Chloride and pseudohalide hydride-carbonyl ruthenium(II) complexes with 4-pyrrolidinopyridine as co-ligand

Chloride and pseudohalide (N₃ ^?, NCS^?) hydride-carbonyl ruthenium(II) complexes with 4-pyrrolidinopyridine as co-ligand were synthesized and characterized by IR, ¹H, and ³¹P NMR, electronic absorption and emission spectroscopy and X-ray crystallography. The electronic structures of the complexes were calculated by density functional theory (DFT) on their crystal structures. The spin-allowed singlet–singlet electronic transitions of the complexes were calculated by time-dependent DFT, and the UV–Vis spectra have been discussed on these basis. The emission properties of the complexes were also studied.     

Experimental and Theoretical Studies of Charge Delocalization in Biruthenium–Alkynyl Complexes Bridged by Thiophenes

A series of binuclear ruthenium–alkynyl complexes that are bridged by thiophene groups (thiophene, bithiophene, and terthiophene) have been synthesized. All of these complexes have been well‐characterized by NMR spectroscopy, X‐ray diffraction, and elemental analysis. The electronic properties of these complexes have been examined by using cyclic voltammetry, UV/Vis/NIR and IR spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and density functional theory (DFT) calculations. Electrochemical results showed that the potential difference (ΔE) and comproportionation constant (K_c) decreased with increasing size of the thiophene bridging unit. The UV/Vis/NIR spectra and TDDFT calculations of the monocations indicated that the NIR transitions displayed aromatic bridging character. EPR studies of the mono‐oxidized radical species further demonstrated that the unpaired electron/hole was delocalized over both metals and the bridging ligand and established significant participation in the ligand oxidation.     

Electronic structure and excited states of rhenium(I) amido and phosphido carbonyl-bipyridine complexes studied by picosecond time-resolved IR spectroscopy and DFT calculations

UV-vis absorption and picosecond time-resolved IR (TRIR) spectra of amido and phosphido complexes fac-[Re(ER2)(CO)3(bpy)] (ER2 = NHPh, NTol2, PPh2, bpy = 2,2'-bipyridine, Tol = 4-methylphenyl) were investigated in conjunction with DFT and TD-DFT calculations in order to understand their ground-state electronic structure, low-lying electronic transitions and excited-state character and dynamics. The HOMO is localized at the amido/phosphido ligand. Amide and phosphide ligands are sigma-bonded to Re, the pi interaction being negligible. Absorption spectra show a weak band at low energies (1.7-2.1 eV) that arises from essentially pure ER(2) --> bpy ligand-to-ligand charge transfer (LLCT). The lowest excited state is the corresponding triplet, (3)LLCT. Low triplet energies and large distortions diminish the excited-state lifetimes to 85 and 270 ps for NHPh and NTol(2), respectively, and to ca. 30 ps for PPh2. nu(CO) vibrations undergo only very small ( bpy MLCT character, is a unique feature of the amido/phoshido complexes, whose lowest excited state can be viewed as containing a highly unusual aminyl/phosphinyl radical-cationic ligand. For comparison, the amino and phosphino complexes fac-[Re(NHPh(2))(CO)3(bpy)]+ and fac-[Re(PPh3)(CO)3(bpy)]+ are shown to have the usual Re --> bpy (3)MLCT lowest excited states, characterized by upshifted nu(CO) bands.     

Luminescent alkynylplatinum(II) complexes of 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine-type ligands with ready tunability of the nature of the emissive states by solvent and electronic property modulation

A new class of luminescent alkynylplatinum(II) complexes of tridentate bis(N-alkylbenzimidazol-2'-yl)pyridines (bzimpy), [Pt(R,R'-bzimpy)(C[triple chemical bond]C-R')]X (X=PF(6), OTf), and one of their chloro precursor complexes, [Pt(R,R'-bzimpy)Cl]PF(6), have been synthesized and characterized; one of the alkynyl complexes has also been structurally characterized by X-ray crystallography. Electrochemical studies showed that the oxidation wave is alkynyl ligand-based in nature with some mixing of the metal center-based contribution, whereas the two quasi-reversible reduction couples are mainly bzimpy-based reductions. The electronic absorption and luminescence properties of the complexes have also been investigated. In solution, the high-energy and intense absorption bands are assigned as the pi-pi* intraligand (IL) transitions of the bzimpy and alkynyl ligands, whereas the low-energy and moderately intense absorptions are assigned to an admixture of metal-to-ligand charge-transfer (MLCT) (dpi(Pt)-->pi*(R,R'-bzimpy)) and ligand-to-ligand charge-transfer (LLCT) (pi(C[triple chemical bond]C-R')-->pi*(R,R'-bzimpy)) transitions. Upon variation of the electronic effects of the arylalkynyl ligands, vibronic-structured or structureless emission bands, originating from triplet metal-perturbed intraligand (IL) or an admixture of triplet metal-to-ligand charge-transfer (MLCT) and ligand-to-ligand charge-transfer (LLCT) excited states respectively, were observed in solution. Interestingly, two of the complexes showed a dual luminescence that was sensitive to the polarity of the solvents. Upon cooling from 298 K to 155 K, drastic color, UV/Vis, and luminescence changes were observed in a butyronitrile solution of 1, and were ascribed to the formation of aggregate species through PtPt and pi-pi stacking interactions. DFT and time-dependent DFT (TD-DFT) calculations have been performed to verify and elucidate the results of the electrochemical and photophysical properties.     

Novel sulfonated hydrophilic indium(III) and gallium(III) phthalocyanine photosensitizers: preparation and investigation of photophysicochemical properties

The new tetra-non-peripherally benzenesulfonic acid-substituted hydrophilic gallium chloride and indium chloride phthalocyanine complexes have been synthesized by cyclotetramerization of 4-(2,3-dicyanophenyl)benzenesulfonic acid (1). The newly synthesized phthalocyanines have been characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, mass and UV–vis spectroscopy techniques. The water-soluble gallium(III) phthalocyanine derivative (2) was aggregated in aqueous media but was fully disaggregated in the presence of a surfactant Triton X-100. The incorporation of sulfonate moieties of the phthalocyanine macrocycle provides hydrophilic character to the new compounds, which is useful for drug administration and serves as crucial in PDT application. So, the photochemical properties (singlet oxygen quantum yields and photodegradation quantum yields) and photophysical properties (fluorescence behavior) of the complexes were reported in different solutions (DMSO and water). The results of spectral measurements showed that both np-GaPc (2) and np-InPc (3) can be used as sensitizers in PDT because of their singlet oxygen efficiencies.     

Synthesis,crystal and spectroscopic characterization of [RuHCl(CO)(PPh3)2(pyrazine)]

The reaction of [RuHCl(CO)(PPh₃)₃] with pyrazine has been examined and a ruthenium(II) complex – [RuHCl(CO)(PPh₃)₂(C₄H₄N₂)] -- has been obtained. The compound has been studied by IR, UV–Vis spectroscopy, and X-ray crystallography. The molecular orbital diagram of the complex has been calculated with density functional theory (DFT). The spin-allowed singlet--singlet electronic transitions of the complex have been calculated with the time-dependent DFT method, and the UV–Vis spectrum of the compound has been discussed on this basis.     

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.     

Cyclometalated Ir(III) complexes containing N-aryl picolinamide ancillary ligands

The reaction of the cyclometalated chloro-bridged iridium(III) dimer, [(ppy)₂ Ir(μ-Cl)]₂ (ppy - 2-phenyl pyridine) with N-aryl picolinamides (LH, LH-NO₂, LH-CH₃, LH-l, LH-F) resulted in the formation of neutral heteroleptic complexes [Ir(ppy)₂L] (1), [Ir(ppy)₂L-NO₂](2), [Ir(ppy)₂L-CH₃](3), [Ir(ppy)₂L-Cl](4) and [Ir(ppy)₂L-F] (5). These complexes contain a six-coordinate iridium with a 2C, 4N coordination environment. The N-aryl picolinamide ligands are deprotonated during complexation and the resulting amidates bind to iridium in a chelating manner (N, N). Optical spectroscopic studies revealed that the complexes 1-5 exhibited intense π→π^∗ absorptions in the ultraviolet region. In addition low energy transitions due to ¹MLCT, ¹LLCT and ³MLCT are also seen. The emission spectra of 1-5, upon excitation at 450 nm, show a single emission with a λ_max around 513 nm. The lifetimes of this emission are in between 7.4 and 9.6 μs while the quantum yields are quite high and range from 0.2 to 0.5. Based on density functional theory (DFT) calculations on 1 and 3, the three highest occupied orbitals are composed of ligand π orbitals mixed with Ir-d orbitals while the three lowest unoccupied orbitals are mostly π orbitals of the ligands. From the time dependent DFT calculations it is revealed that the lowest energy electronic singlet and triplet excitations are a mixture of MLCT and LLCT.     

DFT and TD-DFT calculations on the electronic structures and spectroscopic properties of cyclometalated platinum(II) complexes

The electronic structures and spectroscopic properties of the three tridentate cyclometalated Pt(II) complexes Pt(N/\N/\C)C(triple bond)CPh (N/\N/\CH = 6-phenyl-2,2'-bipyridine) (1), Pt(N/\N/\S)C(triple bond)CPh (N/\N/\SH = 6-thienyl-2,2'-bipyridine) (2), and Pt(N/\N/\O)C(triple bond)CPh (N/\N/\OH = 6-furyl-2,2'-bipyridine) (3) were investigated theoretically using the density functional theory (DFT) method. The geometric structures of the complexes in the ground and excited states were explored at the B3LYP and UB3LYP levels, respectively. The absorption and emission spectra of the complexes in CH2Cl2 and CH3CN solutions were calculated by time-dependent density functional theory (TD-DFT) with the PCM solvent model. The calculated energies of the lowest singlet state and lowest triplet state in the three complexes are in good agreement with the results of experimental absorption and luminescence studies. All of the lowest-lying transitions were categorized as LLCT combined with MLCT transitions. The 623-nm emission of 1 from the 3A' --> 1A' transition was assigned as 3LLCT and 3MLCT transitions, whereas the 657- and 681-nm emissions of 2 and 3, respectively, were attributed to 3ILCT perturbed by 3MLCT transitions. NLO response calculations revealed that the nonzero values of the static first hyperpolarizability (beta0) for 1-3 are greatly enhanced through the introduction of the metal Pt(II) into the cyclometalated ligands, an effect that is determined by MLCT and LLCT transitions.     

Thermochromism of CuI Tetrakisguanidine Complexes: Reversible Activation of Metal‐to‐Ligand Charge‐Transfer Bands

Tetranuclear, intensely blue‐coloured Cu^I complexes were synthesised in which two Cu₂X₃^? units (X=Br or I) are bridged by a dicationic GFA (guanidino‐functionalised aromatic) ligand. The UV/Vis spectra show a large metal‐to‐ligand charge‐transfer (MLCT) band around 638 nm. The tetranuclear “low‐temperature” complexes are in a temperature‐dependent equilibrium with dinuclear Cu^I “high‐temperature” complexes, which result from the reversible elimination of two CuX groups. A massive thermochromism effect results from the extinction of the strong MLCT band upon CuX elimination with increasing temperature. For all complexes, quantum chemical calculations predict a small and method‐dependent energy difference between the possible electronic structures, namely Cu^I and dicationic GFA ligand (closed‐shell singlet) versus Cu^II and neutral GFA ligand (triplet or broken‐symmetry state). The closed‐shell singlet state is disfavoured by hybrid‐DFT functionals, which mix in exact Hartree–Fock exchange, and is favoured by larger basis sets and consideration of a polar medium.     

Synthesis,photophysical and photochemical properties of tetra- and octa-substituted gallium and indium phthalocyanines

The synthesis, photophysical and photochemical properties of the tetra- and octa-[4-(benzyloxyphenoxy)] substituted gallium(III) and indium(III) phthalocyanines are reported for the first time. The new compounds have been characterized by elemental analysis, IR, ¹H NMR spectroscopy and electronic spectroscopy. General trends are described for quantum yields of photodegredation, fluorescence quantum yields and lifetimes, triplet lifetimes and triplet quantum yields as well as singlet oxygen quantum yields of these compounds in dimethylsulfoxide (DMSO). Substituted indium phthalocyanine complexes (7b–9b) showed much higher quantum yields of triplet state and shorter triplet lifetimes, compared to the substituted GaPc derivatives due to enhanced intersystem crossing (ISC) in the former. The gallium and indium phthalocyanine complexes showed phototransformation during laser irradiation due to ring reduction. The singlet oxygen quantum yields (Φ_Δ), which give an indication of the potential of the complexes as photosensitizers in applications where singlet oxygen is required (Type II mechanism) ranged from 0.51 to 0.94. Thus, these complexes show potential as photodynamic therapy of cancer.     

Synthesis,Structure, and Electronic Properties of Extended π‐Conjugated Group 6 Fischer Alkoxy–Bis(carbene) Complexes

The synthesis, structure and electronic properties of novel Group 6 Fischer alkoxy–bis(carbene) complexes are reported. The UV/Vis spectra of these species display two main absorptions at approximately 350 and 550 nm attributable to a ligand‐field (LF) and metal‐to‐ligand charge‐transfer (MLCT) transitions, respectively. The planarity of the system and the cooperative effect of both pentacarbonyl metal moieties greatly enhance the conjugation between the group at the end of the spacer and the metal carbene fragment provoking dramatic changes in the LF and MLCT absorptions. This is in contrast to related push–pull Fischer monocarbenes, where the position of the MLCT band remains mostly unaltered regardless the substituent attached to the donor fragment. In addition, the MLCT maxima can be tuned with subtle modifications of the electronic nature of the central aryl fragment in the novel A–π‐D–π‐A (A=acceptor, D=donor) systems. DFT and time‐dependent (TD) DFT quantum chemical calculations at the B3LYP/def2‐SVP level have also been performed to determine the minimum‐energy molecular structure of this family of compounds and to analyse the nature of the vertical one‐electron excitations associated to the observed UV/Vis absorptions as well as to rationalise their electrochemical behaviour. The ability of tuning up the electronic properties of the compounds studied herein may be of future use in material chemistry.     

Synthesis,characterization, crystal structure determination and computational study of the high-spin iron(II) 2-cyanopyrazine complex trans-[Fe(pzCN)4Cl2]

A new mononuclear high-spin complex, trans-[Fe(pzCN)₄Cl₂] (1), was prepared from the reaction of FeCl₂.4H₂O and 2-cyanopyrazine (pzCN) in acetonitrile as a solvent. Suitable crystals of this complex for crystal structure determination were collected by slow evaporation of the produced pale orange solution. Complex 1 was characterized by elemental analysis (CHN), spectral methods (IR and UV–Vis), and single-crystal X-ray diffraction. The X-ray structural analysis indicated that the iron(II) is six-coordinated in an octahedral configuration by four N atoms from four 2-cyanopyrazine ligands and two chloride anions. Furthermore, the average of Fe–N bond lengths is 2.284(1)Å. It is well known that in the high-spin iron(II) phenanthroline and bipyridine complexes, the Fe–N bond lengths are around 2.2 Å. So, due to the Fe–N bond length in this complex, the iron(II) is unambiguously high-spin. The experimental evaluations on 1 have been complemented theoretically by the density functional theory (DFT) and TD-DFT calculations. The character of the Fe–N and Fe–Cl bonds was investigated using quantum theory of atoms in molecules. Additionally, electron delocalization and hyper-conjugative interactions of the synthesized complex were evaluated by natural bond orbital calculations.

     

Monocyclometalated (C N) Gold(III) Metallacycles: Tunable Emission and Singlet Oxygen (1O2) Generation Properties

The synthesis, characterization and photoluminescent properties of four cyclometalated (C N)-type gold(III) complexes bearing a bidentate diacetylide ligand, tolan-2,2’-diacetylide (tda), are reported. The complexes exhibit highly tunable excited state properties and show photoluminescence (PL) across the entire visible spectrum from sky-blue (λ_PL=493 nm) to red (λ_PL=675 nm) with absolute PL quantum yields (PLQY) of up to 75 % in solution, the highest PLQY found for any monocyclometalated Au(III) complex in solution. As a consequence of the use of the strongly rigidifying diacetylide bidentate ligand, a significant increase in the excited state lifetimes (τ₀=16–258 μs) was found in solution and in thin films. The complexes showed remarkable singlet oxygen generation in aerated solution with absolute singlet oxygen quantum yield (ϕ^1Δ) values reaching up to 7.5×10⁻⁵ and singlet oxygen lifetimes (τ₀^1Δ) in the range of 66–95 μs. Furthermore, the radiative and non-radiative rates of singlet oxygen were determined using the ϕ^1Δ and τ₀^1Δ values and correlations are drawn between the formation of singlet oxygen and its interaction with cyclometalated (C N) gold(III) complexes.     

Supramolecular assembly of hydrogen bonding,ESR studies and theoretical calculations of Cu(II) complexes

A series of copper(II) complexes were synthesized by the reaction of copper(II) chlorid with 1‐phenyl‐3methyl‐(3‐dervitives phenylhydrazo)‐5‐pyrazolone (HL_n) yields 1:1 and 1:2 (M:L) complexes depending on the reaction conditions. The elemental analysis, spectral (IR, ¹H NMR, UV‐Vis and ESR), conductance and magnetic measurements were used to characterize the isolated complexes. The IR spectral data indicate that the metal ions are coordinated through the oxygen of the keto and nitrogen of hydrazone groups. The UV‐Vis spectra, magnetic moments and ESR studies indicate square planar geometry for Cu(II) complexes ( 1–3 ) by NO monobasic bidentate and the two monobasic trans bidentate in octahedral geometry for Cu(II) complexes ( 4–6 ). It is found that the change of substituent affects the theoretical calculations of Cu(II) complexes. Molecular docking was used to predict the binding between the ligands (HL_n) and the receptors of prostate cancer mutant (2Q7K), breast cancer mutant (3HB5), crystal structure of E. coli (3T88) and crystal structure of S. aureus (3Q8U). The molecular and electronic structures of Cu(II) complexes and quantum chemical calculations were studied. According to intramolecular hydrogen bond leads to increasing of the complexes stability.     

Complexation of U(VI) with diphenyldithiophosphinic acid: spectroscopy,structure and DFT calculations

The complexation of U(VI) with diphenyldithiophosphinic acid (denoted as HL) in acetonitrile was studied by UV–Vis, FT-IR, crystallography and DFT calculations. UV–Vis absorption spectrophotometry implies that three successive complexes, UO₂L⁺, UO₂L₂, UO₂L₃^?, form in the solution. Significant ligand to metal charge transfer occurs from soft atom S to U(VI) in all the three complexes. A crystal of UO₂L₂ complex was successfully synthesized from the solution. In the crystal both the two ligands coordinate to U(VI) in bidentate form. DFT calculations confirm the formation of UO₂L₃^? complex and help illustrate the structures of all the U(VI) species in the solution.     

Nitration of Norcorrolatonickel(II): First Observation of a Diatropic Current in a System Comprising a Norcorrole Ring

A one‐pot reaction of 5,14‐bis(mesityl)‐norcorrolatonickel(II) with isoamyl nitrite under mild reaction conditions resulted in the consecutive formation of 3‐nitro‐, 3,12‐dinitro‐ and 3,16‐dinitro‐, 3,7,12‐trinitro‐, and 3,7,12,16‐tetranitro‐norcorrolatonickel(II) in 50–80 % yield. The substituted macrocycles retained their antiaromatic character. The observed regioselectivity of the substitution was analyzed by comparing the relative energies of the DFT energy‐optimized models of the radical or arenium cationic intermediates that can be formed upon reaction with NO₂. The nitrated systems were characterized by high‐resolution mass spectrometry, NMR and UV/Vis spectroscopy, X‐ray diffraction analysis, cyclic voltammetry, and DFT calculations. A significant and systematic cathodic shift of the redox couples was observed to correlate with an increasing number of the NO₂ group. A decrease of the LUMO energies in the tri‐ and tetra‐nitrated products stabilizes mono‐ and bis‐reduced complexes of these ligands. The reduction takes place on the macrocycle rather than on the metal ion leading to the consecutive formation of stable paramagnetic monoanion radicals and water‐soluble diamagnetic dianions with an aromatic character, which were revealed by ESR and ¹H NMR measurements, respectively. The electronic structures of the reduced forms were analyzed by extensive TD‐DFT calculations.     

Reactivity of a Tetra(o‐tolyl)diborane(4) Dianion as a Diarylboryl Anion Equivalent

Lithium and magnesium salts of tetra(o‐tolyl)diborane(4) dianion, having B=B double bond character, were synthesized. It was clarified that the lithium salt of the dianion has a high‐lying HOMO and a narrow HOMO–LUMO gap, which were perturbed by dissociation of Li⁺ cation, as judged by UV/Vis spectroscopy and DFT calculations. The lithium salt of the dianion reacted as two equivalents of a diarylboryl anion with CH₂Cl₂ or S₈ to give boryl‐substituted products.     

Physical, photophysical and structural properties of ruthenium(II) complexes containing a tetradentate bipyridine ligand

The focus of this report is the synthesis and properties of two new analogues of ruthenium(ii) tris-bipyridine, a monomer and dimer. The complexes contain the ligand 6,6'-(ethan-1,2-diyl)bis-2,2'-bipyridine (O-bpy) which contains two bipyridine units bridged in the 6,6' positions by an ethylene bridge. Crystal structures of the two complexes formulated as [Ru(bpy)(O-bpy)](PF6)2 and [(Ru(bpy)2)2(O-bpy)](PF6)4 reveal structures of lower symmetry than D3 which affects the electronic properties of the complexes as substantiated by density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations. The HOMO lies largely on the ruthenium center; the LUMO spreads its electron density over the bipyridine units, but not equally in the mixed O-bpy-bpy complexes. Calculated Vis/UV spectra using TDDFT methods agree with experimental spectra. The lowest lying triplet excited state for [Ru(bpy)(O-bpy)](PF6)2 is 3MC resulting in a low emission quantum yield and a large chloride ion photosubstitution quantum yield.     

Ligand-to-diimine/metal-to-diimine charge-transfer excited states of [Re(NCS)(CO)3(alpha-diimine)] (alpha-diimine = 2,2'-bipyridine, di-iPr-N,N-1,4-diazabutadiene). A spectroscopic and computational study

Two new complexes fac-[Re(NCS)(CO)3(N,N)] (N,N = 2,2'-bipyridine (bpy), di-iPr-N,N-1,4-diazabutadiene (iPr-DAB)) were synthesized and their molecular structures determined by X-ray diffraction. UV-vis absorption, resonance Raman, emission, and picosecond time-resolved IR spectra were measured experimentally and calculated with TD-DFT. A good agreement between experimental and calculated ground- and excited-state spectra is obtained, but only if the solvent (MeCN) is included into calculations and excited state structures are fully optimized at the TD-DFT level. The lowest excited states of the bpy and iPr-DAB complexes are assigned by TD-DFT as 3aA' by comparison of calculated and experimental IR spectra. Excited-state lifetimes of 23 ns and ca. 625 ps were determined for the bpy and DAB complex, respectively, in a fluid solution at room temperature. Biexponential emission decay (1.3, 2.7 micros) observed for [Re(NCS)(CO)3(bpy)] in a 77 K glass indicates the presence of two unequilibrated emissive states. Low-lying electronic transitions and excited states of both complexes have a mixed NCS --> N,N ligand-to-ligand and Re --> N,N metal-to-ligand charge-transfer character (LLCT/MLCT). It originates in mixing between Re d(pi) and NCS pi characters in high-lying occupied MOs. Experimentally, the LLCT/MLCT mixing in the lowest excited state is manifested by shifting the nu(CO) and nu(NC) IR bands to higher and lower wavenumbers, respectively, upon excitation. Resonant enhancement of both nu(CO) and nu(NC) Raman bands indicates that the same LLCT/MLCT character mixing occurs in the lowest allowed electronic transition.