Site-differentiated clusters of the general formula [Re₆(μ₃-Se)₈(PEt₃)_nL_6−n](SbF₆)₂ [L = nicotinamide: 1 (n = 5), 2 (n = 4, trans-), and 3 (n = 4, cis-)] have been made by ligand substitution reactions of the corresponding acetonitrile solvates [Re₆(μ₃-Se)₈(PEt₃)_n(MeCN)_6−n](SbF₆)₂ (n = 5; n = 4, cis- and trans-) with nicotinamide. De-iodination of [Re₆(μ₃-Se)₈(PEt₃)_nI_6−n]I_n−4 [n = 4 (cis- and trans-), 5] with AgSbF₆ in the presence of 3,5-pyridinedicarboxylic acid (PDCA) produced a related series of cluster complexes [Re₆(μ₃-Se)₈(PEt₃)_nL_6−n](SbF₆)₂ [L = PDCA: 4 (n = 5), 5 (n = 4, trans-), and 6 (n = 4, cis-)]. Retention of stereochemistry in each case was confirmed by ¹H and ³¹P NMR and these new cluster derivatives were further characterized by satisfactory microanalyses (CHN). In addition, the solid-state structure of trans-[Re₆(μ₃-Se)₈(PEt₃)₄(PDCA)₂](SbF₆)₂ (5) was established crystallographically, which revealed zigzag arrays of clusters mediated by complementary hydrogen-bonding interactions involving only one of the acid groups per PDCA ligand; the second acid group extends into a small space between the chains and appears to be in close contact with a Se atom on a neighboring cluster, as well as a hydrogen atom of that cluster's triethylphosphine ligands. Each polymer chain is skewed with respect to its neighbors, forming a pronounced lamellar structure.