Syntheses, electronic absorption, emission, and ion-binding studies of platinum(III) C empty set N empty set C and terpyridyl complexes containing crown ether pendants.

Abstract

A series of platinum (II) C empty set N empty set C complexes, [Pt(C empty set N empty set C) (L)] (HC empty set N empty set CH=2,6-diphenylpyridine (dppy); L=Ph(2)PB15C5 (1, B15C5=benzo[15]crown-5), Ph(2)PDMP (2, DMP=3,4-dimethoxyphenyl), pyCOA15C5 (3, A15C5=aza[15]crown-5), pyCON(CH(2)CH(2)OCH(3))(2) (4), pyC[triple bond]CB15C5 (5), pyC[triple bond]CDMP (6)) and terpyridyl complexes, [Pt(trpy)(L)](X)(2) (trpy=2,2':6',2''-terpyridine; L=Ph(2)PB15C5, X=OTf (7 a), PF(6) (7 b); X=PF(6), L=Ph(2)PDMP (8), pyC[triple bond]CB15C5 (9), and pyC[triple bond]CDMP (10)) have been successfully synthesized and characterized. The structures of 1, 3, and 7 a have been determined by X-ray crystallography. Excitation of complexes 1-6 in EtOH/MeOH (4:1 v/v) glass gave high-energy structured emission bands, assigned as derived from states of metal-perturbed intraligand (IL) origin. At higher concentrations, complexes 3-6 each displayed an additional, structureless emission band at 600-615 nm, with complexes 5 and 6 showing an obvious increase in the intensity of this emission band when the concentration was increased further. In dichloromethane at room temperature, complexes 3-6 showed, in addition to the high-energy emission at 490-505 nm, an extra, broad emission band at 620-625 nm when the concentration was increased. The emission origins of the low-energy band in glass and in fluid solutions are suggested to be derived from the ground-state oligomerization or aggregation process of the complexes. In the solid state at room temperature, complexes 1-6 each showed a broad, unstructured emission band at 560-600 nm, which was shifted to lower energy upon cooling to 77 K. On the other hand, the terpyridyl analogues 7-10 displayed intense vibronic-structured intraligand (IL) emissions at 460-472 nm in butyronitrile glass at 77 K. Solid-state samples of 9 and 10 displayed strong phosphorescence upon photoexcitation at 298 K and 77 K, tentatively assigned as derived from states of Pt(d pi)-->pi*(trpy) (3)MLCT origin(MLCT=metal-to-ligand charge transfer). The ion-binding properties of complexes 5 and 9 for Na(+), Ba(2+), and K(+) ions have been studied by UV/Vis spectrophotometric methods, and confirmed by ESI mass spectrometric studies. The ion-binding properties for Na(+) ions have also been probed by (1)H NMR experiments. For the same crown ether-containing ligand and the same metal ions, the neutral cyclometalated complexes gave larger binding constants than the positively charged terpyridyl analogues.