Bridge‐Localized HOMO‐Binding Character of Divinylanthracene‐Bridged Dinuclear Ruthenium Carbonyl Complexes: Spectroscopic,Spectroelectrochemical, and Computational Studies

The electronic properties of four divinylanthracene‐bridged diruthenium carbonyl complexes [{RuCl(CO)(PMe₃)₃}₂(μ? CH?CHArCH?CH)] (Ar=9,10‐anthracene ( 1 ), 1,5‐anthracene ( 2 ), 2,6‐anthracene ( 3 ), 1,8‐anthracene ( 4 )) obtained by molecular spectroscopic methods (IR, UV/Vis/near‐IR, and EPR spectroscopy) and DFT calculations are reported. IR spectroelectrochemical studies have revealed that these complexes are first oxidized at the noninnocent bridging ligand, which is in line with the very small ν(C?O) wavenumber shift that accompanies this process and also supported by DFT calculations. Because of poor conjugation in complex 1 , except oxidized 1⁺ , the electronic absorption spectra of complexes 2⁺ , 3⁺ , and 4⁺ all display the characteristic near‐IR band envelopes that have been deconvoluted into three Gaussian sub‐bands. Two of the sub‐bands belong mainly to metal‐to‐ligand charge‐transfer (MLCT) transitions according to results from time‐dependent DFT calculations. EPR spectroscopy of chemically generated 1⁺ – 4⁺ proves largely ligand‐centered spin density, again in accordance with IR spectra and DFT calculations results.     

Synthesis and Photophysical Properties of a Series of Biscyclometalated Platinum(II) Complexes on the Basis of a Tridentate 2,6-Diphenylpyridine

The complexes C,C-trans-[Pt(C^N^C)L] ^z [C^N^C is bisdeprotonated 2,6-diphenylpyridinate (dppy^2-); L = CO, Me2SO (dmso), ethylenediamine (en), CN^-, pyrazine (pz), P(C₆F₅)₃, 4,4'-bipyridine (4,4'-bpy)] were synthesized and characterized by ¹H NMR, electronic, and emission spectroscopy. Spectralluminescence properties of the chromophoric group (platinum-cyclometalating ligand) in the C,C-trans-bis-cyclometalated complexes depend on the nature of the noncyclometalating ligand L, which is explained by its donor-acceptor effects on the form of existence of the complex in solution.     

Electrochemical properties of 2,2":6",2″-terpyridine complexes of platinum(ii) with arenethiolate ligands. Alkylation of reduced forms of the complexes

Three mixed-ligand terpyridine-thiolate Pt^II complexes containing 2,2":6",2-terpyridine (tpy) and para-substituted thiophenolate ions, [(tpy)Pt(SC₆H₄-4-X)]BF₄ (X = NMe₂, H, NO₂) were synthesized. The complexes were isolated as chlorides or tetrafluoroborates and characterized by electrochemistry, visible electronic spectroscopy and ¹H NMR spectroscopy, and elemental analysis. Remarkable influence of the electron-donating/withdrawing properties of the substituent in the thiolate ligand on the physicochemical properties of the complexes, in particular, on the electrochemical reduction potentials, was found. The reduced forms of the complexes undergo electrochemically initiated alkylation with alkyl halides, resulting in the formation of Pt alkyl compounds.     

Proton‐Induced Generation of Remote N‐Heterocyclic Carbene–Ru Complexes

The proton‐induced Ru?C bond variation, which was previously found to be relevant in the water oxidation, has been investigated by using cyclometalated ruthenium complexes with three phenanthroline (phen) isomers. The designed complexes, [Ru(bpy)₂(1,5‐phen)]⁺ ([ 2 ]⁺), [Ru(bpy)₂(1,6‐phen)]⁺ ([ 3 ]⁺), and [Ru(bpy)₂(1,7‐phen)]⁺ ([ 4 ]⁺) were newly synthesized and their structural and electronic properties were analyzed by various spectroscopy and theoretical protocols. Protonation of [ 4 ]⁺ triggered profound electronic structural change to form remote N‐heterocyclic carbene (rNHC), whereas protonation of [ 2 ]⁺ and [ 3 ]⁺ did not affect their structures. It was found that changes in the electronic structure of phen beyond classical resonance forms control the rNHC behavior. The present study provides new insights into the ligand design of related ruthenium catalysts.     

Heteroligand bipyridyl-pyridylbenzimidazole Ru(II) complexes. Synthesis,structural characterization,and investigation of electronic structure

Ruthenium(II) complexes with pyridylbenzimidazole derivatives were synthesized and investigated by NMR (¹H and ¹H-¹H COSY), mass, and electronic spectroscopy. Proceeding from quantum-chemical calculations by the density functionsl methods the analysis was performed of electronic and geometric structure of free ligands and Ru(II)complexes, and the electron absorption spectra of complexes under study were interpreted. Compared to [Ru(bpy)₃]²⁺ (bpy = 2,2′-bipyridyl) the charge transfer band in the visible range of the electronic spectra of the complexes in question suffered a red shift by ～10 nm, and its intensity in the absorption maximum is several times smaller. The introduction of acceptor substituents into the benzene ring of the pyridylbenzimidazole ligand did not affect significantly the spectral properties of the complexes.     

How Does Peripheral Functionalization of Ruthenium(II)–Terpyridine Complexes Affect Spatial Charge Redistribution after Photoexcitation at the Franck–Condon Point?

Ruthenium polypyridine‐type complexes are extensively used sensitizers to convert solar energy into chemical and/or electrical energy, and they can be tailored through their metal‐to‐ligand charge‐transfer (MLCT) properties. Much work has been directed at harnessing the triplet MLCT state in photoinduced processes, from sophisticated molecular architectures to dye‐sensitized solar cells. In dye‐sensitized solar cells, strong coupling to the semiconductor exploits the high reactivity of the (hot) singlet/triplet MLCT state. In this work, we explore the nature of the ¹MLCT states of remotely substituted Ru^II model complexes by both experimental and theoretical techniques. Two model complexes with electron‐withdrawing (i.e. NO₂) and electron‐donating (i.e. NH₂) groups were synthesized; these complexes contained a phenylene spacer to serve as a spectroscopic handle and to confirm the contribution of the remote substituent to the ¹MLCT transition. [Ru(tpy)₂]²⁺‐based complexes (tpy=2,2′:6′,2′′‐terpyridine) were further desymmetrized by tert‐butyl groups to yield unidirectional ¹MLCTs with large transition dipole moments, which are beneficial for related directional charge‐transfer processes. Detailed comparison of experimental spectra (deconvoluted UV/Vis and resonance Raman spectroscopy data) with theoretical calculations based on density functional theory (including vibronic broadening) revealed different properties of the optically active bright ¹MLCT states already at the Franck–Condon point.     

Synthesis,mesomorphic behaviour and optoelectronic properties of phosphorus-based thermotropic liquid crystalline dendrimers

A new series of thermotropic phosphorus-based liquid crystalline (LC) dendrimers based on a thiophosphoryl-phenoxymethyl(methylhydrazono) core (thiophosphoryl-PMMH) up to the fifth generation has been synthesised by solution condensation of aldehyde groups, surface-functionalised thiophosphoryl-PMMH dendritic substrates of generation numbers G_0.5 to G_5.5, with the appropriate molar equivalents of the pro-mesogenic n-hexadecylaniline mono-functional building block. Their chemical composition has been confirmed by ¹H/¹³C/³¹P nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, elemental analysis. Optical properties have been studied by ultraviolet-visible absorption, photoluminescence spectroscopy and polarised optical microscopy, and thermal characteristics by differential scanning calorimetry. Electrical studies have been made using the current-voltage characteristics of organic light-emitting diodes consisting of multi-layered indium tin oxide/dendrimer/aluminium tris(8-hydroxyquinoline)Al architecture. It has been demonstrated that the molecular engineering approach adopted can successfully lead to phosphorus-containing dendritic organic semiconductors (OSCs) which show tunable mesomorphic behaviour (extension of the observed smectic mesophase) and (opto) electronic properties, owing to their peripheral decoration with a tunable number of azomethine-based optically active chromophoric units. This rare combination of ‘tunable by design’ properties makes this series of thermostable thiophosphoryl-PMMH-based LC dendrimers a particularly appealing class of OSCs for use in optically and/or electronically active layers of (opto)electronic devices such as light-emitting diodes, field-effect transistors, solar cells and lasers.     

Characterization and Thermal Study of Schiff-Base Monomers and Its Transition Metal Polychelates and Their Photovoltaic Performance on Dye Sensitized Solar Cells

Azo dye monomer 4,4′-(4,4′-biphenylylenebisazo)-disalicylaldehyde-4n-butylphenyl aniline (H₂A) is synthesised by the reaction of 4,4′-bis[(salicylaldehyde-5)-azo]biphenyl (Azo) and n-butylaniline in the 1:2 molar ratio and its metal polychelates are also synthesized with Co(II), Ni(II), Cu(II), and Zn(II) metal ions. The synthesized compounds are characterized by ¹H, ¹³C NMR, Fourier transform infrared (FT-IR) spectroscopy, electronic spectra (UV-Vis), elemental analysis (C, H, N, O), gas chromatography-mass (GCmass) spectrometry, magnetic susceptibility and molar conductivity techniques. Thermal properties of the title compounds are studied using the thermogravimetric analysis (TGA). The metal molar ratio in all of the polychelates is found to be consistent with 1:1 (metal/ligand) stoichiometry. The influence of organic dyes H₂A and the [CuA(H₂O)₂] _n polychelate are investigated as photosensitizers on the photovoltaic parameters by current–voltage (I–V) measurements on TiO₂ photoelectrode dye sensitized solar cells (DSSCs). The [CuA(H₂O)₂] _n metal polychelate demonstrates the best performance as compared to the cell sensitized with H₂A.     

Characterization of a Ferryl Flip in Electronically Tuned Nonheme Complexes. Consequences in Hydrogen Atom Transfer Reactivity

Two oxoiron(IV) isomers ( ^R 2a and ^R 2b ) of general formula [Fe^IV(O)(^RPyNMe₃)(CH₃CN)]²⁺ are obtained by reaction of their iron(II) precursor with NBu₄IO₄. The two isomers differ in the position of the oxo ligand, cis and trans to the pyridine donor. The mechanism of isomerization between ^R 2a and ^R 2b has been determined by kinetic and computational analyses uncovering an unprecedented path for interconversion of geometrical oxoiron(IV) isomers. The activity of the two oxoiron(IV) isomers in hydrogen atom transfer (HAT) reactions shows that ^R 2a reacts one order of magnitude faster than ^R 2b , which is explained by a repulsive noncovalent interaction between the ligand and the substrate in ^R 2b . Interestingly, the electronic properties of the R substituent in the ligand pyridine ring do not have a significant effect on reaction rates. Overall, the intrinsic structural aspects of each isomer define their relative HAT reactivity, overcoming changes in electronic properties of the ligand.     

Synthesis and structure of the chiral palladium-fullerene C60 and C70 complexes with enantiomeric ligand 2,2′,5,5′-tetramethyl-4,4′-bis(diphenylphosphino)-3,3′-bithiophene [(−)tetraMe-BITIOP]

η²-Fullerene (C₆₀ and C₇₀) palladium optically active complexes with the axially chiral enantiomeric ligand of bithienyl series, [(−)tetraMe-BITIOP], have been synthesized and investigated by ³¹P-{¹H} NMR, electronic spectroscopy, CD spectroscopy, cyclic voltammetry and by single crystal X-ray diffraction.     

Potentiometric Titrations and Nickel(II) Complexes of Four Topologically Constrained Tetraazamacrocycles

Abstract

The novel high spin Ni²⁺ complexes of the topologically constrained tetraazamacrocycles (1–4) [4,11-dimethyl-1,4,8,11 - tetraazabicyclo[6.6.2]hexadecane (1); 4,10-dimethyl-1,4,7,10-tetraazabicyclo[6.5.2]pentadecane (2); 4,10-dimethyl-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane (3); racemic-4,5,7,7,11,12,14,14-octamethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (4)] show striking properties. Potentiometric titrations of the ligands 2 and 4 revealed them to be proton sponges, as reported earlier for 1 [1]. Ligand 3 is less basic, losing its last proton with a pK = 11.3(2). Despite high proton affinities, complexation reactions in the absence of protons successfully yielded Ni²⁺ complexes in all cases. The X-ray crystal structures of Ni(1)(acac)⁺, Ni(3)(acac)⁺ and Ni(1)(OH₂)₂ ²⁺ demonstrate that the ligands enforce a distorted octahedral geometry on Ni²⁺ with two cis sites occupied by other ligands. Magnetic measurements and electronic spectroscopy on the corresponding Ni(L)Cl₂ (L = 1–3) complexes reveal that all are high spin and six-coordinate with typical magnetic moments. In contrast, [Ni(4)Cl⁺] is five-coordinate with a slightly higher magnetic moment and its own characteristic electronic spectrum. The extra methyl groups on ligand 4 define a shallow cavity, sterically allowing only one chloride ligand to bind to the nickel(II) ion.     

Structurally Diverse Boron–Nitrogen Heterocycles from an N2O23− Formazanate Ligand

Five new compounds comprised of unprecedented boron–nitrogen heterocycles have been isolated from a single reaction of a potentially tetradentate N₂O₂³⁻ formazanate ligand with BF₃⋅OEt₂ and NEt₃. Optimized yields for each product were obtained through variation of experimental conditions and rationalized in terms of relative Gibbs free energies of the products as determined by electronic structure calculations. Chemical reduction of two of these compounds resulted in the formation of a stable anion, radical anion, and diradical dianion. Structural and electronic properties of this new family of redox‐active heterocycles were characterized using UV/vis absorption spectroscopy, cyclic voltammetry and X‐ray crystallography.     

Structurally Diverse Boron–Nitrogen Heterocycles from an N2O23− Formazanate Ligand

Five new compounds comprised of unprecedented boron–nitrogen heterocycles have been isolated from a single reaction of a potentially tetradentate N₂O₂³⁻ formazanate ligand with BF₃⋅OEt₂ and NEt₃. Optimized yields for each product were obtained through variation of experimental conditions and rationalized in terms of relative Gibbs free energies of the products as determined by electronic structure calculations. Chemical reduction of two of these compounds resulted in the formation of a stable anion, radical anion, and diradical dianion. Structural and electronic properties of this new family of redox-active heterocycles were characterized using UV/vis absorption spectroscopy, cyclic voltammetry and X-ray crystallography.     

Low‐cost Nickel Complex Dye‐sensitized Titania Nanoparticle/nanotube Composites for Solar Cells

In this work, high‐performance dye‐sensitized solar cells (DSSCs) based on new low‐cost visible nickel complex dye (VisDye), TiO₂ nanoparticle/nanotube composites electrodes, carbon nanoparticles counter electrodes, and ionic liquids electrolytes have been fabricated. The electronic structure, optical spectroscopy, and electrochemical properties of the VisDye were studied. Experimental results indicate that it is beneficial to improve the electron transport and power conversion efficiency using the nickel complex VisDye and TiO₂ nanoparticle/nanotube composites. Under optimized conditions, the solar energy conversion efficiencies were measured. The short‐circuit current density (J_SC), the open‐circuit voltage (V_OC), the fill factor (FF), and the overall efficiency (η) of the DSSCs are 10.01 mA/cm², 516 mV, 0.68, and 3.52%, respectively. This study demonstrates that the combination of new VisDye with TiO₂ nanoparticle/nanotube composites electrodes and carbon nanoparticles counter electrodes provide a way to fabricate highly efficient dye‐sensitized solar cells in low‐cost production.     

Luminescent mononuclear and dinuclear cycloplatinated (II) complexes comprising azide and phosphine ancillary ligands

A new series of cycloplatinated (II) complexes with general formulas of [Pt (bhq)(N₃)(P)] [bhq = deprotonated 7,8‐benzo[h]quinoline, P = triphenyl phosphine (PPh₃) and methyldiphenyl phosphine], [Pt (bhq)(P^P)]N₃ [P^P = 1,1‐bis (diphenylphosphino)methane (dppm) and 1,2‐bis (diphenylphosphino)ethane] and [Pt₂(bhq)₂(μ‐P^P)(N₃)₂] [P^P = dppm and 1,2‐bis (diphenylphosphino)acetylene] is reported in this investigation. A combination of azide (N₃^?) and phosphine (monodentate and bidentate) was used as ancillary ligands to study their influences on the chromophoric cyclometalated ligand. All complexes were characterized by nuclear magnetic resonance spectroscopy. To confirm the presence of the N₃^? ligand directly connected to the platinum center, complex [Pt (bhq)(N₃)(PPh₃)] was further characterized by single‐crystal X‐ray crystallography. The photophysical properties of the new products were studied by UV–Vis spectroscopy in CH₂Cl₂ and photoluminescence spectroscopy in solid state (298 or 77 K) and in solution (77 K). Using density functional theory calculations, it was proved that, in addition to intraligand charge‐transfer (ILCT) and metal‐to‐ligand charge‐transfer (MLCT) transitions, the L′LCT (L′ = N₃, L = C^N) electronic transition has a remarkable contribution in low energy bands of the absorption spectra (for complexes [Pt (bhq)(N₃)(P)] and [Pt₂(bhq)₂(μ‐P^P)(N₃)₂]). It is indicative of the determining role of the N₃^? ligand in electronic transitions of these complexes, specifically in the low energy region. In this regard, the photoluminescence studies indicated that the emissions in such complexes originate from a mixed ³ILCT/³MLCT (intramolecular) and also from aggregations (intermolecular).     

Effect of the nature of axial ligand on the effective charge of the metal center in PcFe(II) complexes

Disubstituted iron phthalocyanine complexes were studied by X-ray photoelectron spectroscopy (XPS). Fe2p _3/2, N1s, and C1s XPS spectra were analyzed, and the role of the ligand in their generation was determined. Assignment of the magnetic properties of phthalocyanine iron complexes was done. Covalence of the metal-ligand bond was determined. The nature of the axial ligand in Pc^tFe affects the electronic state of the central iron atom.     

N,S,O-Containing organic ligands based on salicylaldehyde and 2-thiosubstituted ethylamines and their complexes with CoII, NiII, and CuII

The reaction of 2,2′-di(2-hydroxybenzaliminoethyl) disulfide (H₂L¹) and 2-[(2-thioethyl)iminomethyl]phenol (H₂L²) with MCl₂·xH₂O (M = Co, Ni, Cu) afforded the [M₂(L¹)Cl₂] and [M(L²)]₂ complexes, respectively. Their structures were determined by the data of electronic and IR spectroscopy and PM3 quantum chemical calculations. The H₂L¹ ligand and the complexes were studied by electrochemistry (CV and using a rotating disk electrode). The primary electronic changes are localized on the ligand fragment upon the electrochemical oxidation and reduction of the complexes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1325–1330, July, 2007.     

Luminescent Cyclometalated Alkynylplatinum(II) Complexes with a Tridentate Pyridine‐Based N‐Heterocyclic Carbene Ligand: Synthesis,Characterization, Electrochemistry,Photophysics, and Computational Studies

A new class of luminescent alkynylplatinum(II) complexes with a tridentate pyridine‐based N‐heterocyclic carbene (2,6‐bis(1‐butylimidazol‐2‐ylidenyl)pyridine) ligand, [Pt^II(C^N^C)(C?CR)][PF₆], and their chloroplatinum(II) precursor complex, [Pt^II(C^N^C)Cl][PF₆], have been synthesized and characterized. One of the alkynylplatinum(II) complexes has also been structurally characterized by X‐ray crystallography. The electrochemistry, electronic absorption and luminescence properties of the complexes have been studied. Nanosecond transient absorption (TA) spectroscopy has also been performed to probe the nature of the excited state. The origin of the absorption and emission properties has been supported by computational studies.     

From the {FeIII2Ln2} Butterfly's Perspective: the Magnetic Benefits and Challenges of Cooperativity within 3 d–4 f Based Coordination Clusters

In this Review we discuss the tuning handles which can be used to steer the magnetic properties of Fe^III-4 f “butterfly” compounds. The majority of presented compounds were produced in the context of project A3 “Di- to tetranuclear compounds incorporating highly anisotropic paramagnetic metal ions” within the SFB/TRR88 “3MET”. These contain {Fe^III₂Ln₂} cores encapsulated in ligand shells which are easy to tune in a “test-bed” system. We identify the following advantages and variables in such systems: (i) the complexes are structurally simple usually with one crystallographically independent Fe^III and Ln^III, respectively. This simplifies theory and anaylsis; (ii) choosing Fe allows ⁵⁷Fe Mössbauer spectroscopy to be used as an additional technique which can give information about oxidation levels and spin states, local moments at the iron nuclei and spin-relaxation and, more importantly, about the anisotropy not only of the studied isotope, but also of elements interacting with this isotope; (iii) isostructural analogues with all the available (i. e. not Pm) 4 f ions can be synthesised, enabling a systematic survey of the influence of the 4 f ion on the electronic structure; (iv) this cluster type is obtained by reacting [Fe^III₃O(O₂CR)₆(L)₃](X) (X=anion, L=solvent such as H₂O, py) with an ethanolamine-based ligand L′ and lanthanide salts. This allows to study analogues of [Fe^III₂Ln₂(μ₃-OH)₂(L′)₂(O₂CR)₆] using the appropriate iron trinuclear starting materials. (v) the organic main ligand can be readily functionalised, facilitating a systematic investigation of the effect of organic substituents on the ligands on the magnetic properties of the complexes. We describe and discuss 34 {M^III₂Ln₂} (M=Fe or in one case Al) butterfly compounds which have been reported up to 2020. The analysis of these gives perspectives for designing new SMM systems with specific electronic and magnetic signatures