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Considering the relevance of room temperature phosphorescent (RTP) materials, we discuss the influence of donor and acceptor groups substituted on to a twisted three-fold symmetric hydrocarbon homotruxene, which presents a persistent RTP, even in the absence of donor or acceptor moieties, under ambient conditions as a result of the twisted π-system. Compared to a fluorine acceptor, a donor methoxy group increases the phosphorescence decay rate in solution, while in the solid-state, molecular aggregation and packing yield a very persistent phosphorescence visible by the eye. The RTP of the intrinsically apolar homotruxene is found to be modulated by polar substituents, whose main impact on the solid-state emission is due to altered packing in the crystal.

International audience; A rigid propeller-shaped conjugated triple macrocycle consisting of two nearly perfectly stacked benzene rings and three linking [5]helicene moieties has been synthesized using a glyoxylic Perkin approach. Analysis of the electron delocalization in this atypical aromatic molecule revealed global aromaticity and a 78 π-electron circuit along the edge of its triple loop, to the detriment of the two 6 π-electron circuits in the two stacked benzene rings.

The switching properties of a cyanido-bridged Fe/Co square molecule were investigated by single-crystal X-ray diffraction and X-ray absorption spectroscopy at both Fe and Co K-edges. Combining these two techniques, a complete picture of the thermal-, light- and X-ray-induced metal-to-metal electron transfer is obtained, illustrating the concerted role played by the Fe and Co sites.

The chemistry of the InX3/2-benzoylpyridine reaction systems (X = Cl, Br) is interesting, including InBr3-assisted reactivity patterns of the coordinated ligand.

Reactions of di(2-pyridyl) ketone, (py)2CO, with indium(III) halides in CH3NO2 have been studied, and a new transformation of the ligand has been revealed. In the presence of InIII, the C═O bond of (py)2CO is subjected to nucleophilic attack by the carbanion -:CH2NO2, yielding the dinuclear complexes [In2X4{(py)2C(CH2NO2)(O)}2] (X = Cl, 1; X = Br, 2; X = I, 3) in moderate to good yields. The alkoxo oxygens of the two η1:η2:η1-(py)2C(CH2NO2)(O)- ligands doubly bridge the InIII centers and create a {In2(μ2-OR)2}4+ core. Two pyridyl nitrogens of different organic ligands and two terminal halogeno ions complete a distorted-octahedral stereochemistry around each In(III) ion. After maximum excitation at 360 or 380 nm, the solid chloro complex 1 emits blue light at 420 and 440 nm at room temperature, the emission being attributed to charge transfer within the coordinated organic ligand. Solid-state 115In NMR spectra, in combination with DFT calculations, of 1-3 have been studied in detail at both 9.4 and 14.1 T magnetic fields. The nuclear quadrupolar and chemical shift parameters provide valuable findings concerning the electric field gradients and magnetic shielding at the nuclei of indium, respectively. The experimentally derived CQ values are 40 ± 3 MHz for 1, 46 ± 5 MHz for 2, and 50 ± 10 and 64 ± 7 MHz for the two crystallographically independent InIII sites for 3, while the δiso values fall in the range 130 ± 30 to -290 ± 60 ppm. The calculated CQ and asymmetry parameter (ηQ) values are fully consistent with the experimental values for 1 and 2 and are in fairly good agreement for 3. The results have been analyzed and discussed in terms of the known (1, 3) and proposed (2) structural features of the complexes, demonstrating that 115In NMR is an effective solid-state technique for the study of indium(III) complexes.

Halogenation of a twisted three-fold symmetric hydrocarbon with F, Cl or Br leads to strong modulation of triplet–triplet annihilation and dual phosphorescence, one thermally activated and the other very persistent and visible by eye, with different relative contributions depending on the halide. The room temperature phosphorescence is highly unusual given the absence of lone-pair-contributing heteroatoms. The interplay between the spin–orbit coupling matrix elements and the spatial configuration of the triplet state induces efficient intersystem crossing and thus room temperature phosphorescence even without relying on heteroatomic electron lone pairs. A ninefold increase of the ISC rate after introduction of three bromine atoms is accompanied by a much higher 34-fold increase of phosphorescence rate., Twisted π-systems investigation showed a very unusual HAE, influencing independently the ISC and the dual phosphorescence emission, one being very persistent at room temperature and visible by eye in powder.

International audience; A cyanide-bridged [Fe 2 Co 2 ] molecular square complex, {[Fe(Tp)(CN) 3 ] 2 [Co(L) 2 ] 2 }(BF 4) 2 •2CH 3 CN•6H 2 O [1; Tp = hydrotris(pyrazol-1-yl)borate and L = bis(1-ethyl-1Himidazol-2-yl)ketone], has been synthesized and characterized fully by single-crystal X-ray diffraction, (photo)magnetic measurements, optical reflectivity, and other physical measurements. 1 exhibits a two-step metal-to-metal electron-transfer (MMET)induced spin transition accompanied by thermal hysteresis (T 1/2 ↑ = 332 and 407 K and T 1/2 ↓ = 320 and 405 K, respectively), converting the low-temperature diamagnetic {Fe II LS −CN−Co III LS } ground state into the high-temperature paramagnetic {Fe III LS − CN−Co II HS } state. Additionally, 1 displays reversible photoinduced MMET under light irradiation (ON mode using 808 nm laser light and OFF mode using 532 nm laser light), as confirmed by optical reflectivity and (photo)magnetic measurements. The photoinduced paramagnetic metastable state relaxes back to the diamagnetic ground state at 91 K (T LIESST = 91 K). Astonishingly, 1 also exhibits a 27 K wide light-induced thermal hysteresis below 100 K. The overall results show that 1 is a multistimuli-responsive bistable material that exhibits reversible switching between the diamagnetic state, {Fe II LS −CN−Co III LS }, and the paramagnetic state, {Fe III LS −CN−Co II HS }, under the application of temperature and light.

A cyanide-bridged [Fe

A family of four Ln(III) complexes has been synthesized with the general formula [Ln2(NO3)4(L)2(S)] (Ln = Gd, Tb, Er, and S = H2O, 1, 2 and 4, respectively/Ln = Dy, S = MeOH, complex 3), where HL is the flexible ditopic ligand N&rsquo, (1-(pyridin-2-yl)ethylidene)pyridine-2-carbohydrazide. The structures of isostructural MeOH/H2O solvates of these complexes were determined by single-crystal X-ray diffraction. The two LnIII ions are doubly bridged by the deprotonated oxygen atoms of two &ldquo, head-to-head&rdquo, 2.21011 (Harris notation) L&macr, ligands, forming a central, nearly rhombic {LnIII2(&mu, OR)2}4+ core. Two bidentate chelating nitrato groups complete a sphenocoronal 10-coordination at one metal ion, while two bidentate chelating nitrato groups and one solvent molecule (H2O or MeOH) complete a spherical capped square antiprismatic 9-coordination at the other. The structures are critically compared with those of other, previously reported metal complexes of HL or L&macr, The IR spectra of 1&ndash, 4 are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The f-f transitions in the solid-state (diffuse reflectance) spectra of the Tb(III), Dy(III), and Er(III) complexes have been fully assigned in the UV/Vis and near-IR regions. Magnetic susceptibility studies in the 1.85&ndash, 300 K range reveal the presence of weak, intramolecular GdIII∙∙∙GdIII antiferromagnetic exchange interactions in 1 [J/kB = &minus, 0.020(6) K based on the spin Hamiltonian Ĥ = &minus, 2J(ŜGd1∙ ŜGd2)] and probably weak antiferromagnetic LnIII∙∙∙LnIII exchange interactions in 2&ndash, 4. Ac susceptibility measurements in zero dc field do not show frequency dependent out-of-phase signals, and this experimental fact is discussed for 3 in terms of the magnetic anisotropy axis for each DyIII center and the oblate electron density of this metal ion. Complexes 3 and 4 are Single-Molecule Magnets (SMMs) and this behavior is optimally observed under external dc fields of 600 and 1000 Oe, respectively. The magnetization relaxation pathways are discussed and a satisfactory fit of the temperature and field dependencies of the relaxation time &tau, was achieved considering a model that employs Raman, direct, and Orbach relaxation mechanisms.

International audience; Molecular complexes based on Prussian Blue analogues have recently attracted considerable interest for their unique bistable properties combined to ultimately reduced dimensions. Here, we investigate the first dinuclear FeCo complex exhibiting both thermal and photomagnetic bistability in the solid state. Through an experimental and theoretical approach combining local techniques—X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD), and ligand field multiplet calculations—we were able to evidence the changes occurring at the atomic scale in the electronic and magnetic properties. The spectroscopic studies were able to fully support at the atomic level the following conclusions: (i) the 300 K phase and the light-induced excited state at 4 K are both built from FeLSIII–CoHSII paramagnetic pairs with no apparent reorganization of the local structure, (ii) the 100 K phase is composed of FeLSII–CoLSIII diamagnetic pairs, and (iii) the light-induced excited state is fully relaxed at an average temperature of ≈50 K. In the paramagnetic phase at 2 K, XAS and XMCD reveal that both Fe and Co ions exhibit a rather large orbital magnetic moment (0.65 μB and 0.46 μB, respectively, under an external magnetic induction of 6.5 T), but it was not possible to detect a magnetic interaction between spin centers above 2 K.

International audience; The iron(II) [2´2] grid complex Fe-8H has been synthesized and characterized. It undergoes spin-crossover (SCO) upon deprotonation of the hydrazine-based terpyridine-like ligand. The deprotonation patterns have been determined by X-ray crystallography and 1H NMR spectroscopy and discussed in relation to the spin state of the iron(II) centers which influences greatly the pKa of the ligand. The synthesis of the magnetically-silent zinc(II) analogue is also reported and its (de)protonation behavior has been characterized to serve as reference for the study of the Fe II grid complexes. DFT computations have also been performed in order to investigate how the successive deproto-nation of the bridging ligands affects the SCO behavior within the grid. n INTRODUCTION The search for materials having tunable properties is a very active research area. 1 In this context, special attention has been given to the modulation of magnetic properties by physical means such as temperature, 2 pressure and light, 2,3 or through chemical processes affecting the ligand field in complexes. 4 Spin crossover (SCO) complexes are interesting candidates, particularly iron(II) complexes, which exhibit a switching process between a paramagnetic high spin state (HS, S = 2) and a dia-magnetic low spin state (LS, S = 0). 5 Polymetallic [2´2] grid-like complexes 6 with modulable properties can be seen as molecular precursors of metallosupramolecular architectures or materials due to their ability to generate ordered arrangements of multiple grid entities by self-assembly at the air-water interface, 7 through hydrogen-bond formation in the solid array 8 and on adsorption onto a graphite surface. 9 It has been shown that tetranuclear iron(II) [2´2] grids undergo multiple spin state switching under the action of three physical triggers, temperature, pressure and light. 2,10 The influence of hydrogen-bond donors, 11 as well as that of counterions and solvent, 12 have also been shown to allow the modulation of the magnetism of these architectures. On the other hand, [2´2] grids presenting ionizable N-H sites undergo reversible protonic modulation of optical and redox properties. 13 One thus expects that the magnetic properties of such entities may also be modulated by reversible ligand deprotonation without destruction of the initial complex. 2,13 The hydrazine-based ditopic isomeric ligand H2L (Scheme 1) offers the opportunity to both generate [2´2] grid architectures by self-assembly and to study the protonic modulation of their physico-chemical properties, due to their ionizable N-H sites. The final step of the synthesis of such a ditopic ligand consists in the condensation reaction of one equivalent of 4,6-bis(hydrazino)-2-phenyl-pyrimidine with two equivalents of 2-pyri-dine-carboxaldehyde to yield ligand H2L. This ligand contains two com-plexation subunits of terpyridine (terpy) type, where the hydrazone function acts as an ionizable group whose acidity is greatly enhanced on complexation, as compared to the free ligands. Scheme 1. Synthesis of the ditopic ionizable hydrazine-based ligand H2L and its self-assembly into the corresponding tetranu-clear [Fe4(H2L)4] 8+ [2´2] grid complex by coordination with Fe II cations. Red spheres represent Fe metal ions. Hydrogen atoms that are colored in blue emphasize the deprotonation sites on the [2´2] grid. ABSTRACT: When immersed in solutions containing Cu(II) cations, the microporous metal−organic material P11 ([Cd 4 (BPT) 4 ]·[Cd(C 44 H 36 N 8)(S)]·[S], BPT = bi-phenyl-3,4′,5-tricarboxylate) undergoes a transformation of its [Cd 2 (COO) 6 ] 2− molecular building blocks (MBBs) into novel tetranuclear [Cu 4 X 2 (COO) 6 (S) 2 ] MBBs to form P11-Cu. The transformation occurs in single-crystal to single-crystal fashion, and its stepwise mechanism was studied by varying the Cd 2+ /Cu 2+ ratio of the solution in which crystals of P11 were immersed. P11-16/1 (Cd in framework retained, Cd in encapsulated porphyrins exchanged) and other intermediate phases were thereby isolated and structurally characterized. P11-16/1 and P11-Cu retain the microporosity of P11, and the relatively larger MBBs in P11-Cu permit a 20% unit cell expansion and afford a higher surface area and a larger pore size. P orous metal−organic materials (MOMs) that incorporate

An iron(II) pyridyl-benzohydrazonate-based complex decorated with long alkyl chains is reported as a rare spin-crossover compound displaying a wide thermal hysteresis spanning room temperature. On heating, this compound exhibits a spin transition between a LS ground state and an ordered HS-LS phase with symmetry breaking from monoclinic P21/n into orthorhombic P21212 space groups. During cooling, the compound first transits into a magnetically distinguishable HS-LS phase with monoclinic P21 symmetry before returning into the LS phase. Interconversion between the two distinct HS-LS phases is the result of subtle structural changes in the alkyl chains and produces a second minor thermal hysteresis that superposes to the large one. This unprecedented result shows that the combination of a conventional cooperative spin transition and ligand-driven magnetic changes can promote magnetic tristability at room temperature.

International audience; Without employing high dilution conditions, the fourfold 2+2 Perkin reaction of 1,6-pyrenylene-diglyoxylic acid withits reduction product 1,6-pyrenylene-diacetic acid yields the corresponding tetrameric conjugated macrocycle in 25% overallyield after in-situ esterification. The macrocycle adopts a square fourfold symmetry in the crystal, with near-vertical pyrene wallsthat alternatingly tilt upwards and downwards.

Perkin condensation of chrysenyl-6-acetic acid with chrysenylene-6,12-diglyoxylic acid followed by in situ esterification gives a bismaleate, whose conjugated stilbene moieties are efficiently shielded against intermolecular condensations and undergo iodine-catalyzed oxidative photocyclization in toluene without the need for high dilution. The concentration is limited by the low solubility of the flexible bismaleate at room temperature. The so-obtained double [7]helicene crystallizes in a nonchiral meso form. It is notably more soluble than its flexible precursor because it cannot fold to optimize π-π stacking.

A mononuclear Fe

Intramolecular magnetic interactions in the dinuclear complexes [(tpy)Ni(tphz)Ni(tpy)]n+ (n = 4, 3, and 2; tpy, terpyridine; tphz, tetrapyridophenazine) were tailored by changing the oxidation state of the pyrazine-based bridging ligand. While its neutral form mediates a weak antiferromagnetic (AF) coupling between the two S = 1 Ni(II), its reduced form, tphz•-, promotes a remarkably large ferromagnetic exchange of +214(5) K with Ni(II) spins. Reducing twice the bridging ligand affords weak Ni-Ni interactions, in marked contrast to the Co(II) analogue. Those experimental results, supported by a careful examination of the involved orbitals, provide a clear understanding of the factors which govern strength and sign of the magnetic exchange through an aromatic bridging ligand, a prerequisite for the rational design of strongly coupled molecular systems and high TC molecule-based magnets.

The dehydrating cyclotrimerization of 1-tetralone in the presence of titanium tetrachloride at high temperature leads to homotruxene, a nonplanararene in which the twist angles between its three outer benzene rings and the central benzene are stabilized by ethylene bridges. This non-planar configuration allows for pronounced spin-orbit coupling and a high triplet energy, leading to room temperature phosphorescence in air with a lifetime of 0.38 s and a quantum yield of 5.6%, cleanly visible to the human eye after switch-off of excitation. Triplet-triplet annihilation is found to simultaneously lead to an intense delayed fluorescence, unprecedented from a pure hydrocarbon at ambient conditions, with a lifetime of 0.11 s.

International audience; A mononuclear FeII complex that shows a high‐spin (S=2) paramagnetic behavior at all temperatures (with standard temperature‐scan rates, ≈1 K min−1) has, in fact, a low‐spin (S=0) ground state below 100 K. This low‐spin state is not easily accessible due to the extremely slow dynamics of the spin‐crossover process—a full relaxation from the metastable high‐spin state to the low‐spin ground state takes more than 5 h below 80 K. Bidirectional photo‐switching of the FeII state is achieved reproducibly by two selective irradiations (at 530–590 and 830–850 nm). The slow dynamics of the spin‐crossover and the strong structural cooperativity result in a remarkably wide 95‐K hysteresis loop induced by both temperature and selected light stimuli.

International audience; A number of singly (180°) twisted, largely single-stranded and thus conformationally rather fragile, Möbius molecules have been synthesized within the last 15 years, which are aromatic with 4n electrons, thus violating the Hückel rule. Annulenes with significantly higher twist (e.g. 540°) that retain a full cyclic conjugation path have been elusive, mainly because of the high strain and loss of orbital overlap. Recently, a topological strategy was devised to project the “twist” into “writhe”, thus reducing the strain. However, orbital overlap was still severely reduced within the flexible building blocks. We now present a single and a triple twisted annulene with fully conjugated peripheries. They are unique in their pronounced band shape and conformational robustness as they are made up of three fully kata-condensed [5]helicene fragments. The triple twisted molecule exhibits a strong diatropic ring current in the outer periphery, even though the π system includes 4n electrons. The diatropic current is counterbalanced by a paratropic current in the σ system, resulting in no net manifestation of macrocyclic aromaticity. The key step of the synthesis of both Möbius compounds is a Perkin condensation of complementary bifunctional bismaleates leading to a flexible macrocycle containing alternating benzene and biphenyl fragments. Subsequent photocyclization yields a separable mixture of rigid diastereomeric tris-helicene macrocycles of the above topologies.

International audience; The neutral radical 4-(2′-benzimidazolyl)- 1,2,3,5-dithiadiazolyl (HbimDTDA) exhibits a first order phase transition around 270 K without symmetry breaking, preserving its orthorhombic Pbca space group between 340 and 100 K. Associated with this reversible single-crystal-to-single-crystal phase transition, thermal hysteresis of the magnetic susceptibility is observed. The low temperature (LT) phase is diamagnetic owing to pancake bonding between the π-radicals. In the paramagnetic high temperature (HT) phase, the pancake bonds are broken, and new electrostatic contacts are apparent. As a result of the dense 3D network of supramolecular contacts, which includes H-bonds, the HbimDTDA system provides the first example of magnetic bistability for a DTDA radical.

International audience; A dinuclear CoII complex, [Co2(tphz)(tpy)2]n+ (n=4, 3 or 2; tphz: tetrapyridophenazine; tpy: terpyridine), has been assembled using the redox-active and strongly complexing tphz bridging ligand. The magnetic properties of this complex can be tuned from spin-crossover with T1/2&470 K for the pristine compound (n=4) to single-molecule magnet with an ST=5/2 spin ground state when once reduced (n=3) to finally a diamagnetic species when twice reduced (n=2). The two successive and reversible reductions are concomitant with an increase of the spin delocalization within the complex, promoting remarkably large magnetic exchange couplings and high-spin species even at room temperature.

The iron(II) [2×2] grid complex Fe-8H has been synthesized and characterized. It undergoes spin-crossover (SCO) upon deprotonation of the hydrazine-based terpyridine-like ligand. The deprotonation patterns have been determined by X-ray crystallography and

International audience; Dibenzo[a,j]coronene-tetracarboxylic alkyl esters and imides with either a centrosymmetric bis-peri substitutionpattern or a polar bis-ortho substitution pattern form hexagonal columnar mesophases, which in the case of theimides persist at room temperature. The bis-peri isomers are obtained via a two-fold oxidative photocyclization; the bisortho isomers are accessed via a glyoxylic Perkin reaction of triphenylene and naphthalene building blocks. Steric congestion between the substituents and the adjacent benzo protrusion in the bis-ortho esters and imides leads to bending of the aromatic plane, which thus avoids twisting. These isomers surprisingly show a more pronounced liquid crystalline behaviour than their non-bent bis-peri homologs, accommodating non-planarity with columnar order by slipped stacking. Whereas both types of ester and the bis-peri imide show an optical behaviour typical for perylene chromophores, the strongly bent bis-ortho imide distinguishes itself notably from them by its absorption spectrum. The electron acceptor strength of the isomeric diimides is found to differ, the hexagonal (peri) diimide having a 0.20 eV lower LUMO energy than the pentagonal (ortho) isomer.

One-dimensional coordination polymers of alternating metal-metal bonded trinuclear [Co3(dpa)4]2+ (dpa = the anion of 2,2'-dipyridylamine) building blocks and [ReF6]2- (1), [ZrF6]2- (2) or [SnF6]2- (3) linkers have been self-assembled and crystallographically characterized. Magnetic measurements reveal a significant ferromagnetic coupling (J/kB = +9.9 K) between S = 1/2 {Co36+} and S = 3/2 ReIV magnetic sites through a single, unsupported fluoride bridge in 1.

International audience; Saddle- and propeller-shaped macrocycles are obtained by fourfold Perkin condensations in transient high dilution of 4,40-bis(phenylglyoxylic acid) with either 4,40-bis(phenylacetic acid) or p-phenylenediacetic acid, followed by four-fold oxidative photocyclizations. In the saddle-shaped tetraphenanthrylene, the angle between opposite phenanthrene planes is close to the value of 908 of an ideal saddle. In the two helicene fragments of the propeller-shaped double [5]helicene, the geometry of unsubstituted [5]helicene is preserved without major macrocycle-induced distortions.

A detailed crystallographic study of [FeII(LN5)(CN)2]·MeOH (LN5 = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene) shows the light-induced formation and thermally-assisted rupture of a metal–ligand coordination bond concomitantly with a spin-crossover process occurring at the Fe(II) center between its low spin (LS) and high spin (HS) states. These results illustrate the remarkable reversibility and non-destructive character of this photo-induced magneto-structural process in a single crystal.

Glyoxylic functionalization of chrysene by Friedel–Crafts acylation with ethyl chloroglyoxylate or by bromination followed by substituent exchange enables the formation of bis[5]helicene-tetracarboxylates and tetracarboxdiimides through Perkin reactions and palladium-catalyzed cyclizations. Tetrasubstituted bishelicenic dichrysenoanthracenes and dinaphthochrysenes are thus obtained from chrysene in four to six steps. In the cyclization to dinaphthochrysenes, a rearrangement of the conjugated carbon skeleton is identified as side reaction. In solution, the diimides form mixtures of M,P- and M,M/P,P-diastereomers, which equilibrate at room temperature when the helices are distant but equilibrate only upon heating when the helices are close and acting in concert. The nonplanar arene geometry allows close π-contacts in two dimensions between neighboring molecules in the crystal.

6 pages; International audience; The trinuclear complex [{CoII(Me6tren)}2(m-NC)2RuIII(salen)](NO3)3.3CH3CN.H2O (2) (salen = N,N0-ethylenebis( salicylideneiminato); Me6tren=tris((dimethylamino)ethyl)amine) was synthesized by the reaction of trans-(PPh4)[RuIII(salen)(CN)2] and two equivalents of [CoII(Me6tren)(OH2)](NO3)2 (1). Magnetic susceptibility measurements of 1 reveal its single-molecule magnet behaviour whilst 2 shows no appreciable slow dynamics of the magnetization even under an applied dc field. A comparison of the electrochemical properties of complex 2 with the trans-(PPh4)[RuIII(salen)(CN)2] precursor reveals anodic shifts of the reduction and oxidation waves. The absorption spectrum of 2 obtained from surface optical reflectivity methods is also reported and discussed.

The reaction between (Bu 4 N)[Ru(salen)(CN) 2 ] and MnCl 2 yielded a bidimensional (2D) network [{Ru(salen)(CN) 2 } 2 Mn(CH 3 CN)]·H 2 O ( 1 ) incorporating square pyramidal Mn II centers. The single crystal X-ray structure, heat capacity and magnetic properties of 1 are herein reported. From the magnetic measurements, antiferromagnetic interactions were detected between Ru III ( s = 1/2) and Mn II ( S = 5/2) ions through the cyanido bridges ( J ) in the 2D framework as well as antiferromagnetic interplane interactions ( J ′). These interactions were estimated using a three-dimensional model in the frame of the mean field approximation ( J / k B = −0.86(2) K and J ′/ k B = −0.067(6) K, g Ru = 2.33(5)). Furthermore, a three dimensional antiferromagnetic order was evidenced by dc susceptibility measurements with a Neel temperature of 2.6 ± 0.1 K that was also confirmed by heat capacity measurements.

International audience; Photomagnetism in three-dimensional Co/Fe Prussian blue analogues is a complex phenomenon, whose detailed mechanism is not yet fully understood. Recently, researchers have been able to prepare molecular fragments of these networks using a building block synthetic approach from mononuclear precursors. The main objective in this strategy is to isolate the smallest units that show an intramolecular electron transfer to have a better understanding of the electronic processes. A prior requirement to the development of this kind of system is to understand to what extent electronic and magnetic properties are inherited from the corresponding precursors. In this work, we investigate the electronic and magnetic properties of the FeTp precursor (N(C4H9)4)[TpFe(III)(CN)3], (Tp being tris-pyrazolyl borate) of a recently reported binuclear cyanido-bridged Fe/Co complex. X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements at the Fe L2,3 edges (2p → 3d) supported by ligand field multiplet calculations have allowed to determine the spin and orbit magnetic moments. Inaccuracy of the spin sum rule in the case of low-spin Fe(III) ion was demonstrated. An exceptionally large value of the orbital magnetic moment is found (0.9 μB at T = 2 K and B = 6.5 T) that is likely to play an important role in the magnetic and photomagnetic properties of molecular Fe/Co Prussian blue analogues.

International audience; Structural, spectroscopic and magnetic methods have been used to characterize the tris(carbene)borate compound PhB(MesIm)3Mn^N as a four-coordinate manganese(IV) complex with a low spin (S ¼ 1/2) configuration. The slow relaxation of the magnetization in this complex, i.e. its single-molecule magnet(SMM) properties, is revealed under an applied dc field. Multireference quantum mechanical calculations indicate that this SMM behavior originates from an anisotropic ground doublet stabilized by spin–orbit coupling. Consistent theoretical and experiment data show that the resulting magnetization dynamics inthis system is dominated by ground state quantum tunneling, while its temperature dependence is influenced by Raman relaxation.

The cyclization of esters of Perkin condensation products by oxi- dation with 2,3-dichloro-5,6-dicyano- benzoquinone (DDQ) in the presence of MeSO3H is examined as a three- step approach from arylacetic acids and aromatic aldehydes to functional- ized condensed arenes. The method is limited to systems in which one or both of the two aryl moieties are more reactive than a phenyl group, such as 1-naphthyl or, especially, 3- thienyl. Alkoxycarbonyl derivatives of picene, benzo(c)chrysene, three iso- meric phenanthrothiophenes, a naph- thothiophene, and a benzodithiophene were obtained. The extension of this approach to multiple cyclizations and, thus, to extended partially condensed systems with multiple alkoxycarbonyl substituents appears promising with highly active precursors derived from 3-thienylacetic acid. In this case, con- jugated polymers made of short ribbon fragments linked by thio- phene-thiophene single bonds appear conceivable. A bifunctional chryseno- dithiophene was obtained from 1,5-di- formylnaphthalene, together with a highly unusual asymmetric dimer that contains a cyclohepta(de)naphtha- lene (pleiadiene) moiety.

4 pages; International audience; The Scholl reaction with quinquephenyl derivatives has been shown to have an unexpectedly strong preference for forming twisted, helicene aromatic polycycles, instead of their flat counterparts. This tendency is so strong that it will overcome even severe steric hindrance, and the procedure can be used in the efficient synthesis of hexa-tert-butylhexabenzotriphenylene from a simple biaryl starting material.

The combinations of bisamidium dicationic tectons 1-2H+ and 2-2H+ bearing two OH groups as additional H-bond donor/acceptor sites with [M(CN)6](3-)2 (M = Fe, Co, Cr) anions lead to the formation of robust porous crystals (decomposition temperature in the range of 240-300 degrees C) offering channels occupied by water molecules. The release and uptake of solvent molecules takes place through a reversible single crystal-to-single crystal transformation. Importantly, the temperature of dehydration can be increased by ca 40 degrees C through the decoration of the channels by introduction of OH groups on the backbone of the organic tecton.

International audience; π−π radical interactions have exacting geometry requirements, significantly more stringent than those of a hydrogen bond or a van der Waals interaction. Here, supramolecular synthons based on such radical−radical recognition are employed to generate switchable structuraland magnetic properties. Interactions between neighboring paramagnetic ligands of the La(hfac)3(pyDTDA)2 coordination complex cause a rare re-entrant phase transition (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-; pyDTDA = 4-(2′-pyridyl)- 1,2,3,5-dithiadiazolyl). Below 100 K, the complex is diamagnetic in the solid state, consistent with an f 0 lanthanum(III) ion and “pancake bonding” of the π-radical ligands. Upon heating, the supramolecular one-dimensional arrangement undergoes two sequential structural phase transitions, observed at ca. 160 and 310 K, successively involving the rupture of half and then the totality of the “pancake bonds” and generating stepwise increases in the paramagnetic susceptibility. We use the structural and magnetic data to develop a theoretical model that clearly predicts the unprecedented re-entrant behavior of this radical-La(III)-radical complex. Moreover, this microscopic free-energy model demonstrates that any system with essentially noninteracting “dimers” contains within itself the possibility of a distortion associated with re-entrant phase transitions if the lattice is “soft” enough (i.e., low rigidity).

4 pages; International audience; Perkin condensations of arylglyoxylic acids with arylacetic acids, followed by the addition of alkylamine, yield diarylmaleimides in a one-pot procedure. The arylglyoxylic acids are obtained by arene acylation with ClCOCO2Et and reduced with NaI and hypophosphorous acid to the arylacetic acids. With 2,7-di-tert-butyl-pyren-4-yl or chrysen-6-yl as the aryl, photocyclodehydrogenation of the diarylmaleimides yields substituted helicenes which can be reduced to stable anions. The helicenes combine bathochromically shifted absorption with hypsochromically shifted fluorescence with respect to their precursors.

International audience; Co/Fe Prussian Blue analogues are known to display both thermally and light induced electron transfer attributed to the switching between diamagnetic {Fe(II)LS(μ-CN)Co(III)LS} and paramagnetic {Fe(III)LS(μ-CN)Co(II)HS} pairs (LS = low spin; HS = high spin). In this work, a dinuclear cyanido-bridged Co/Fe complex, the smallest {Fe(μ-CN)Co} moiety at the origin of the remarkable physical properties of these systems, has been designed by a rational building-block approach. Combined structural, spectroscopic, magnetic and photomagnetic studies reveal that a metal-to-metal electron transfer that can be triggered in solid state by light, temperature and solvent contents, is observed for the first time in a dinuclear complex.

A combination of the tecton 12+ with [MII(CN)6]4- (M = Fe, Ru) complex anions leads to the formation of analogous two-dimensional (2-D) H-bonded networks and isomorphous crystals. Based on the isomorphous nature of the two crystalline systems, the three-dimensional (3-D) epitaxial growth of composite crystals up to generation three was achieved and visually demonstrated.

International audience; Upon combining KCu(CN)2 with six different symmetrical dicationic bisamidinium moieties possessing different shapes and geometries, seven new coordination networks of the cyanocuprate type displaying 1-, 2- and 3-D dimensionality have been obtained. The formation of networks results from the interconnection of Cu(I) centres by cyanide anions through different bridging modes. The organic dicationic tectons interact with the anionic networks by charge-assisted H-bonds and, depending on their geometric features, they play different structuring roles. In the case of the 1D cyanocuprate networks, theorganic cation interconnects consecutive anionic chains, increasing thus the overall dimensionality of the arrangement to 2D. For the 2D networks, either riveting or intercalation has been observed. For the riveting case, either the process takes place only between two consecutive sheets leading to a double layer type arrangement and thus without an increase of dimensionality, or between consecutive 2D networks in an alternate fashion. In the latter case, the dimensionality of the overall architecture is increased to 3 as for the intercalated case. For the 3D architectures, the dicationic moieties are located within the generated channels.

9 pages; International audience; With the aim of opening an efficient access to large and sterically crowded polycyclic arenes as well as improving insight into the geometrical preferences of the Scholl reaction, a versatile synthesis strategy has been developed to form a family of flexible yet strongly crowded substrates for multiple dehydrocyclizations. Their intramolecular Scholl reactions lead with high selectivity either to considerably twisted species where the initial C3 symmetry is maintained, or to strongly rearranged products where the formation of multiple [6]helicene fragments is avoided by the formation of unusual hexa[7]circulene moieties under loss of the C3 symmetry.

International audience; The design of molecule-based systems displaying tuneable optical and/or magnetic properties under external stimuli has received a great deal of attention in the past few years. This interest is driven by the potential applications in high-performance molecule-based electronics in the areas of recording media, switches, sensors, and displays. As an example, three-dimensional Fe/Co Prussian blue compounds exhibit a concomitant change in magnetic and optical properties due to a temperature- or light-induced metal-to-metal electron transfer. The foregoing remarkable properties in Prussian blues prompted us to design soluble molecular fragments of these coordination networks through a rational building-block approach in order to mimic their properties on a single molecule. With a judicious choice of the ligands for the iron and cobalt molecular precursors, we prepared a dinuclear cyanido-bridged Fe/Co complex that exhibits an unexpected temperature-dependent spin crossover in the solid state while an intramolecular electron transfer triggered by protonation is observed in solution.

8 pages; International audience; Many square-planar Pt(II) complexes are strongly photoluminescent, particularly when they contain cyclometalating and/or NHC ligands which produce strong ligand fields. In this work we investigated the possibility of obtaining isoelectronic Au(III) complexes with favorable luminescence properties. Toward this end, the coordination chemistry of gold with three different (potentially) tridentate ligands was explored: 1,3-bis(1-hexyl-2′-benzimidazoyl)- benzene (L1H), 2,6-bis(3-butylimidazol-1-ium)pyridine (L2H2 2+), and 2,6-bis(3-hexylbenzimidazol-1-ium)pyridine (L3H2 2+). Pt(II) or Pd(II) complexes are known for all of these ligands or closely related analogues, and hence we anticipated that similar Au(III) complexes would be synthetically accessible as well. This turned out to be the case only for L1, despite exploration of different synthetic routes including (i) direct complexation of Au(III), (ii) transmetalation from Ag(I) precursor complexes, and (iii) transmetalation from suitable Hg(II) precursors. Only the mercury procedure was successful (at least in the case of L1); transmetalation from silver or direct complexation yields other reaction products containing Au(I) in most cases. Likewise, with ligands L2 and L3 mainly complexes of Au(I) were obtained: i.e., the propensity of gold for low oxidation states is a major obstacle to obtaining the desired Au(III) compounds. Several new complexes of Au(I) and Au(III) were characterized crystallographically. Our results provide insight into the differences between the coordination chemistry of isoelectronic Pt(II) and Au(III) with tridentate cyclometalating and NHC ligands.

3 pages; International audience; A new cyanido-bridged ReIV-MnIII heterometallic 1D system, [MnIII(5-Me-saltmen)]2[ReIVCl4(CN)2] 3CH3CN (1), was designed and structurally characterized. Interchain interactions stabilize a canted antiferromagnetic ordered state below 6.2 K that does not prevent slow relaxation of the magnetization reminiscent of the single-chain magnet properties of the individual chains.

8 pages; International audience; Three new cyanido-bridged heterometallic ReIVNiII and ReIVCuII one-dimensional systems were synthesized and extensively characterized both structurally and magnetically. Single-crystal X-ray diffraction analysis revealed that these compounds display a common topology, with chains composed of alternating [ReIVCl4(CN)2]2- and [MII(cyclam)]2+ (M = Ni in 1, Cu in 2) or [CuII(N,N′-dimethylcyclam)]2+ (in 3) building units. Two different chain orientations with a tilt angle of ca. 51° to 55° are present in the crystal packing of these compounds. The magnetic susceptibility measurements suggest the presence of intrachain ferromagnetic interactions between the S = 3/2 ReIV centers and the 3d metal ions: S = 1 NiII or S = 1/2 CuII. At low temperature, a three-dimensional ordered magnetic phase induced by interchain antiferromagnetic interactions (antiferromagnetic for 1 and 2; canted antiferromagnetic for 3) is detected for the three compounds.