The synthesis and characterization-of the tetrathiomolybdatorhodium(I) monoanionic complexes [L2Rh(mu-S)(2)MoS2](-) (L = CO (3); P(OPh)(3), (4), P(O-o-Tol)(3) (O-o-CH3C6H4)(3); 5), p(OMe)(3) (6), P(OEt)(3) (7), P(O-i-Pr)(3) (8); L-2 = COD (1,5-cyclooctadiene; 2), cis-dppen (cis-Ph2PCH=CHPPh2; 9), dppe (Ph2PCH2CH2PPh2; 10), dppb-(Ph2P(CH2)(4)PPh2; 11)) is presented. The complex 2 (NEt4+ salt) was characterized by X-ray diffraction analysis. A detailed DFT study of-the electronic structures of 2-4 and 6-8 has revealed the existence of extended electron-delocalization-Over the four-membered Rh(mu-S)(2)Mo ring and hence the possibility of electronic communication between-the metal centers. The electronic spectra were studied with TDDFT calculations, and the main absorption band in the visible region, was assigned to v(Rh -> Mo) :electron transfer transition, which is actually a HOMO-LUMO transition. The, v(Rh -> Mo) transition was found to correlate linearly both with Tolman's electronic parameter of the phosphite ligands and the calculated HOMO-LUMO gap of the complexes, rendering it a well-defined ligand electronic parameter, which describes the net donating ability of monodentate and bidentate ligands (CO, COD, phosphites, diphosphines). The study of the variation of Delta delta(P-31) and (1)J(Rh-P) of the phosphite complexes with respect to the QALE model electronic parameters chi(d), pi(p), and E-ar has succeeded in the assessment of the sigma and pi effects on these NMR. spectral parameters,