The ground and metal-to-ligand (MLCT) excited electronic states of the complexes O~(bpy),,(P~)~-?+ (bpy = 2,2'-bipyridine, P2 = C~~-( C~H~)~P C H~H P ( C~H~)~; n = 1-3) have been studied by resonance Raman spectroscopy, time-resolved resonance Raman spectroscopy, and emission spectroscopy. The time-resolved resonance Raman evidence confirms that the charge-transfer electron density is localized in the lowest x * orbital of one bpy ligand rather than delocalized over the P* orbitals of all of the available bpy ligands on the vibrational time scale. The amount of charge transferred from the metal to bpy T * in the MLCT state has been determined. Application of Badger's rule to the Raman data and Franck-Condon analysis of the emission data lead to two independent determinations of average bond length displacements in the MLCT state. The two approaches yield displacement values that agree within 0.00 1-0.003 8, for the three complexes studied, suggesting that it may be possible to determine excited-state structures in solution with a precision similar to that of a good X-ray crystal structure. Analysis of time-resolved resonance Raman and emission data for Ru(bpy)?+, Ru(bpy),(en)2+, andfac-Re(bpy)(CO),CI by these methods yields results in agreement with the osmium data. The results suggest a general prescription for the determination of the molecular and electronic structures of electronically excited states in solution.As photochemical systems in solution, the metal-to-ligand charge-transfer (MLCT) excited states of d6 transition-metal complexes are rapidly becoming a paradigm. Information has appeared detailing both the photochemical and photophysical properties of many such systems.'-8 However, to date, essentially no quantitative information has emerged concerning molecular structure in this class of excited state in fluid solution. In this report we describe a study of this kind on the emitting MLCT excited states for the series of complexes Os(bpy),,(P2)3-;+ (bpy = 2,2'-bipyridine, P, = cis-l,2-bis(diphenylphosphino)ethylene (cis-Ph2PCH=CHPPh2); n = 1-3), which appear to be largely triplet in character but which contain considerable single character via spin-orbit coupling. The bases for our studies include both emission bandshape analyses and time-resolved resonance Raman spectroscopy. The results obtained allow us to infer quantitative information concerning both electronic and molecular structures for the M L C T excited states.Previously, time-resolved resonance Raman studies9-' I have conclusively established that the realistic formulation of the 600-ns-lived MLCT state of Ru(bpy)32+ is Ru"'(bpy), (bpy--),+; Le., the MLCT electron density is localized on a single bpy ligand on the time scale of molecular vibrations. This possibility had been suggested previously1as2 and has since been supported by several lines of evidence from a number of l a b o r a t~r i e s .~~~~~~J~J 'The experimental approaches employed in this study extend the conclusions concerning localization in MLCT excited states to the Os comp...

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The syntheses and characterization of several complexes of Mn(II) with cyclen derivatives having variable numbers of pendant N-acetic acid or N-acetamide arms are reported. X-ray crystallographic results are presented for Mn(DOTAM)Cl2·2H2O (monoclinic C2/c, a=18.5798(15), b=13.6006(11), c=10.5800(8) Å, β=110.490(1)°, Z=4), [Mn(DO3AM)][MnCl4]·EtOH (monoclinic P21/n, a=8.366(8), b=19.483(2), c=16.3627(16) Å, β=99.254(2)°, Z=4), and Mn(H2DOTA) (monoclinic C2/c, a=16.374(3), b=6.6559(13), c=16.750(3) Å, β=98.381(3)°, Z=4), which exhibit 8-, 7-, and 6-coordinate Mn(II), respectively. 1H relaxivity data in water at 20 MHz and 37°C is presented and interpreted in terms of a mechanism involving transient binding of water in an associative intermediate. Relaxivity studies in mixed water/methanol solvents are consistent with this interpretation.

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