The substitution reactions by bulky tricyclohexylphosphine (PCy3) ligands on W6S8L6 (L = 4-tert-butylpyridine or PI-butylamine) clusters were investigated to prepare clusters with mixed axial ligands for low-dimensional cluster linking. When 4- 6 equiv of PCy3 are used to react with W6S8(4-tert-butylpyridine)(6) (4) in THF, cis-W6S8(PCy3)(4)(4- -tert-butylpyridine)(2) (1) is preferentially formed. But when starting with W6S8(n-butylamine)(6) (2), only W6S8(PCy3)(6) (3) is produced with 6 equiv of PCy3. Other conditions with fewer equivalents of PCy3 led to mixtures of partially substituted complexes in the W6S8L6-n(PCy3), (0 less than or equal to n less than or equal to 6, L = 4-tert-butylpyridine or n-butylamine) series. A significantly distorted structure for 1 helps to explain its preferential formation.H-1 NMR spectra were collected for clusters 1 and 2 and P-31 NMR spectre for 1 and W6S8(4-tert-butylpyridine)(6-n)(PCy3)(n) complexes. P-P coupling through P-W-W-P is reported for the first time in octahedral metal clusters and shown to be very useful in identifying nearly all the W6S8L6-n(PR3)(n) complexes and their stereoisomers in the mixtures even before individual species are isolated.