Structural variability in Ag(I) and Cu(I) coordination polymers with thioether-functionalized bis(pyrazolyl)methane ligands

We present here two ligand classes based on a bis(pyrazolyl)methane scaffold functionalized with a rigid (-Ph-S-Ph) or flexible (-CH(2)-S-Ph) thioether function: L(R)PhS (R = H, Me) and L(R)CH(2)S (R = H, Me, iPr). The X-ray molecular structures of Ag(I) and Cu(I) binary complexes with L(R)PhS or L(R)CH(2)S using different types of counterions (BF(4)(-), PF(6)(-), and CF(3)SO(3)(-)) are reported. In these complexes, the ligands are N(2) bound on a metal center and bridge on a second metal with the thioether group. In contrast, when using triphenylphosphine (PPh(3)) as an ancillary ligand, mononuclear ternary complexes M(L)PPh(3)](+) (M = Cu(I), Ag(I); L = L(R)PhS, L(R)CH(2)S) are formed. In these complexes, the more flexible ligand type, L(R)CH(2)S, is able to provide the N(2)S chelation, whereas the more rigid L(R)PhS ligand class is capable of chelating only N(2) because the thioether function preorganized, as it did in the coordination polymers, to point away from the metal center. Rigid potential-energy surface scans were performed by means of density functional theory (DFT) calculations (B3LYP/6-31+G) on the two representative ligands, L(H)PhS and L(H)CH(2)S. The surface scans proved that the thioether function is preferably oriented on the opposite side of the bispyrazole N(2) chelate system. These results confirm that both ligand classes are suitable components for the construction of coordination polymers. Nevertheless, the methylene group that acts as a spacer in L(H)CH(2)S imparts an inherent flexibility to this ligand class so that the conformation responsible for the N(2)S chelation is energetically accessible.