Pt-Pt Interactions Research Articles

Chromophore-labelled, luminescent platinum complexes: syntheses, structures, and spectroscopic properties.

Ligands based upon 4-carboxamide-2-phenylquinoline derivatives have been synthesised with solubilising octyl hydrocarbon chains and tethered aromatic chromophores to give naphthyl (), anthracenyl () and pyrenyl () ligand variants, together with a non-chromophoric analogue () for comparison. (1)H NMR spectroscopic studies of the ligands showed that two non-interchangeable isomers exist for and while only one isomer exists for and . Supporting DFT calculations on suggest that the two isomers may be closely isoenergetic with a relatively high barrier to exchange of ca. 100 kJ mol(-1). These new ligands were cyclometalated with Pt(ii) to give complexes [Pt()(acac)] (acac = acetylacetonate). The spectroscopically characterised complexes were studied using multinuclear NMR spectroscopy including (195)Pt{(1)H} NMR studies which revealed δPtca. -2785 ppm for [Pt()(acac)]. X-ray crystallographic studies were undertaken on [Pt()(acac)] and [Pt()(acac)], each showing the weakly distorted square planar geometry at Pt(ii); the structure of [Pt()(acac)] showed evidence for intermolecular Pt-Pt interactions. The UV-vis. absorption studies show that the spectral profiles for [Pt()(acac)] are a composite of the organic chromophore centred bands and a broad (1)MLCT (5d → π*) band (ca. 440 nm) associated with the complex. Luminescence studies showed that complexes [Pt()(acac)] are dual emissive with fluorescence characteristic of the tethered fluorophore and long-lived phosphorescence attributed to (3)MLCT emission. In the case of the pyrenyl derivative, [Pt()(acac)], the close energetic matching of the (3)MLCT and (3)LCpyr excited states led to an elongation of the (3)MLCT emission lifetime (τ = 42 μs) under degassed solvent conditions, suggestive of energy transfer processes between the two states.

Phosphorescent, Cyclometalated Cinchophen-Derived Platinum Complexes: Syntheses, Structures, and Electronic Properties.

The syntheses of nine new monometallic heteroleptic platinum complexes [Pt(L1-4)(acac)], [Pt(L1)(hmacac/hfacac)], [PtCl(L1)(py)], [Pt(L1)(8-Q)], [Pt(L1)(bpy)](PF6) (where L1 = 2-phenyl-4-ethyl-quinolinecarboxylate; L2/L3 = N-functionalization of 2-phenyl-N-aryl/alkyl-quinoline-4-carboxamides; L4 = 2-phenyl-4-quinolinecarboxylic acid (cinchophen); acac = acetylacetonato; hmacac =2,2,6,6-tetramethyl-3,5-heptanedionate; hfacac = hexafluoroacetylacetonate; py = pyridine; 8-Q = 8-quinolinato; bpy =2,2'-bipyridine) are described from precursor dimeric Pt(II) species via an intermediate DMSO adduct of the general form [PtCl(L1-4)(DMSO)]. Single crystal X-ray diffraction studies were undertaken on three complexes, [Pt(L1)(acac)], [PtCl(L1)(DMSO)], and [Pt(L1)(bpy)](PF6). The structures show that the complexes each adopt a distorted square planar geometry (most severely in the case of [Pt(L1)(bpy)](PF6)) with indications of intermolecular Pt-Pt interactions in one example. The complexes were investigated using (195)Pt{(1)H} NMR spectroscopy, revealing varied chemical shifts that were strongly dependent upon the specific coordination environment of Pt(II). Luminescence studies showed the complexes possess a phosphorescent character with tunable emission wavelengths between 605 and 641 nm and luminescent lifetimes up to ∼450 ns. Supporting TD-DFT studies provided descriptions of the HOMO and LUMO energy levels of the key complex types, confirming an MLCT contribution to the lowest energy absorption that generally correlated well with the experimental spectra. The contribution of the Pt(5d) center to the calculated HOMOs was strongly ligand dependent, whereas the LUMOs are generally localized over the quinoline component of the cyclometalated ligand.

A new sensor for detection of CH3CN and ClCH2CN vapors based on vapoluminescent platinum(ii) complex

The planar platinum(II) complex [Pt(Me3SiC≡CbpyC≡CSiMe3)(C≡CC6H4Et-4)2] (1) with 5,5-bis(trimethylsilylethynyl)-2,2'-bipyridine was prepared and characterized. Solid-state 1 exhibits unusual, selective and reversible luminescence vapochromism to CH3CN and ClCH2CN vapors, which is useful for the detection of these hazardous vapors. A vapochromic cycle was monitored by dynamic variations in emission spectra and X-ray diffraction (XRD) patterns. Both X-ray crystallographic and density functional theory studies suggest that the vapochromic and vapoluminescent behavior of 1 are induced by the variation in the intermolecular Pt-Pt interactions.

Terpyridine platinum(ii) complexes containing triazine di- or tri-thiolate bridges: structures, luminescence, electrochemistry, and aggregation

Dinuclear complexes [{Pt(trpy)}(2)(L)](PF(6))(2) (trpy = 2,2':6',2''-terpyridine, L = 2-octylthio-1,3,5-triazine-4,6-dithiolate ion (1), L = 2-octadecylthio-1,3,5-triazine-4,6-dithiolate ion (2), L = 2-di-n-butylamino-1,3,5-triazine-4,6-dithiolate ion (3)) and a trinuclear complex [{Pt(trpy)}(3)(L)](PF(6))(3) (L = 1,3,5-triazine-2,4,6-trithiolate ion (4)) have been synthesized and characterized. The single crystal X-ray analysis revealed that the two {Pt(trpy)}(2+) fragments in 1 and 3 adopt a syn-configuration. The PtPt distances are around 4.3 Å, suggesting no intramolecular PtPt interactions. Complexes 1-4 in acetonitrile show broad absorption bands at around 470 nm, assigned to mainly the ligand-to-ligand charge transfer ((1)LLCT) from triazine thiolates to trpy based on the comparison to the related complexes and the density functional theory (DFT) calculations. The red luminescence of 1-4 in acetonitrile is attributable to emission predominantly from (3)LLCT. Cyclic voltammograms of 1-3 exhibit four redox couples from -2.0 V to 0 V vs. Ag/AgCl. The two consecutive processes at around -0.70 V are assigned to the sequential reduction of two trpy ligands. This assignment was further supported by the observation of the anion radical of trpy in spectroelectrochemical experiments. The splitting of the redox potentials of two trpy ligands evidences the moderate electronic coupling interactions mediated by the triazine dithiolate bridges. Complex 2 formed a transparent red gel in CH(3)CN, whereas 4 produced a gel-like solid in the mixtures of CH(3)CN and other solvents. The interactions dominating the aggregative behaviours have been discussed based on the results of electronic absorption and emission spectroscopy.

From red to near infra-red OLEDs: the remarkable effect of changing from X = –Cl to –NCS in a cyclometallated [Pt(N∧C∧N)X] complex {N∧C∧N = 5-mesityl-1,3-di-(2-pyridyl)benzene}

[PtL(6)X] {X = Cl or NCS and L(6) = 5-mesityl-1,3-di(2-pyridyl)-benzene} display similar luminescence in solution but, in the solid state, the packing of the molecules is different, with short PtPt interactions for X = NCS, leading to a red-shifted emission band. The effect has been used to generate OLEDs that emit squarely in the NIR region (855 nm).

Bright Sky-Blue Phosphorescence of [n-Bu4N][Pt(4,6-dFppy)(CN)2]: Synthesis, Crystal Structure, and Detailed Photophysical Studies

This work describes the synthesis, crystal structure, and detailed photophysical studies of [n-Bu(4)N][Pt(4,6-dFppy)(CN)(2)] (n-Bu = n-butyl, 4,6-dFppy = (4',6'-difluorophenyl)pyridinate). The material can easily be prepared in high yield and purity by the reaction of [Pt(4,6-dFppy)(H-4,6-dFppy)Cl], [n-Bu(4)N]Cl, and KCN in CH(2)Cl(2). Because of the bulky counterion [n-Bu(4)N](+), Pt-Pt interactions, which frequently lead to aggregate formation, are suppressed in the solid state. Thus, monomer emission is observed. The phosphorescence quantum yield of the neat powder amounts to phi(PL) = 60% at ambient temperature and decays with 19 micros. In tetrahydrofuran (THF) solution, on the other hand, the emission decay time is with 0.26 micros distinctly shorter, and the quantum yield is very low. By means of emission decay time studies in frozen THF and investigations of the highly resolved single crystal emission at 1.2 K, we can assign the emitting T(1) state of the compound as being largely of ligand centered ((3)LC, (3)pi pi*) character. The observed differences of the emission properties of the neat powder compared to the fluid solution are rationalized with an energy stabilization of quenching dd* states in solution because of molecular distortions and/or bond elongations.

Cyclometalated platinum(II) complexes with sterically bulky camphor-derived groups as β-diketonate ancillary ligand: a new route to efficiently reducing π-π interactions and Pt-Pt interactions

A new series of mono-cyclometalated square planar platinum(II) complexes have been synthesized and the single-crystal X-ray structures of complex 1 and 2 have been determined. The complexes have the general formula ppyPt(O∧O), where ppy is 2-phenylpyridyl, and O∧O is β-diketonate ancillary ligands with the acyl substituent group in position 3 of (D)-(+)-camphor. Although, like the many Pt(II) complexes with square-planar geometry, these complexes have plane stacking modes in crystal structure, the sterically bulky camphor-derived groups compel extensive slipping of the molecular stacking planes, resulting in the negligible overlapping of the aromatic ring fragments between molecules and the considerable Pt-Pt distance. The resolved spectra and a little shifted emission in solid state of complexes show that there is significant reduction of π-π interactions and Pt-Pt interactions, and suggest these complexes may be good candidates for doped phosphorescent organic light emitting diodes (PhOLEDs) and even for nondoped PhOLEDs.

Speciation in solution, solid state spectroscopy and vapochromism of [Pt(trpy)(NCS)]SbF6where trpy = 2,2′:6′,2′′-terpyridine

Treatment of [Pt(trpy)Cl]SbF(6) with AgSCN in a metathesis reaction affords after work-up yellow crystals of [Pt(trpy)(NCS)]SbF(6).CH(3)CN where trpy is 2,2':6',2''-terpyridine. A single crystal structure determination of the solvate shows that the SCN(-) ion is N-bound to the Pt atom, and that the planar cations stack as Pt(2) dimers with a PtPt separation of 3.293(1) A. The crystals rapidly de-solvate under ambient conditions to give a polycrystalline maroon material characterised as [Pt(trpy)(NCS)]SbF(6) (). A (15)N NMR spectroscopic study of a solution of isotopically labeled [Pt(trpy)((15)N(13)CS)]SbF(6) in CD(3)CN shows that both linkage isomers of the SCN(-) ion co-exist in solution with the N-bound isomer dominant, and the S-bound isomer present at a much lower concentration. Compound exhibits temperature dependent (3)MMLCT emission in the solid state; at 280 K the emission maximises at 692 nm, but red-shifts systematically on cooling to reach 762 nm at 80 K. Compound shows vapochromic behaviour that is selective and reversible for vapours of acetonitrile, DMF and pyridine. The colour change is from maroon for to yellow for all three solvates. The emission spectra recorded for the solvates maximise at wavelengths that are all significantly blue-shifted compared to lambda(em)(max) recorded for : the blue-shifts measured at 77 K are 90, 115 and 155 nm for the acetonitrile, DMF and pyridine solvates respectively. The origin of the vapochromic properties of compound is likely to do with the breaking and making of metallophilic PtPt interactions in the solid state.

Synthesis, Structural Characterization, and Photophysical Properties of Palladium and Platinum(II) Complexes Containing 7,8-Benzoquinolinate and Various Phosphine Ligands

A series of mononuclear cyclometalated benzo[h]quinolinate platinum and palladium(II) complexes with phosphine ligands, namely, [M(bzq)ClL] (L=PPh2H, Pt 1, Pd 2; PPh2CCPh, Pt 3, Pd 4), [Pt(bzq)(PPh2H)(PPh2CCPh)]ClO4 5, [Pt(bzq)(PPh2C(Ph)=C(H)PPh2)]ClO4 6, and [Pt(bzq)(CCPh)(PPh2CCPh)] (7a, 7b), were synthesized. The X-ray crystal structures of 1, 6.CH3COCH3.1/2CH3(CH2)4CH3, and 7b.CH3COCH3 have been determined. In 1, the metalated carbon atom and the P atom are mutually cis, whereas in 7b they are trans located. For complex 6, C and N are crystallographically indistinguishable. Reaction of [Pt(bzq)(mu-Cl)]2 with PPh2H and excess of NEt3 leads to the phosphide-bridge platinum dimer [Pt(bzq)(mu-PPh2)]2 8 (X-ray). Moderate pi-pi intermolecular interactions and no evident Pt-Pt interactions are found in 1, 7b, and in 8. All of the complexes exhibit absorption bands at high energy due to the intraligand transitions (1IL pi --> pi) and absorptions at lower energy which are attributed to MLCT (5d) pi --> pi (CLambdaN) transition. Platinum complexes show strong luminescence in both solid state and frozen solutions. The influence of the coligands on the photophysics of the platinum complexes has been examined by absorption and emission spectroscopy.

Covalently Bonded [Pt]- Chains in BaPt: Extension of the Zintl−Klemm Concept to Anionic Transition Metals?

BaPt has been synthesized by reaction of a 1:1 mixture of Ba and Pt at 1223 K in argon and characterized by single-crystal X-ray structure determination and electrical resistivity and magnetic susceptibility measurements. The compound crystallizes in the NiAs structure type with an extremely low value for the c/a ratio (hexagonal space group P6(3)/mmc with a = 5.057(2) A, c = 5.420(3) A, c/a = 1.072, R1 = 0.0297, N(hkl)() = 93). This c/a ratio reflects structural features that are unusual for the NiAs type: Pt is coordinated linearly by two other Pt atoms at a distance as short as 2.71 A, thus forming a chain along [001] of homonuclearly bonded platinum. Band structure calculations and electron localization function analyses reveal a covalent character of Pt-Pt interactions along the c axis and two-dimensional metallic conductivity parallel to the ab plane. In terms of the Zintl-Klemm concept, in its most general sense, BaPt can be formulated as (Ba(2+)(1(infinity)[Pt]-) x e-), and it can be considered a new example of platinide anions in the solid state.

Cyclometalated Analogues of Platinum Terpyridine Complexes: Kinetic Study of the Strong σ-Donor Cis and Trans Effects of Carbon in the Presence of a π-Acceptor Ligand Backbone

The substitution kinetics of the complexes [Pt(N-N-C)Cl] (N-N-CH = 6-phenyl-2,2'-bipyridine), [Pt(N-C-N)Cl] (N-CH-N = 1,3-di(2-pyridyl)benzene), and [Pt(N-N-N)Cl]Cl (N-N-N = 2,2':6',2' '-terpyridine) with the nucleophiles Br(-), I(-), and, for the first two complexes, also thiourea, N,N-dimethylthiourea, and N,N,N',N'-tetramethylthiourea, have been studied in methanol as solvent. In case of the thioureas, the activation parameters DeltaH, DeltaS, and DeltaV were also determined from the temperature and pressure dependence of the reactions. Two crystal structures of [Pt(N-N-C)Cl] were determined (yellow and red polymorphs); the intense red color of the latter polymorph results from Pt-Pt interactions (Pt-Pt distance = 3.366 A). The data enable an analysis of the cis and trans effects and the influence of the strong sigma-donor carbon in the presence of an electron withdrawing pi-acceptor ligand backbone. The results indicate that the intrinsic reactivity is enhanced greatly by the labilizing effect of the trans carbon donor, but the nucleophilic discrimination is dramatically reduced due to the decrease in electrophilicity on the metal center. However, although the electron withdrawing pi-acceptor effect is partly counteracted by the sigma-donor effect, the complex still benefits from a higher nucleophilic discrimination than in the comparable Pt(II) trans carbon donor complexes, where no or fewer pi-acceptors are present. In the case of the cis carbon donor complex, the intrinsic reactivity remains unchanged, but the nucleophilic discrimination is reduced and leads to a reduced reactivity of the [Pt(N-N-C)Cl] complex in comparison to [Pt(N-N-N)Cl]Cl. On the basis of these results, a more detailed treatment of the nature of the cis effect is offered.

Platinum nanoclusters on graphite substrates: a molecular dynamics study

Molecular dynamics simulations are used to investigate the shape and structure evolution of single platinum clusters of cubic and spherical shape containing 256 and 260 atoms, respectively, deposited on a static graphite substrate. The evolution is monitored at variable temperature, and as a function of metal-substrate interactions at constant temperature. The Pt-Pt interactions are modelled with the many-body Sutton-Chen potential, whereas a Lennard-Jones potential is used to describe the Pt-C interactions. Heating and cooling curves calculated between 200 K and 1800 K are used to determine solid-solid and solid-liquid transitions. Structural changes are detected through analyses of density profiles and diffusion coefficients. A clear analogy is observed between temperature-induced wetting phenomena and those resulting from enhancement of the metal-substrate interactions.

Synthesis and characterization of phosphorescent cyclometalated platinum complexes.

The synthesis, electrochemistry, and photophysics of a series of square planar Pt(II) complexes are reported. The complexes have the general structure C(wedge)NPt(O(wedge)O),where C(wedge)N is a monoanionic cyclometalating ligand (e.g., 2-phenylpyridyl, 2-(2'-thienyl)pyridyl, 2-(4,6-difluorophenyl)pyridyl, etc.) and O(wedge)O is a beta-diketonato ligand. Reaction of K(2)PtCl(4) with a HC(wedge)N ligand precursor forms the chloride-bridged dimer, C(wedge)NPt(mu-Cl)(2)PtC(wedge)N, which is cleaved with beta-diketones such as acetyl acetone (acacH) and dipivaloylmethane (dpmH) to give the corresponding monomeric C(wedge)NPt(O(wedge)O) complex. The thpyPt(dpm) (thpy = 2-(2'-thienyl)pyridyl) complex has been characterized using X-ray crystallography. The bond lengths and angles for this complex are similar to those of related cyclometalated Pt complexes. There are two independent molecular dimers in the asymmetric unit, with intermolecular spacings of 3.45 and 3.56 A, consistent with moderate pi-pi interactions and no evident Pt-Pt interactions. Most of the C(wedge)NPt(O(wedge)O) complexes display a single reversible reduction wave between -1.9 and -2.6 V (vs Cp(2)Fe/Cp(2)Fe(+)), assigned to largely C(wedge)N ligand based reduction, and an irreversible oxidation, assigned to predominantly Pt based oxidation. DFT calculations were carried out on both the ground (singlet) and excited (triplet) states of these complexes. The HOMO levels are a mixture of Pt and ligand orbitals, while the LUMO is predominantly C(wedge)N ligand based. The emission characteristics of these complexes are governed by the nature of the organometallic cyclometalating ligand allowing the emission to be tuned throughout the visible spectrum. Twenty-three different C(wedge)N ligands have been examined, which gave emission lambda(max) values ranging from 456 to 600 nm. Well-resolved vibronic fine structure is observed in all of the emission spectra (room temperature and 77 K). Strong spin-orbit coupling of the platinum atom allows for the formally forbidden mixing of the (1)MLCT with the (3)MCLT and (3)pi-pi states. This mixing leads to high emission quantum efficiencies (0.02-0.25) and lifetimes on the order of microseconds for the platinum complexes.

Dinuclear compounds with a μ-cyano ligand. Part XIII. Synthesis, characterization and solid state kinetics of the formation of (μ-cyano)(tricyanometal(II))pentaamminerhodium(III) and iridium(III) (metal(II) = nickel, palladium, platinum). Influence of the PtPt interactions

Six new dinuclear complexes of (μ-cyano)(tricyanometal(II))pentaamminerhodium(III) or iridium(III), metal(II) being nickel, palladium and platinum, have been obtained by solid state reaction of the tetracyanometallate(II) of aquopentaamminerhodium(III) and iridium(III), respectively. All these complexes have been characterized by chemical analysis, electronic and IR spectra and TG measurements. The kinetics of the solid-state deaquation-anation has been studied by thermogravimetric measurements under both nonisothermal and isothermal conditions. The activation energies so obtained are 105.3 and 107.7 kJ/mol for the Ni compounds; 115.0 and 118.1 kJ/mol for the Pd compounds and 90.2 and 92.2 kJ/ mol for the Pt compounds. These low values of activation energy can indicate an S N1 dissociative mechanism with an activated complex of square- based-pyramidal geometry. The marked difference in the kinetic parameters between the Ni, Pd compounds and Pt compounds may be explained in terms of Pt-Pt association in the crystal lattice, which causes distortion and allows the water molecules to escape easily from the crystal structure. These Pt-Pt interactions are shown in the electronic spectrum by the appearance of a very strong band at about 355 nm in the solid state and at about 330 nm and 300 nm in solution.

Dinuclear complexes with a ?-cyano ligand. Part XI(1). Synthesis and characterization of several derivatives ofcis-[Co(NH3)(en)2(H2O)]3+

The new complex double saltscw-[Co(NH3)(en)2(H2O)]2 [M(CN)4]3 (en = ethylenediamine; M = Ni, Pd or Pt),cis-[Co(NH3(en)2(H2O)]2[FeNO(CN)5]3 andcis-[Co(NH3)(en)2(H2O)][Co(CN)6] have been synthesized and by anation in the solid state the corresponding new dinuclear complexes with a cyano bridgecis- ortrans-[(NH3)(en)2Co-NC-M(CN)3]2 [M(CN)4] (M = Ni, Pd or Pt);cis-, trans-[(NH3)(en)2Co-NC-FeNO(CN)4]2[FeNO(CN)5] andcis-[(NH3)(en)2Co-NC-Co(CN)5 have been prepared. The complexes have been characterized by chemical analysis, t.g. measurements, and by i.r. and electronic spectroscopy. With [Ni(CN)4][2− and [Co(CN)in]63− only thecis-isomer is produced; with [Pd(CN)4]2−, [Pt(CN)4]2− and [FeNO(CN)5]2− thetrans- isomer is the dominant species. The dinuclear complex derived from [Pt(CN)4]2− shows strong Pt-Pt interactions both in the solid state and in solution.

Dinuclear complexes with a ?-cyano ligand. Part VIII(1). Synthesis and characterization of several derivatives ofcis-[CrX(H2O)(en)2]2+ (X=Cl or Br)

The new complex double saltscis-[CrX(H2O)(en)2][M(CN)4] (X=Cl or Br; M=Ni, Pd or Pt) have been synthesised and by anation either in the solid-state or in non-aqueous solvents the corresponding new dinuclear complexes with cyano bridgecis-[(en)2XCr-NC-M(CN)3] have been prepared. The complexes have been characterized by chemical analysis and by i.r. and electronic spectroscopy. Powder diffraction patterns indicate that the double salts are isostructural within each series. On the other hand, the dinuclear complexes show low crystallinity. The two dinuclear complexes derived from [Pt(CN)4]2− show strong Pt-Pt interactions both in the solid state and in solution.

Dinuclear complexes with a ?-cyano-ligand. ? Part VII. Synthesis and characterization of several derivatives oftrans-[CrF(H2O)(1,2-diaminopropane)2]2+

Six new dinuclear complexes obtained by reaction oftrans-[CrF(H2O)(pn)2](ClO4) (pn=1,2-diaminopropane) and [M(CN)4]2− (M=Ni, Pd or Pt), [Co(CN)6]3−, [Cr(CN)6]3− and [CrNO(CN)5]3− have been isolated. They have been characterised by chemical analysis, electronic and i.r. spectra and conductivity measurements. In order to compare the behaviour of these compounds with the ethylenediamine(en) and 1,3-diaminopropane (tn) analogues, previously described, the new compoundscis-[CrFX(pn)2]X (X=Cl, Br or I) have been also obtained and characterised. The derivatives of the anion [Pt(CN)4]2− show Pt-Pt interactions in both the solid state and in solution.