Complexes In Solid State Research Articles

Investigation of Aggregation‐Induced Phosphorescence of Non‐Symmetric [Pt(C^N*N′^C′)] Complexes in Block Copolymer Micelles: Effects of Pt(II) Сomplex and Micellar Core

AbstractThe aggregation‐induced phosphorescence emission (AIPE) phenomenon (emergence or increase in phosphorescence intensity as a result of aggregation of phosphorescent emitters) is regarded nowadays as an effective tool for improving brightness and tuning photophysical properties of phosphors. The intrinsic drawback of the aggregates featuring AIPE—their instability in aqueous dispersions, which hampers their utility in biomedical applications—can be overcome by their stabilization inside block copolymer micelles. Herein, we investigate the effects of both ligand and micellar core chemistries on the emergence of AIPE by using a series of the [Pt(C^N*N′^C′)] complexes embedded into three block copolymers with different micellar cores. It has been shown that the only micelles that supported AIPE revealed for the corresponding complexes in solid state are those with poly(ε‐caprolactone) cores. The latter observation can be explained by the ability of poly(ε‐caprolactone) to demonstrate non‐negligible swelling in water, the content of which in the micellar core formed by this polymer seems to be high enough to induce the aggregation of the complexes and the concomitant AIPE effect.

Inclusion complexes of α-cyclodextrin with p-aminobenzoic acid and nicotinic acid: Crystal structure, DSC and IR spectroscopy analysis in solid state and 1H NMR and ITC calorimetric studies of complexation in solutions

In this work, inclusion complexes of α-cyclodextrin with p-aminobenzoic acid (PABA) and nicotinic acid (NIK) were studied. Solid-state complexes were obtained and studied with single-crystal X-ray diffraction, powder X-ray diffraction, differential scanning calorimetry, and FT-IR spectroscopy. Additionally, the formation of complexes was studied in aqueous solutions with isothermal titration calorimetry and 1H NMR spectroscopy in DMSO‑d6 solutions. Single crystal studies, FT-IR spectroscopy and powder diffraction confirmed the inclusion of PABA and NIK inside the cyclodextrin cavity. From the results of the isothermal titration calorimetry, the stoichiometry (n) and standard thermodynamic functions (ΔH, ΔG, ΔS) of complexation, as well as binding constants (K) for the formed complexes were calculated. The obtained results confirmed the thermodynamically spontaneous formation of complexes in exothermic reactions. Furthermore, the results obtained were compared for complexes of PABA/NIK acids with β-cyclodextrin. A database survey of α-cyclodextrin complexes with different benzoic acids available in the CSD database was performed.

Solution studies, synthesis and antibacterial activity of Ga(III) complexes with bis-kojate derivatives

Given the recognized major problem of microbial drug resistance for human health, new metal-based drugs have been currently explored for their antimicrobial properties, including gallium-based compounds as potential metallophores that could perturb Fe’s interactions with proteins. Herein we have designed and synthesized two bis-kojate ligands (named L4 and L6) and studied their Ga(III) complexes for their physico-chemical and biological properties. In particular a detailed study of their complexation properties in aqueous solution, showed equilibrium models with formation of quite stable dinuclear 2:3 metal:ligand complexes, though with different stability. Solid state complexes were also prepared and characterized and complementary DFT studies indicated that [Ga2(L4)3] complex, with higher stability, seems to adopt a three-ligand bridging conformation, while that for L6 adopt a one ligand bridging conformation. Preliminary investigation of the antibacterial activity of these gallium complexes showed antipseudomonal activity, which appeared higher for the complex with L4, a feature of potential interest for the scientific community.

Luminescence under UV(A, B and C) and sunlight exposure of tetrakis Tb3+ carboxylate complexes doped in different polymers

New tetrakis Lanthanide(III) carboxylate-based complexes (Ln3+: Eu and Tb) were successfully synthesized via a facile one-pot method with flufenamic acid (fluf) as ligand and benzimidazole (Bzim) or 1-ethyl-3-methylimidazole (C2mim) as counterions. In addition, the Q[Tb(fluf)4] complexes (Q+: Bzim and C2mim) were doped into polymethylmethacrylate (PMMA), polystyrene (PS), polycaprolactone (PCL) and poly(9-vinylcarbazole) (PVK) polymeric matrices at a 1 % (w/w) concentration and revealed highly desirable photophysical features such as wide range excitation wavelengths for the PMMA and PCL matrices and a very uncommon emission under sunlight exposure arising from the Tb3+ ion for the PMMA material. Thus, the tetrakis compounds with general formula Q[Ln(fluf)4] were characterized by elemental and thermal analysis, ESI-MS mass spectrometry, and FTIR absorption spectroscopy. The PMMA:(1 %)Q[Tb(fluf)4] doped films revealed higher thermal stability than the complexes. The tetrakis Eu3+ complex with Bzim as counterion shows no luminescence either for room or low temperature due to a highly operative low-lying ligand to metal charge transfer (LMCT) state quenching, while the corresponding C2mim-based analogous complex reveals some weak intensity emission, showing very low intrinsic quantum yield (QEuEu) values. On the other hand, the corresponding Tb3+ compounds presented bright green emission for the solid-state complexes and, particularly, for the PMMA:(1 %)Q[Tb(fluf)4] doped films when excited at UVA, UVB, and UVC radiation. Moreover, when the doped PMMA films are exposed to sunlight radiation in an open external environment, a bright green emission arising from the 5D4 → 7F5 transition from the Tb3+ ion can be seen. In this way, these optical results suggest that the PMMA:(1 %)Q[Tb(fluf)4] luminescent photonic materials can act as versatile and efficient light-converting molecular devices (LCMDs).

Optimizing hexafluoro-2,4-pentanedione based Eu(III) complexes: A comprehensive study on the synthesis, spectroscopic characterization with Judd-Ofelt calculation

Utilizing Europium(III), compounds having eight-coordination geometry of the type [Eu(hfpd)3L2] and [Eu(hfpd)3Lʹ] were synthesized [hfpd = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, L = tri-octyl-phosphine oxide (TOPO) and Lʹ = 1,10-phenanthroline (phen), Neocuproine (neoc) and bathocuproine (bathoc)] and characterized through elemental, FTIR, CV and Proton-NMR techniques. Photoluminescent studies and quantum yield helped to understand the role of coordination environment and ligands on the emission intensity. Luminescence decay curves served as the basis for calculating the excited-state lifetimes of the synthesized complexes. JO parameters (Ω2, Ω4) and asymmetry ratio were also evaluated to study the coordination environment around the central metal ion. Solid-state complexes exhibited an intense, monochromatic bright red emission, as characterized by its Commission International de l’Eclairage (CIE) color coordinates. Owing to red luminescence and semi-conducting properties, these Eu(III) complexes can be employed as red-emitting material for fabricating lighting devices.

Understanding electronic structure tunability by metal dopants for promoting MgB2 hydrogenation

Hydrogen is a promising energy carrier, but its onboard application is limited by the need for compact, low-pressure storage solutions. Solid-state complex metal hydride systems, such as MgB2/Mg(BH4)2, offer high storage capacities but suffer from sluggish kinetics and poor reversibility. One avenue for improving reactivity is to introduce metal dopants to alter electronic and atomic properties, but the role of these chemical additives remains poorly understood, particularly for the hydrogenation reaction. In this work, we used density functional theory calculations on model MgB2 systems to rationalize the potential role of metal dopants in destabilizing B–B bonding within the MgB2 lattice. We carried out detailed electronic structure analyses for 28 different metal dopant adatoms to identify properties that contribute to a dopant’s efficacy. Based on the simulation results, we propose that an intermediate ionic and covalent character of the bonds between adatoms and B atoms is desirable for facilitating charge redistribution, disrupting the B–B bond network, and promoting H2 dissociation and H atom chemisorption on MgB2.

Heteroleptic samarium complexes with high quantum yields for temperature sensing applications.

Two new crystallographically characterized samarium complexes, [Sm(fod)3(L1)] (1) and [Sm(fod)3(L2)] (2) {L1 = 4,7-diphenyl-1,10-phenanthroline (bath), L2 = 2,2':6',2''-terpyridine and fod = anion of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione (Hfod)}, were synthesized and thoroughly characterized. Single-crystal (SC) analysis shows that complex 1 is an eight-coordinate structure with a distorted square antiprism geometry (D4d), whereas complex 2 possesses a nine-coordinate structure with distorted muffin geometry (Cs). The NMR results are in line with SC-XRD analysis, which further validate that the complexes remain intact in solutions. The photophysical characteristics of the complexes were studied in both visible and near infra-red (NIR) regions. The PLQY values of the present complexes were found to be higher than those reported in the literature except for a tetrakis Sm complex. This result indicates that both the ligands act as effective antennas for the present systems. A comparison of PLQY and emission lifetime values within the present complexes (in solid state) reveals that energy transfer from terpy to Sm3+ is more effective than that from the bath ligand. Various color parameters of the complexes were calculated, and the determined CCT values suggest that the complexes may be used as warm light sources. The determined band gap values for the complexes are in the range of those for semiconductors, which suggest the application of present systems in the field of optoelectronics. The curve between the emission intensity and temperature for complex 1 shows a perfect linearity (χ2 = 0.99), which suggests that this complex can have potential application as a temperature sensor in the range 60-350 K.

Structure of the caffeine-pyrogallol complex: revisiting a pioneering structural analysis of a model pharmaceutical cocrystal.

The 1967 attempt of structural analysis of the solid-state complex of caffeine and pyrogallol was a pioneering structural investigation in the supramolecular chemistry of caffeine, of what today would easily be considered an archetype of a model pharmaceutical cocrystal. Re-investigating this historically important system demonstrates that this long overlooked complex is most likely a tetrahydrate with a different structure and composition than initially proposed, and provides the crystal structure of the anhydrous cocrystal.

Supramolecular "baking powder": a hexameric halogen-bonded phosphonium salt cage encapsulates and functionalises small-molecule carbonyl compounds.

We report a hexameric supramolecular cage assembled from the components of a Wittig-type phosphonium salt, held together by charge-assisted halogen bonds. The cage reliably encapsulates small polar molecules, including aldehydes and ketones, to provide host-guest systems where components are pre-formulated in a near-ideal stoichiometry for a mechanochemical base-activated Wittig olefination. These pre-formulated solids represent a proof-of-principle for a previously not reported supramolecular design of solid-state reactivity in which the host for molecular inclusion also acts as a complementary reagent for the subsequent chemical transformation of an array of guests. The host-guest solid-state complexes can act as supramolecular surrogates to their Wittig olefination vinylbromide products in a Sonogashira-type coupling that enables one-pot mechanochemical conversion of an aldehyde to an enediyne.

Solid-State [4+4] Cycloaddition and Cycloreversion with Use of Unpaired Hydrogen-Bond Donors to Achieve Solvatomorphism and Stabilization.

The crystal structure of a commercially available anthracene derivative, anthracene-9-thiocarboxamide, is reported here for the first time. The compound undergoes a [4+4] cycloaddition in the solid state to afford facile synthesis of the cycloadduct (CA). The cycloaddition is also reversible in the solid state using heat or mechanical force. Due to the presence of unpaired, strong hydrogen-bond donor atoms on the CA, significant solvatomorphism is achieved, and components of the solvatomorphs self-assemble into four different classes of supramolecular structures. The CA readily crystallizes with a variety of structurally-diverse solvents including those containing oxygen-, nitrogen-, or pi-acceptors. Some of the solvents the CA crystallized with include thiophene, benzene, and the three xylene isomers; thus, the CA was employed in industrially-relevant solvent separation. However, in competition studies, the CA did not exhibit selectivity. Lastly, it is demonstrated that the CA crystallizes with vinyl-containing monomers and is currently the only compound that crystallizes with both widely used monomers 4-vinylpyridine and styrene. Solid-state complexation of the CA with the monomers affords over a 50 °C increase in the monomer's thermal stabilities. The strategy of designing molecules with unused donors can be applied to achieve separations or volatile liquid stabilization.

Applications of macrocycle-based solid-state host-guest chemistry.

Macrocyclic molecules have been used in various fields owing to their guest binding properties. Macrocycle-based host-guest chemistry in solution can allow for precise control of complex formation. Although solution-phase host-guest complexes are easily prepared, their limited stability and processability prevent widespread application. Extending host-guest chemistry from solution to the solid state results in complexes that are generally more robust, enabling easier processing and broadened applications. Macrocyclic compounds in the solid state can encapsulate guests with larger affinities than their soluble counterparts. This is crucial for use in applications such as separation science and devices. In this Review, we summarize recent progress in macrocycle-based solid-state host-guest chemistry and discuss the basic physical chemistry of these complexes. Representative macrocycles and their solid-state complexes are explored, as well as potential applications. Finally, perspectives and challenges are discussed.

Cis/trans-[Pt(C∧N)(C≡CR)(CNBut)] Isomers: Synthesis, Photophysical, DFT Studies, and Chemosensory Behavior.

cis/trans Isomerism can be a crucial factor for photophysical properties. Here, we report the synthesis and optical properties of a series of trans- and cis-alkynyl/isocyanide cycloplatinated compounds [Pt(C∧N)(C≡CR)(CNBut)] [R = C6H4-4-OMe 1, 3-C4H3S 2; C∧N = 2-(2,4-difluorophenyl)pyridine (dfppy) (a), 4-(2-pyridyl)benzaldehyde (ppy-CHO) (b)]. The trans-forms do not isomerize thermally in MeCN solution to the cis forms, but upon photochemical irradiation in this medium at 298 K, a variable isomerization to the cis forms was observed. This behavior is in good agreement with the theoretically calculated energy values. The trans/cis configuration, the identity of the cyclometalated, and the alkynyl ligand influence on the absorption and emission properties of the complexes in solution, polystyrene (PS) films, and solid state are reported. All complexes are efficient triplet emitters in all media (except for trans-1a and trans-2a in CH2Cl2 solution at 298 K), with emission wavelengths depending mainly on the cyclometalated ligand in the region 473-490 nm (dfppy), 510-550 (ppy-CHO), and quantum yields (ϕ) ranging from 18.5 to 40.7% in PS films. The combined photophysical data and time-dependent density functional theory calculations (TD-DFT) at the excited-state T1 geometry reveal triplet excited states of 3L'LCT (C≡CR → C∧N)/3IL (C∧N) character with minor 3MLCT contribution. The dfppy (a) complexes show a greater tendency to aggregate in rigid media than the ppy-CHO (b) and the cis with respect to the trans, showing red-shifted structureless bands of 3MMLCT and/or excimer-like nature. Interestingly, trans-1a,2a and cis-1a,2a undergo significant changes in the ultraviolet (UV) and emission spectra with Hg2+ ions enabling their use for sensing of Hg2+ ions in solution. This is clearly shown by the hypsochromic shift and substantial decrease of the low-energy absorption band and an increase of the intensity of the emission in the MeCN solution upon the addition of a solution of Hg(ClO4)2 (1:5 molar ratio). Job's plot analysis estimated a 1:1 stoichiometry in the complexation mode of Hg2+ by trans-2a. The binding constant (log K) calculated for this system from absorption titration data resulted to be 2.56, and the limit of the detection (LOD) was 6.54 × 10-7 M.

Thermal Analysis and Biocidal Studies of Copper (II) Soapgroundnut Complex Containing Urea and Thiourea as a Ligand

Background: Studies on the thermal decomposition of synthesized complexes have great importance for calculating the thermal stability and characterization of copper (II) soap complexes, and represent new investigations on the solution of environmental problems. Aim: The present research work aims to report new findings in the field of thermogravimetric analysis and biocidal studies for copper (II) groundnut complexes with urea and thiourea ligands. Objective: The objective of this study was to conduct the kinetic analysis of copper (II) soap complexes of nitrogen and sulphur-containing ligands with the help of a thermogravimetric analyser (TGA), as this technique is commonly applied for thermal analysis. Methods: In relevance of aforesaid applications, the present work deals with determining the different thermal degradation steps of newly synthesized copper (II) groundnut urea complex (CGU) and copper (II) groundnut thiourea complex (CGT) by using Coats- Redfern, Horowitz-Metzger, Broido, and Piloyan-Novikova equations for determining kinetic parameters, i.e., the energy of activation (E), rate constant, order of decomposition reaction, and pre-exponential factor (Z). Results: The results obtained from kinetic parameters were used to evaluate the thermodynamic parameters, i.e., entropy of activation (ΔS), enthalpy of activation (ΔH), and Gibbs free energy of activation (ΔG), corresponding to the activation by using previously mentioned equations. Kinetics of degradation for the synthesized complexes in solid state were studied using thermogravimetric analysis technique (TGA) in nitrogen atmosphere. Conclusion: The present study has discussed the biocidal activities of these complexes against Staphylococcus aureus and an explicit correlation between structure and biological activity has also been provided.

Structures, Thermal Properties, and Reactivities of Cationic Rh-cod Complexes in Solid State (cod = 1,5-Cyclooctadiene).

Cationic rhodium complexes with 1,5-cyclooctadiene (cod) ligands are important organometallic compounds that are useful as precatalysts; however, their solid-state structures and thermal properties have not been adequately investigated. In this study, we synthesized [Rh(cod)L]X (L = cod, C6H6, PhMe; X = SbF6, (FSO2)2N (= FSA), CF3BF3, CB11H12) and investigated their phase behaviors, crystal structures, and reactivities. The phase transitions of these salts result in disordered solid-state structures. Moreover, the structural disorder increases with a decrease in the cation symmetry in the SbF6 salts; [Rh(cod)(PhMe)]SbF6 exhibits a rotator phase, and the cations in other salts exhibit a dynamic rotational disorder. In contrast, a lower crystal symmetry with less cation disorder is observed for FSA salts. The thermal stabilities and reactivities of these salts were further investigated. FSA salts with arene ligands produce anion-coordinated complexes upon melting, and SbF6 salts with arene ligands produce [Rh(cod)L'2]SbF6 (L' = MeCN and SMe2) via an in situ single-crystal-to-single-crystal ligand-exchange reaction.

Pure red-light emitting europium based complexes as efficient UV light converters: synthesis, crystal structure and photoluminescence properties.

This paper reports three new crystallographically characterized europium complexes with composition as follows: [Eu(fod)3(L1)] (1), [Eu(fod)3(L2)] (2) and [Eu(fod)3(L3)] (3) {L1 = benzimidazole (bzi), L2 = 4,7-diphenyl-1,10-phenanthroline (bath), L3 = 2-(2-pyridyl) benzimidazole (py-im) and fod = anion of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione (Hfod)}. The single crystal (SC) XRD analysis shows that complex 1 is seven-coordinated while complexes 2 and 3 are eight-coordinated with the geometrical structures of a mono-capped octahedron and a trigonal dodecahedron, respectively. The NMR spectra of the complexes validate the SC-XRD results in solution. The complexes are stable in solution as no dissociation of any ligand was observed in the NMR spectra of the complexes. The photophysical properties of the complexes in solution, solid state, and PMMA thin films were studied. The hypersensitive transition 5D0 → 7F2 dominates the emission spectra in all phases, showing the highly asymmetric environment around the Eu(III) ion. The bath ligand is found to be the best sensitizer of the Eu ion and hence complex 2 shows the strongest luminescence properties with the highest absolute quantum yield among the three complexes. The CIE coordinate analysis shows that pure red-luminescence is emitted by the Eu complexes in the solid state since the coordinates found in this phase are closer to the standard NTSC 1987 values. The optical band gaps were determined for the complexes and the observed values suggest that the complexes can have possible applications in the field of semiconductor materials.

An insight into the hydrogen bonding, halogen bonding and chalcogen bonding interactions in manganese(iii) complexes with N2O2donor salicylidine Schiff base ligands.

Four manganese(iii) complexes, [MnL1(H2O)2]ClO4·H2O (1), [MnL2(H2O)2]ClO4 (2), [MnL3(DMSO)(H2O)]ClO4 (3) and [MnL4(DMSO)(H2O)]ClO4 (4), where H2L1 = N,N'-bis(5-bromosalicylidene)-1,3-diaminopropane, H2L2 = 2,2-dimethyl-N,N-bis(3-methyloxysalicylidene)-1,3-diaminopropane, H2L3 = N,N'-bis(5-chlorosalicylidene)-2,2-dimethyl-1,3-diaminopropane and H2L4 = 2-hydroxy-N,N'-bis(3-ethyloxysalicylidene)-1,3-diaminopropane are tetradentate N2O2-donor ligands and DMSO = dimethyl sulfoxide, have been synthesized and characterised by elemental analysis, IR and UV-vis spectroscopy and single-crystal X-ray diffraction studies. All are monomeric complexes. Complex 1 crystallises in orthorhombic space group P212121, complex 3 crystallises in triclinic space group P-1, whereas complexes 2 and 4 crystallize in monoclinic space groups, C2/c and C2/m respectively. In all the complexes, manganese(iii) has a six-coordinated pseudo-octahedral geometry in which imine nitrogen atoms and phenolate oxygen atoms of the deprotonated di-Schiff base constitute the equatorial plane. In complexes 1 and 2, water molecules are present in the fifth and sixth coordination sites in the axial positions while in complexes 3 and 4 they are occupied by one water and one DMSO. The coordinated water molecules initiate hydrogen-bonded networks in all complexes. DFT calculations have been carried out to analyze two aspects of these complexes viz. the formation of halogen (HaB) and chalcogen bonding (ChB) interactions in complexes 1 and 3 where the electron donor is the perchlorate anion and the acceptor either bromine or chlorine atoms for the HaBs and the sulfur atom of the coordinated DMSO for the ChB. In addition, other intermolecular effects are discussed in the solid state for complexes 1, 2 and 4, where the hydrogen atoms of the coordinated water molecules interact with the electron rich cavities formed by the phenolate and alkyloxy oxygen atoms of the Schiff-base ligand.

Synthesis, characterization, Hirshfeld surface analysis, and the study of antimicrobial, and acaricidal properties of copper(II) complexes with 2-(hydroxymethyl)benzimidazole ligand

Three new methylsalicylatocopper and four methylbenzoatocopper complexes with 2-(hydroxymethyl)benzimidazole with structures, [Cu(3-MeSal)2(2-MeBzim)2]∙2H2O (1), [Cu(4-MeSal)2(2-MeBzim)2] (2), [Cu(5-MeSal)2(2-MeBzim)2]∙2H2O (3), [Cu(2-MeBenz)2(2-MeBzim)2] (4), [Cu(3-MeBenz)2(2-MeBzim)2] (5), [Cu(4-MeBenz)2(2-MeBzim)2] (6), [Cu(4-MeBenz)2(2-MeBzim)2]∙EtOH (7), where 3-MeSal- = 3-methylsalicylate, 4-MeSal- = 4-methylsalicylate, 5-MeSal- = 5-methylsalicylate, 2-MeBenz- = 2-methylbenzoate, 3-MeBenz- = 3-methylbenzoate and 4-MeBenz- = 4-methylbenzoate anion and 2-MeBzim = 2-(hydroxymethyl)benzimidazole were synthesized. Solid-state complexes were characterized by diffraction methods, elemental analysis, UV/VIS, IR, and EPR measurements. Hirshfeld surface analyses were made for crystal structures of all complexes. Coordination polyhedron around the copper central atom is elongated tetragonal bipyramid and two molecules of 2-(hydroxymethyl)benzimidazole and two anions of methylsalicylate or methylbenzoate are bonded in a monodentate way to the copper center. For six prepared complexes the antimicrobial and acaricidal activities have been studied. Antifungal activity has been studies on fungal species Aspergillus fumigatus, Microsporum gypseum, and Candida albicans. Antibacterial activity has been studied on bacterial strains Escherichia coli, and Staphylococcus aureus, and acaricidal activity was determined on Phytoseiulus perimilis. Complexes 1, 2 and 3 almost entirely inhibited the growth of S. aureus and complexes 1, 5 and 6 practically completely suppressed the growth of yeast strain C. albicans.

Computational studies on the excited state decay rates in aggregates of two‐coordinate Cu (I) complexes: Thermally Activated Delayed Fluorescence and Aggregation Induced Emis

AbstractTwo‐coordinate Cu (I) complexes have attracted great interest recently because of the rich photophysical property in solid state, including the aggregation‐induced thermal activated delayed fluorescence. Here, we summarize our theoretical investigations on the excited state structure and decay dynamics for the two‐coordinate Cu (I) complexes in solution phase and solid state by the thermal vibration correlation function rate formalism we developed earlier coupled with time‐dependent density‐functional theory within polarizable continuum model and hybrid quantum and molecular mechanics. First, for the CAACCu (I)Cl complex, we found that the nature of the excited state undergoes a change from metal‐to‐ligand charge transfer (MLCT) in solution to hybrid halogen‐to‐ligand charge transfer and MLCT in solid state. The bending vibrations of the CCuCl and CuCN bonds are restricted in aggregates, reducing the non‐radiative decay rate to cause strong solid‐state fluorescence. Second, for CAACCu (I)Cz, we found that both intersystem crossing (ISC) and reverse intersystem crossing (rISC) are enhanced by 2–4 orders of magnitudes upon aggregation, leading to highly efficient thermally activated delayed fluorescence (TADF). The enhanced ISC and rISC rates can be attributed to the increase of the metal proportion in the frontier molecular orbitals, leading to an enhanced spin−orbit coupling between S1 and T1. The reaction barriers for ISC and rISC are much lower in solution than that in aggregate phase resulting in a decrease in energy gap and an increase in the relative reorganization energy through bending the angle ∠C − Cu − N for T1. Our theoretical studies provide a clear rationalization for the highly efficient solid‐state luminescence character of two‐coordinate Cu (I) complexes and may clarify the ongoing dispute on the understanding of the high TADF quantum efficiency.

Hydrogen bond-directed coordination of phosphine-amino-alcohol (P,N,OH) ligands: Stereochemical considerations and catalytic studies

Novel phosphine-aminoalcohol type chiral ligands of the chemical formula Ph2PCH(CH3)CH2CH(CH3)NHCH(R)CH2OH (1a: (R,R)-(S), R = CH3, 1b: (S,S)-(S), R = CH3, 1c: (S,S), R = H) have been synthesized in two simple steps using cyclic sulfates. The coordination behavior of 1a-c having stereochemically labile nitrogen donor to square planar Pd(II) center was investigated by X-ray crystallography, 1D and 2D NMR methods and by DFT calculations. In the solid state of complex [Pd(1a)Cl2] an intramolecular hydrogen bond could be observed between the OH-moiety and one of the Cl co-ligands, while intermolecular hydrogen bonds were detected in the case of [Pd(1b)Cl2] between the same functionalities. In the dichloromethane solution of the complexes the hydrogen bond was identified as a crucial factor in determining ring conformation and nitrogen configuration. Ligand 1a coordinated stereoselectively to the metal in [Pd(1a)Cl2] leading to a complex having a single conformationally rigid six-membered chelate and a configurationally fixed N-donor. In contrast, coordination of ligands 1b-c resulted in the formation of a mixture of isomers with different chelate conformation and nitrogen configuration. The ligands were utilized in Pd-catalyzed asymmetric allylic alkylation where high enantioselectivities (ees up to 96 %) and activities could be obtained.

Synthesis, structures, and photophysical properties of two Cu(I) complexes supported by N-heterocyclic carbene and phosphine ligands

Abstract Two new cationic four-coordinate Cu(I) complexes supported by different chelating N-heterocyclic carbene ligands and the diphosphine ligand bis[2-(diphenylphosphino)phenyl]ether (POP) have been synthesized. The chemical structures of both complexes have been characterized by 1H NMR, 13C NMR, 31P NMR, and mass spectroscopy, and the crystal structure of one complex has been determined by single-crystal X-ray diffraction. Results of theoretical calculations indicate that the lowest energy electronic transitions of these complexes are mainly the metal-to-ligand charge transfer and ligand-to-ligand charge transfer transitions. The complexes in solid state show intense emissions with high photoluminescence quantum yields. The photophysical behavior at 298 and 77K shows that emissions of these complexes at room temperature are thermally activated delayed fluorescence mixed with phosphorescence.