Organometallic Mesogens

Producción CientíficaThis chapter discusses organometallic complexes that behave like liquid crystals. The most common syntheses, types of compounds and ligands for these derivatives are described. It is reviewed how these organometallic mesogens self-organize within the phases, what are the mesophases obtained and their transition temperatures. The relevant physical properties of these compounds are also reviewed, especially the optical and electro-optical properties. The reader is provided with an introduction to the topic, an overview of the state of the art at this time, and many references are collected to delve into it.Ministerio de Economía y Competitividad (Project CTQ2017–89217– P)Junta de Castilla y León (Project VA224P20

The Amide Group as Modulator of Crystalline and Liquid Crystalline Structures in Isocyano-alkylanilide Silver (I) Complexes

Producción CientíficaSilver(I) complexes [AgX(CNR] and [Ag(CNR)2]X (X = anionic ligand), containing an amide-functionalized isocyanide, CNR = CN-C6H4-NHCOR, have been synthesized and their X-ray structures have been determined for [Ag(X)(CN-C6H4-NHCOCH3)] (X = NO3ˉ, CF3SO3ˉ) and [Ag(CN-C6H4-NHCOCH3)2]X (X = NO3ˉ, CF3SO3ˉ, BF4ˉ). All the crystal structures show a packing of polymeric chains formed through Ag–O=Camide interactions. These chains associate in layers through hydrogen bonds involving the amide group, and by further interactions of the metal ion with oxygen-donor moieties. Substitution of the Me group in the amide by a nonyl chain (R = C9H19) leads to neutral [Ag(NO3)(CN-C6H4-NHCOC9H19)] and ionic [Ag(CN-C6H4-NHCOC9H19)2]X (X = NO3ˉ, CF3SO3ˉ, H25C12OSO3ˉ, BF4ˉ) mesomorphic complexes. All of them display smectic liquid crystalline phases compatible with the crystal structures found for the methyl derivatives, and FTIR/ATR spectroscopy confirms that the intermolecular interactions observed in the solid state are preserved in the mesophase.Ministerio de Economía, Industria y Competitividad (CTQ2011-25137)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13

Supramolecular aggregates of metallo–organic acids with stilbazoles. Formation of columnar mesophases and Langmuir films

Producción CientíficaSupramolecular metal complexes formed through hydrogen bonding between tris(3,4,5-decyloxy)stilbazole and several metallo–organic acids of the type [Au(R)(CNC6H4CO2H)] (R = C6F5, C6F4OC10H21), [cis-[MCl2(CNC6H4COOH)2] and [trans-[MI2(CNC6H4COOH)2] (M = Pd, Pt) have been synthesized. All the supramolecular palladium and platinum polycatenar aggregates display a hexagonal columnar mesophase at temperatures close to room temperature. Most of the supramolecular trisalkoxystilbazole complexes exhibit luminescent behaviour. Aggregates of [Au(C6F4OC10H21)(CNC6H4CO2H)] and [trans-[MI2(CNC6H4COOH)2] (M = Pd, Pt) form stable Langmuir films at the air–water interface.Ministerio de Ciencia e Innovación (Projects CTQ2011-2513)Junta de Castilla y León (programa de apoyo a proyectos de investigación - Ref. VA248A11-2

Perylenecarboxydiimide-Gold(I) Organometallic Dyes. Optical Properties and Langmuir Films

Producción CientíficaA new perylenediimide-isocyanide N,N’-bis(1-ethylpropyl)-1-isocyanide-perylene-3,4:9,10-bis(dicarboximide) (CN-PDI), as well as the isocyanide [AuY(CN-PDI)] and carbene [Au-Y-{C(NH-PDI) (NMe2)}] (Y = Cl, C6F5, 4-C6F4OC6H13, 1/2-μ-C6F4C6F4) gold complexes therefrom, have been synthesized and characterized. All complexes are strongly colored and display fluorescence in solution associated with the perylene fragment. The influence of the metal fragment on these properties is very small in the isocyanide complexes, but more pronounced in the carbene derivatives, revealing a higher electronic connection between the metal and the PDI group in the carbene-complexes. Stable Langmuir films are formed by CN-PDI, [C6F5-Au-CN-PDI] and [H13C6OC6F4-Au-CN-PDI], in which, remarkably, by varying the compression of the films at the air/water interface it is possible to modulate the molecular arrangement in LS multi-layered films.Ministerio de Economía, Industria y Competitividad ((Project CTQ2014-52796-P)Junta de Castilla y León (programa de apoyo a proyectos de investigación - Ref. VA302U13

Room‐Temperature Columnar Mesophases in Triazine–Gold Thiolate Metal–Organic Supramolecular Aggregates

Producción CientíficaSupramolecular mono‐ and dinuclear liquid‐crystalline gold(I) aggregates have been synthesized by means of hydrogen bond interactions of 2,4,6‐triarylamino‐1,3,5‐triazine with thiolate moities of gold metalloacids [Au(PR3)(SC6H4COOH)] or [μ‐(binap){Au(SC6H4COOH)}2], in 1:1 and 2:1 molar ratio, respectively. All of the supramolecular aggregates display a stable columnar hexagonal mesophase (Colh) at room‐temperature. The supramolecular arrangement within the columns consists of the one‐dimensional stacking of triazine units, with the core of the attached metallic thioacid fragments acting as the fourth branch. The phosphine‐containing moieties of the metallic thioacid protrude out in the aliphatic continuum. These complexes do not show metallophilic interactions, but this strategy appears very promising for the future design of room‐temperature LC mesophases containing interacting metallic fragments.Ministerio de Ciencia e Innovación (Proyect CTQ2011–25137)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA248 A11‐2

Feasibility of Storing Latent Heat with Liquid Crystals. Proof of Concept at Lab Scale

In this work, the first experimental results of thermotropic liquid crystals used as phase change materials for thermal storage are presented. For that purpose, the n = 10 derivative from the family of 4-n-alkoxybiphenyl-4-carboxylic acids has been prepared. Different techniques like polarized-light microscopy, differential scanning calorimetry, thermogravimetric analysis and rheological measurements have been applied for its characterization. Having a mesophase/isotropic transition temperature around 251 degrees C, a clearing enthalpy of 55 kJ/kg, a thermal heat capacity of around 2.4 kJ/kg and a dynamic viscosity lower than 0.6 Pas, this compound fulfills the main requirements for being considered as latent heat storage material. Although further studies on thermal stability are necessary, the results already obtained are both promising and encouraging since they demonstrate de viability of this new application of liquid crystals as thermal storage media.The authors would like to acknowledge the E. U. through the 7th FP for the financial support of this work under the STAGE-STE Project (Ctr. Nr. 609837), the Community of Madrid for its support under the ALCCONES Project (S2013/MAE-2985) through the Program of R&D activities between research groups in Technologies 2013 and the Spanish government in the framework of the DETECSOL project (Ref. ENE2014-56079-R) both co-financed by ERDF funds, the Spanish Ministry of Economy and Competitiveness through the Project with ref. CTQ2014-52796-P and the Community of Castilla y Leon through the Project with ref. VA302U13

Diphenylphosphinobenzoic Acids as Linkers in [2,4,6– {(C10H21O)3C6H2NH}3C3N3] Triazine Adducts with Metal Complex, which Self–Organize into Room Temperature Hexagonal Columnar Mesophases

Producción CientíficaDisplacement of a labile ligand from appropriate precursor complexes by 2- or 4-PPh2C6H4COOH yields neutral gold(I) and gold(III) [AuXn(PPh2C6H4COOH)] (n = 1, X = Cl; n = 3, X = C6F5), cationic gold(I) [Au(PPh2C6H4COOH)2](CF3SO3), and neutral chromium(0) [Cr(CO)5(PPh2C6H4COOH)] metallo-organic acids. [AuCl(4-PPh2C6H4COOH)], [Au(C6F5)3(4-PPh2C6H4COOH)], and [Cr(CO)5(2-PPh2C6H4COOH)] have dimeric structures with typical carboxylic H-bond bridges, whereas [Au(C6F5)3(2-PPh2C6H4COOH)] gives a monomeric species with the carboxylic acid H bonded to cocrystallized solvent molecules. All gold-containing acids are emissive at 77 K in the range 404-520 nm and some of them also at 298 K with emission maxima from 441 to 485 nm. Reaction of these acid metal complexes with the triazine mesogen 2,4,6-{(C10H21O)3C6H2NH}3C3N3 affords some new hydrogen-bonded gold(I) and chromium(0) supramolecular adducts, but the related gold(III) complexes do not form adducts. The 4-diphenylphosphinobenzoic adducts display a columnar hexagonal mesophase (Colhex) at room temperature, with a random one-dimensional stacking of the pseudo-discoid triazine-metallo-organic adducts into columns, where the metallo-phosphinoacid fragments act as the fourth branch of the trifold triazine core. The 2-diphenylphosphinobenzoic mixtures do not display mesophases, as they appear in the X-ray studies as mixtures of the triazine and the metallo-phosphinoacid complex. The aggregates are luminescent at 77 K, with emission maxima in the range 419-455 nm.Ministerio de Economía, Industria y Competitividad (CTQ2011–25137)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13

Modulating Organic/Inorganic Segregation in Columnar Mesophases

This work reports an uncommon modulation of columnar segregation of metal–organic triphenylene liquid crystals by blending two structurally dissimilar metallomesogens that can self-associate through complementary electron donor–acceptor interactions. The constituent molecules are cis-[PtCl2(CNR)2] (CNR = 2-(6-(4-isocyanophenoxy)hexyloxy)-3,6,7,10,11-pentakisdodecyloxytriphenylene) that displays an organic/inorganic segregated columnar mesophase and [PtCl2(Bipy)] (Bipy = didodecyl 2,2′-bipyridyl-4,4′-dicarboxylate) that shows a lamellar mesomorphism. The phase diagram of this system was constructed using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray scattering data. The phase diagram corresponds to a typical binary system with an intermediate compound (in this case a supramolecular aggregate) of stoichiometry [PtCl2(CNR)2]/2[PtCl2(Bipy)], which is maintained in solution. This species shows an unusual columnar mesophase formed by the stacking of alternating organic/inorganic fragments. Quantum chemical calculations show that the columnar structure is mainly supported by complementary π electron donor–acceptor interactions between each triphenylene group of the isocyanide complex and a platinum-bipyridine molecule. This induces the elimination of the organic/inorganic columnar segregation of the isocyano parent component and constitutes an unconventional example of modulation of organic/inorganic segregation in columnar mesophases by the intercalation of metal complexes into hexaalkoxytriphenylene stacks.This work was sponsored by the Ministerio de Ciencia e Innovación (Project PID2020-118547GB-I00), the Junta de Castilla y León (Project VA224P20), and the Basque Government (Project IT1458-22). E.D. thanks MECD for a FPU grant. The authors thankfully acknowledge the computer resources at Lusitania II and CIERZO-CAESARAUGUSTA III and the Technical support provided by Cénits-COMPUTAEX (FI-2022-1-0009, FI-2022-3-0008), Centro de Supercomputación de Aragón (QHS-2023-3-0005, QH-2023-1-0002) and Red Española de Supercomputación. We thank Dr. S. Ferrero (University of Valladolid) for his help in the NMR titration experiments

Triphenylene-Imidazolium Salts and Their NHC Metal Complexes, Materials with Segregated Multicolumnar Mesophases

Producción CientíficaTwo imidazolium salts containing one or two pentadodecyloxytriphenylene units linked through a hexyloxy chain and Br–, [AuBrmCl4–m]−, or [PtBrmCl4–m]2– (m = 0−3) as counterion have been prepared. Reaction of the imidazolium bromides with M2O (M = Cu, Ag), or carbene transmetalation from the silver product, leads to N-heterocyclic carbene complexes [MX(NHC)] (M = Cu, X = Br; M = Au, X = Cl, C≡CPh), [Ag(NHC)2][AgBr2], and [PtCl2(NHC)2], with NHC bearing one or two triphenylene fragments. Except for the gold derivatives and one Cu complex, the rest of them behave as liquid crystals organized in columnar mesophases (rectangular c2mm or p2mg or hexagonal p6mm symmetries) with melting points in the range 30 to 60 °C and clearing points in the range 57–112 °C. The mesophase structures were determined by small-angle X-ray scattering. Structural studies and models point to nanosegregation of triphenylene columns and imidazolium/metal carbene moieties, separated by alkoxy chains, leading to multicolumnar systems. The compounds display emission spectra related to the triphenylene core in solution, in the mesophase, in the isotropic liquid, and in the solid state.2019-04-16Ministerio de Ciencia e Innovación (Project CTQ2014-52796-P

Synergistic π-π and Pt-Pt interactions in Luminescent Hybrid Inorganic/Organic Dual Columnar Liquid Crystals

Producción CientíficaA new triphenylene-isocyanide CN-C6H4-O-(CH2)6-TriPh, non mesogenic, and their ortho-metallated benzoquinolate (bzq) complexes, [M(bzq)X(CN-C6H4-O-(CH2)6-TriPh)] (M = Pd, Pt; X = Cl, I) and [Pt(bzq)(CN-C6H4-O-(CH2)6-TriPh)2]A (A = NO3−, BF4−, PF6−), all displaying a columnar mesophase, have been prepared. The structure of the mesophase, determined by X-ray diffraction methods, is uncommon and consists of a central column formed by stacking of the organometallic benzoquinoline-platinum fragments, surrounded by six columns in hexagonal disposition formed by stacking of the triphenylene groups. These materials show aggregation-induced phosphorescence based on inter-disk Pt⋯Pt interactions.2017-02-15Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13)Ministerio de Economía, Industria y Competitividad (CTQ2014-52796-P)Ministerio de Economía, Industria y Competitividad (MAT2012-38538-C03-02)Gobierno Vasco (GI/IT-449-10