20)2]12,where py is pyridine, and [Ni(im)4(H20)2]Br2,where im is imidazole, have been measured with polarized light a t liquid N2 temperature. The tetragonally split components of the first and second spin-allowed cubic bands in the pyridine complexes show definite polarization characteristics and are assigned on the basis of a comparison of the observed polarization pattern with that predicted for D4h vibronic intensity mechanism and the knowledge that the lower energy component of the first cubic band is 3E, in tetragonal complexes when the substituting axial ligands are of weaker field than the equatorial ligands of the parent octahedral system. No distinct polarization of the bands was observed in the spectrum of the tetraimidazole complex, and thus the quadrate components of the second cubic band were assigned assuming the same order of levels as in the corresponding tetrapyridine system. Only one component of the highest energy spin-allowed cubic band has been uncovered at -27 kK in all the systems. The assignment of this band and the spin-forbidden bands is based on fitting the observed band maxima with the calculated transition energies using d8 quadrate energy levels without and with spin-orbit perturbation and full configuration interaction. The importance of full configuration interaction has been underscored in arriving at the assignments by energy level fitting. It has been shown further that the differences in the bonding nature of ligands in the quadrate complexes in general can be understood in terms of ligand field parameters without recourse to the other kinds of parameters.
Introduction Although it is necessary to make use of complete crystal structure data for a definitive interpretation of assignments of the observed polarized bands in the polarized electronic spectra of a single crystal, it is still possible to obtain meaningful spectral data by measuring the polarized spectra along the extinction directions on a well-defined face of the single crystal. We use all accessible well-defined faces of the crystal for this purpose and only when we observe distinct polarized bands, will we be able to verify the predicted polarization pattern for a certain intensity mechanism and make assignments. All the polarized spectral data available on the quadrate chromium(II1) complexes, for instance, have been obtained by this p r ~ c e d u r e We .~ have obtained such polarized spectral data on four quadrate nickel(I1) systems. The assignments of the observed The Journal of Physical Chemistry, Vol. 79,No. 2, 1975
spectral bands and the derivation of electronic energy levels of these systems form the subject of this report. The complexes studied are [Ni(py)4Brz], [Ni(py)&lz], [Ni(py)4(H20)2]12,and [Ni(im)dHzO)~]Br~, all trans disubstituted derivative^.^^^ The spectra of dibromo- and dichlorotetrapyridine systems have been studied previously in the mull form6 and in the diffuse reflectance form.7 The diaquotetrapyridine system had been characterizeds although no spectral data had been reported. The [Ni(im)4(HzO)z]Brpsystem is new. We have synthesized it in this work and characterized it by elemental analysis and ascertained the trans structure from its electronic spectrum. Experimental Techniques Preparation of Complexes and Growth of Single Crystals. [Ni(py)4Brz] and [Ni(~y)~C12] were prepared by the
