[Pt(SCN)(4)](2-)-Based Coordination Polymers and Supramolecular Squares: Intermolecular Pt center dot center dot center dot H-C Interactions Probed by Luminescence Spectroscopy at Variable Pressure
Résumé
The structures of four types of supramolecular systems containing [Pt(SCN)(4)](2-) molecular units have been characterized. [Mn(bipy)(2)Pt(SCN)(4)](2)center dot 2MeOH (1) and [Zn(bipy)(2)-Pt(SCN)(4)](2)center dot 2MeOH (2) show cis-thiocyanato ligands bridging the Pt-II and Mn-II or Zn-II ions, leading to a molecular square motif. [Zn(bipy)(2)Pt(SCN)(4)](2) (3) presents chains where trans-thio-cyanato ligands bridge the Zn-II and Pt-II ions. For 1-3, free thio-cyanato ligands are coordinated to the Pt-II centers to complete the square-planar coordination. [Pb(bipy)(2)Pt(SCN)(4)](2) (4) reveals a two-dimensional sheet structure where all SCN-ligands bridge the Pb-II and Pt-II ions. [Pb(terpy) Pt(SCN)(4)](2) (5) is similar to 3, with two bridging trans-SCN-ligands and two that are coordinated only to the Pt-II centers. For all compounds, d-d luminescence is observed with band maxima at approximately 14600 cm(-1) (690 nm). Spectra show characteristic shifts with pressure, indicative of either intramolecular or intermolecular effects, depending on the sign of the shift. The pressure-dependent shifts for 1-5 show rich variations. A well-documented shift to higher energy due to metal-ligand bond compression is observed for 5 and can be used as a basis for a comparison. Compounds 1-4 show a shift of E-max to lower energy with pressures below 10 kbar. A change in sign for the shift of Emax occurs at 20, 12, and 10 kbar for 1, 2, and 3, respectively. For 4, only a shift to lower energy is observed. Competing intra-and intermolecular effects lead to these variations.