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The synthesis and structures of two polymorphs, A and B, of Co(NCS)2(abpt)2 and Ni(NCS)2(abpt)2 are reported. The polymorph structures of A with CoII or NiII were found to be isostructural, as were the corresponding pair of polymorph B structures with the different metals., The synthesis and structures of bis­[4-amino-3,5-bis­(pyridin-2-yl)-1,2,4-triazole-κ2 N 2,N 3]bis­(thio­cyanato-κN)cobalt(II), [Co(NCS)2(C12H10N6)2] or Co(NCS)2(abpt)2, and bis­[4-amino-3,5-bis­(pyridin-2-yl)-1,2,4-triazole-κ2 N 2,N 3]bis­(thio­cyan­ato-κN)nickel(II), [Ni(NCS)2(C12H10N6)2] or Ni(NCS)2(abpt)2, are reported. In both cases, two polymorphs, A and B, were identified and structurally characterized. For both polymorphs, the structures obtained with the different metals, i.e. CoII or NiII, were found to be isostructural. All of the structures contained an intra­molecular N—H⋯N hydrogen bond, C—H⋯N inter­actions and π–π stacking inter­actions. No structural evidence was observed for a thermal spin crossover for either of the Co(NCS)2(abpt)2 polymorphs between 300 (2) and 120 (2) K.

Three di-tert-butyl-substituted N-salicylideneaniline derivatives were synthesized, structurally characterized and their chromic properties investigated. Polymorphism was found to affect the photochromic behaviour of the first com­pound, while the second two com­pounds were found to display a temperature-induced phase transition. All of the structures contained an intra­molecular O—H⋯N hydrogen bond., The synthesis, single-crystal structures and chromic behaviour of three related Schiff bases, namely, (E)-2,4-di-tert-butyl-6-{[(4-fluoro­phen­yl)imino]­meth­yl}phenol, C21H26FNO, 1, (E)-2,4-di-tert-butyl-6-{[(4-chloro­phen­yl)imino]­meth­yl}phenol, C21H26ClNO, 2, and (E)-6-{[(4-bromo­phen­yl)imino]­meth­yl}-2,4-di-tert-butyl­phenol, C21H26BrNO, 3, are reported. Two polymorphs of 1 were obtained, which were found to have different photochromic properties. Schiff bases 2 and 3 were found to be isostructural and underwent a phase transition upon cooling which was attributed to the dynamic disorder in one of the tert-butyl groups resolving at low temperature. All of the structures were found to exist in the enol rather than the keto form based on the C—O(H) and imine C=N bond lengths, and contained an intra­molecular O—H⋯N hydrogen bond alongside weaker inter­molecular C—H⋯O contacts.

The spin-crossover behaviour of [Fe(abpt)2(NCS)2] (abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) polymorphs B and D have been studied using single crystal X-ray diffraction to monitor changes in structural features. High pressure single crystal measurements on polymorph B showed that it underwent a monoclinic P21/n (Z’ = 0.5) to triclinic P-1 (Z’ = 2 x 0.5) phase transition between 11.5-13.5 kbar. At which point, it also starts to undergo a thermally inaccessible spin crossover. In polymorph D which also crystallises in the mononclinic space group P21/n (Z’ = 2 x 0.5) one of the unique Fe centres undergoes a thermal spin transition. It also displays light-induced excited spin-state trapping (LIESST), and a structure has been obtained at 30 K through continuous irradiation with a 670 nm 5 mW CW laser. In addition high pressure single crystal measurements on polymorph D showed a stepped pressure induced spin transition. At ~9.6 kbar one of the unique Fe centres had undergone a spin transition and by ~15 kbar both of the unique Fe centres are shown to be essentially low spin, a situation that is thermally inaccessible. Crystallographic data were collected for both polymorphs using variable temperature or high pressure single crystal X-ray diffraction to allow changes in cell parameters, bond lengths and distortion parameters to be monitored for the spin crossover or phase transitions.

A novel poly­morph of (E)-4-bromo-2-[(phenyl­imino)­meth­yl]phenol is reported, with a dihedral angle between the planes of the two aromatic rings of 45.6 (1)°, significantly different to that of the previously published poly­morph. The structure contains an intra­molecular O—H⋯N hydrogen bond forming an S(6) ring., A new poly­morph of (E)-4-bromo-2-[(phenyl­imino)­meth­yl]phenol, C13H10BrNO, is reported, together with a low-temperature structure determination of the previously published poly­morph. Both poly­morphs were found to have an intra­molecular O—H⋯N hydrogen bond between the phenol OH group and the imine N atom, forming an S(6) ring. The crystals were observed to have different colours at room temperature, with the previously published poly­morph being more orange and the new poly­morph more yellow. The planarity of the mol­ecule in the two poly­morphs was found to be significantly different, with dihedral angles (Φ) between the two aromatic rings for the previously published ‘orange’ poly­morph of Φ = 1.8 (2)° at 120 K, while the new ‘yellow’ poly­morph had Φ = 45.6 (1)° at 150 K. It was also observed that both poly­morphs displayed some degree of thermochromism and upon cooling the ‘orange’ poly­morph became more yellow, while the ‘yellow’ poly­morph became paler upon cooling.

Invited for the cover of this issue are Yann Garcia from Université catholique de Louvain, Belgium, and collaborators from partner universities and research centers. The cover image shows the square grid shape of an unprecedented Cu(II) coordination polymer with an “ancient temple architecture”.

The acylation of unsymmetrical N-benzylbispidinols in aromatic solvents without an external base led to the formation of supramolecular gels, which possess different thicknesses and degrees of stability depending on the substituents in para-positions of the benzylic group as well as on the nature of the acylating agent and of the solvent used. Structural features of the native gels as well as of their dried forms were studied by complementary techniques including Fourier-transform infrared (FTIR) and attenuated total reflection (ATR) spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and small-angle X-ray scattering and diffraction (SAXS). Structures of the key crystalline compounds were established by X-ray diffraction. An analysis of the obtained data allowed speculation on the crucial structural and condition factors that governed the gel formation. The most important factors were as follows: (i) absence of base, either external or internal, (ii) presence of HCl, (iii) presence of carbonyl and hydroxyl groups to allow hydrogen bonding, and (iv) presence of two (hetero)aromatic rings at both sides of the molecule. The hydrogen bonding involving amide carbonyl, hydroxyl at position 9, and, very probably, ammonium N-H+ and Cl&minus, anion appears to be responsible for the formation of infinite molecular chains required for the first step of gel formation. Subsequent lateral cooperation of molecular chains into fibers occurred, presumably, due to the aromatic &pi, &minus, &pi, stacking interactions. Supercritical carbon dioxide drying of the organogels gave rise to aerogels with morphologies different from that of air-dried samples.

Hirshfeld atom refinement (HAR) is a novel X-ray structure refinement technique that employs aspherical atomic scattering factors obtained from stockholder partitioning of a theoretically determined tailor-made static electron density. HAR overcomes many of the known limitations of independent atom modelling (IAM), such as too short element–hydrogen distances, r(X—H), or too large atomic displacement parameters (ADPs). This study probes the accuracy and precision of anisotropic hydrogen and non-hydrogen ADPs and of r(X—H) values obtained from HAR. These quantities are compared and found to agree with those obtained from (i) accurate neutron diffraction data measured at the same temperatures as the X-ray data and (ii) multipole modelling (MM), an established alternative method for interpreting X-ray diffraction data with the help of aspherical atomic scattering factors. Results are presented for three chemically different systems: the aromatic hydrocarbon rubrene (orthorhombic 5,6,11,12-tetraphenyltetracene), a co-crystal of zwitterionic betaine, imidazolium cations and picrate anions (BIPa), and the salt potassium hydrogen oxalate (KHOx). The non-hydrogen HAR-ADPs are as accurate and precise as the MM-ADPs. Both show excellent agreement with the neutron-based values and are superior to IAM-ADPs. The anisotropic hydrogen HAR-ADPs show a somewhat larger deviation from neutron-based values than the hydrogen SHADE-ADPs used in MM. Element–hydrogen bond lengths from HAR are in excellent agreement with those obtained from neutron diffraction experiments, although they are somewhat less precise. The residual density contour maps after HAR show fewer features than those after MM. Calculating the static electron density with the def2-TZVP basis set instead of the simpler def2-SVP one does not improve the refinement results significantly. All HARs were performed within the recently introduced HARt option implemented in the Olex2 program. They are easily launched inside its graphical user interface following a conventional IAM.

Diethyl 2-fluoromalonate ester is utilised as a building block for the synthesis of 2-fluoro-2-arylacetic acid and fluorooxindole derivatives by a strategy involving nucleophilic aromatic substitution reactions with ortho-fluoronitrobenzene substrates followed by decarboxylation, esterification and reductive cyclisation processes.

Reactions of Cp(NAr)NbMe2 with H2 and HSiMe2Cl are described. With H2 (1 atm) an apparent σ-bond metathesis process is accompanied by reduction to form the binuclear, metal-metal bonded species [CpNb(μ-NAr)Me]2 (Nb-Nb=2.6852(4) Å). With HSiMe2Cl (excess) Cp(NAr)NbMeCl is obtained in quantitative yield. © 2001 Elsevier Science B.V.

The ready construction of 24 stereochemically and functionally diverse carbohydrate ligand structures from a core D-glucosamine scaffold has allowed the evaluation of broad ranging structure activity relationships in ligand accelerated zincate additions to aldehydes, with variations in deltadeltaG+/+(R-S) of up to 5650 J mol(-1) that create opposing senses of asymmetric induction and that are consistent with models based on several ligand X-ray structures and molecular mechanics analysis. Factorial analysis of enantioselectivity using key dihedral angles and steric volume on N-2 also highlight the potential for the use of factorial design in ligand construction.

The triple decker dinuclear Cr(ii) salt [(η5-C 5Me5)Cr(μ2:η5-P 5)Cr(η5-C5Me5)]+ (SbF6)- has been structurally characterised by multiple temperature X-ray diffraction experiments from 290 K to 12 K. This material shows changes in its structural features which correlate with its magnetic response, including a structural transition with a change of symmetry from the orthorhombic space group Fddd to the monoclinic I2/a at ∼160 K and an abrupt rearrangement of electron density at ∼23 K This journal is © The Royal Society of Chemistry.

Methacrylate derivatives bearing β-D-glucopyranoside and β-D-galactopyranoside residues are synthesised by glycosylation of 2-hydroxyethyl methacrylate (HEMA) with 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide and 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl bromide, respectively. β-Selectivity in the glycosylation reactions is ensured by neighbouring-group participation of acetyl groups at O-2 in the glycosyl donors. 2-(2′,3′,4′,6′-tetra-O-acetyl-β-D-glucosyloxy)ethyl methacrylate (AcGlcEMA, 1a) was obtained as a crystalline solid and its crystal structure was determined by single-crystal X-ray diffraction. Deprotected polymers are synthesised in two parallel ways; either polymerisation of the protected monomers and subsequent deacetylation of the resulting polymers, or polymerisation of the previously deprotected monomers. The number- and weight-average relative molecular masses of both the protected and deprotected polymers are determined by size exclusion chromatography (SEC). Absolute molecular masses are obtained using the previously estimated refractive-index increments, dn/dc. It is found that polymerisation of deprotected monomers leads to polymers of well-defined composition, in contrast to the deacetylation of protected polymers.

iotbx.cif is a comprehensive toolbox for the development of applications that make use of the CIF format., iotbx.cif is a new software module for the development of applications that make use of the CIF format. Comprehensive tools are provided for input, output and validation of CIFs, as well as for interconversion with high-level cctbx [Grosse-Kunstleve, Sauter, Moriarty & Adams (2002). J. Appl. Cryst. 35, 126–136] crystallographic objects. The interface to the library is written in Python, whilst parsing is carried out using a compiled parser, combining the performance of a compiled language (C++) with the benefits of using an interpreted language.

4-Fluoropyrazole systems may be prepared by a single, sequential telescoped two-step continuous gas/liquid–liquid/liquid flow process from diketone, fluorine gas and hydrazine starting materials.

International audience; Quadrupolar oligothiophene chromophores composed of four to five thiophene rings with two terminal (E)-dimesitylborylvinyl groups (4 V-5 V), and five thiophene rings with two terminal aryldimesitylboryl groups (5 B), as well as an analogue of 5 V with a central EDOT ring (5 VE), have been synthesized via Pd-catalyzed cross-coupling reactions in high yields (66-89 %). Crystal structures of 4 V, 5 B, bithiophene 2 V, and five thiophene-derived intermediates are reported. Chromophores 4 V, 5 V, 5 B and 5 VE have photoluminescence quantum yields of 0.26-0.29, which are higher than those of the shorter analogues 1 V-3 V (0.01-0.20), and short fluorescence lifetimes (0.50-1.05 ns). Two-photon absorption (TPA) spectra have been measured for 2 V-5 V, 5 B and 5 VE in the range 750-920 nm. The measured TPA cross-sections for the series 2 V-5 V increase steadily with length up to a maximum of 1930 GM. We compare the TPA properties of 2 V-5 V with the related compounds 5 B and 5 VE, giving insight into the structure-property relationship for this class of chromophore. DFT and TD-DFT results, including calculated TPA spectra, complement the experimental findings and contribute to their interpretation. A comparison to other related thiophene and dimesitylboryl compounds indicates that our design strategy is promising for the synthesis of efficient dyes for two-photon-excited fluorescence applications.

We have determined the ultra-low temperature crystal structure of the archetypal single-molecule magnet (SMM) [Mn12O12(O2CMe)16(H2O)4]·4H2O·2MeCO2H (1) at 2 K, by using a combination of single-crystal X-ray and single-crystal neutron diffraction. This is the first structural study of any SMM in the same temperature regime where slow magnetic relaxation occurs. We reveal an additional hydrogen bonding interaction between the {Mn12} cluster and its solvent of crystallisation, which shows how the lattice solvent transmits disorder to the acetate ligands in the {Mn12} complex. Unusual quantum properties observed in 1 have long been attributed to disorder. Hence, we studied the desolvation products of 1, in order to understand precisely the influence of lattice solvent on the structure of the cluster. We present two new axially symmetric structures corresponding to different levels of desolvation of 1, [Mn12O12(O2CMe)16(H2O)4]·4H2O (2) and [Mn12O12(O2CMe)16(H2O)4] (3). In 2, removal of acetic acid of crystallisation largely resolves positional disorder in the affected acetate ligands, whereas removal of lattice water molecules further resolves the acetate ligand disorder in 3. Due to the absence of acetic acid of crystallisation, both 2 and 3 have true, unbroken S4 symmetry, showing for the first time that it is possible to prepare fully axial Mn12-acetate analogues from 1, via single-crystal to single-crystal transformations.

1099-0682; New imido bis(borohydride) complexes [(RN=)M(PMe3)2(η2-BH4)2] [R = Ar, M = Ti (3); R = Ar, M = V (5); R = Ar, M = Mo (6); R = Ar', M = Mo (7); Ar = 2,6-iPr2C6H3, Ar' = 2,6-Me2C6H3] were prepared by the reaction of dichlorides [(RN=)MCl2(PMe3)n] (M = Ti, n = 2; M = V, n = 2, M = Mo, n = 3) with LiBH4 (2 equiv) in THF. Compounds 3, 5, 6 and 7 were studied by IR spectroscopy and X-ray diffraction, and an EPR spectroscopy study was performed for paramagnetic compound 5. In 3, the two borohydride units are orthogonal to each other as a result of the overlap of an antiphase combination of B-H orbitals with the empty dxy orbital of Ti. In contrast, the dxy orbital of the metal atom is singly occupied in 5 and fully occupied in 6 and 7, and both borohydride ligands are oriented in the same way, with the B(μ-H2)M moieties orthogonal to the P-M-P vector.

International audience; Variable temperature single crystal X-ray diffraction and SQUID magnetometry experiments have revealed a gradual spin transition in [FeII(L)](ClO4)2 (where L=1,4,7-tris(2-aminophenyl)-1,4,7-triazacyclononane), centred around room temperature. The gradual nature of the spin transition has been attributed to the lack of significant intermolecular interactions between iron centres and the propensity of the counter ions to accommodate the internal strain in the crystal caused by spin crossover.

Stepping up: A two-step magnetic spin transition with accompanying structural phase transitions is reported for the first time for Fe III. The transitions are observed at 187 K and 90 K on cooling with a hysteretic transition recorded upon heating during the first crossover at 106 K. The intermediate phase persists over 97 K and contains an unprecedented [HS-HS-LS] motif with tripling of the unit cell. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rhodium complexes have potential uses in both catalysis and promoting the cleavage of C—C bonds. In order to further our understanding of these species and their potential applications, it is vital to obtain insight into the bonding within the species, particularly the Rh—C interactions, and to this end experimental charge-density studies have been undertaken on the title complexes. High-resolution single-crystal datasets to sin θ/λ = 1.06 Å−1 were obtained at 100 K and analysed using Bader's `Atoms in Molecules' (AIM) approach. The results of the studies have provided unique insights into the bonding involving rhodium and highlight the importance of undertaking such investigations for transition metal compounds.

Reaction of tetrafluoropyridazine with catechol gives a tricyclic 9,10-dioxa-1,2-diaza-anthracene system by a sequential nucleophilic aromatic substitution ring annelation process, further extending the use of perfluoroheteroaromatic derivatives for the synthesis of unusual polyfunctional heterocyclic architectures. The tricyclic scaffold reacts with amines and sodium ethoxide providing a short series of functional 9,10-dioxa-1,2-diaza-anthracene systems.

International audience; A series of bis(E-dimesitylborylethenyl)-substituted arenes, namely arene = 1,4-benzene, 1,4-tetrafluorobenzene, 2,5-thiophene, 1,4-naphthalene, 9,10-anthracene, 4,4′-biphenyl, 2,7-fluorene, 4,4′-E-stilbene, 4,4′-tolan, 5,5′-(2,2′-bithiophene), 1,4-bis(4-phenylethynyl)benzene, 1,4-bis(4-phenylethynyl)tetrafluorobenzene and 5,5″-(2,2′:5′,2″-terthiophene), have been synthesised via hydroboration of the corresponding diethynylarenes with dimesitylborane. Their absorption and emission maxima, fluorescence lifetimes and quantum yields are reported along with the two-photon absorption (TPA) spectra and TPA cross-sections for the 5,5′-bis(E-dimesitylborylethenyl)-2,2′-bithiophene and 5,5′-bis(E-dimesitylborylethenyl)-2,2′:5′,2″-terthiophene derivatives. The TPA cross-section of the latter compound of ca. 1800 GM is the largest yet reported for a 3-coordinate boron compound and is in the range of the largest values measured for quadrupolar compounds with similar conjugation lengths. The X-ray crystal structures of 1,4-benzene, 2,5-thiophene, 4,4′-biphenyl and 5,5″-(2,2′:5′,2″-terthiophene) derivatives indicate π-conjugation along the BC[double bond, length as m-dash]C-arene-C[double bond, length as m-dash]CB chain. Theoretical studies show that the second molecular hyperpolarisabilities, γ, in each series of compounds are generally related to the HOMO energy, which itself increases with increasing donor strength of the spacer. A strong enhancement of γ is predicted as the number of thiophene rings in the spacer increases.

A well-characterised 14-electron rhodium phosphine complex, [Rh(PiPr3)3][BArF4], which contains a beta-CH agostic interaction, is observed to undergo spontaneous dehydrogenation to afford [Rh(PiPr3)2(PiPr2(C3H5))][BArF4]; calculations on a model system show that while C-H activation is equally accessible from the beta-CH agostic species or an alternative gamma-CH agostic isomer, subsequent beta-H-transfer can only be achieved along pathways originating from the beta-CH agostic form.

cited By 101; International audience; Coordination of an ambiphilic diphosphine-borane (DPB) ligand to the RhCl(CO) fragment affords two isomeric complexes. According to Xray diffraction analysis, each complex adopts a square-pyramidal geometry with trans coordination of the two phosphine buttresses and axial RhB contacts, but the two differ in the relative orientations around the rhodium and boron centres. DFT calculations on the actual complexes provide insight into the influence of the π-accepting CO co-ligand, compared with previously reported complexes [Rh(μ-Cl)(dpb)]2 and [RhCl(dmap)(dpb)]. In addition, comparison of the C(CO) frequency of [RhCl(CO)(dpb)l with that of the related borane-free complex [RhCl(CO)(iPr2PPh)2] substantiatesthe significant electron-withdrawing effect that the σ-accepting borane moiety exerts on the metal. Valence isoelectronic [PtCl2(dpb)] and [PdCl2- (dpb)] complexes have also been prepared and characterized spectroscopically and structurally. The pronounced influence of the transition metal on the magnitude of the M→B interaction is highlighted by geometric considerations and NBO analyses. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

International audience; A new 1-D polymeric chain complex [Mn(pydc)(1,10-phen)]n· nH2O (pydc = pyridine-2,3-dicarboxylate, 1,10-phen = 1,10-phenanthroline) has been synthesised and characterised by elemental analysis, FT-IR spectrum, thermal analysis and variable temperature magnetic susceptibility studies. Single crystal X-ray diffraction study reveals that the central Mn(II) ion is in a distorted octahedral coordination geometry, and is coordinated to pydc and 1,10-phen. The complex shows interesting hydrogen bond modes involving the dicarboxylates and lattice water molecules. The presence of weak antiferromagnetic coupling with J = −0.72 cm−1 for the complex has been concluded from the cryomagnetic susceptibility studies.

The nature and the mechanism of the magnetic hysteresis for the thermal spin crossover exhibited by an iron (II) compound is investigated by means of variable-temperature powder and single-crystal x-ray diffraction. The unit cell temperature dependence clearly evidences the amplitude of the strong structural rearrangement that accompanies the spin crossover—corresponding to a variation of 8.6% for one of the unit cell parameters—as well as the structural hysteresis width. In this regard, the present x-ray study reveals significant differences in the spin crossover features according to the nature of the sample—powder or single crystal—that should be taken into account in the analysis of physical properties. Concerning the interplay between structural and magnetic transitions, quenching effects show that the structural transition and the spin crossover are indissociable. Furthermore, investigations of the mechanism itself of the thermal spin crossover confirm the presence of spin-like domains in the conversion region, either in the cooling or in the warming loops. The non-dependence with temperature of these domains inside the hysteresis loop demonstrates the stability of the microscopic and macroscopic structures in the corresponding thermodynamic conditions. This result is of interest in the context of the potential use of hysteresis loops to obtain high-temperature photo-conversion.

Zinc(II)–binol has been employed as an efficient Lewis acid catalyst (10 or 100 mol-% loading) for the formal aza-Diels–Alder reaction of ester, furyl and dimethyl acetal-substituted N-aryl imines. Asymmetric induction varies from poor to good, with the major enantiomer obtained being (S) when the (S)-binol complex has been employed. The absolute stereochemistry of the dimethyl acetal-substituted cycloaduct was determined by CD, and both efficient aza-Diels–Alder reaction and asymmetric induction are proposed to be dependent upon the formation of bidentate zinc-imine complexes. These complexes have been modelled using semi-empirical methods. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

This paper describes the first material to show the well-known light-induced excited spin-state trapping (LIESST) effect, the metastable excited state of which relaxes at a temperature approaching its thermal spin-crossover. Cooling polycrystalline [FeL(2)][BF(4)](2).x H(2)O (L=2,6-bis[3-methylpyrazol-1-yl]pyridine; x=0-1/3) at 1 K min(-1) leads to a cooperative spin transition, taking place in two steps centered at 147 and 105 K, that is only 54 % complete by magnetic susceptibility. Annealing the sample at 100 K for 2 h results in a slow decrease in chi(M)T to zero, showing that the remainder of the spin-crossover can proceed, but is kinetically slow. The crystalline high- and fully low-spin phases of [FeL(2)][BF(4)](2).x H(2)O are isostructural (C2/c, Z=8), but the spin-crossover proceeds via a mixed-spin intermediate phase that has a triple unit cell (C2/c, Z=24). The water content of the crystals is slowly lost on exposure to air without causing decomposition. However, the high-spin/mixed-spin transition in the crystal proceeds at 110+/-20 K when x=1/3 and 155+/-5 K when x=0, which correspond to the two spin-crossover steps seen in the bulk material. The high-spin state of the compound is generated quantitatively by irradiation of the low-spin or the mixed-spin phase at 10 K, and in approximately 70 % yield by rapidly quenching the sample to 10 K. This metastable high-spin state relaxes back to the low-spin ground state at 87+/-1 K in one, not two, steps, and without passing through the intermediate phase. This implies that thermal spin-crossover and thermally activated high-spin-low-spin relaxation in this material become decoupled, thus avoiding the physical impossibility of T(LIESST) being greater than T(1/2).

International audience; he photomagnetic properties of the following iron(II) complexes have been investigated: [Fe(L1)2][BF4]2 (1), [Fe(L2)2][BF4]2 (2), [Fe(L2)2][ClO4]2 (3), [Fe(L3)2][BF4]2 (4), [Fe(L3)2][ClO4]2 (5) and [Fe(L4)2][ClO4]2 (6) (L1 = 2,6-di{pyrazol-1-yl}pyridine; L2 = 2,6-di{pyrazol-1-yl}pyrazine; L3 = 2,6-di{pyrazol-1-yl}-4-{hydroxymethyl}pyridine; and L4 = 2,6-di{4-methylpyrazol-1-yl}pyridine). Compounds 1–6 display a complete thermal spin transition centred between 200–300 K, and undergo the light-induced excited spin state trapping (LIESST) effect at low temperatures. The T(LIESST) relaxation temperature of the photoinduced high-spin state for each compound has been determined. The presence of sigmoidal kinetics in the HS - > LS relaxation process, and the observation of LITH hysteresis loops under constant irradiation, demonstrate the cooperative nature of the spin transitions undergone by these materials. All the compounds in this study follow a previously proposed linear relation between T(LIESST) and their thermal spin-transition temperatures T1/2: T(LIESST) = T0– 0.3T1/2. T0 for these compounds is identical to that found previously for another family of iron(II) complexes of a related tridentate ligand, the first time such a comparison has been made. Crystallographic characterisation of the high- and low-spin forms of 5 and 6, the light-induced high-spin state of 5, and the low-spin complex [Fe(L4)2][BF4]2 (7), are described.

The electrochemical response of bis-Co2C2(CO)4(μ-dppm) complexes featuring bridging para-CB10H10C (5) and para-C6H4 (6) moieties are similar, each exhibiting two oxidations separated by ca. 100 mV, and two reductions separated by 80 mV, evidencing a degree of "electronic communication". A computational study of these systems and of the butadiyndiyl-bridged species (7) reveals an increasing contribution from the bridge π-orbitals in the frontier MO's of the monocations 5+

Optical and x-ray experiments showed the possibility of studying 4-styrylpyridine with a 15-crown-5 ether fragment to bind metal cations through the participation of two centres: the crown ether moiety and the heterocyclic part. The metal cations studied can be divided into three groups. Alkaline earth metal cations form complexes with the crown ether centre, H+, Co2+ and Cd2+ prefer coordination with the N-atom of heterocyclic part and Hg2+ cations form complexes through coordination with both binding centres. Copyright © 2005 John Wiley & Sons, Ltd.

Oxidative addition reactions of Cl2CPR (R = 2,4,6- tris(trifluoromethyl)phenyl (Ar) or 2,6-bis(trifluoromethyl)phenyl (Ar′) with Pt(PPh3)4 yield the cis and trans (at platinum) complexes [PtCl(ClCPAr)(PPh3)2] and [PtCl(ClCPAr′) (PPh3)2]. All starting materials and intermediates have been characterised by NMR spectroscopy. The crystal and molecular structures of the trans-platinum complexes have been determined by single-crystal X-ray diffraction at low temperature. © 2005 Elsevier B.V. All rights reserved.

Since the spin-crossover (SCO) effect was first discovered, considerable efforts have been made to study compounds that exhibit this phenomenon. Herein we present a selection of our most exciting results from structural studies carried out on some of the fascinating iron(II) SCO compounds we have investigated over the past few years. We discuss a range of compounds from mononuclear to bimetallic polymeric complexes. To cite this article: Amber L. Thompson, Victoria A. Money et al., C. R. Chimie 8 (2005).

N-Phosphoryl imines react with oxygenated dienes in the presence of Lewis acids to provide either the formal aza-Diels-Alder adduct. or the acyclic Mannich-type addition product, depending upon the catalyst and work up used, which is in agreement with the hypothesis that these reactions are mediated by zwitterionic Lewis acid-complex intermediates, rather than a concerted cycloaddition transition-state followed by hydrolytic ring opening. Stoichiometric asymmetric induction can he achieved using a zinc(II)-binol complex, producing up 77% ee.

The possibilities to trap by flash cooling the high spin (HS) state of iron(II) in the [Fe(PM–BiA)2(NCS)2] complex have been investigated by X-ray diffraction. This study reveals that trapping the HS state is possible under some conditions depending on the final temperature. If the latter is lower than the T(LIESST) temperature, the HS→LS (low spin) relaxation is slow enough to determine the trapped HS crystal structure by X-ray diffraction. The crystal structure of this complex in the 30 K trapped HS state shows differences from either the room temperature (HS) or the 30 K (LS) crystal structures, as for example differences in the strength of the S⋯H–C hydrogen bond like intermolecular interaction or the π–π interactions, known to play a crucial role in this compound for the propagation of the change in spin at the spin crossover (SCO), i.e. the cooperativity. The differences in intermolecular interactions are directly linked to the differences between the crystallographic unit cell modifications induced by pure thermal effects and those induced by the SCO.