Search

We investigate the structural, magnetic, and dielectric properties of the organic-inorganic hybrid material CuCl4(C6H5CH2CH2NH3)(2) and demonstrate that spontaneous ferroelectric order sets in below 340 K, which coexists with ferromagnetic ordering below 13 K. We use X-ray diffraction to show that the electric polarization results from the spatial ordering of hydrogen bonds that link the organic block comprised of phenylethylammonium cations to the inorganic copper chloride block. The hydrogen bond ordering is driven by buckling of the corner-linked copper chloride octahedra. Because the magnetic exchange pathways are also determined by this octahedral buckling, a potentially large coupling is induced. Our results imply that such hybrids form a new family of multiferroic materials. KEYWORDS: multiferroic, ferroelectric, ferromagnetic, organic inorganic hybrid, metal-oxide framework

Decamethylzirconocene cation [Cp*2ZrMe](+) (2) decomposes in bromobenzene-d(5) solution to generate sigma-aryl species [Cp*Zr-2(2-C6H4Br-kappa Br,C)][B(C6F5)(4)] (3). This a-bond metathesis reaction is catalyzed by tertiary amines via a two-step mechanism, in which the amine acts as a proton relay. In benzene-d(6) compound 2 decomposes via C H bond activation of one of the Cp* ligands to generate tucked-in compound [Cp*{eta(5):eta(1)-C5Me4(CH2)}Zr](+) (4). In the presence of Et3N, no formation of tucked-in compound 4 is observed, but instead an overall double C-H bond activation and C-N bond cleavage of the tertiary amine is observed, resulting in [Cp*Zr-2{C(Me)NEt-kappa C,N}](+) (6). A mechanism is proposed that nominates [Cp*2ZrNEt2](+) as an intermediate, the result of a C-H bond activation of Et3N, followed by beta-amide elimination. Attempted synthesis of this species by treatment of Cp*Zr-2(NEt2)Me with [Ph3C][B(C6F5)(4)] results, again, in formation of compound [6](+). The presence of Et3N also has an effect on the stability of THF adduct [Cp*2ZrMe(THF)](+) as the amine performs a nucleophilic THF ring-opening to generate [Cp*2ZrMe{O(CH2)(4)NEt3}](+) (7). The results show that amine coproducts, often generated in the synthesis of cationic transition-metal complexes, are not necessarily innocent.

Synthesis and characterisation of ether adducts of bis(amidinate) Fe-II complexes are described [amidinate = 2,6-iPr(2)C(6)H(3)-NC(Ph)N-Ph]. The isolation of these five-coordinate complexes contrasts with the homoleptic bis(amidinate) Fe complexes obtained previously with the sterically more demanding amidinate ligands 2,6-iPr(2)C(6)H(3)-NC(Ph)N-Ar (Ar = 2,6-iPr(2)C(6)H(3), 2,6-Me2C6H3) The more accessible ether adducts show enhanced reactivity towards Lewis bases and towards the pi-acid carbon monoxide. Reaction with excess amounts of CO results in carbonyl insertion into the Fe-N bonds, thereby giving rise to a diamagnetic bis(CO) adduct supported by two carbamoyl ligands.

Thermolysis of half-sandwich vanadium imido complexes Cp(RN)V(i-Pr(2)N)Me (R = p-Tol, 1a; R = t-Bu, 1b) results in a mixture of products, including vanadium(IV) dimers [CpVMe](2)(mu-RN)(2), i-Pr(2)NH, i-PrNCMe(2), CH(4), and one or more paramagnetic species. In the presence of dmpe (dmpe = bis(dimethylphosphino)ethane), PMe(3), or PhSSPh, the initially formed paramagnetic species can be trapped, providing Cp(RN)VL(2)(R = p-Tol, L(2) = dmpe, 2a; R = t-Bu, L(2) = dmpe, 2b; R = p-Tol, L = PMe(3), 3a; R = t-Bu, L = PMe(3), 3b; R = t-Bu, L = SPh,4b). This suggests that the initially formed species is [Cp(RN)V]. When generated in situ, [Cp(RN)V] is active in the [2+2+2] cyclotrimerization of PhCCH (R = p-Tol, t-Bu) and PhCCPh (R = t-Bu). Furthermore, the data presented indicate a mechanism in which both [CpVMe](2)(mu-RN)(2) and [Cp(RN)V] originate from a common intermediate, vanadium(IV) imido species [Cp(RN)VMe].

In this contribution, we describe the preparation and single-crystal X-ray diffraction of a new building block for bimetallic solid state materials. X-ray diffraction data of these complexes indicate that (PPh4)(2)[Fe(CN)(5)imidazole]center dot 2H(2)O crystallizes in the triclinic space group P (1) over bar with a = 9.8108(15) angstrom, b = 11.1655(17) angstrom, c = 23.848(4) angstrom, alpha = 87.219(2)degrees, beta = 85.573(2)degrees, gamma = 70.729(2)degrees, and Z = 2, while its precursor Na-3[Fe(CN)(5)(en)]center dot 5H(2)O crystallizes in the monoclinic space group P2(1)/n with a = 8.3607(7) angstrom, b = 11.1624(9) angstrom, c = 17.4233(14) angstrom, beta = 90.1293(9)degrees, and Z = 4. Spectroscopic and magnetic properties of a series of bimetallic materials were obtained by reaction of the complex [Fe(CN)(5)imidazole](2-) with hydrated transition metal ions [M(H2O)(n)](2+) (M = Mn, Co, Zn; n = 4 or 6). The new bimetallic materials obtained are [Co(H2O)(2)][Fe(CN)(5)imidazole]center dot 2H(2)O (1), [Mn(CH3OH)(2)][Fe(CN)(5)imidazole] (2), Zn[Fe(CN)(5)imidazole]center dot H2O (3), and [Mn(bpy)][Fe(CN)(5)imidazole]center dot H2O (4). All of the complexes crystallize in the orthorhombic system. X-ray single-crystal analysis of the compounds identified the Imma space group with a = 7.3558(10) angstrom, b = 14.627(2) angstrom, c = 14.909(2) angstrom, and Z = 4 for 1; the P2(1)2(1)2(1) space group with a = 7.385(5) angstrom, b = 13.767(9) angstrom, c = 14.895(10) angstrom, and Z = 4 for 2; the Pnma space group with a = 13.783(2) angstrom, b = 7.167(11) angstrom, c = 12.599(2) angstrom, and Z = 4 for 3; and the Pnma space group with a = 13.192(3) angstrom, b = 7.224(16) angstrom, c = 22.294(5) angstrom, and Z = 4 for 4. The structures of 1, 2, and 4 consist of two-dimensional network layers containing, as the repeating unit, a cyclic tetramer [M2Fe2(CN)(4)] (M = Mn, Co). H bonding between the layers in the structure of 1 results in a quasi-three-dimensional networ

Four novel mononuclear coordination compounds namely: [Fe(Hthpy)(2)](SO(4))(1/2)center dot 3.5H(2)O 1, [Fe(Hthpy)(2)]NO(3)center dot 3H(2)O 2, [Fe(H(2)mthpy)(2)](CH(3)C(6)H(4)SO(3))(3)center dot CH(3)CH(2)OH 3 and [Fe(Hethpy)(ethpy)]center dot 8H(2)O 4, (H(2)thpy = pyridoxalthiosemicarbazone, H(2)mthpy = pyridoxal-4-methylthiosemicarbazone, H(2)ethpy = pyridoxal-4-ethylthiosemicarbazone), were synthesized in the absence or presence of organic base, Et(3)N and NH(3). Compounds 1 and 2 are monocationic, and were prepared using the singly deprotonated form of pyridoxalthiosemicarbazone. Both compounds crystallise in the monoclinic system, C2/c and P2(1)/c space group for 1 and 2, respectively. Complex 3 is tricationic, it is formed with neutral bis(ligand) complex and possesses an interesting 3D channel architecture, the unit cell is triclinic, P (1) over bar space group. For complex 4, the pH value plays an important role during its synthesis; 4 is neutral and crystallises with two inequivalent forms of the ligand: the singly and the doubly deprotonated chelate of H(2)ethpy, the unit cell is monoclinic, C2/c space group. Notably, in 1 and 4, there is an attractive infinite three dimensional hydrogen bonding network in the crystal lattice. Magnetic measurements of 1 and 4 revealed that a rather steep spin transition from the low spin to high spin Fe(III) states occurs above 300 K in the first heating step. This transition is accompanied by the elimination of solvate molecules and thus, stabilizes the high spin form due to the breaking of hydrogen bonding networks; compared to 2 and 3, which keep their low spin state up to 400 K.

The solvent dependence of the gelation properties, the thermotropic behavior, and the melting enthalpy of a series of enantiomerically pure cyclohexane-based bisamide and bisurea compounds are reported. The two series of gelators examined are related structurally with the intermolecular interactions responsible for gelation differing in a systematic manner through varying the length of the alkyl tail and the number of hydrogen bonding units present. The gelation properties of the compounds in decalin, DMSO, and 1-propanol were studied by FTIR spectroscopy and by comparison of the thermal stability of their gels as determired by dropping ball experiments and by differential scanning calorimetry (DSC). FTIR spectroscopy, Supported by the single-crystal X-ray diffraction of a3, indicates that the gelator molecules are aggregated through intermolecular hydrogen bonding in all of the solvents examined. The thermal stability of the gels in apolar and polar solvents was found to be dependent primarily on the relative strength of intermolecular hydrogen bonding and van der Waals interactions, respectively, compared with the strength of solvent-gelator interactions. The results of DSC indicated that the contribution of the difference in intergelator van der Waals interactions, compared with the gelator-solvent van der Waals and hydrogen bonding interactions, provided by the alkyl tail to the stability of the gel has a linear relationship with the number of methylene units in alkyl chains of length greater than six. In polar solvents, this contribution lies between 3.5 and 4.2 kJ mol(-1) per methylene unit, and in apolar solvents, it is 2.2 kJ mol(-1). The hydrogen bonding interactions were weaker in polar solvents and hence gelation occurred only where sufficient compensation was provided by intergelator van der Waals interactions. The results show that the direct relation of gelation strength to changes in solvent properties is not possible and more complex relationships

1,4,6-Trimethyl-N-(2-pyrrolidin-1-ylethyl)-1,4-diazepan-6-amine (HL) reacts with M(CH(2)Ph)(3)(THF)(3) to give the dibenzyl complexes (L)M(CH(2)Ph)(2) (M = SC, 1; M = Y, 2; M = La, 3). Compounds 1, 2, and 3 can be converted to their corresponding cationic monobenzyl species [(L)M(CH(2)Ph)](+) (M = Sc, Y and La) by reaction with [PhNMe(2)H][B(C(6)F(5))(4)]. Reaction of (L)Sc(CH(2)Ph)(2) with 2 equiv of phenylacetylene affords the monomeric dialkynyl complex (L)Sc(C CPh)(2) (4), while reactions of (L)M(CH(2)Ph)(2) (M = Y and La) give the dimeric dialkynyl complexes [(L)M(C CPh)(mu-C CPh)](2) (M = Y, 5; M = La, 6). The neutral complexes (2, 3, 5, and 6) and the cationic monobenzyl species [(L)M(CH(2)Ph)](+) (M = Y and La) are catalysts for the Z-selective linear head-to-head dimerization of phenylacetylenes. The cationic yttrium and the neutral lanthanum systems are the most effective catalysts in the series. The related scandium species show poor activity and selectivity.

Cationic titanium(IV) complexes with ansa-(eta(5)-cyclopentadienyl,eta(6)-arene) ligands were synthesized and characterized by X-ray crystallography. The strength of the metal-arene interaction in these systems was studied by variable-temperature NMR spectroscopy. Complexes with a C, bridge between the cyclopentadienyl and arene moieties feature hemilabile coordination behavior of the ligand and consequently are active ethylene trimerization catalysts. Reaction of the titanium(IV) dimethyl cations with CO results in conversion to the analogous cationic titanium(II) dicarbonyl species. Metal-to-ligand backdonation in these formally low-valent complexes gives rise to a strongly bonded, partially reduced arene moiety. In contrast to the eta(6)-arene coordination mode observed for titanium, the more electron-rich vanadium(V) cations [cyclopentadienyl-arene]V(N(i)Pr(2))(NC(6)H(4)-4-Me)+ feature eta(1)-arene binding, as determined by a crystallographic study. The three different metal-arene coordination modes that we experimentally observed model intermediates in the cycle for titanium-catalyzed ethylene trimerization. The nature of the metal-arene interaction in these systems was studied by DFT calculations.

Treatment of (eta(5)-C(5)H(4)C(2)H(4)NR)V(N-t-Bu)Me (R = Me, i-Pr) and CpV(N-p-Tol)(N-i-Pr(2))Me (Cp = eta(5)-C(5)H(5)) with B(C(6)F(5))(3) or [Ph(3)C][B(C(6)F(5))(4)] results in formation of the corresponding cations, [(eta(5)-C(5)H(4)C(2)H(4)NR)V(N-t-Bu)](+) and [CpV(N-p-Tol)(N-i-Pr(2))](+). The latter could also be generated as its N,N-dimethylaniline adduct by treatment of the methyl complex with [PhNMe(2)H][BAr(4)] (Ar = Ph, C(6)F(5)). Instead, the analogous reaction with the linked Cp-amido precursor results in protonation of the imido-nitrogen atom. Sequential cyclometalation of the amide substituents gave cationic imine complexes [(eta(5)-C(5)H(4)C(2)H(4)NCR'(2))V(NH-t-Bu)](+) (R'= H, Me) and methane. Reaction of cationic [(eta(5)-C(5)H(4)C(2)H(4)NR)V(N-t-Bu)](+) with olefins affords the corresponding olefin adducts, whereas treatment with 1 or 2 equiv of 2-butyne results in insertion of the alkyne into the vanadium-nitrogen single bond, affording the mono- and bis-insertion products [(eta(5)-C(5)H(4)C(2)H(4)N(i-Pr)C(2)Me(2))V(N-t-Bu)](+) and [(eta(5)-C(5)H(4)C(2)H(4)N(i-Pr)C(4)Me(4))V(N-t-Bu)](+). The same reaction with the half-sandwich compound [CpV(N-p-Tol)(N-i-Pr(2))](+) results in a paramagnetic compound that, upon alcoholysis, affords sec-butylidene-p-tolylamine, suggesting an initial [2+2] cycloaddition reaction. The difference in reactivity between the V-N bond versus the V=N bond was further studied using computational methods. Results were compared to the isoelectronic titanium system CpTi(NH)(NH(2)). These studies indicate that the kinetic product in each system is derived from a [2+2] cycloaddition reaction. For titanium, this was found as the thermodynamic product as well, whereas the insertion reaction was found to be thermodynamically more favorable in the case of vanadium.

The reactivity of three nitrogen-containing olefins with a cationic (alpha-diimine)Pd-Me species was studied to evaluate possibilities for their catalytic copolymerization with ethylene. Allyl dimethyl amine gives 1,2-insertion into the Pd-Me bond, but the resulting five-membered chelate is inert toward ethylene. Olefins bearing carbazole substituents insert to form three-membered chelate complexes after a chain-walking process. These chelates are reactive toward ethylene, and N-pentenylcarbazole was successfully copolymerized with ethylene to yield branched polyethylene copolymers bearing carbazole functionalities. The fluorescence of these copolymers is dependent on the amount of incorporated comonomer.

The crystal structure of the title compound, C(14)H(14)N(2)O, determined at 100 K, shows that the molecules are not planar in the solid state, in contrast to other diazene (azobenzene) derivatives. The dihedral angle between the planes of the two aromatic rings is 42.32 (7)degrees. The molecules are linked by intermolecular O-H center dot center dot center dot N hydrogen bonds, forming an infinite one-dimensional chain.

Scandium and lutetium benzyl complexes were prepared. Reaction of [ScCl3(THF)(3)] with potassium benzyl afforded [Sc(CH2Ph)(3)(THF)(3)] (1). In the solid state the coordination polyhedron is a distorted octahedron, in which the benzyl groups are located in a facial arrangement on one side of the molecule. One of the coordinated THF molecules could be removed by trituration with toluene and recrystallization of I from toluene to give [Sc(CH2Ph)(3)(THF)(2)] (2). A significantly different compound is obtained by starting the transmetalation reaction at -196 degrees C. Under these conditions the reaction of ScCl3 with KCH2Ph led to a two-dimensional coordination polymer of composition [Sc(CH2Ph)(5)K-2(THF)(3)]. (3), in which the scandium atom is surrounded by five benzyl groups in a trigonal bipyramidal fashion. Under the same reaction conditions, but using LuCl3 as the starting material, the analogue of 1, [Lu(CH2Ph)(3)(THF)(3)] (4), is obtained, which can also be induced to lose a coordinated THF ligand to give [Lu(CH2Ph)(3)(THF)(2)] (5).

Dithienylhexafluorocyclopentene with (R)- or (S)-N-phenylethylamide substituents formed rod-like and 0.2-1.0 mu m-thick plate-like crystals by sublimation; upon UV irradiation, the crystals bent concavely to the incident light and finally rolled crystals were obtained; the bent crystals were reconverted to flat crystals by visible light irradiation.

The crystal structure of the title compound, (C8H9NH3)(2)[NiCl2(H2O)(4)]Cl-2 center dot 2H(2)O, was determined at 100 K. The nickel(II) ion is surrounded by an octahedron in which four water molecules and two Cl atoms are coordinated. These freestanding octahedra form a hydrogen-bonding network with the ammonium group of the 2-phenylethylammonium cations and the solvent water molecules and chloride ions. This results in sheets of freestanding octahedra alternating with layers of organic material.

In the title compound, C8H14N22+.2Cl(-), the cation possesses a crystallographically imposed center of symmetry. The crystal packing is stabilized by intermolecular N-H...Cl hydrogen bonds and pi-pi stacking interactions.

The crystal structure of the title compound, C8H12N+center dot Cl-, determined at 100 K, is stabilized by intermolecular N-H center dot center dot center dot Cl hydrogen bonds. The benzene rings stack along the a axis, with a distance between the substituted C atom and the para C atom of a neighbouring molecule at (x + 1, y, z) of 3.600 (3) angstrom, which suggests that pi-pi stacking interactions also contribute to the stabilization.

The mechanism of the enantioselective 1,4-addition of Grignard reagents to alpha,beta-unsaturated carbonyl compounds promoted by copper complexes of chiral ferrocenyl diphosphines is explored through kinetic, spectroscopic, and electrochemical analysis. On the basis of these studies, a structure of the active catalyst is proposed. The roles of the solvent, copper halide, and the Grignard reagent have been examined. Kinetic studies support a reductive elimination as the rate-limiting step in which the chiral catalyst, the substrate, and the Grignard reagent are involved. The thermodynamic activation parameters were determined from the temperature dependence of the reaction rate. The putative active species and the catalytic cycle of the reaction are discussed.

The 6-amino-6-methyl-1,4-diazepine framework is a readily available neutral 6-electron ligand moiety, suitable to support cationic group 3 metal alkyl catalysts; it also provides convenient access to tri- and tetradentate monoanionic ligand derivatives.

New methodology is described to construct the olefinic bond in overcrowded alkenes using a hypervalent iodine reagent, and applied in the synthesis of molecular motors.

Surprisingly, a new motor with a tetrahydronaphthalene upper part rotates slower than the original molecular motor with a tetrahydrophenanthrene upper part despite decreased steric hindrance.

The crystal structure of hexagonal LuMnO3 at room temperature is isomorphous with YMnO3 and deviates in important details from early work. Mn is near the centre of its oxygen coordination environment. On the threefold axes, the apical O-Lu bonds have alternating long and short bond lengths, leading to ferroelectric behaviour. The sample studied was composed of almost equal volumes of inversion twins.

The hydrogen bonding properties, the nature of the tautomeric structure and dimerization of N-(2-carboxyphenyl)salicylidenimine 1 has been studied. The crystal and molecular structure of 1 has been determined by single-crystal X-ray diffraction analysis. This compound forms a dimer in the solid state, which is held together by two strong intermolecular O–H · · · O bridges [O(1) · · · O(2a) = 2.455(1) Å]. This dimeric structure is further stabilized by two intramolecular N–H · · · O hydrogen bonds [N(1) · · · O(1) = 2.654(1) and N(1) · · · O(2) = 2.663(1) Å]. In this way, an eight-membered pseudocycle is created. However, in methanol or acetonitrile solution, no dimerization was observed according to 1H-NMR, IR and UV measurements. It was also found that this compound exists as an intermediate form between a phenol-imine and an o-quinoid structure. In addition, a derivative soluble in chloroform, 2-[2-hydroxy-5-(2-butyl)benzylideneamino]benzoic acid 3, was examined for comparison.

The copper(II) catalyzed enantioselective 1,4-addition reactions of diethylzinc to cyclic enones in the presence of novel phosphorus amidite ligands, easily prepared from α,α,α',α'-tetraphenyl-2,2'-dimethyl-1,3-dioxolane-4,5-dimethanol (TADDOL) derivatives, resulted in e.e.s up to 71% for cyclohexenone and up to 62% for cyclopentenone. A remarkable enhancement of enantioselectivity was observed upon the addition of powdered molecular sieves to the reaction mixture.

One of the most striking features in many dinuclear metalloenzymes is the different coordination environments for the two metal centers. Nevertheless most of the reported enzyme mimics which are small molecule analogues for the active sites of these complicated enzymes, are based on symmetric dinucleating ligands. These ligands generally result in the formation of dinuclear coordination complexes with identical coordination environments for the metal centers. However, a limited number of non-symmetric dinuclear complexes is known to be formed by spontaneous self-assembly in solution.

One of the most striking features in many dinuclear metalloenzymes is the different coordination environments for the two metal centers. Nevertheless most of the reported enzyme mimics which are small molecule analogues for the active sites of these complicated enzymes, are based on symmetric dinucleating ligands. These ligands generally result in the formation of dinuclear coordination complexes with identical coordination environments for the metal centers. However, a limited number of non-symmetric dinuclear complexes is known to be formed by spontaneous self-assembly in solution.