Supramolecular Frameworks Based on Rhenium Clusters Using the Synthons Approach

The reaction of the K(4)[{Re(6)S(i)(8)}(OH)(a)(6)]·8H(2)O rhenium cluster salt with pyrazine (Pz) in aqueous solutions of alkaline or alkaline earth salts at 4 °C or at room temperature leads to apical ligand exchange and to the formation of five new compounds: [trans-{Re(6)S(i)(8)}(Pz)(a)(2)(OH)(a)(2)(H(2)O)(a)(2)] (1), [cis-{Re(6)S(i)(8)}(Pz)(a)(2)(OH)(a)(2)(H(2)O)(a)(2)] (2), (NO(3))[cis-{Re(6)S(i)(8)}(Pz)(a)(2)(OH)(a)(H(2)O)(a)(3)](Pz)·3H(2)O (3), [Mg(H(2)O)(6)](0.5)[cis-{Re(6)S(i)(8)}(Pz)(a)(2)(OH)(a)(3)(H(2)O)(a)]·8.5H(2)O (4), and K[cis-{Re(6)S(i)(8)}(Pz)(a)(2)(OH)(a)(3)(H(2)O)(a)]·8H(2)O (5). Their crystal structures are built up from trans- or cis-[{Re(6)S(i)(8)}(Pz)(a)(2)(OH)(a)(4−x)(H(2)O)(a)(x)](x−2) cluster units. The cohesions of the 3D supramolecular frameworks are based on stacking and H bonding, as well as on H(3)O(2−)bridges in the cases of (1), (2), (4), and (5) compounds, while (3) is built from stacking and H bonding only. This evidences that the nature of the synthons governing the cluster unit assembly is dependent on the hydration rate of the unit.