A series of luminescent mono-and binuclear cyclometalated platinum(II) complexes, namely [Pt(L [1][2][3][4][5][6] )Cl] (1a-6a; HL 1-6 ) 4-(aryl)-6-phenyl-2,2′-bipyridine; aryl ) H (1), phenyl (2), 4-chlorophenyl (3), 4-tolyl (4), 4-methoxyphenyl (5), 3,4,5-trimethoxyphenyl ( 6)), [Pt(L 1 )E] + (E ) py ( 7), PPh 3 (8)), [Pt 2 (L 1-6 ) 2 (µ-dppm)] 2+ (1b-6b, dppm ) bis(diphenylphosphino)methane), [Pt 2 (L 1 ) 2 (µ-pz)] + (9, Hpz ) pyrazole), and [Pt 2 (L 1 ) 2 (µ-dppC n )] 2+ (dppC n ) bis(diphenylphosphino)propane (10, n ) 3) and -pentane (11, n ) 5)), were synthesized in order to examine fluid-and solid-state oligomeric d 8 -d 8 and ligand-ligand interactions. The molecular structures of 4b(ClO 4 ) 2 and 9(PF 6 ) reveal intramolecular Pt-Pt distances of 3.245(1) and 3.612(2) Å, respectively. While minimal metal-metal communication is expected for 9, weak π-π interactions are possible. All complexes described in this work are emissive in fluid solution at room temperature. Negligible changes in emission energy are detected by incorporating different aryl substituents into the 4-position of 6-phenyl-2,2′-bipyridine, and this indicates little electronic delocalization between them. Self-quenching of the 3 MLCT emission by the mononuclear derivatives are observed in CH 2 Cl 2 at 298 K, and a red shift in the emission energy is exhibited by complex 7 in acetonitrile at 77 K. The fluid emissions of the µ-dppm species 1b-6b at λ max 652-662 nm appear at substantially lower energies than their mononuclear counterparts and show dramatic solvatochromic effects. These emissions are ascribed to 3 [dσ*, π*] excited states. In contrast, the emission of 10 and 11, bearing long bridging diphosphine ligands, are attributed to 3 MLCT states of non-interacting [Pt(L 1 )] moieties. Significantly, the luminescence of the µ-pyrazolate complex 9 displays transitional features which are reminiscent of both 3 [dσ*, π*] and 3 MLCT excited states. Hence a relationship is observed between emission energy, the nature of the lowest energy excited state, and metal-metal interactions. The excited-state redox potential [E(*Pt 2 2+ /Pt 2 + )] of 1b has been estimated by electrochemical studies (1.61 V vs NHE) and by quenching experiments with aromatic hydrocarbons (1.63 V vs NHE).

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The mononuclear cyclometalated Pd(II) complexes [Pd(L1)X] (HL1 = 6-phenyl-2,2'-bipyridine; X = Cl, la; Br, 1b; I, 1c), [Pd(L1)PPh3]+ (1d), [Pd(L2-5)Cl] [2a-5a, HL2-5 = 4-(aryl)-6-phenyl-2,2'-bipyridine; aryl = phenyl (2), 4-chlorophenyl (3), 4-tolyl (4), 4-methoxyphenyl (5)] and the binuclear derivatives [Pd2(L1-5)2(mu-dppm)]2+ (1e-5e, dppm = bis(diphenylphosphino)methane) and [Pd2(L1)2(mu-dppCs)]2+, (1f, dppC5 = 1,5-bis(diphenylphosphino)pentane) were prepared. The crystal structures of 1d(ClO4), 1e(ClO4)2 x DMF, and 2e(ClO4)2 have been determined by X-ray crystallography. The magnitude of the Pd-Pd distances in le and 2e (3.230(1) and 3.320(2) A, respectively) suggest minimal metal-metal interaction, although pi-stacking of the aromatic ligands (interplanar separations 3.34 and 3.35 A, respectively) is evident. All complexes display low-energy UV absorptions at lambda approximately 390 nm, which are tentatively assigned to 1MLCT transitions; red shifts resulting from Pd-Pd interactions in the binuclear species are not apparent. The complexes in this work are non-emissive at 298 K, but the cationic derivatives exhibit intense luminescence at 77 K. The structured emissions of 1d and 1f in MeOH/EtOH glass (lambdamax 467-586 nm) and all cationic species in the solid state (lambdamax 493-578 nm) are assigned to intraligand excited states. Complexes le-5e display dual emissions in MeOH/EtOH glass at 77 K, and the broad structureless bands at lambdamax 626-658 nm are attributed to pi-pi excimeric IL transitions. A comparison between the photophysical properties of Pd(II) and Pt(II) congeners is presented.

Two gold complexes, [AuV4-MeOPh-(Phbipy)}Cl1CF3SO3 1 and [A~~~l(4-MeOPh-terpy)CII.(ClO~)~ 2 [CMeOPh-(Phbipy) = 4'-(4-methoxyphenyl)-6'-phenyl-Z,Z'-bipyridine, 4-MeOPh-terpy = 4'-(4-methoxyphenyl) -Z,Z',6',Z''-terpyridinel are prepared, and their interactions with calf-thymus DNA, poly(dG-dC)* and poly(dA-dT)2, investigated by spectroscopic means; in the reaction with ct DNA, 1 has a higher binding constant than 2, but the latter has a higher degree of AT specificity.