Luminescent Platinum(II) Dimers with a Cyclometallating Aryldiamine Ligand

General Design Rules for Bimetallic Platinum(II) Complexes

A series of platinum(II) bimetallic complexes were studied to investigate the effects of ligands on both the geometric and electronic structure. Modulating the Pt-Pt distance through the bridging ligand architecture was found to dictate the nature of the lowest energy electronic transitions, localized in one-half of the molecule or delocalized across the entire molecule. By reducing the separation between the platinum atoms, the lowest energy electronic transitions will be dominated by the metal-metal-to-ligand charge transfer transition. Conversely, by increasing the distance between the platinum atoms, the lowest electronic transition will be largely localized metal-to-ligand charge transfer or ligand centered in nature. Additionally, the cyclometalating ligands were observed to have a noticeable stabilizing effect on the triplet excited states as the conjugation increased, arising from geometric reorientation and increased electron delocalization of the ligands. Such stabilization of the triplet state energy has been shown to alter the excited state potential energy landscape as well as the excited state trajectory.

Halide exchange studies of novel Pd(ii) NNN-pincer complexes

Palladium(ii) complexes with an NNN type pincer ligand (pip2NNN = 2,6-bis(piperdyl-methyl)pyridine) are synthesized and characterized. Electronic and 1H NMR spectra point to decreasing filled/filled repulsions between the dπ(Pd) orbitals and the halide lone pair orbitals along the Cl < Br < I series. For all complexes, the most downfield α-piperidyl resonance of the pip2NNN ligand is sensitive to changes in the coordinated halide while the meta-pyridyl and benzylic resonances are sensitive to changes in the counter anion. This sensitivity is utilized to study halide association and exchange at the fourth coordination site. Conductivity and 1H NMR spectroscopy confirm the interaction between the exogenous anion (Cl-, Br-, BF4 -) and Pd(pip2NNN)X+ (X = Cl, Br).

X-ray and synchrotron diffraction studies of 2-(pyridin-2-yl)-1,10-phenanthroline in the role of ligand for two copper polymorphs or hydrogen bonded with 2,2,6,6-tetramethyl-4-oxopiperidinium hexafluorophosphate

Different extended packing motifs of dichlorido[2-(pyridin-2-yl)-1,10-phenanthroline]copper(II), [CuCl2(C17H11N3)], are obtained, depending on the crystallization conditions. A triclinic form, (I), is obtained from dimethylformamide-diethyl ether or methanol, whereas crystallization from dimethylformamide-water yields a monoclinic form, (II). In each case, the Cu(II) centre is in a five-coordinate distorted square-pyramidal geometry. The extended packing for both forms can be described as a highly offset π-stacking arrangement, with interlayer distances of 3.674 (3) and 3.679 (3) Å for forms (I) and (II), respectively. The reaction of diprotonated Pt(tmpip2NCN)Cl [tmpip2NCN = 2,6-bis(2,2,6,6-tetramethylpiperidylmethyl)benzyl] with AgPF6 under acidic conditions, followed by the addition of 2-(pyridin-2-yl)-1,10-phenanthroline, results in a hydrogen-bonded cocrystal, 2,2,6,6-tetramethyl-4-oxopiperidinium hexafluorophosphate-2-(pyridin-2-yl)-1,10-phenanthroline (1/1), C9H18NO(+)·PF6(-)·C17H11N3, (III). The extended packing maximizes π-π interactions in a parallel face-to-face arrangement, with an interlayer stacking distance of 3.4960 (14) Å.

Bridging, terminal, free, anti and gauche BPA ligands in a 1D hybrid organic-inorganic Mn(II)-cyanate system

A hybrid organic-inorganic chain compound of the family Mn(II)-bpa-(NCO) is presented. It contains, unusually, five different dispositions for the bpa [1,2-bis(4-pyridyl)ethane] ligand. Water molecules and free bpa ligands occupy the voids of the structure. The compound shows significant antiferromagnetic-type interactions as a consequence of different exchange pathways.

Characterization of divalent and trivalent species generated in the chemical and electrochemical oxidation of a dimeric pincer complex of nickel

The electrolytic and chemical oxidation of the dimeric pincer complex [κ(P),κ(C),κ(N),μ(N)-(2,6-(i-Pr(2)POC(6)H(3)CH(2)NBn)Ni](2) (1; Bn = CH(2)Ph) has been investigated by various analytic techniques. Cyclic voltammetry measurements have shown that 1 undergoes a quasi-reversible, one electron, Ni-based redox process (ΔE(0)(1/2) = -0.07 V vs Cp(2)Fe/[Cp(2)Fe](+)), and spectroelectrochemical measurements conducted on the product of the electrolytic oxidation, [1](+•), have shown multiple low-energy electronic transitions in the range of 10,000-15,000 cm(-1). Computational studies using Density Functional Theory (B3LYP) have corroborated the experimentally obtained structure of 1, provided the electronic structure description, and helped interpret the experimentally obtained absorption spectra for 1 and [1](+·). These calculations indicate that the radical cation [1](+·) is a dimeric, mixed-valent species (class III) wherein most of the spin density is delocalized over the two nickel centers (Ni(+2.5)(2)N(2)), but some spin density is also present over the two nitrogen atoms (Ni(2+)(2)N(2)·). Examination of alternative structures for open shell species generated from 1 has shown that the spin density distribution is highly sensitive toward changes in the ligand environment of the Ni ions. NMR, UV-vis, electron paramagnetic resonance (EPR), and single crystal X-ray diffraction analyses have shown that chemical oxidation of 1 with N-Bromosuccinimide (NBS) follows a complex process that gives multiple products, including the monomeric trivalent species κ(P),κ(C),κ(N)-{2,6-(i-Pr(2)PO)(C(6)H(3))(CH═NBn)}NiBr(2) (2). These studies also indicate that oxidation of 1 with 1 equiv of NBS gives an unstable, paramagnetic intermediate that decomposes to a number of divalent species, including succinimide and the monomeric divalent complexes κ(P),κ(C),κ(N)-{2,6-(i-Pr(2)PO)(C(6)H(3))(CH═NBn)}NiBr (3) and κ(P),κ(C),κ(N)-{2,6-(i-Pr(2)PO)(C(6)H(3))(CH(2)N(H)Bn)}NiBr(2) (4); a second equivalent of NBS then oxidizes 3 and 4 to 2 and other unidentified products. The divalent complex 3 was synthesized independently and shown to react with NBS or bromine to form its trivalent homologue 2. The new complexes 2 and 3 have been characterized fully.

Hydroxy- and mercaptopyridine pincer platinum and palladium complexes generated by silver-free halide abstraction

A silver-free route has been employed for the synthesis of a number of Pd and Pt complexes supported by an NCN "pincer" ligand (NCN = [2,6-(Me2NCH2)2C6H3]-) via halide abstraction. This was achieved by the use of o-, m-, and p-hydroxypyridines or o- and p-mercaptopyridines in basic ethanol solutions. The acidic OH or SH protons are removed to generate the formally anionic ligands. X-ray crystal structure determination of these complexes shows that the bonding of the substituted pyridine ligands occurs exclusively through the pyridine N for hydroxypyridines and exclusively through the thiol S in mercaptopyridines. In the hydroxypyridine case, the ortho and para isomers tautomerize to generate pyridone structures with a covalent M-N bond, whereas the m-hydroxypyridine complex, which is unable to tautomerize, is found to still be bound through the pyridine N but in a zwitterionic structure. The mercaptopyridine complexes are the first reported examples of pincer-ligated Pd and Pt thiolate species. The pyridine ligands can be quantitatively exchanged for chloride by reaction with excess NH4Cl, a potentially useful chemical switch for ligation/decomplexation of this ligand type.

Iridium(I) Pyridyl Azolate Complexes with Saturated Red Metal-to-Ligand Charge Transfer Phosphorescence; Fundamental and Potential Applications in Organic Light-Emitting Diodes

Preparation of a new series of neutral metal complexes [(cod)Ir(fppz)] (1), [(cod)Ir(bppz)] (2), [(cod)Ir(fptz)] (3) and [(cod)Ir(bptz)] (4), bearing one cod ligand and a pyridyl azolate chelate are reported. A single-crystal X-ray diffraction study of 3 reveals the expected distorted square-planar geometry. The lowest absorption band consists of IrI atom increased triplet dpi-->pi* transitions (3MLCT), the assignment of which is firmly supported by the theoretical approaches. Complexes 1-4 exhibit weak phosphorescence in degassed solution at room temperature, whereas much more intense, solid-state phosphorescence appears in the range 622-649 nm. The pure MLCT emission was used as a prototypical model to address its remarkable spectral differences from the IrIII isoquinoline pyrrolide complex (5), which has mainly 3pipi phosphorescence. Complex 3 was used as a dopant to fabricate red-emitting phosphorescent organic light-emitting diodes (OLEDs). For the 7 % doped device, a maximum brightness of 3010 cd m-2 was achieved at an applied voltage of 15 V and with CIE coordinates of (0.56, 0.33), demonstrating for the first time the potential of neutral IrI complexes in OLED applications.