The complex [7,10-
![](/images/entities/mgr.gif)
-H-7-CO-7,7-(PPh
3)
2-
isonido-7,8,9-ReC
2B
7H
9] has been synthesized by treatment of the complexsalt [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. Spectroscopic 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 spectra in particular have indicated seven distinct boron vertexes, although the resulting cage degradation byremoval of two BH vertexes was confirmed only following X-ray crystallographic analysis, which revealed thepentadecahedral
isonido-7,8,9-ReC
2B
7 architecture. The
11B NMR resonances span an enormous chemical shiftrange (
![](/images/gifchars/Delta.gif)
![](/images/gifchars/delta.gif)
= 113), and this appears to be a direct consequence of the deshielding of the boron vertex directlyopposite the quadrilateral
ReCCB aperture. The new complex has been shown by electrochemical measurementsto undergo a reversible one-electron oxidation. Digitally simulated cyclic voltammograms support a proposed squarescheme (
E1/2 = 0.58, 0.69 V vs ferrocene) involving a reversible
isonido-closo transition of the metallacarboranecage. Most unusually for a metallacarborane complex, ambient temperature solutions in CH
2Cl
2 and DMF havebeen shown to be intensely turquoise-blue fluorescent (
em = 442 nm,
![](/images/gifchars/Phi.gif)
= 0.012). Fluorescence spectroscopymeasurements 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 displaying 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 complex.