Hydrogen-bonded supramolecular arrays of the [Re6(μ3-Se)8]2+core-containing clusters

Abstract

Site-differentiated clusters of the general formula [Re6(μ3-Se)8(PEt3)nL6−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)nI6−n]In−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)nL6−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.