Heteropolynuclear Pt(II)-M(I) Clusters with a C∧N∧C Biscyclometalated Ligand

The mononuclear complex [(EtO2C-C boolean AND N boolean AND C)Pt(dmpyz)] (1) (dmpyz = 2,5-dimethylpyrazine) has been synthesized by reaction of [(EtO2C-C boolean AND N boolean AND C)Pt(dmso)] (A) with dmpyz in a 1:1 molar ratio in dichloromethane. Complex 1 is the precursor for preparing the homodinuclear complex [{(EtO2C-C boolean AND N boolean AND C)Pt}(2)(mu-dmpyz)] (2) and the heterotrinuclear clusters [{(EtO2C-C boolean AND N boolean AND C)Pt(dmpyz)}(2)M]X (M = Cu, X = PF6 (3); M = Ag, X = BF4 (4)). Compounds 1, 2, and 4 were studied by X-ray diffraction methods. In the crystal packing of 1 and 2, the molecules display short intermolecular pi center dot center dot center dot pi contacts, which control the solid-state emissive behavior. X-ray study on 4 shows two [Pt2Ag] sandwich-type clusters in the asymmetric unit, both with the two square-planar (R-CNC)Pt(dmpyz) moieties stabilized by two Pt -> Ag donor-acceptor bonds as well as by eta(1)- and eta(2)-Ag-C interactions. Intramolecular pi-pi contacts were found between the pyridine rings of the CNC ligands within the same Pt2Ag cluster. H-1 and Pt-195 NMR studies confirm that the Pt2M cluster is also retained in solution at room temperature. Pt-195 NMR spectra of 3 and 4 show signals shifted significantly downfield when comparing with that for the monomer (1), which is attributed to the presence of Pt M dative bonds. At lower temperatures (T = 193 K), the copper derivative definitely falls apart, whereas the silver one still holds up unbroken. In the solid state at 77 K, compounds 1-4 give red emissions arising from (3)pi pi excited states due to the intra- or intermolecular pi-pi contacts observed in the crystal structures. As expected, in glassy solutions (77 K), compound 3 displays analogous emissions to those from the starting material (1). Complexes 1 and 2 show structured emission bands that are particularly sensitive to the lambda(ex) (HE and LE). In contrast, 4 displays an unstructured emission at 680 nm with a shoulder at 556 nm; both are not dependent on the lambda(ex) DFT and TDDFT computational studies have been performed on 1 and 2, which support the conclusions drawn from the photophysical studies.