Density Functional Calculations on Electronic Circular Dichroism Spectra of Chiral Transition Metal Complexes Jochen Autschbach,* ,² Francisco E. Jorge, ‡ and Tom Ziegler ²,§ Department of Chemistry, UniVersity of Calgary, Calgary, Alberta, Canada T2N 1N4, and Departamento de Fisica, UniVersidade Federal do Espirito Santo, 29060-900 Vitoria, ES, Brazil Received September 24, 2002 Time-dependent density functional theory (TD-DFT) has for the first time been applied to the computation of circular dichroism (CD) spectra of transition metal complexes, and a detailed comparison with experimental spectra has been made. Absorption spectra are also reported. Various Co III complexes as well as [Rh(en) 3 ] 3+ are studied in this work. The resulting simulated CD spectra are generally in good agreement with experimental spectra after corrections for systematic errors in a few of the lowest excitation energies are applied. This allows for an interpretation and assignment of the spectra for the whole experimentally accessible energy range (UV/vis). Solvent effects on the excitations are estimated via inclusion of a continuum solvent model. This significantly improves the computed excitation energies for charge-transfer bands for complexes of charge + 3, but has only a small effect on those for neutral or singly charged complexes. The energies of the weak d-to-d transitions of the Co complexes are systematically overestimated due to deficiencies of the density functionals. These errors are much smaller for the 4d metal complex. Taking these systematic errors and the effect of a solvent into consideration, TD-DFT computations are demonstrated to be a reliable tool in order to assist with the assignment and interpretation of CD spectra of chiral transition metal complexes. 1. Introduction Circular dichroism (CD) spectroscopy 1-4 is one of the major experimental tools employed in the characterization of chiral metal complexes and the investigation of their electronic and geometric structure. Theoretical methods 5-9 can help greatly in the assignment and interpretation of electronic CD spectra for these compounds. Much has been learned since the 1960s from theoretical approaches based on the ligand field model. 3,10-18 However, these methods are specifically developed in order to describe the d-to-d (or f-to- f) transitions at the metal center, while the nature of the charge-transfer ligand-to-d excitations cannot be addressed. Excitations within the ligands of chiral complexes have also * Author to whom correspondence should be addressed. E-mail: jochen.autschbach@chemie.uni-erlangen.de. Present address: Lehrstuhl fu¨r Theoretische Chemie, Universita¨t Erlangen, Egerlandstrasse 3, D-91058 Erlangen, Germany. ² University of Calgary. ‡ Universidade Federal do Espirito Santo. § E-mail: ziegler@ucalgary.ca. (1) Charney, E. The molecular basis of optical actiVity; John Wiley & Sons Ltd.: New York, 1979. (2) Caldwell, D. J.; Eyring, H. The theory of optical actiVity; Wiley- Interscience: New York, 1971. (3) Ballhausen, C. J. Molecular Electronic Structures of Transition Metal Complexes; McGraw-Hill: London, 1979. (4) Nakanishi, K., Berova, N., Woody, R. W., Eds. Circular dichroism: principles and applications; VCH Publishers Inc.: New York, 1994. (5) Condon, E. U. ReV. Mod. Phys. 1937, 9, 432-457. (6) Moscowitz, A. AdV. Chem. Phys. 1962, 4, 67-112. (7) Hansen, A. E.; Bouman, T. D. AdV. Chem. Phys. 1980, 44, 545-644. (8) Oddershede, J. Propagator methods. In Ab initio methods in quantum chemistry; Lawley, K. P., Ed.; John Wiley & Sons: London, 1987; Vol. II. (9) Oddershede, J. AdV. Quantum Chem. 1978, 11, 275-352. (10) Volosov, A.; Woody, R. W. Theoretical approach to natural electronic optical activity. In Circular Dichroism. Principles and Applications; Nakanishi, K., Berova, N., Woody, R. W., Eds.; VCH: New York, 1994. (11) Kuroda, R.; Saito, Y. Circular dichroism of inorganic complexes: Interpretation and applications. In Circular Dichroism. Principles and Applications; Nakanishi, K., Berova, N., Woody, R. W., Eds.; VCH: New York, 1994. (12) Douglas, B. E., Saito, Y., Eds. Stereochemistry of Optically ActiVe Transition Metal Compounds; ACS Symposium Series 119; Americal Chemical Society: Washington, DC, 1980. (13) Mason, S. F.; Seal, R. H. Mol. Phys. 1976, 31, 755-775. (14) Schipper, P. E. J. Am. Chem. Soc. 1978, 100, 1433-1441. (15) Richardson, F. S.; Faulkner, T. R. J. Chem. Phys. 1982, 76, 1595- 1606. (16) Saxe, J. D.; Faulkner, T. R.; Richardson, F. S. J. Chem. Phys. 1982, 76, 1607-1623. (17) Strickland, R. W.; Richardson, F. S. Inorg. Chem. 1973, 12, 1025- 1036. (18) Evans, R. S.; Schreiner, A. F.; Hauser, P. J. Inorg. Chem. 1974, 13, 2185-2192. Inorg. Chem. 2003, 42, 2867-2877 10.1021/ic020580w CCC: $25.00 © 2003 American Chemical Society Inorganic Chemistry, Vol. 42, No. 9, 2003 2867 Published on Web 04/08/2003