Photophysical and electrochemical properties of heteroleptic tris-cyclometalated iridium(III) complexes

Mixed (difluoro)phenylpyridine/(difluoro)phenylpyrazole tris-cyclometalated iridium complexes were prepared in order to study the effect of fluorination and the pyridine/pyrazole ratio on the emission and electrochemical properties. Increasing fluorination and replacement of pyridine by pyrazole both leads to a widening of the HOMO-LUMO gap and generally leads to a blue shift in emission.     

Theoretical study on the spectroscopic properties and electronic structures of heteroleptic phosphorescent Ir(III) complexes

The geometries, spectroscopic and electronic structures properties of a series of heteroleptic phosphorescent Ir(III) complexes including N981, N982, N983, N984 have been characterized by density functional theory calculations. The excited‐state properties of the Ir(III) complexes have been characterized by CIS method. The ground‐ and excited‐state geometries were optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ levels, respectively. By using the time‐dependent density functional theory method, the absorption and phosphorescence spectra were calculated based on the optimized ground‐ and excited‐state geometries, respectively. The results show that the absorption and emission data agree well with the corresponding experimental results. The calculated results also revealed that the nature of the substituent at the 4‐position of the pyridyl moiety can influence the distributions of HOMO and LUMO and their energies. In addition, the charge transport quality has been estimated approximately by the calculated reorganization energy (λ). Our result also indicates that the positions of the substitute groups not only change the transition characters but also affect the charge transfer rate and balance, and complex N982 is a very good charge transfer material for green OLEDs. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Synthesis,Characterization and Photophysical Properties of Iridium(III) Bis‐cyclometallated Complexes Containing 1,1‐Dithiolates

A series of neutral Ir(III)‐based heteroleptic complexes with a formula of [Ir(η²‐(C^∧N))₂(η²‐(S^∧S))] ((C^∧N)^‐ = ppy^‐, (S^∧S)^‐ = Et₂NCS₂^‐ ( 2a ), MeOCS₂^‐ ( 2b ), EtOCS₂^‐ ( 2c ), ⁱPrOCS₂^‐ ( 2d ); (C^∧N)^‐ = tpy^‐, (S^∧S) = Et₂NCS₂^‐ ( 3a ), MeOCS₂^‐ ( 3b ), EtOCS₂^‐ ( 3c ), ⁱPrOCS₂^‐ ( 3d ); (C^∧N)^‐ = epb^‐ , (S^∧S)^‐ = Et₂NCS₂^‐ ( 4a ), MeOCS₂^‐ ( 4a ), EtOCS₂^‐ ( 4a ); ppyH = 2‐phenylpyridine; tpyH = 2‐(4′‐tolyl)pyridine; epbH = ethyl 4‐(2′‐pyridyl)benzate) was synthesized and characterized. The crystal structure of complex 2d was also determined. The electron‐releasing substituents on (C^∧N)^‐ or (S^∧S)^‐ blueshift λ_max values.     

Probing the mer- to fac-isomerization of tris-cyclometallated homo- and heteroleptic (C,N)3 iridium(III) complexes

We have developed techniques which allow for covalent tethering, via a "hetero" cyclometallating ligand, of heteroleptic tris-cyclometallated iridium(III) complexes to polymeric supports (for application in light-emitting diode technologies). This involved the selective synthesis and thorough characterization of heteroleptic [Ir(C,N) 2(C',N')] tris-cyclometallated iridium(III) complexes. Furthermore, the synthesis and characterization of heteroleptic [Ir(C,N) 2OR] complexes is presented. Under standard thermal conditions for the synthesis of the facial ( fac) isomer of tris-cyclometallated complexes, it was not possible to synthesize pure heteroleptic complexes of the form [Ir(C,N) 2(C',N')]. Instead, a mixture of homo- and heteroleptic complexes was acquired. It was found that a stepwise procedure involving the synthesis of a pure meridonial ( mer) isomer followed by photochemical isomerization of this mer to the fac isomer was necessary to synthesize pure fac-[Ir(C,N) 2(C',N')] complexes. Under thermal isomerization conditions, the conversion of mer-[Ir(C,N) 2(C',N')] to fac-[Ir(C,N) 2(C',N')] was also not a clean reaction, with again a mixture of homo- and heteroleptic complexes acquired. An investigation into the thermal mer to fac isomerization of both homo- and heteroleptic tris-cyclometallated complexes is presented. It was found that the process is an alcohol-catalyzed reaction with the formation of an iridium alkoxide [Ir(C,N) 2OR] intermediate in the isomerization process. This catalyzed reaction can be carried out between 50 and 100 degrees C, the first such example of low-temperature mer-fac thermal isomerization. We have synthesized analogous complexes and have shown that they do indeed react so as to give fac-tris-cyclometallated products. A detailed explanation of the intermediates (and all of their stereoisomers, in particular when systems of the generic formula [M(a,b) 2(a',b')] are synthesized) formed in the mer to fac isomerization process is presented, including how the formed intermediates react further, and the stereoisomeric products they yield.     

Synthesis,structural, photophysical and thermal properties of some praseodymium(III) complexes

Some carboxylato-bridged praseodymium(III) complexes (1–5) having tp [hydrotris(pyrazol-1-yl)borate] and sodium p-X-benzoate (where X =?H, F, Cl, NO₂) have been synthesized and characterized by different techniques including X-ray crystallography. The X-ray studies demonstrated that 1, 3 and 5 crystallized in triclinic space group P 1 with cell dimensions a =?11.761(13) Å, b =?12.536(13) Å, c =?17.726(19) Å for 1, a =?9.309(8) Å, b =?12.667(11) Å, c =?14.421(12) Å for 3, a =?11.5688(9) Å, b =?12.0055(9) Å, c =?12.3005(10) Å for 5. In 1–4 the coordination number of praseodymium is seven, whereas in 5 it is eight. IR suggested that the benzoate groups in 1–5 are bidentate bridging. The photophysical properties of these complexes have been studied in solution at room temperature. Thermogravimetric analysis showed that these complexes undergo complete decomposition with formation of praseodymium oxide.     

Photophysical properties of charged cyclometalated Ir(III) complexes: a joint theoretical and experimental study

The photophysical properties of a series of charged biscyclometalated [Ir(ppy)(2)(N^N)](1+) complexes, where ppyH is 2-phenylpyridine and N^N is 2,2'-bipyridine (bpy), 6-phenyl-2,2'-bipyridine (pbpy), and 6,6'-diphenyl-2,2'-bipyridine (dpbpy) for complexes 1, 2, and 3, respectively, have been investigated in detail. The photoluminescence performance in solution decreases from 1 to 3 upon attachment of phenyl groups to the ancillary ligand. The absorption spectra recorded over time suggest that complex 3 is less stable compared to complexes 1 and 2 likely due to a nucleophilic-assisted ancillary ligand-exchange reaction. To clarify this behavior, the temperature dependence of the experimental intrinsic deactivation rate constant, k(in) = 1/τ, has been investigated from 77 K to room temperature. Temperature-dependent studies show that nonemitting metal-centered (MC) states are accessible at room temperature for complex 3. The experimental results are interpreted with the help of theoretical calculations performed within the density functional theory (DFT) approach. Calculations suggest that attachment of a phenyl group to the ancillary ligand (2) promotes the temperature-independent deactivation pathways, whereas attachment of a second phenyl group (3) also makes the temperature-dependent ones accessible through population of nonradiative (3)MC excited states.     

Synthetic, structural, spectroscopic, and electrochemical studies of mixed sandwich Rh(III) and Ir(III) complexes involving Cp* and tridentate macrocycles

The syntheses, structures, spectroscopy, and electrochemistry for six Ir(III) and Rh(III) mixed sandwich mononuclear complexes involving tridentate macrocycles and pentamethylcyclopentadienide (Cp*) are reported. The complexes are readily prepared by direct ligand substitution reactions from the dichloro bridged binuclear complexes, [{M(Cp*)(Cl)₂}₂]. All complexes have the general formula [M(L)(Cp*)]X₂ (M = Ir(III) or Rh(III), L = macrocycle, or Cl⁻) and exhibit a distorted octahedral structure involving three donor atoms from the macrocycle and the facially coordinating carbocyclic Cp* ligand. The complex cations include: [Rh(η⁵ -Cp*)(9S3)]²⁺ (1), [Rh(η⁵-Cp*)(9N3)]²⁺ (2), [Rh(η⁵-Cp*)(10S3)]²⁺ (3), [Ir(η⁵-Cp*)(9S3)]²⁺ (4), [Ir(η⁵-Cp*)(9N3)]²⁺ (5), and [Ir(η⁵-Cp*)(10S3)]²⁺ (6), where 9S3 = 1,4,7-trithiacyclononane, 9N3 = 1,4,7-triazacyclononane, and 10S3 = 1,4,7-trithiacyclodecane. The structures for all six complexes are supported by ¹H and ¹³C{¹H} NMR spectroscopy, and five complexes are also characterized by single-crystal X-ray crystallography (complexes 1-5). The ¹H NMR splittings between the two sets of methylene protons for both the Rh(III) and Ir(III) 9S3 complexes are much larger (0.4 vs. 0.2 ppm) compared to those in the two 9N3 complexes. Similarly, the ¹³C{¹H} NMR spectra in all four thioether complexes show that the ring carbons in the Cp* ligand are shifted by over 10 ppm downfield compared to the azacrown complexes. The electrochemistry of the complexes is surprisingly invariable and is dominated by a single irreversible metal-centered reduction near −1.2 V vs. Fc/Fc⁺.     

Preparation and characterization of ruthenium(II), rhodium(III) and iridium(III) complexes of isocyanide bearing the azo group

Reactions of [(η⁶-arene)RuCl₂]₂ (1) (η⁶-arene=p-cymene (1a), 1,3,5-Me₃C₆H₃ (1b), 1,2,3-Me₃C₆H₃ (1c) 1,2,3,4-Me₄C₆H₂(1d), 1,2,3,5-Me₄C₆H₂ (1e) and C₆Me₆ (1f)) or [Cp*MCl₂]₂ (M=Rh (2), Ir (3); Cp*=C₅Me₅) with 4-isocyanoazobenzene (RNC) and 4,4′-diisocyanoazobenzene (CN–R–NC) gave mononuclear and dinuclear complexes, [(η⁶-arene)Ru(CNC₆H₄N=NC₆H₅)Cl₂] (4a–f), [Cp*M(CNC₆H₄N=NC₆H₅)Cl₂] (5: M=Rh; 6: M=Ir)_, [{(η⁶-arene)RuCl₂}₂{μ-CNC₆H₄N=NC₆H₄NC}] (8a–f) and [(Cp*MCl₂)₂(μ-CNC₆H₄N=NC₆H₄NC)}] (9: M=Rh; 10: M=Ir)_, respectively. It was confirmed by X-ray analyses of 4a and 5 that these complexes have trans-forms for the ---N=N--- moieties. Reaction of [Cp*Rh(dppf)(MeCN)](PF₆)₂ (dppf=1,1′-bis (diphenylphosphino)ferrocene) with 4-isocyanoazobenzene gave [Cp*Rh(dppf)(CNC₆H₄N=NC₆H₅)](PF₆)₂ (7), confirmed by X-ray analysis. Complex 8b reacted with Ag(CF₃SO₃), giving a rectangular tetranuclear complex 11b, [{(η⁶-1,3,5-Me₃C₆H₃)Ru(μ-Cl}₄(μ-CNC₆H₄N=NC₆H₄NC)₂](CF₃SO₃)₄ bridged by four Cl atoms and two μ-diisocyanoazobenzene ligands. Photochemical reactions of the ruthenium complexes (4 and 8) led to the decomposition of the complexes, whereas those of 5, 7, 9 and 10 underwent a trans-to-cis isomerization. In the electrochemical reactions the reductive waves about −1.50 V for 4 and −1.44 V for 8 are due to the reduction of azo group, [---N=N---]→[---N=N---]²⁻. The irreversible oxidative waves at ca. 0.87 V for the 4 and at ca. 0.85 V for 8 came from the oxidation of Ru(II)→Ru(III).     

Effect of substituents on the photoluminescence performance of Ir(III) complexes: Synthesis, electrochemistry and photophysical properties

We have prepared and characterized a series of substituted imidazole ligands namely dmmppi, dmmpfpi, dmdmppi and dmdmpfpi. These compounds will readily undergo cyclometalation with iridium trichloride and form di-irrido and the six coordinated iridium(III) dopants of the substituted imidazole ligands. They emit green colour both in solid and in solution phase. The peak emission wavelength of the dopants (λ_max = 428–497 nm) can be finely tuned depending upon the electronic properties of the phenyl, fluorophyenyl, methoxy phenyl and dimethoxyphenyl substituents as well as their positions in the imidazole ring. These iridium complexes namely Ir(dmmppi)₂(pic) 1a, Ir(dmmpfpi)₂(pic) 1b, Ir(dmdmppi)₂(pic) 1c and Ir(dmdmpfpi)₂(pic) 1d were characterized by ¹H NMR, MS and elemental analysis. All these iridium complexes 1a–1d show unusual high HOMO levels (E_HOMO = 5.21–5.41 eV) and high phosphorescence. These complexes emit green light with exceedingly high efficiency.     

Heteroleptic half-sandwich Ru(II), Rh(III) and Ir(III) complexes based on 5-ferrocenyldipyrromethene

The synthesis and characterization of heteroleptic complexes with the formulations [(η⁶-arene)RuCl(fcdpm)] (η⁶-arene = C₆H₆, C₁₀H₁₄) and [(η⁵-C₅Me₅)MCl(fcdpm)] (M = Rh, Ir; fcdpm = 5-ferrocenyldipyrromethene) have been reported. All the complexes have been characterized by elemental analyses, IR, ¹H NMR and electronic spectral studies. Structures of [(η⁶-C₆H₆)RuCl(fcdpm)] and [(η⁶-C₁₀H₁₄)RuCl(fcdpm)] have been determined crystallographically. Chelating monoanionic linkage of fcdpm to the respective metal centres has been supported by spectral and structural studies. Further, reactivity of the representative complex [(η⁶-C₁₀H₁₄)RuCl(fcdpm)] with ammonium thiocyanate (NH₄SCN) and triphenylphosphine (PPh₃) have been examined.     

Synthesis,characterization, photophysical and electrochemical properties of triazinooxacalix[2]arenes with bisphenol A motif

Oxygen atom bridged calixarene derivatives called oxacalixarenes were synthesized from bisphenol A and cyanuric chloride by aromatic nucleophilic substitution through addition elimination mechanism. All the synthesized oxacalixarenes exhibit strong absorbance band between 225 and 286?nm due to the presence of triazine and phenoxy units. The oxacalixarenes 7 and 10 show strong fluorescence emission and higher λ_em values than all other oxacalixarenes due to the presence of rigid aromatic spacer units such as binol and biphenyl. All the oxacalixarenes exhibit quasi-reversible behaviour and potential shift observed in cyclic voltammetry.     

Preparation and electrochemical properties of catalysts based on macrobicyclic d-metal tris-dioximate complexes

The use of macrobicyclic tris-dioximate complexes of cobalt, K₃[Co(Dmg)₃] (where DmgH₂=C₄H₈N₂O₂), and iron, (BPh)₂[Fe(Nx)₃] (where NxH₂=C₆H₁₀N₂O₂), and the carbon-supported complexes and their pyrolyzates, as catalysts for oxygen reduction was examined utilizing the combination of thermogravimetry, infrared spectroscopy, mass spectrometry and electrochemical techniques. The results have shown that macrobicyclic cobalt complexes adsorbed on the surface of carbon- based synthetic porous polymers have a pronounced catalytic effect on the reduction of molecular oxygen. A reduction in the oxygen overpotential was observed with heat treatment of the catalysts prepared in an inert atmosphere. The optimum pyrolysis temperature for the electrochemically most active catalysts for oxygen reduction was estimated. Electronic Publication     

Photophysical properties of praseodymium complexes with aromatic carboxylic acids: double light conversion both in ultraviolet and visible region

A series of luminescent praseodymium complexes with different aromatic carboxylic acids have been synthesized and characterized. The photophysical properties of these complexes have been studied with ultraviolet spectra, phosphorescence spectra and fluorescence spectra. Ultraviolet absorption spectra show that the praseodymium complexes systems with aromatic carboxylate form the more extensive conjugated systems to be suitable for the distribution of electron in the whole coordination environment, resulting in the energy decrease and red-shifts of ultraviolet spectral bands. Phosphorescence spectra suggest that excited triplet state of aromatic carboxylic acids, which can indicate the energy match and intermolecular energy transfer process between the excited triplet state of ligands and the resonant emissive energy level of Pr ions. The emission spectra of all praseodymium complexes show two emission peaks under the excitation band of 245 nm at about 395 and 595 nm, respectively, while one peak at about 595 nm under 415 nm excitation, which attributed to be 1S0-->1I6 (395 nm) transition and the characteristic emission 1D2-->3H4 (595 nm) transition of Pr3+ ion. The 1S0-->1I6 transition can be speculated to belong to the transition of charge transfer state, and the 1D2-->3H4 can be further proved that there exists an antenna effect in the luminescence of praseodymium with aromatic carboxylic acids. In conclusion, the praseodymium complexes systems can realize the double proton light conversion both in the ultraviolet and visible region, which can be further studied to have potential application.     

Color tuning associated with heteroleptic cyclometalated Ir(III) complexes: influence of the ancillary ligand

We report the preparation of a series of new heteroleptic Ir(III) metal complexes chelated by two cyclometalated 1-(2,4-difluorophenyl)pyrazole ligands (dfpz)H and a third ancillary bidentate ligand (L=X). Such an intricate design lies in a core concept that the cyclometalated dfpz ligands always warrant a greater pi pi* gap in these series of iridium complexes. Accordingly, the lowest one-electron excitation would accommodate the pi* orbital of the ancillary L=X ligands, the functionalization of which is then exploited to fine-tune the phosphorescent emission wavelengths. Amongst the L=X ligands designed, three classes (series 1-3) can be categorized, and remarkable bathochromic shifts of phosphorescence were observed by (i) replacing the 2-benzoxazol-2-yl substituent (1a) with the 2-benzothiazol-2-yl group (1b) in the phenolate complexes, (ii) converting the pyridyl group (2a) to the pyrazolyl group (2b) and even to the isoquinolyl group (2c) in the pyrazolate complexes and (iii) extending the pi-conjugation of the benzimidazolate ligand from 3a to 3b. Single-crystal X-ray diffraction study on complex [(dfpz)Ir(bzpz)] (2b) was conducted to confirm their general molecular architectures. Complex 2b was also used as a representative example for fabrication of multilayered, green-emitting phosphorescent OLEDs using the direct thermal evaporation technique.     

Photophysical and electrochemical properties of chlorophyll a-cyclodextrins complexes

In this work, we have studied the interactions between two different cyclodextrins (CDs) and chlorophyll a (Chl a) in the presence of electrolyte by means of absorption, fluorescence spectroscopy, circular dichroism and cyclic voltammetry. The results obtained indicate that the presence of both CDs gives rise to an increase of Chl a solubility in water. In particular, heptakis-(2,3,6-tri-O-methyl)-beta-cyclodextrin (TRIMEB) favours the dissolution of Chl a monomer in aqueous solution, whereas the presence of hydroxypropyl-beta-cyclodextrin (beta-HP-CD) promotes the pigment aggregation.     

Half-sandwich Ru(II), Ir(III) and Rh(III) complexes with bridging or chelating N-heterocyclic bis-carbene ligand: Synthesis and characterization

N-heterocyclic bis-carbene ligand (bis-NHC) which was derived from 1,1′-diisopropyl-3,3′-ethylenediimidazolium dibromide (L·2HBr) via silver carbene transfer method, reacted with [(η⁶-p-cymene)RuCl₂]₂ and [Cp^∗MCl₂]₂ (Cp^∗ = η⁵-C₅Me_5, M = Ir, Rh) respectively, afforded complexes [(η⁶-p-cymene)RuCl₂]₂(L) (1), [Cp^∗IrCl₂]₂(L) (2) and [Cp^∗RhCl(L)][Cp^∗RhCl₃] (3). When [Cp^∗IrCl₂]₂ was treated with 2 equiv AgOTf at first, and then reacted with bis-NHC ligand, [Cp^∗IrCl(L)]OTf (4) was obtained. The molecular structures of complexes 1-4 were determined by X-ray single crystal analysis, showing that 1 and 2 adopted bridging coordination mode, 3 and 4 adopted chelating coordination mode. All of these complexes were characterized by ¹H, ¹³C NMR spectroscopy and element analysis.     

Polydentate Schiff-base ligands and their Cd(II) and Cu(II) metal complexes: synthesis,characterization, biological activity and electrochemical properties

Synthesis, characterization, microbiological activity and electrochemical properties of the Schiff-base ligands A¹–A⁵ and their Cd(II) and Cu(II) metal complexes are reported. The ligands and their complexes have been characterized by elemental analysis, FT–IR, UV–Vis, ¹H- and ¹³C-NMR, mass spectra, magnetic susceptibility and conductance measurements. In the complexes, all the ligands are bidentate, the oxygen in the ortho position and azomethine nitrogen atoms of the ligands coordinate to the metal ions. The keto-enol tautomeric forms of the Schiff-base ligands A¹–A⁵ have been investigated in polar and non-polar organic solvents. Antimicrobial activity of the ligands and metal complexes were tested using the disc diffusion method and the chosen strains include Bacillus megaterium and Candida tropicalis. The electrochemical properties of the ligands A¹–A⁵ and their Cu(II) metal complexes have been investigated at different scan rates (100–500?mV?s^?1) in DMSO.     

Photophysical and electrochemical properties of Ru(II) complexes containing tridentate bisphosphino-oligothiophene ligands

Nine Ru(II) complexes containing the conjugated oligothiophene ligands 3,3'-bis(diphenylphosphino)-2,2':5',2'-terthiophene (P(2)T(3)) and 4',3'-bis(diphenylphosphino)-3,3'-dihexyl- 2,2':5',2':5',2':5',2'-pentathiophene (P(2)T(5)) were prepared and characterized. P(2)T(3) and P(2)T(5) bond as tridentate ligands and three of the complexes (1, 2 and 5) form green five-coordinate Ru(II) complexes in solution. Cyclic voltammetry, variable temperature UV-vis spectroscopy and time-resolved transient absorption spectroscopy were used to characterize the electronic properties of the complexes. Increased conjugation in the complexes containing the P(2)T(5) ligand resulted in a lowering of the oxidation potential of the oligothiophene, but electropolymerization was not observed. The electronic spectra were dominated by π-π* transitions. All of the complexes were non-emissive both at room temperature and low temperature, indicating the excited state decays by other, non-radiative pathways. The transient absorption spectrum of complex 7 shows a species with a band at 475 nm and a lifetime of ～100 ns, assigned to a ligand-based triplet state.     

Ruthenium(III) and iridium(III) complexes with nicotine

A new chloride-dimethylsulfoxide-ruthenium(III) complex with nicotine trans-[Ru^IIICl₄(DMSO)[H-(Nicotine)]] (1) and three related iridium(III) complexes; [H-(Nicotine)]trans-[Ir^IIICl₄(DMSO)₂] (2), trans-[Ir^IIICl₄(DMSO)[H-(Nicotine)]] (3) and mer-[Ir^IIICl₃(DMSO)(Nicotine)₂] (4) have been synthesized and characterized by spectroscopic techniques and by single crystal X-ray diffraction (1, 2, and 4). Protonated nicotine at pyrrolidine nitrogen is present in complexes 1 and 3 while two neutral nicotine ligands are observed in 4. In these three inner-sphere complexes coordination occurs through the pyridine nitrogen. Moreover, in the outer-sphere complex 2, an electrostatic interaction is observed between a cationic protonated nicotine at the pyrrolidine nitrogen and the anionic trans-[Ir^IIICl₄(DMSO)₂]^¯ complex.     

Synthesis,structure and electrochemical properties of some thiosemicarbazone complexes of iridium

Reaction of thiosemicarbazones of salicylaldehyde and 2-hydroxyacetophenone (H₂L¹ and H₂L²) with [Ir(PPh₃)₃Cl] affords complexes of type [Ir(PPh₃)₂(L)(H)] (L = L¹ or L²) in ethanol. A similar reaction carried out in toluene affords the [Ir(PPh₃)₂(L)(H)] complexes along with complexes of type [Ir(PPh₃)₂(L)Cl], where a chloride is coordinated to iridium instead of the hydride. The structure of the [Ir(PPh₃)₂(L²)(H)] and [Ir(PPh₃)₂(L²)Cl] complexes has been determined by X-ray crystallography. Crystal data for [Ir(PPh₃)₂(L²)(H)]: space group, P2₁/c; crystal system, monoclinic; a=12.110(2) Å, b=17.983(4) Å, c=18.437(4) Å, β=103.42(3)°, Z=4; R ₁=0.0591, wR ₂=0.1107. Crystal data for [Ir(PPh₃)₂(L²)Cl]: space group, P2₁/c; crystal system, monoclinic; a=17.9374(11) Å, b=19.2570(10) Å, c=24.9135(16) Å, β=108.145(5)°, Z=4; R ₁=0.0463, wR ₂=0.0901. In all the complexes the thiosemicarbazones are coordinated to the metal center as dianionic tridentate O, N, S-donors and the two triphenylphosphines are trans. The complexes are diamagnetic (low-spin d? ⁶, S=0) and show intense MLCT transitions in the visible region. Cyclic voltammetry on all the [Ir(PPh₃)₂(L)(H)] and [Ir(PPh₃)₂(L)Cl] complexes shows a quasi-reversible Ir(III)–Ir(IV) oxidation within 0.55–0.78 V vs. SCE followed by an irreversible oxidation of the thiosemicarbazone within 0.91–1.27 V vs. SCE. An irreversible reduction of the thiosemicarbazone is also observed within ?1.10 to ?1.23 V vs. SCE.