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•Diselenides act as ChB donors with σ-holes along the SeSe and CSe bonds.•Numerous examples of intramolecular 1,5 ChB interactions.•Charge activation of ChB in dicationic or cation ...radical diselenides.•ChB in selenocyanates leads to 1D structures ⋯Se(R)CN⋯Se(R)CN⋯.•Anion recognition effects of poly-substituted selenocyanates.
Organic diselenides are nowadays investigated for pharmaceutical applications, as well as in material science in molecular (semi)conductors. In both application’s domains, their interactions with Lewis bases, in solution or in the solid state, has been shown to play a crucial role in their biological activity or in their electronic structure. The current comprehensive survey of reported crystal structures of organic diselenides demonstrates the recurrent setting of intermolecular as well as intramolecular chalcogen bonding interactions (ChB) between the selenium atoms acting as ChB donors and Lewis bases. These interactions take place along the two covalent bonds of the selenium atom. In diselenides, stronger interactions are found in the prolongation of the SeSe bond than in the prolongation of the CSe bond. Charge activation of ChB is demonstrated in dicationic diselenides or in cation radical salts of 1,2-diselenole derivatives. This survey is extended to the structures of organic selenocyanates whose crystal structures reflect also the presence of two σ-holes, with a much stronger one in the prolongation of the NCSe bond. Such ChB interactions of selenocyanates with polytopic Lewis bases or with halide anions open novel strategies in crystal engineering and anion recognition strategies.
In this review, we describe solid solution strategies employed in molecular conductors, where the control of their transport and magnetic properties (metallic or superconducting behavior, ...metal-insulator transitions,
etc.
) is the main goal. We first describe the main features of molecular conductors in order to identify which molecular entities are prone to be substituted by others in solid solutions, to which extent and for what purpose. We then describe the different crystal growth techniques used toward solid solution preparation and the nature of the molecular species, whether electroactive or not, which have been used, in cation or anion radical salts, in charge transfer salts and in single component conductors, in more than sixty reported examples. Topics such as preferential insertion and miscibility, the nature of disorder and the different analytical tools used for characterizing these alloys are presented. The consequences of alloying on conductivity and on phase transitions (superconductivity, anion ordering, Peierls transition, spin-Peierls transition), and the concepts of chemical pressure effects, band filling manipulation, and π-d interactions with magnetic anions are also discussed.
Solid solutions in molecular conductors are key tools for investigating their conducting and magnetic properties, addressing phase transitions, chemical pressure effects and band filling manipulation.
Halogen bonding interactions between halide anions and neutral polyiodinated linkers are used for the elaboration of anion organic frameworks, by analogy with well-known MOF derivatives. The ...extended, 3-fold symmetry, 1,3,5-tris(iodoethynyl)-2,4,6-trifluorobenzene (1) cocrystallizes with a variety of halide salts, namely, Et3S+I–, Et3MeN+I–, Et4N+Br–, Et3BuN+Br–, Me-DABCO+I–, Bu3S+I–, Bu4N+Br–, Ph3S+Br–, Ph4P+Br–, and PPN+Br–. Salts with 1:1 stoichiometry formulated as (1)·(C+,X–) show recurrent formation of corrugated (6,3) networks, with the large cavities thus generated, filled either by the cations and solvent (CHCl3) molecules and/or by interpenetration (up to 4-fold interpenetration). The 2:1 salt formulated as (1)2·(Et3BuN+Br–) crystallizes in the cubic Ia3̅ space group (a = 22.573(5) Å, V = 11502(4) Å3), with the Br– ion located on 3̅ site and molecule 1 on a 3-fold axis. The 6-fold, unprecedented octahedral coordination of the bromide anion generates an hexagonal three-dimensional network of Pa3̅ symmetry, as observed in the pyrite model structure, at variance with the usual, but lower-symmetry, rutile-type topology. In this complex system, the I centering gives rise to a 2-fold interpenetration of class Ia, while the cations and solvent molecules are found disordered within interconnected cavities. Another related cubic structure of comparable unit cell volume (space group Pa3̅, a = 22.4310(15) Å, V = 11286.2(13) Å3) is found with (1)2·(Et3S+I–).
Conspectus Among the noncovalent interactions available in the toolbox of crystal engineering, chalcogen bonding (ChB) has recently entered the growing family of σ-hole interactions, following the ...strong developments based on the halogen bonding (XB) interaction over the last 30 years. The monovalent character of halogens provides halogen bonding directionality and strength. Combined with the extensive organic chemistry of Br and I derivatives, it has led to many applications of XB, in solution (organo-catalysis, anion recognition and transport), in the solid state (cocrystals, conducting materials, fluorescent materials, topochemical reactions, ...), in soft matter (liquid crystals, gels,···), and in biochemistry. The recognition of the presence of two σ-holes on divalent chalcogens and the ability to activate them, as in XB, with electron-withdrawing groups (EWG) has fueled more recent interest in chalcogen bonding. However, despite being identified for many years, ChB still struggles to make a mark due to (i) the underdeveloped synthetic chemistry of heavier Se and Te; (ii) the limited stability of organic chalcogenides, especially tellurides; and (iii) the poor predictability of ChB associated with the presence of two σ-holes. It therefore invites a great deal of attention of molecular chemists to design and develop selected ChB donors, for the scrutiny of fundamentals of ChB and their successful use in different applications. This Account aims to summarize our own contributions in this direction that extend from fundamental studies focused on addressing the lack of directionality/predictability in ChB to a systematic demonstration of its potential, specifically in crystal engineering, and particularly toward anionic networks on the one hand, topochemical reactions on the other hand. In this Account, we share our recent results aimed at recovering with ChB the same degree of strength and predictability found with XB, by focusing on divalent Se and Te systems with two different substituents, one of them with an EWG, to strongly unbalance both σ-holes. For that purpose, we explored this dissymmetrization concept within three chemical families, selenocyanates R–SeCN, alkynyl derivatives R–CC–(Se/Te)Me, and o-carborane derivatives. Such compounds were systematically engaged in cocrystals with either halides or neutral bipyridines as ChB acceptors, revealing their strong potential to chelate halides as well as their ability to organize reactive molecules such as alkenes and butadiynes toward 2+2 cycloadditions and polydiacetylene formation, respectively. This selective activation concept is not limited to ChB but can be effectively used on all other σ-hole interactions (pnictogen bond, tetrel bond, etc.) where one needs to control the directionality of the interaction.
Halogen bonding: Recent advances Fourmigue, M
Current opinion in solid state & materials science,
06/2009, Letnik:
13, Številka:
3
Journal Article
Recenzirano
Halogen bonding (XB), as a directional interaction between covalently bound halogen atoms (XB donor) and Lewis bases (A, XB acceptor), has been recently intensively investigated as a powerful tool in ...crystal engineering. After a short review on the origin and general features of halogen bonding, current developments towards (i) the elaboration of three-dimensional networks, (ii) the interaction with anionic XB acceptors, (iii) its identification in biological systems and (iv) the formation of liquid crystal phases will be described. Theoretical analyses, statistical studies and experimental electron density determinations converge to describe halogen bonding as a relatively weak structure directing tool, when compared with hydrogen bonding. However, when the halogen atom is strongly activated as in iodoperfluorinated molecules or cationic aromatic systems can halogen bonding act as an efficient and reliable structure directing tool.
The distinction between cocrystals and salts is usually investigated in hydrogen-bonded systems as A–H···B ⇆ A−···H–B+, where the position of the hydrogen atom actually defines the ionicity of the ...complex. The same distinction, but in halogen-bonded systems, is addressed here, in complexes formed out of N-iodoimide derivatives as halogen bond donors, and pyridines as halogen-bond acceptors, anticipating that the position of the iodine atom in these A–I···B ⇆ A−···I–B+ systems will also define their degree of ionicity. We show that the crystalline halogen-bonded complexes of N-iodosuccinimide (NIS) with pyridine, 4-methylpyridine, and 4-dimethylaminopyridine can be described as “close-to-neutral” cocrystals while the crystalline halogen-bonded complex of N-iodosaccharin (NISac) with 4-dimethylaminopyridine adopts a “close-to-ionic” structure. Theoretical calculations were performed (i) in gas phase on isolated NIS···Py-NMe2 and NISac···Py-NMe2 complexes, and (ii) on the periodic crystal phases, and combined with the topological analysis of the electron density distribution ρ(r). We demonstrate unambiguously that the crystal environment actually plays a crucial role in the stabilization of the “close-to-ionic” structure of the NISac···Py-NMe2 complex. An external homogeneous electric field ε applied to this complex (all atoms frozen at the crystalline geometry, except iodine) in either gas phase (ε = 3.7 GV m–1) or periodic pseudo-isolated configuration (ε = 2.8 GV m–1) is able to shift the iodine atom at the crystal geometry, miming the polarization effect induced by the local crystal electric field. The strong influence of the crystalline environment on the iodine position is demonstrated by using plane wave DFT periodic calculations on optimized NIS·Py-NMe2 and NISac·Py-NMe2 crystal structures, as well as by applying this plane wave basis set formalism to a hypothetical solid where the halogen-bonded complexes are pushed apart from each other within a periodic system.
Organic bis(selenocyanate) derivatives act as powerful chalcogen bond donors for the elaboration of 1D extended structures upon co-crystallization with 4,4'-bipyridine as a ditopic chalcogen bond ...acceptor.
The face‐to‐face association of (E)‐1,2‐di(4‐pyridyl)ethylene (bpen) molecules into rectangular motifs stabilized for the first time by chalcogen bonding (ChB) interactions is shown to provide ...photoreactive systems leading to cyclobutane formation through single‐crystal‐to‐single‐crystal 2+2 photodimerizations. The chelating chalcogen bond donors are based on original aromatic, ortho‐substituted bis(selenocyanato)benzene derivatives 1–3, prepared from ortho‐diboronic acid bis(pinacol) ester precursors and SeO2 and malononitrile in 75–90 % yield. The very short intramolecular Se⋅⋅⋅Se distance in 1–3 (3.22–3.24 Å), a consequence of a strong intramolecular ChB interaction, expands to 3.52–3.54 Å in the chalcogen‐bonded adducts with bpen, a distance (<4 Å) well adapted to the face‐to‐face association of the bpen molecules into the reactive position toward photochemical dimerization.
Chalcogen bonding (ChB) interactions are used for the first time to organize photoreactive systems, here (E)‐1,2‐di(4‐pyridyl)ethylene (bpen) molecules, into rectangular motifs favoring cyclobutane formation through single‐crystal‐to‐single‐crystal 2+2 photodimerizations, demonstrating the efficiency and robustness of strong and directional ChB donors such as selenocyanate moieties toward topochemical reactions.
Square‐planar bis(dithiolene) complexes are characterized with a planar delocalized structure and a strong and tunable near infrared (NIR) absorption; they are highly stable under laser irradiation, ...and their conversion efficiency (light to heat) reaches up to 40–50 %. Their involvement in soft matter, namely liquid crystals, gels, and nanoparticles, opens many possibilities to control the actual state of a material, particularly under light irradiation. Thus, liquid crystalline phases can easily be modified, (i) with temperature to modulate the extended magnetic interactions of paramagnetic complexes, or (ii) under laser irradiation to unravel these remarkable photothermal properties, toward the development of light‐responsive materials. Dithiolene complexes can be also functionalized to produce very effective gelation agents, while the photothermal effect can be used to destabilize at will their supramolecular organization. Besides photothermal therapy, new therapeutic agents were also developed for photo‐controlled drug delivery and bioimaging, combining chemotherapy and phototherapy. Hydrophobic complexes were accordingly designed for their encapsulation in block copolymer nanoparticles for photothermal therapy and photo‐controlled drug delivery under laser irradiation. This class of complexes can be also used as exogenous contrast agents for photoacoustic bioimaging.
Proper functionalization of metal‐bis(dithiolene) complexes enables the development of stimuli‐responsive soft materials for applications in biotechnology and materials science.
Introduction of hydrogen bonding (HB) interactions in single component conductors derived from nickel and gold bis(dithiolene) complexes is explored with the 2-alkylthio-1,3-thiazole-4,5-dithiolate ...(RS-tzdt) with R = CH
2
CH
2
OH through the preparation of the neutral Ni(HOEtS-tzdt)
2
0
(closed-shell) and Au(HOEtS-tzdt)
2
&z.rad; (radical) complexes. At variance with many other radical gold dithiolene complexes which have a strong tendency to dimerize in the solid state, Au(HOEtS-tzdt)
2
&z.rad; crystallizes into uniform stacks interconnected by strong O-H N HB involving the nitrogen atom of the thiazole ring. Au(HOEtS-tzdt)
2
&z.rad; is isostructural with its neutral, closed-shell nickel analog Ni(HOEtS-tzdt)
2
0
, a rare situation in this metal bis(dithiolene) chemistry. It demonstrates how the strength of the HB directing motif can control the overall structural arrangement to stabilize the same structure despite a different electron count. The nickel complex behaves as a band semiconductor with weak room temperature conductivity (1.6 × 10
−5
S cm
−1
), while the gold complex is described as a Mott insulator with a three orders of magnitude improved conductivity (6 × 10
−2
S cm
−1
).
Nickel (closed-shell) or gold (radical) bis(dithiolene) neutral complexes, functionalized with hydroxyethyl and thiazole moieties, afford hydrogen-bonded single component conductors.
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