Resonance Raman (RR) and time-resolved resonance Raman (TR3) spectra are reported for the complexes of divalent ruthenium with the ligands 4,4º-bipyrimidine (bpm) and 2,2º-bipyridine (bpy), i.e. and Ru(bpm) 3 2' Ground-state RR studies of the latter employing excitation with radiation of 413.1, 457.9 and Ru(bpy) 2 (bpm)2'. 514.5 nm permit the assignment of an electronic absorption band maximizing at 428.5 nm to a Ru(II)-to-bpy charge-transfer transition, while the band maximum at 516.0 nm is assigned to the Ru(II)-to-bpm charge-transfer band. The TR3 studies employing the 354.7 nm harmonic of a 10 ns pulsed Nd : YAG laser provide deÐnitive evidence for selective population of the bpm-localized excited state for the heteroleptic complex Ru(bpy) 2 (bpm)2'.

Titanium dioxide and a 100 W mercury spotlamp were used to photoreduce 100 ppm Hg aqueous mercuric chloride solutions. The solution's basicity and temperature were varied. Two optimum photoreduction conditions were determined: pH 9, 0 °C and pH 11, 40 °C. TiO 2 -assisted photoreduction at these two conditions lowered the concentration of mercury left in the solution to below 200 ppb. Methodology was developed to perform an overall mercury mass balance on the process. The overall mercury balance revealed that more than 97% (average 103% ( 6%) of the mercury removed from solution was deposited as mercury metal on the surface of the TiO 2 for the pH 9, 0 °C treatment conditions. This mercury could be driven off the TiO 2 surface by heating to 100 °C for half of an hour under nitrogen flow. The pH and temperature information under light and dark conditions is consistent with a pH-dependent adsorption of a dissociated mercuric species by hydroxide ions on the TiO 2 surface followed by nucleation of the reduced species. The TiO 2 assisted photoreduction process shows promise for remediation of mercuric waste below the EPA 200 ppb mercury disposal limit as well as the potential for recycling the mercury and TiO 2 catalyst.

The primary objectives of the present work are to investigate the extent to which an entrapped, tris-ligated polypyridine complex of divalent ruthenium is restricted from rotating within the supercage of Y-zeolite and to provide additional evidence for the high efficiency of synthetic procedures developed for the preparation of adjacent cage dyads entrapped within the Y-zeolite framework. Specifically, the Y-zeolite entrapped complex, Z-[Ru(bpy)(2)(pypz)(2+) ] (where the prefix, Z, indicated a zeolite entrapped complex, bpy = 2,2'-bipyridine and pypz = 2-2-pyridylpyrazine), which contains only one reactive peripheral nitrogen atom, is shown to react with the reagent, (H(2)O)Ru(NH(3))(5)(2+), to yield the entrapped Z-[Ru(bpy)(2)(pypz)-Ru(NH(3))(5)](4+) complex. Treatment with a large excess of bpy, according to previously documented procedures, leads to the formation of the entrapped adjacent cage dyad, Z-[Ru(bpy)(2)(pypz)(2+)/Ru(bpy)(3)(2+)], wherein the two-component complexes are entrapped in adjacent supercages. Spectroscopic measurements confirm the integrity of the component complexes and document a strong interaction between them. Most importantly, it is shown that a second treatment of this material with a large excess of the[(H(2)O)Ru(NH(3))(5)](2+) reagent does not lead to formation of significant amounts of Z-[Ru(bpy)(2)(pypz)-Ru(NH(3))(5)](4+); i.e., the presence of the Ru(bpy)(3)(2+) in the cage adjacent to the primary complex shields the latter from further reaction with the ruthenium pentammine reagent. This result demonstrates that, during the formation of the Ru(bpy)(3)(2+) secondary complex, the detached Ru(NH(3))(5)(2+) fragment does not drift into remote supercages, thereby providing unequivocal evidence for the high efficiency of the synthetic procedure for adjacent cage dyad formation. Furthermore, this result also makes it clear that rotation of the tris-ligated primary complex is restricted by the confinement of the Y-zeolite supercage to the extent that the single reactive peripheral nitrogen cannot be repositioned to a different window of the surrounding supercage.

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