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).

Mononuclear cationic cyclometalated palladium complexes [Pd(C∧N)(NCMe)2]ClO4 [C∧N = benzoquinolinate (bzq) 1, 2-phenylpyridinate (ppy) 2], analogous to the previously described platinum complexes [Pt(C∧N)(NCMe)2]ClO4 [C∧N = bzq 3, ppy 4], and the isocyanide platinum benzoquinolinate [Pt(bzq)(CNR)2]X (R = tert-butyl (t-Bu, 5), 2,6-dimethylphenyl (Xyl, 6), 2-naphthyl (2-Np, 7); X = ClO4 − a, PF6 − b) have been prepared and characterized. The solid-state structures of the cation [Pt(C∧N)(CN-Xyl)2]+ with different counteranions (6a and 6b) were found to be different in terms of packing, although in both cases they were dominated by π−π intermolecular interactions. The influence of the counteranion in the UV−vis spectra, both in solution and in the solid state of 5−7, is negligible. Time-dependent density-functional theory calculations on cation [Pt(C∧N)(CN-Xyl)2]+ (6 + ) have been performed, suggesting that the lowest absorption is 1IL in nature mixed with some 1MLCT character. Acetonitrile platinum complexes (3, 4) are photoluminescent at low temperature (77 K) and at room temperature, whereas analogous palladium complexes (1, 2) are emissive only at 77 K (solid-state and glassy acetonitrile). Isocyanide derivatives 5−7 are intensely luminescent in all media. The emissions are assigned to ligand-centered fluorescence, to mixed 3LC/3MLCT phosphorescence, or to excimeric (or ground-state) 3ππ* or 3MMLCT [σ*(M)→π*(C∧N)] transitions depending on the medium and the excitation wavelength. The effect of the counteranion in governing the degree of aggregation and the extent of the interactions seem to be relatively important, especially in a rigid medium, with the smaller ClO4 − inducing a more excimeric character. The tendency to form π−π excimers and/or Pt···Pt oligomerization follows the order CN-2-Np > CN-t-Bu > CN-Xyl and ClO4 − > PF6 −.

The reaction of fac-[IrH2(NCCH3)3(PiPr3)]BF4 (1) with potassium pyrazolate gave the binuclear 34-electron complex [Ir2(μ-H)(μ-Pz)2H3(NCCH3)(PiPr3)2] (2). The structure of 2 was determined by X-ray diffraction. An electrostatic potential calculation located three terminal hydride ligands and one hydride bridging both iridium centers. The feasibility of this arrangement was studied by EHMO calculations. The spectroscopic data for 2 show that the complex is rigid in solution on the NMR time scale. In solution, the acetonitrile ligand of 2 dissociates. The activation parameters for this dissociation process in toluene-d 8 are ΔH ⧧ = 20.9 ± 0.6 kcal mol-1 and ΔS ⧧ = 2.5 ± 1.3 e.u. Reaction of 2 with various Lewis bases (L) gives the substitution products [Ir2(μ-H)(μ-Pz)2H3(L)(PiPr3)2] (L = C2H4 (3), CO (4), HPz (5)). The reaction of complex 5 with C2H4 yields the ethyl derivative [Ir2(μ-H)(μ-Pz)2(C2H5)H2(HPz)(PiPr3)2] (6); this reaction is reversible. Complexes 2 and 3 react with CHCl3 to give CH2Cl2 and the compounds [Ir2(μ-H)(μ-Pz)2H2(Cl)(L)(PiPr3)2] (L = NCCH3 (7), C2H4 (8)). In the 1H NMR spectra of 2 − 6, the signal of the bridging hydride ligand shows two very different J HP couplings; in contrast, for the chloride complexes 7 and 8, two equal J HP couplings are observed. NOE and T 1 measurements lead to the conclusion that in complexes 2 − 6 the hydride bridges the iridium centers in a nonsymmetric fashion, whereas for 7 and 8 the bridge is symmetrical. This structural feature largely influences the reactivity. Compounds 2 and 3 undergo H/D exchange under a D2 atmosphere. Analysis of the isotopomeric mixtures of 2 reveals downfield isotopic shifts in the 31P{1H} NMR spectrum. Downfield as well as high-field shifts are found for the hydride signals in the 1H NMR spectrum of partially deuterated 2. Further reaction of 3 with H2 gave ethane and the dihydrogen complex [Ir2(μ-H)(μ-Pz)2H3(η2-H2)(PiPr3)2] (9). Under a deficiency of H2, in toluene-d 8 solution, 9 undergoes H/D scrambling with the participation of the solvent. It has also been found that under H2 complex 3 catalyzes the hydrogenation of cyclohexene.