The com
plex [7,10-
-H-7-CO-7,7-(PPh
3)
2-
isonido-7,8,9-ReC
2B
7H
9] has been synthesized by treatment of the com
plexsalt [NHMe
3][3,3-Cl
2-3,3-(CO)
2-
closo-3,1,2-ReC
2B
9H
11] with PPh
3 in refluxing THF (tetrahydrofuran) and isolated asintensely colored orange-red microcrystals. S
pectrosco
pic NMR and IR data have suggested that the
product hasa highly asymmetric structure with two inequivalent PPh
3 ligands and a single CO ligand. Measurement of
11BNMR s
pectra in
particular have indicated seven distinct boron vertexes, although the resulting cage degradation byremoval of two BH vertexes was confirmed only following X-ray crystallogra
phic analysis, which revealed the
pentadecahedral
isonido-7,8,9-ReC
2B
7 architecture. The
11B NMR resonances s
pan an enormous chemical shiftrange (
= 113), and this a
ppears to be a direct consequence of the deshielding of the boron vertex directlyo
pposite the quadrilateral
ReCCB a
perture. The new com
plex has been shown by electrochemical measurementsto undergo a reversible one-electron oxidation. Digitally simulated cyclic voltammograms su
pport a
pro
posed squarescheme (
E1/2 = 0.58, 0.69 V vs ferrocene) involving a reversible
isonido-closo transition of the metallacarboranecage. Most unusually for a metallacarborane com
plex, ambient tem
perature solutions in CH
2Cl
2 and DMF havebeen shown to be intensely
turquoise-blue fluorescent (
em = 442 nm,
= 0.012). Fluorescence s
pectrosco
pymeasurements in MeTHF (2-methyltetrahydrofuran) glass at 77 K have indicated that the likely cause of such abroad emission is dual fluorescence (
em = 404, 505 nm), with both emissions dis
playing vibronic structure. Followingexcited-state lifetime decay analysis, the emissive behavior has been accredited to metal-
perturbed
1IL states, withthe lower energy emission arising from a slight geometric distortion of the initially excited com
plex.