Clustomesogens: Liquid Crystal Materials Containing Transition‐Metal Clusters

Abstract

Octahedral metal atom clusters in which metallic atoms are held together by metal-metal bonds are commonly found in solid-state compounds prepared by high-temperature synthesis.[1] The metallic octahedron is surrounded by eight facecapping and six terminal ligands to form a [M 6 units (X = halogen) that exhibit, either in the liquid or solid state, specific electronic, magnetic, and photophysical properties related to the number of metallic electrons available for metal-metal bonds. [3] In particular, they are highly emissive in the red-NIR region, have photoluminescence quantum yields of up to 0.23, [3d] display long excited-state lifetimes, [3d, 4] and undergo facile ground-and excited-state electron transfer by electrogenerated luminescence.[5] Owing to the stronger covalent nature of the M À Q i bond relative to the M À X a one, halogen apical atoms can be replaced by inorganic or organic ligands without any alteration of the (M 6 Q i 8 ) m+ core, leading to functional building blocks usable for the design of supramolecular architectures, polymeric frameworks, or nanomaterials with unique properties.[6] Although many examples of hexasubstituted [M 6 xÀ units (L = organic ligand) have been reported, [6d, 7] their integration in macroscopic devices by a bottom-up approach remains a challenge. This task requires systems with self-organization abilities on the one hand and fluidity on the other hand, to correct automatically the positioning errors that can occur during the assembly process. Metal-containing liquid crystals (metallomesogens) are the typical examples in which the unique properties of anisotropic fluids are combined with the specific properties of metals (e.g. geometry of coordination, optic, electronic, magnetic).[8] However, mesomorphic materials containing covalent metal-metal-bonded entities are rare, and all examples described up to now, since the pioneer work of Marchon and co-workers, [9] are based on dinuclear metalmetal-bonded species.[10] The association of mesomorphism with the peculiar properties of metallic clusters should lead to clustomesogens that offer great potential in the design of new electricity-to-light energy conversion systems, optically based sensors, and displays.In the scope of our work dedicated to transition-metalcluster based multifunctional materials, [11] we report herein the elaboration and characterization of liquid-crystalline materials based on a Mo 6 cluster. The synthesis is straightforward and consists of the one-step reaction of [Mo 6 Br 8 F 6 ] 2À units with carboxylic acid derivatives (Scheme 1), which results in the in situ exchange of apical F À by carboxylate anion along with the formation of HF.Owing to the bulkiness of the cluster unit and to its octahedral coordination, [12] we used a strategy based on the

From Cs2Mo6Cl14 to Cs2Mo6Cl14·H2O and Vice Versa: Crystal Chemistry Investigations

“…Face-capped Mo 6 X i 8 X a 6 units containing octahedral molybdenum clusters are the basic buildings blocks of many inorganic solid state compounds, hybrid frameworks and nanomaterials [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Formation of Mo 6 cluster occurs at high temperatures via solid state reactions.…”

From Mesomorphic Phosphine Oxide to Clustomesogens Containing Molybdenum and Tungsten Octahedral Cluster Cores

“…[3] In the light of recent findings,q uantum yields of nanometer-sized octahedral clusters can reach values above 60 %. The LC properties were studied by ac ombination of polarizing optical microscopy( POM), differential scanning calorimetry (DSC), and X-ray powder diffraction analyses.While the organic ligands showed various mesophase types ranging from nematic, SmA columnar (SmA Col ), SmA, and SmC phases,i tt urned out that the corresponding clustomesogens formed layered phases (SmA) over aw ide range of temperatures that depend on the nature and density of mesogenic groups employed.…”

“…[3] In the light of recent findings,q uantum yields of nanometer-sized octahedral clusters can reach values above 60 %. [1] On the other hand, metal atom clusters are versatile building blocks for the design of hybrid nanomaterials with potential applications, for instance,inthe fields of lighting,displays,and biolabeling technologies.…”

Metallomesogens: Retrospectives and Perspectives

“…Недавно была получена очень интересная полиядерная система на основе молибденовых металлокластеров -соединение 17 [133], проявляющая смектическую мезофазу с типичной веерной конфокальной текстурой при комнатной температуре. Кроме того, соединение 17 обладает яркой люминесценцией в красной и ближней инфракрасной области.…”