This work describes the synthesis of compounds [Pt(C=N)(NCMe) 2]ClO 4 (C=N = 7,8-benzoquinolinato (bzq), 2-phenylpyridinato (ppy)) and their use as precursors for the preparation of the cyanido complexes [Pt(C=N)(CN) 2] (-), which were isolated as the potassium, [K(H 2O)][Pt(C=N)(CN) 2] [C=N = bzq ( 3a), ppy ( 4a)], and the tetrabutylammonium, NBu 4[Pt(C=N)(CN) 2] [C=N = bzq ( 5), ppy ( 6)], salts. The difference in the cation has an influence on the solubility, color, and emission properties of these compounds. Compounds 5 and 6 are yellow and soluble in organic solvents, while the potassium salts are also soluble in water and exhibit two forms: the water-containing [K(H 2O)][Pt(C=N)(CN) 2] [C=N = bzq ( 3a), ppy ( 4a)] complexes and the anhydrous ones K[Pt(C=N)(CN) 2] [C=N = bzq ( 3b), ppy ( 4b)], the former being strongly colored [red ( 3a) or purple ( 4a)] and the latter being yellow. Compounds 3a and 4a transform reversibly into the yellow, 3b and 4b, compounds upon desorption/ reabsorption of water molecules from the environment. The red solid, 3a, also exhibits vapochromic behavior when it is exposed to volatile organic compounds, the shortest response times being those observed for methanol and ethanol. UV-vis and emission spectra of all compounds were recorded both in solution and in the solid state. In methanol solution, the difference in the cation causes no differences in the absorption nor in the emission spectra, which is as expected for the monomer species. However, in the solid state, the differences are notable. For both the red ( 3a) and purple ( 4a) compounds, a prominent absorption, which has maxima at about 550 nm and is responsible for their intense colors, as well as a structureless emission at lambda > 700 nm that suffers a significant red-shift upon cooling, are due to (1,3)MMLCT (= metal-metal-to-ligand charge transfer) [dsigma*(Pt) --> pi*(C=N)] transitions characteristic of linear-chain platinum complexes with short Pt...Pt contacts. Time-dependent density-functional theory calculations on complex 5 and the X-ray diffraction study on compound [K(OCMe 2) 2][Pt(ppy)(CN) 2] ( 4c) are also included.

The half-lantern compound [{Pt(bzq)(μ-C(7)H(4)NS(2)-κN,S)}(2)]·Me(2)CO (1) was obtained by reaction of equimolar amounts of potassium 2-mercaptobenzothiazolate (KC(7)H(4)NS(2)) and [Pt(bzq)(NCMe)(2)]ClO(4). The Pt(II)···Pt(II) separation in the neutral complex [{Pt(bzq)(μ-C(7)H(4)NS(2)-κN,S)}(2)] is 2.910 (2) Å, this being among the shortest observed in half-lantern divalent platinum complexes. Within the complex, the benzo[h]quinoline (bzq) groups lie in close proximity with most C···C distances being between 3.3 and 3.7 Å, which is indicative of significant π-π interactions. The reaction of 1 with halogens X(2) (X(2) = Cl(2), Br(2), or I(2)) proceeds with a two-electron oxidation to give the corresponding dihalodiplatinum(III) complexes [{Pt(bzq)(μ-C(7)H(4)NS(2)-κN,S)X}(2)] (X = Cl 2, Br 3, I 4). Their X-ray structures confirm the retention of the half-lantern structure and the coordination mode of the bzq and the bridging ligand μ-C(7)H(4)NS(2)-κN,S. The Pt-Pt distances (Pt-Pt = 2.6420(3) Å 2, 2.6435(4) Å 3, 2.6690(3) Å 4) are shorter than that in 1 because of the Pt-Pt bond formation. Time dependent-density functional theory (TD-DFT) studies performed on 1 show a formal bond order of 0 between the metal atoms, with the 6p(z) contribution diminishing the antibonding character of the highest occupied molecular orbital (HOMO) and being responsible for an attractive intermetallic interaction. A shortening of the Pt-Pt distance from 2.959 Å in the ground state S(0) to 2.760 Å in the optimized first excited state (T(1)) is consistent with an increase in the Pt-Pt bond order to 0.5. In agreement with TD-DFT calculations, the intense, structureless, red emission of 1 in the solid state and in solution can be mainly attributed to triplet metal-metal-to-ligand charge transfer ((3)MMLCT) [dσ*(Pt-Pt) → π*(bzq)] excited states. The high quantum yields of this emission measured in toluene (44%) and solid state (62%) at room temperature indicate that 1 is a very efficient and stable (3)MMLCT emitter, even in solution. The high luminescence quantum yield of its red emission, added to its neutral character and the thermal stability of 1, make it a potential compound to be incorporated as phosphorescent dopant in multilayer organic light-emitting devices (OLEDs).

Neutralization reactions of the appropriate precursors (NBu(4))[Pt(bzq)(C[triple bond, length as m-dash]C-R)(2)] and (NBu(4))[Pt(Cinsertion markN)(CN)(2)] (Cinsertion markN = bzq, ppy) with Tl(I) salts afford [{PtTl(bzq)(C[triple bond, length as m-dash]C-R)(2)}(2)] [R = Ph (), C(5)H(4)N-2 ()] and [PtTl(Cinsertion markN)(CN)(2)] [Cinsertion markN = bzq (), ppy ()], respectively. X-Ray diffraction studies of complexes show the existence of Pt(II)-Tl(I) bonds. In .CH(2)Cl(2) the platinum-thallium units are associated in tetranuclear Pt(2)Tl(2) entities which generate a 3-D network through short Tlpi(2-py) and pipi(bzq) contacts and additional weak Cl(2)HC-Hpi(C[triple bond, length as m-dash]C) nonclassical interactions. Compounds and show extended 2-D networks by connection of the organometallic "PtTl(Cinsertion markN)(CN)(2)" units, through secondary TlN[triple bond, length as m-dash]C contacts and moderate pipi(bzq) interactions in the case of . Complexes containing the bzq group exhibit in the solid state "luminescence thermochromism" associated to dual emission. At room temperature they show an intense, visible orange (: lambda(max) 625 nm), orange-red (: lambda(max) 640 nm) or yellow (: lambda(max) 582 nm) luminescence that changes to yellowish-green (: lambda(max) 532 nm) or green [: lambda(max) 524 nm; : lambda(max) 512 nm] upon cooling to 77 K. The unstructured low energy (LE) bands attributed to (3)pi-pi* excimeric emissions due to extensive pi-pi interactions are dominant at room temperature. By contrast, the high energy (HE) bands are highly structured and predominant at 77 K. Due to the presence of Pt-Tl bonds these HE emissions are bathochromically shifted in relation to the precursors' ones and have been tentatively assigned to a metal-metal'-to-ligand (bzq) charge transfer MM'LCT [d/s sigma*(Pt,Tl) -->pi*(Cinsertion markN)] mixed, as in the corresponding precursors, with some intraligand (3)IL[pi(Cinsertion markN') -->pi*(Cinsertion markN)] in and or ligand-to-ligand charge transfer (alkynyl to bzq) (3)LL'CT in complexes and . Complex [PtTl(ppy)(CN)(2)] , which does not show short contacts between the phenylpyridinate groups in solid state, only shows the HE green structured band both at 298 K and at 77 K. Only the cyanide derivatives are soluble and both spectroscopic (NMR and UV-Vis) and emission data (MeOH, 298 K and 77 K) indicate that the Pt(II)-Tl(I) bond breaks down in solution.

The imidazolium salt 3-methyl-1-(naphthalen-2-yl)-1H-imidazolium iodide (2) has been treated with silver(I) oxide and [{Pt(μ-Cl)(η(3)-2-Me-C3H4)}2] (η(3)-2-Me-C3H4 = η(3)-2-methylallyl) to give the intermediate N-heterocyclic carbene complex [PtCl(η(3)-2-Me-C3H4)(HCC*-κC*)] (3) (HCC*-κC* = 3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene). Compound 3 undergoes regiospecific cyclometallation at the naphthyl ring of the NHC ligand to give the five-membered platinacycle compound [{Pt(μ-Cl)(CC*)}2] (4). Chlorine abstraction from 4 with β-diketonate Tl derivatives rendered the corresponding neutral compounds [Pt(CC*)(L-O,O')] {L = acac (HL = acetylacetone) 5, phacac (HL = 1,3-diphenyl-1,3-propanedione) 6, hfacac (HL = hexafluoroacetylacetone) 7}. All of the compounds (3-7) were fully characterized by standard spectroscopic and analytical methods. X-ray diffraction studies were performed on 5-7, revealing short Pt-Pt and π-π interactions in the solid-state structure. The influence of the R-substituents of the β-diketonate ligand on the photophysical properties and the use of the most efficient emitter, 5, as phosphor converter has also been studied.