A systematic substitution of the terminal chlorides coordinated to the hexanuclear cluster [Re(6)S(8)Cl(6)](4-) has been conducted. The following complexes: [Re(6)S(8)(PEt(3))Cl(5)](3-) (1), cis- (cis-2) and trans-[Re(6)S(8)(PEt(3))(2)Cl(4)](2-) (trans-2), mer- (mer-3) and fac-[Re(6)S(8)(PEt(3))(3)Cl(3)](-) (fac-3), and cis- (cis-4) and trans-[Re(6)S(8)(PEt(3))(4)Cl(2)] (trans-4) were synthesized and fully characterized. Compared to the substitution of the halide ligands of the related [Re(6)S(8)Br(6)](4-) and [Re(6)Se(8)I(6)](3-) clusters, the chloride ligands are slower to substitute which allowed us to prepare the first monophosphine cluster (1). In addition, the synthesis of fac-3 was optimized by using cis-2 as the starting material, which led to a significant increase in the overall yield of this isomer. Notably, we observed evidence of phosphine isomerization taking place during the preparation of the facial isomer; this was unexpected based on the relatively inert nature of the Re-P bond. The structures of Bu(4)N(+) salts of trans-2, mer-3, and fac-3 were determined using X-ray crystallography. All compounds display luminescent behavior. A study of the photophysical properties of these complexes includes measurement of the excited state lifetimes (which ranged from 4.1-7.1 μs), the emission quantum yields, the rates of radiative and non-radiative decay, and the rate of quenching with O(2). Quenching studies verify the triplet state nature of the excited state.

The photophysical properties of rhenium selenide cluster complexes containing various nitrogen-donor ligands (nitrile, azide, tetrazolate, and triazolate) are reported. These octahedral clusters are all based on the site-differentiated [Re 6 Se 8 ] 2+ core and have the general formula [Re 6 Se 8 -(PEt 3 ) 5 L] n+ (L = nitrogen-donor ligand). The excited-state lifetimes, emission quantum yields, the rates of radiative and nonradiative decay, and the rate of quenching with O 2 are reported for thirteen different cluster complexes. The longest excited-state lifetime was found for [Re 6 Se 8 (PEt 3 ) 5 (p-amino- [a]2254 benzonitrile)][BF 4 ] 2 . The series of benzonitrile and phenylsubstituted tetrazolate complexes allowed us to investigate the electronic impact of the para substituent; electrochemical and computational studies support metal-to-ligand charge transfer character in the excited-state wave function for the p-nitrobenzonitrile complex. Notably, the substituents of the benzonitrile ligands have a greater effect on the photophysical properties than the substituents of the phenyltetrazolate ring.