Synthesis and characterization of cyclometalated iridium(III) complexes containing pyrimidine-based ligands

New pyrimidine derivatives (pyr) have been synthesized using palladium-catalyzed Suzuki coupling reaction. These compounds can undergo cyclometalation with iridium trichloride to form bis-cyclometalated iridium complexes, (pyr)₂Ir(acac) (acac = acetylacetonate; pyr = cyclometalated pyr). The substituents at the both cyclometalated phenyl ring and pyrimidine ring were found to affect both electrochemical and photophysical properties of the complexes. Computation results on these complexes are consistent with the electrochemical and photophysical data. The complexes are green-emitting with good solution quantum yields at ∼0.30. Light-emitting devices using these complexes as dopants were fabricated, and the device performance at 100 mA/cm² are moderate: 9 (17 481 cd/m², 4.8%, 18 cd/A, 5.1 lm/W); 10 (18 704 cd/m², 4.9%, 18.9 cd/A, 4.7 lm/W); 13 (20 942 cd/m², 5.4%, 21.0 cd/A, 6.1 lm/W).     

Theoretical studies upon the electronic structures and spectroscopic properties for a series of luminescent terpyridyl platinum(II) phenylacetylide complexes

A comprehensive calculations were carried out to get a deep insight into the ground- and excited-state electronic structures and the spectroscopic properties for a series of [Pt(4-X–trpy)CCC₆H₄R]⁺ complexes (trpy = 2,2′,6′,2″-terpyridine; X = H, R = NO₂ (1), Cl (2), C₆H₅ (3) and CH₃ (4); R = Cl, X = CH₃ (5) and C₆H₅ (6)). MP2 (second-order Møller–Plesset perturbation) and CIS (single-excitation configuration interaction) methods were employed to optimize the structures of 1–6 in the ground and excited states, respectively. The investigation showed that substituted phenylacetylide and trpy ligands only give rise to a small variation in geometrical structures but lead to a sizable difference in the electronic structures for 1–6 in the ground and excited states. The introduction of electron-rich groups into the phenylacetylide and/or terpyridyl ligands produces two different low-lying absorptions for 1 and 2–6, i.e., Pt(5d) → π^*(trpy) metal-to-ligand charge transfer (MLCT) mixed with π → π^*(CCPh) intraligand charge transfer (ILCT) for 1 and Pt(5d)/π(CCPh) → π^*(trpy) charge transfer (MLCT and LLCT) for 2–6. Remarkable electronic resonance on the whole Pt–CCPh–NO₂ moiety for 1 may be responsible for the difference. Solvatochromism calculation revealed that only LLCT/MLCT transitions showed the solvent dependence, consistent with the experimental observations.     

Theoretical studies on structures and spectroscopic properties of bis-cyclometalated iridium complexes [Ir(ppy)2X2]

The electronic structures and spectroscopic properties of a series of mixed bis-cyclometalated iridium(III) complexes [Ir(ppy)₂X₂]⁻ (X = CN, 1; X = NCS, 2; X = NCO, 3; ppy = 2-phenylpyridl) were investigated at the B3LYP/LANL2DZ and CIS/LANL2DZ levels. The calculated geometry parameters in the ground state are well consistent with the corresponding experimental values. The HOMO of 1 is dominantly localized on Ir atom and ppy ligand, but the HOMO of 2 and 3 have significant X ligand composition. Under the TD-DFT level with PCM model, the absorption and phosphorescence in CH₂Cl₂ media were calculated based on the optimized geometries in the ground and excited states, respectively. The lowest-lying absorption of 1 at 403 nm is attributed to {[d_x²-y²(Ir)+d_xy(Ir)+π(ppy)]→[π^∗(ppy)]} transition with metal-to-ligand and intraligand charge transfer (MLCT/ILCT) transition characters, whereas those of 2 (449 nm) and 3 (475 nm) are related to {[d_x²-y²(Ir)+d_xy(Ir)+π(ppy)+π(NCS/NCO)]→[π^∗(ppy)]} transition with MLCT/ILCT and ligand-to-ligand charge transfer (LLCT) transition characters. The phosphorescence of 1 at 466 nm can be described as originating from ³{[d_x²-y²(Ir)+d_xy(Ir)+π(ppy)][π^∗(ppy)]} excited state, while those of 2 (487 nm) and 3 (516 nm) originate from ³{[d_x²-y²(Ir)+d_xy(Ir)+π(ppy)+π(NCS/NCO)][π^∗(ppy)]} excited states. The calculated results showed that the transition character of the absorption and emission can be changed by adjusting the π electron-accepting abilities of the X ligands and the phosphorescent color can be tuned by altering the X ligands.     

Theoretical study on the electronic structures and optical properties of blue‐green and blue phosphorescent iridium(III) complexes with tetraphenylimidodiphosphinate ligand

The electronic structures and photophysical properties of five iridium(III) complexes Ir(tfmppy)₂(tpip) (1), Ir(dfppy)₂(tpip) (2), Ir(afCNppy)₂(tpip) (3), Ir(CNpyN₃)₂(tpip) (4), and Ir(2fphpta)₂(tpip) (5) [where tfmppy = 4‐trifluoromethylphenylpyridine; dfppy =4,6‐difluorophenylpyridine; afCNppy = 6‐fluoro‐4‐octyloxy‐5‐cyano‐phenylpyridine; CNpyN₃ = 2‐(4‐cyano‐phenyl)‐[1,2,3]‐triazole; 2fphpta=2‐(2,6‐difluoro‐phenyl‐[1,2,4]‐triazol‐3‐yl)‐pyridine; tpip=tetraphenylimido‐diphosphinate] have been investigated by using density functional theory (DFT) methods and time‐dependent DFT ones, aiming at elucidating the influences of different substituents and cyclometalated ligands on the emission properties and quantum yield. The calculated results revealed that the different substituents in 1 ‐ 3 have a great influence on the energy levels, in particular highest occupied molecular orbital. Meanwhile, we have also get a further insight into the reason for different phosphorescence quantum yields of the studied complexes. The higher quantum yield (Φ) reported for 1 was found to be closely related to both its smaller S₁–T₁ splitting energy ( ) and larger transition electric dipole moment ( ) upon the S₀ → S₁ transition. Complex 5 is expected to be a potential candidate for blue‐emitting material with good organic light‐emitting diodes performances. We propose that the optical properties of this class of materials can be tuned by the modifications of the cyclometalated ligands. © 2013 Wiley Periodicals, Inc.     

Mononuclear gallium(III) complexes based on salicylaldoximes: Synthesis,structure and spectroscopic characterization

The reactions of Ga(acac)₃ with salicylaldoxime (saoH₂) and methyl-salicylaldoxime (Me-saoH₂) in dichloromethane/hexane afforded the complexes [Ga(acac)(saoH)₂] (1) and [Ga(acac)₃][Ga(acac)(MesaoH)₂] (2), respectively, in high yields. The crystal structures of 1 and 2 have been determined by single-crystal X-ray crystallography. Both complexes are mononuclear with the Ga(III) atoms being in octahedral environments surrounded by two bidentate chelate R-saoH⁻ and one bidentate chelate acac⁻ ligands. A [Ga(acac)₃] moiety has co-crystallized along with the methylsalicylaldoximato complex. Characteristic IR as well as NMR data are discussed in terms of the nature of bonding in the structures of the two complexes. ¹H and ¹³C NMR data in CDCl₃ indicate that the salicylaldoximato complexes isomerize in solution.     

Synthesis, structure, redox and spectra of green iridium complexes of tridentate azo-aromatic ligands

Reactions of IrCl₃·xH₂O with the ligands, 2-[(phenylamino)phenylazo]pyridine (HL^1a) and 2-[(p-tolylamino)phenylazo]pyridine (HL^1b) produce [Ir(L¹)₂]Cl (L¹ = L^1a, [1]Cl and L¹ = L^1b, [2]Cl) along with many unidentified products. The iridium complexes have been characterized by various techniques such as X-ray crystallography, mass spectrometry, ¹H and ¹³C NMR, cyclic voltammetry and absorption studies. The complex [1]ClO₄ crystallises in triclinic space group. The crystallographic data have been determined. Notably, the Ir-N (azo) lengths are short (av. 1·9875(4) ?) as compared to the remaining four Ir-N lengths (av. 2·052(5) ?). There is significant degree of ligand backbone conjugation in the coordinated ligands, which result in shortening of the C-N lengths on the other side of the middle phenyl ring and also in lengthening of the diazo (N=N) lengths. The complexes display multiple low energy transitions ranging between 1010 and 450 nm. These are electro active and show three reversible redox responses in the potential range, +1·5 V to −1·5 V. The cathodic potential responses are ascribed as ligand reductions, while the redox process at the anodic potential occurs at a mixed metal-ligand (HOMO) orbital.     

Molecular and spectroscopic properties of hydridecarbonyl ruthenium complexes with pyrazine carboxylic acid ligands

The hydride carbonyl ruthenium(II) [RuH(CO)(pyzCOO)(PPh₃)₂] (1), [RuH(CO)(pyz-2,3-COO[CH₃])(PPh₃)₂]·H₂O (2) and dinuclear Ru(II)/Ru(III) [RuH(CO)(PPh₃)(pyz-2,3-COO)Ru(CO)Cl₂(PPh₃)₂] (3) complexes were synthesized and characterized by IR, ¹H, ³¹P NMR, UV-Vis spectroscopy and X-ray crystallography. The experimental studies were complemented by quantum chemical calculations, which were used to identify the nature of the interactions between the ligands and the central ion, and the orbital composition in the frontier electronic structure. Based on a molecular orbital scheme, the calculated results allowed the interpretation of the UV-Vis spectra obtained at an experimental level. The luminescence property of the complex 2 was determined. The ac magnetic susceptibility measurements showed a residual magnetism evidenced by the small values of the molar susceptibility, not exceeding 0.5 emu/mol at 2 K, a lack of a Curie-Weiss region and weak magnetic interactions below 20 K.     

A theoretical study: Green phosphorescent iridium(III) complexes with low-efficiency roll-off

A series of heterocyclic Ir(III) complexes used in organic light-emitting diode (OLED) materials with low-efficiency roll-off performance have been studied theoretically. Their electronic structures, spectral properties, and their application value in OLEDs are discussed. The geometries, electronic structures, lowest-lying singlet absorptions, and triplet emissions of (dmdppr-dmp)₂Ir(dibm), and the theoretically designed models of (dmdppr-dmp)₂Ir(acac), (dmdppr-dmp)₂Ir(tpip), (dmdppr-Fdmp)₂Ir(dibm), (dmdppr-Fdmp)₂Ir(acac), and (dmdppr-Fdmp)₂Ir(tpip) were investigated with density-functional-theory-based approaches, where dibm denotes 2,6-dimethy-3,5-heptanedionato-κ₂-O,O′, acac denotes acetylacetonate, and tpip denotes tetraphenylimido-diphosphinate.     

Synthesis, characterization of novel half-sandwich iridium and rhodium complexes containing pyridine-based organochalcogen ligands

A series of neutral pyridine-based organochalcogen ligands, 2,6-bis(1-methylimidazole-2-thione)pyridine (Bmtp), 2,6-bis(1-isopropylimidazole-2-thione)pyridine (Bptp), and 2,6-bis(1-tert-butylimidazole-2-thione)pyridine (Bbtp) have been synthesized and characterized. Reactions of [Cp*M(μ-Cl)Cl]₂ (Cp* = η⁵-pentamethylcyclopentadienyl, M = Ir, Rh) with three pyridine-based organochalcogen ligands result in the formation of the complexes Cp*M(L)Cl₂ (M = Ir, L = Bmtp, 1a·Cl₂; M = Rh, L = Bmtp, 1b·Cl₂; M = Ir, L = Bptp, 2a·Cl₂; M = Rh, L = Bptp, 2b·Cl₂; M = Ir, L = Bbtp, 3a·Cl₂; M = Rh, L = Bbtp, 3b·Cl₂), respectively. All compounds have been characterized by elemental analysis, NMR and IR spectra. The molecular structures of Bbtp, 1a·Cl₂, 1b·Cl₂, 2b·Cl₂ and 3b·Cl₂ have been determined by X-ray crystallography.     

Rhodium(III) and iridium(III) complexes of thioarylazoimidazoles: Synthesis,structure, spectral characterization,electrochemistry and DFT calculation

[M(SRaaiNR′)Cl₃] (M = Rh(III), Ir(III) and SRaaiNR′ = 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazole) complexes are described in this article. The single crystal X-ray structure of one of the complexes, [Rh(SMeaaiNEt)Cl₃] (3b), shows a tridentate chelation of SMeaaiNEt via N(imidazole), N(azo) and S(thioether) donor centres. Spectral characterization has been done by IR, UV–Vis and ¹H NMR data. The electronic structure, redox properties and spectra are well supported by DFT and TDDFT computation on the complexes.     

Synthesis,crystal structures and spectroscopic studies of praseodymium(III) malonate complexes

Reactions of malonic acid (H₂mal) with PrCl₃·6H₂O afforded the known complex [Pr₂(mal)₃(H₂O)₆]_n (1), and compounds [Pr₂(mal)₃(H₂O)₆]_n·2nH₂O (2·2nH₂O), [PrCl(mal)(H₂O)₃]_n·0.5nH₂O (3·0.5nH₂O) and [Pr(mal)(Hmal)(H₂O)₃]_n·nH₂O (4·nH₂O) using various reaction ratios, reaction media (H₂O, MeOH) and pH values. Analogous reactions with CeCl₃·7H₂O afforded compounds [Ce₂(mal)₃(H₂O)₆]_n (5), [CeCl(mal)(H₂O)₃]_n·nH₂O (6·nH₂O) and [Ce(mal)(Hmal)(H₂O)₃]_n·nH₂O (7·nH₂O). Compounds 2·2nH₂O and 3·0.5nH₂O were characterized by X-ray crystallography, and 4–7 by microanalytical and spectroscopic data. The malonate(-2) ligand adopts three different coordination modes in the structures of 1–3, i.e., the μ₂-κO:κO′:κO″ and the μ₄-κ²O:κO′:κ²O″:κO? in 1 and 2 leading to a 3D network structure, and the μ₃-κ²O:κO′:κ²O″:κO? in 3 promoting an 1D structure. The thermal decomposition of 1 and 3·0.5nH₂O was monitored by TG/DTA and TG/DTG measurements. The structural features of 1–3 are discussed in terms of known malonato(-2) Ln^III and Ca^II complexes. The bioinorganic chemistry relevance of our results is discussed.     

Highly efficient yellow-emitting iridium(III) complexes based on fluorinated 2-(biphenyl-4-yl)-2H-indazole ligands: Syntheses,structures, properties,and density functional theory calculations

Two new iridium (III) complexes ( Ir1-Ir2 ) bearing different fluorinated 2-(biphenyl-4-yl)-2H-indazole-based compounds as cyclometalated ligands and Xantphos as an ancillary ligand were synthesized and fully characterized. The ultraviolet (UV)–vis absorption, photoluminescence, and electrochemistry properties were studied. The single crystal structures of Ir1-Ir2 were determined by X-ray diffraction, showing each adopts the distorted octahedral coordination geometry. To gain insights into the lowest energy electron transitions and the lowest triplet excited states, density functional theory calculations were used to further investigate the origination. Two complexes emit yellow photoluminescence with quantum yields of 49.7–72.5% in solution at room temperature. Their Commission Internationale de L'Eclairage color coordinates are (0.42, 0.53) and (0.39, 0.47), respectively.     

Crystal structures of (azido)(pentamethylcyclopentadienyl)iridium(III) complexes containing various types of bidentate ligands

Several (azido)iridium(III) complexes having a pentamethylcyclopentadienyl (Cp∗) group, [Cp∗Ir(N₃)₂(Ph₂Ppy-κP)] (1: Ph₂Ppy = 2-diphenylphosphinopyridine), [Cp∗Ir(N₃)(Ph₂Ppy-κP,κN)]CF₃SO₃ (2), [Cp∗Ir(N₃)(dmpm)]PF₆ (3: dmpm = bis(dimethylphosphino)methane), [Cp∗Ir(N₃)(Ph₂Pqn)]PF₆·$·$CH₃OH (4·$·$CH₃OH: Ph₂Pqn = 8-diphenylphosphinoquinoline), and [Cp∗Ir(N₃)(pybim)] (5: Hpybim = 2-(2-pyridyl)benzimidazole) have been prepared and their crystal structures have been analyzed by X-ray diffraction. In complex 1, the Ph₂Ppy ligand is only coordinated via the P atom (-κP), while in 2 it acts as a bidentate ligand through the P and N atoms (-κP,κN) to form a four-membered chelate ring. Comparing the structural parameters of the chelate ring in 2 with those of a similar five-membered chelate ring formed by Ph₂Pqn in 4, it became apparent that the angular distortion in the Ph₂Ppy-κP,κN ring was remarkable, although the Ir–P and Ir–N bonds in the Ph₂Ppy-κP,κN ring were not elongated very much from the corresponding bonds in the Ph₂Pqn-κP,κN ring. In the pybim complex 5, the five-membered chelate ring was coplanar with the pyridine and benzimidazolyl rings. With the related (azido)iridium(III) complexes analyzed previously, comparison of the structural parameters of the Ir–N₃ moiety in [Cp∗Ir^III(N₃)(L–L′)]^+/0 complexes reveals an anomalous feature of the 2,2′-bipyridyl (bpy) complex, [Cp∗Ir(N₃)(bpy)]PF₆.     

Thermogravimetric and spectroscopic studies on La(III) and Ce(III) complexes with some thio-schiff bases

Solid complexes of five derivatives of thio-Schiff bases with La(III) and Ce(III) ions were prepared and characterized by elemental and thermogravimetric analyses. The suggested general formula of the solid complexes is [ML₂(H₂O)X]·2H₂O, whereM=trivalent lanthanide ion,L=Schiff base andX=Cl^? or ClO ₄ ^? . Information about the water of hydration, the coordinated water molecules, the coordination chemistry and the thermal stability of these complexes was obtained and is discussed. Additionally, a general scheme of thermal decomposition of the lanthanide-Schiff base complexes is proposed.     

Theoretical investigation on the spectroscopic properties of cyclometallated iridium (III) complexes and the deprotonation influence on them in solution

Electronic structures and spectroscopic properties of mixed‐ligand cyclometallated iridium complexes with general formula [Ir(N?C)₂(N?N)]⁺ (N?C = 2‐phenylpyridine, N?N = Hcmbpy = 4‐carboxyl‐4^′‐methyl‐2,2^′‐bipyridine, 1 ; H₂dcbpy = 4,4^′‐dicarboxyl‐2,2^′‐bipyridine, 2 ) were studied theoretically. The geometries of the complexes in ground and excited state were optimized at B3LYP and CIS levels, respectively. The absorption and emission of the complexes in CH₃CN solutions were calculated by time‐dependent density functional theory (TD‐DFT) with the PCM solvent model. The calculated absorptions and emissions of the complexes are in good agreement with the measured results. The deprotonation influence on the electronic structure and the optical properties of 2 was also investigated. The results indicate that the deprotonation which occurs on the COOH groups influences the geometries of the complexes in ground and excited state slightly but leads to significant blue‐shifts in low energy absorption and emission maximum. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Theoretical studies on the electronic structure and spectral properties of versatile diarylethene-containing 1,10-phenanthroline ligands and their rhenium(I) complexes

The structures of versatile diarylethene-containing 1,10-phenanthroline ligands (L₁ and L₂) and their rhenium(I) complexes [Re(CO)₃(L)Cl] (1 and 2) in the ground and low-lying excited states have been optimized at the B3LYP functional and the ab initio configuration interaction singlets (CIS) level, respectively. The spectral properties are predicted with use of time-dependent density functional theory (TDDFT). As shown, the transition character of the strongest absorption band and luminescent spectrum for closed-ring complex 1 is different from that of 2, the former has ππ^∗ character and the latter has MLCT and LLCT character. We presume the second triplet excited state contributes to the phosphorescence of 1, while the lowest triplet excited state accounts for the phosphorescence of 2. Spin-orbit coupling influences the excitation energies for d(Re)-joined transitions whereas it has negligible effect on the transition character for complexes 1 and 2.     

Cyclometalated iridium(III) complexes containing 2-phenyl-2H-indazole ligand: Synthesis,photophysical studies,and DFT calculations

Heteroleptic cyclometalated iridium(III) complexes ( Ir1 – Ir5 ) featuring piz-based ligands and acetylacetone ancillary ligand are synthesized and characterized. Their photophysical and electrochemical properties were studied, and DFT calculations were used to further support the experiment results. All the complexes emit yellow color with quantum yields of 12.2–56.5% in dichloromethane solution at room temperature, and the emission originates from a hybrid ³MLCT/³ILCT/³LLCT excited state.     

Ab initio and density functional theory study of the electronic structure of rhenium complexes with noninnocent dioxolene ligands: Localized vs delocalized valence states

The dioxolene type ligands (Diox) derived from ortho-quinones are the most widely studied redox noninnocent ligands existing in the dianionic (Cat), anion radical (SQ) or neutral (Q) forms although a highly delocalized electronic structure is also possible. For [ReO(Diox)₂PPh₃]⁻ ( 2 ) and [ReCl₃(Diox)PPh₃] ( 3 ) complexes, the Re^V-Cat₂ and Re^IV-SQ localized valence states were proposed on the basis of their XRD structures. To understand in detail the electronic structure of these complexes, we performed a series of the all-electron calculations at the DKH2-CASSCF/CASPT2 and DKH2-CASSCF/NEVPT2 levels taking into account scalar relativistic and spin-orbit effects. All calculations predicted that 2 has a singlet ground state with a predominant contribution of a single electronic configuration with doubly occupied molecular orbitals being pure o-quinone LUMOs of both Diox ligands that corresponds to the Re^V-Cat₂ valence state. Complex 3 has a triplet ground state with four electronic configurations contributing mainly into its wavefunction and differing by the occupation of bonding and antibonding combinations of the o-quinone LUMO and rhenium d-AO with nearly equal contributions. This leads to the empirical “metrical oxidation state” of dioxolene ligand being −1 that is usually referred to the Re^IV-SQ oxidation state. However, in fact, the negative charge on the Diox ligand is mainly provided by a pair of electrons on the bonding MO. The standard DFT calculations entirely fail to correctly predict the ground state multiplicity for 3 .     

Synthesis,structure and spectroscopic study of Cu(II) polypyridine complexes with phenylcyanamide derivative ligands

Several new mononuclear copper(II) complexes, [Cu(phen)₂L]PF₆, where phen = 1,10-phenanthroline and L = monoanions of phenylcyanamide (pcyd), 2,5-dichlorophenylcyanamide (2,5-Cl₂pcyd), 2-dichlorophenylcyanamide (2-Clpcyd) and 4-methylphenylcyanamide (4-Mepcyd), have been prepared and characterized by elemental analysis, UV–Vis, IR and ¹H NMR spectroscopies and cyclic voltammetry. [Cu(phen)₂(2,5-Cl₂pcyd)]PF₆ crystallized with a molecule of acetone with empirical formula of C₃₁H₂₀N₆OF₆Cl₂PCu in a triclinic crystal system and space group P 1 with a = 9.2086(6) Å, b = 13.3117(9) Å, c = 15.5313(10) Å, α = 107.8210(10)°, β = 104.6180(10)°, γ = 104.1670(10)°, V = 1643.21(19) ų and Z = 2. The structure was refined using 7555 Mo-Kα reflections with I > 2σ(I) and R ₁ = 0.0276 and Rw = 0.0692. The results are consistent with a mostly σ bonding interaction between Cu(II) and cyanamide anion. The LMCT band intensity and electrochemical potentials are compared with ruthenium phenylcyanamide analogues.     

Stepwise formation of metallo-prisms of iridium and rhodium complexes bearing pentamethylcyclopentadienyl ligands

Reactions of [M(Cp^∗)Cl(μ-Cl)]₂ (M = Ir(1a); M = Rh(1b)) with tridentate ligands tpt (tpt = 2,4,6-tripyridyl-1,3,5-triazine) gave the corresponding trinuclear complexes [M₃(Cp^∗)₃(μ₃-4-tpt-κN)Cl₆] (M = Ir(2a); M = Rh(2b)), which can be converted into hexanuclear complexes [M₆(Cp^∗)₆(μ₃-4-tpt-κN)₂(μ-Cl)₆](O₃SCF₃)₆ (M = Ir(3a); M = Rh(3b)) by treatment with AgO₃SCF₃, respectively. X-ray of 3b revealed that each of six pentamethylcyclopentadienyl metal moieties was connected by two μ-Cl-bridged atoms and a tridentate ligand to construct a cation triangular metallo-prism cavity with the volume of about 273 Å³ based on the distance of the two triazine moieties is 3.62 Å.