Resonance Raman (RR) spectroscopy has been used to probe the interaction between dipyridophenazine (dppz) complexes of ruthenium(II), [Ru(L)2(dppz)]2+ (L = 1,10-phenanthroline (1) and 2,2-bipyridyl (2)), and calf-thymus DNA. Ground electronic state RR spectra at selected probe wavelengths reveal enhancement patterns which reflect perturbation of the dppz-centered electronic transitions in the UV−vis spectra in the presence of DNA. Comparison of the RR spectra recorded of the short-lived MLCT excited states of both complexes in aqueous solution with those of the longer-lived states of the complexes in the DNA environment reveals changes to excited state modes, suggesting perturbation of electronic transitions of the dppz ligand in the excited state as a result of intercalation. The most prominent feature, at 1526 cm-1, appears in the spectra of both 1 and 2 and is a convenient marker band for intercalation. For 1, the excited state studies have been extended to the Δ and Λ enantiomers. The marker band appears at the same frequency for both but with different relative intensities. This is interpreted as reflecting the distinctive response of the enantiomers to the chiral environment of the DNA binding sites. The results, together with some analogous data for other potentially intercalating complexes, are considered in relation to the more general application of time-resolved RR spectroscopy for investigation of intercalative interactions of photoexcited metal complexes with DNA.

The electron-transfer site "Cua" is believed to be common to both nitrous oxide reductase and a number of cytochrome c oxidases.1•2 Mounting spectroscopic and analytical evidence2-5 that this center contains mixed-valence dicopper has rekindled interest in small-molecule models incorporating [Cu15Cu*5],This site is not spontaneously formed without steric enforcement but is achievable within a host which constrains the copper bonding orbitals to approach bonding distance (~2.4 Á) in a symmetric coordination environment which is acceptable to both + 1 and +2 oxidation states. Trigonal bipyramidal coordination geometry is particularly favorable, in terms of both redox preference considerations and effective overlap of the d,2 orbitals when collinear. Ideal hosts6•7 for such purposes are azacryptand ligands8 L1 and L2 whose dicopper cryptates, [Cu2L,]3+ (1) and [Cu2L2]3+ (2) are, on the basis of low-temperature EPR spectra,9 described as average-rather than mixed-valence complexes. 1 and 2 have been structurally characterized;10•11 here we present the X-ray crystal structure of a third variant, [Cu2L3]3+ (3) (synthesized by a Cu(I) template method, followed by Ag+ oxidation). In addition to the structure, we present spectroscopic data which enable a comparative analysis of the unusual electronic properties of 1-3.The X-ray crystallographic study of 314 confirms the close approach of the copper nuclei within the cryptate ligand cage (Figure 1) with a Cu-Cu distance of 2.419(1) Á, compared with 2.448 Á in l10 and 2.415(1) Á in 2.11 Apart from some variation in the torsion angle (N3-Cul-Cu2-N4), where 2 has 43.6°, 1 has 17°, and 3 has 56.3°, there is remarkably similar C3 symmetry in the structures of the three complexes.The similarity of structures 1-3 provides the basis for

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Comparison of the X-ray structures of two pairs of dicopper(I) and dicopper(1.5) cryptates provides evidence (over 0.5 Å contraction of the internuclear distance in one pair) for copper-copper bond formation. Although resonance Raman spectroscopy fails to identify a pure copper-copper stretching mode, because of extensive mixing of several low-frequency stretching and bending modes, isotopic substitution experiments indicate significant Cu-Cu character in a band around 250 cm(-)(1). A normal coordinate analysis broadly supports the spectroscopic findings. X-ray crystal structures are presented for the dicopper(1.5) complex Cu(2)imBT(ClO(4))(3), C(18)H(30)Cl(3)Cu(2)N(8)O(12), a = 9.140(4) Å, c = 30.35(3) Å, rhombohedral, R32, Z = 3, and the dicopper(I) Cu(2)imbistrpn(ClO(4))(2), C(24)H(42)Cl(2)Cu(2)N(8)O(8), a = 9.279(2) Å, c = 32.846(9) Å, rhombohedral, R32, Z = 3.

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