Intersystem crossing rates for 14 (low-spin) ^(high-spin) spin-equilibrium metal complexes of six-coordinate ironill) ( ^5T; AS = 2), iron(III) (2T ==^6A; AS = 2), and cobalt(II) (2E^4T; AS = 1) have been investigated in solution by Raman laser temperature-jump kinetics. Measurable first-order rate constants for the forward (ki) and reverse (/r-i) processes range from 4 X 105 to 2 X 107 s~1 , with four of the complexes having rate constants too large to measure (52 X 107 s"1) by the technique. The results are interpreted in terms of a model in which the spin multiplicity change is treated as an internal electron-transfer reaction.A number of first-row transition metal complexes with d5, d6, and d7 electronic configurations exhibit magnetic and spectroscopic behavior consistent with a thermal equilibrium between two states of differing spin multiplicity. For complexes in which the coordination number is constant and the donor atom set remains intact this phenomenon has come to be known as a "spin-equilibrium", with the state of lesser multiplicity being the low-spin (Is) state and that of higher multiplicity the high-spin (hs) state. Recent efforts have provided a variety of systems in which the spin equilibrium is present in solution.5™10 As a consequence, spin-equilibrium systems can be studied under conditions where perturbing influences from the lattice are minimized, and where the dynamic nature of the spin interconversion process is least likely to be inhibited. In solution

A new method of Internal standardization for capillary zone electrophoresis (CZE) to founded on the linear relation between each Ion's effective volume Injected and Its Inherent moMHy. The use of two internal standards allows the analyst to establish this relation quantitatively for each sample and to correct the analyte concentrations for variations In each Injection. The computational method given to simple, and we demonstrate that H can give reprodudMUtle• for manual CZE hydrodynamic and electrostatic Injections of under 1 % relative standard deviation.

Four new mononuclear ruthenium(II) complexes, [Ru(PTPI)3]2+ (PTPI = 2-p-tolylpyridinecarboxaldimine) and [Ru(bpy)2B]2+ [B = 2,9-dimethyl-1,10-phenanthroline (2,9-Me2phen), 4,4'-dimethyl-2,2'-bipyrimidine (4,4'-Me2bpyrm), and 2,2'-biimidazole (biimH2)], have been prepared as PF6~s alts and their electrochemical and photoemission properties investigated in solution.In addition, the ligand-bridged binuclear species [Ru(bpy)2(B)Ru(bpy)2](PF6)4 (B = bpyrm and 4,4'-Me2bpyrm) have also been obtained as by-products in the synthesis of the mononuclear complexes and separated from their mononuclear analogues by Sephadex chromatography. The mononuclear compounds all exhibit polarograms in acetonitrile consistent with quasi-reversible, one-electron [Ru(II) -* Ru(III)] oxidation processes with Ex¡2 potentials (SCE) ranging from 0.93 to 1.29 V. The E[/2 potentials suggest an ordering in the B ligand x-acceptor ability of biimH2 « 2,9-Me2phen ~bpy < 4,4/-Me2bpyrm < bpyrm. The binuclear [Ru(II),Ru(II)] complexes possess polarograms displaying two, one-electron oxidation processes (AEy/2 = 0.18 V) corresponding to production of the mixed-valence [(Ru(II),Ru(III)] and fully oxidized [Ru(III),Ru(III)] species. At room temperature and in acetonitrile, the mononuclear B = 2,9-Me2phen, bpyrm, 4,4'-Me2bpyrm, and biimH2 complexes have dx* absorption and luminescence spectra similar to that of [Ru(bpy)3]2+, with emission bands occurring between 588 and 600 nm in all cases. Under similar conditions, the bipyrimidine-bridged binuclear complexes do not exhibit emission spectra in the 350-800-nm region. The emission spectrum observed for the [Ru(PTPI)3]2+ complex is probably not of dx* origin, with the emission bands being blue shifted (at ~345 and 400 nm) relative to the 496and 552-nm dx* absorption bands.

content decreases. The reasons for this can be understood by examining correlation analysis in general. In the presence of noise, r0 becomes naturally depressed compared to what it is for less noisy versions of the same spectrum (9). This ultimately leads to failure in the PCA analysis. The autocorrelation of any spectrum gives rise to an r0 value of unity and a full correlation function that is symmetric. Thus, when two spectra are almost identical, their cross-correlation spectrum will also be almost symmetric. Even though the r0 value may be depressed in the presence of noise, the overall correlation function will maintain its symmetry if the spectra are indeed similar. Autoconvolution of the correlation spectrum to give rtym is an efficient method to quantify this symmetry. Thus, rsym utilizes all of the information in the correlation function whereas r0 only uses one point. This suggests that rsym would be an effective replacement for r" even when considering high S/N data. In practical terms, it is not very difficult to use both values and compare the results.

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Bis(N-methylethylenediaminesalicylaldiminato)iron(III) complexes, [ Fe(X-Salmee~~)~] (PF,). with their FeN,02 cores have been shown by variable-temperature magnetic susceptibility (10-300 K) and Mossbauer spectroscopy to be new (low-spin, S = 1/2) ~t (high-spin, S = 5 / 2 ) spin-equilibrium compounds in the solid state. From the Mossbauer spectra, an upper limit of -10' s-' has been estab!ished for the rate of k , k-1 intersystem crossing in the solid state. The spin equilibria are also supported in the solution state, as verified by variable-temperature (200-300 K) magnetic susceptibility and electronic spectroscopy measurements. In solution, laser Raman temperature-jump kinetics has been employed to directly measure the forward ( k , ) and reverse (kI) rate constants for the intersystem crossings with 2 X lo7 s-' 5 k 5 2 X 10' s-'. Intersystem crossing rate constant data for these bis-tridentate [Fe'11(X-Salmeen)2]+ complexes are discussed and compared to data already available for the electronically similar (same FeN402 core) but structurally different (hexadentate ligand) spin-equilibrium species, [Fe"1(Sal)2trien] t.(S = '/ 2 ) (S = 5/ 2)