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 (-CH2-S-Ph) thioether function: (LPhS)-Ph-R (R = H, Me) and (LCH2S)-C-R (R = H, Me, iPr). The X-ray molecular structures of Ag(I) and Cu(I) binary complexes with (LPhS)-Ph-R or (LCH2S)-C-R using different types of counterions (BF4-, PF6-, and CF3SO3-) 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 (PPh3) as an ancillary ligand, mononuclear ternary complexes [M(L)PPh3] (M = Cu(I), Ag(I); L = (LPhS)-Ph-R, (LCH2S)-C-R) are formed. In these complexes, the more flexible ligand type, (LCH2S)-C-R, is able to provide the N2S chelation, whereas the more rigid (LPhS)-Ph-R 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, (LPhS)-Ph-H and (LCH2S)-C-H. 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 (LCH2S)-C-H imparts an inherent flexibility to this ligand class so that the conformation responsible for the N2S chelation is energetically accessible.