Investigating Recurrent Matere Bonds in Pertechnetate Compounds

In this manuscript we evaluate the X-ray structure of five new pertechnetate derivatives of general formula [M(H₂O)₄(TcO₄)₂], M=Mg, Co, Ni, Cu, Zn (compounds 1-5) and one perrhenate compound Zn(H₂O)₄(ReO₄)₂ (6). In these complexes the metal center exhibits an octahedral coordination with the pertechnetate units as axial ligands. All compounds exhibit the formation of directional Tc⋅⋅⋅O Matere bonds (MaBs) that propagate the [M(H₂O)₄(TcO₄)₂], into 1D supramolecular polymers in the solid state. Such 1D polymers are linked, generating 2D layers, by combining additional MaBs and hydrogen bonds (HBs). Such concurrent motifs have been analyzed theoretically, suggesting the noncovalent σ-hole nature of the MaBs. The interaction energies range from weak (~ -2 kcal/mol) for the MaBs to strong (~ -30 kcal/mol) for the MaB+HB assemblies, where HB dominates. In case of M=Zn, the corresponding perrhenate Zn(H₂O)₄(ReO₄)₂ complex, has been also synthesized for comparison purposes, resulting in the formation of an isostructural X-ray structure, corroborating the structure-directing role of Matere bonds.