Heteropolynuclear Pt(II)–M(I) clusters with a C∧N∧C biscyclometalated ligand

The mononuclear complex [(EtO2C-CNC)Pt(dmpyz)] (1) (dmpyz = 2,5-dimethylpyrazine) has been synthesized by reaction of [(EtO2C-CNC)Pt(dmso)] (A) with dmpyz in a 1:1 molar ratio in dichloromethane. Complex 1 is the precursor for preparing the homodinuclear complex [{(EtO2C-CNC)Pt}2(μ-dmpyz)] (2) and the heterotrinuclear clusters [{(EtO2C-CNC)Pt(dmpyz)}2M]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 π···π 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 η1- and η2-Ag–C interactions. Intramolecular π–π contacts were found between the pyridine rings of the CNC ligands within the same Pt2Ag cluster. 1H and 195Pt NMR studies confirm that the Pt2M cluster is also retained in solution at room temperature. 195Pt 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 3ππ excited states due to the intra- or intermolecular π–π 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 λex (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 λex. DFT and TDDFT computational studies have been performed on 1 and 2, which support the conclusions drawn from the photophysical studies.