Search results for "405"
showing 10 items of 3208 documents
Magnetostructural correlations in CuII−NC−WV linkage: the case of [CuII(diimine)]2+−[WV(CN)8]3− 0D assemblies
2009
International audience; We report on the syntheses, crystal structures, and magnetic properties of two cyano-bridged molecular assemblies: [CuII(phen)3]2{[CuII(phen)2]2[WV(CN)8]2}(ClO4)2·10H2O (phen = 1,10-phenanthroline) (1) and {[CuII(bpy)2]2[WV(CN)8]} {[CuII(bpy)2][WV(CN)8]}·4H2O (bpy = 2,2′-bipyridyl) (2). Compound 1 consists of cyano-bridged [CuII2WV2]2− molecular rectangles and isolated [CuII(phen)3]2+ complexes. The molecular structure of 2 reveals cyano-bridged trinuclear [CuII2WV]+ and dinuclear [CuIIWV]− ions. Magnetic interactions in 1 are interpreted in terms of the model of a tetranuclear moiety consisting of two ferromagnetic CuII−NC−WV units (J1 = +39(4) cm−1) interacting ant…
Nature of (C5Me5)2Mo2O5in water–methanol at pH 0–14. On the existence of (C5Me5)MoO2(OH) and (C5Me5)MoO2+: a stopped-flow kinetic analysis
2002
A stopped-flow analysis of compound Cp*2Mo2O5 (Cp* = η5-C5Me5) in 20% MeOH–H2O over the pH range 0–14 has provided the speciation of this molecule as well as the rate and mechanism of interconversion between the various species that are present in solution. The compound is a strong electrolyte in this solvent combination, producing the Cp*MoO2+ and Cp*MoO3− ions in equilibrium with a small amount of Cp*MoO2(OH), the latter attaining ca. 15% relative amount at pH 4. At low pH ( 6. The acid dissociation constant of Cp*MoO2(OH) has been measured directly (pK = 3.65 ± 0.02) while the pK for the protonation equilibrium leading to Cp*MoO3H2+ is estimated as 5. The prevalent pathway at high pH i…
Influence of the solvent and R groups on the structure of (carboranyl)R2PI2 compounds in solution. Crystal structure of the first iodophosphonium sal…
2008
The influence of the electron-donor or electron-acceptor capacity of the R groups (R = (i)Pr, Ph, Et) and the solvent on the molecular geometry in solution of adducts of carboranylphosphanes [(carboranyl)(i)Pr2P, (carboranyl)Ph2P and (carboranyl)Et2P] with I2 in 1 : 1 ratios, has been studied in detail by 31P{1H} and 11B{1H} NMR spectroscopies. The more electron-accepting Ph groups make the (carboranyl)Ph2P less nucleophilic, thus stabilizing the I2 encapsulated neutral biscarboranylphosphane-diiodine adducts in solution, such as (carboranyl)Ph2PI-IPPh2(carboranyl), generating P---I-I---P motifs. Even in a polar solvent, such as EtOH, the arrangement is preserved. The expected basicity of t…
The [Pd(bipy)]2+ “merry-go-round”: Insights into the lability of the Pd–N bond
2009
Abstract Two tripods (1 and 2) featuring pyrimidinyl pendant arms have been synthesized from 5-(1H-pyrazol-3-yl)-pyrimidine (5) and 1,3,5-tribromomethylbenzene derivatives. Reaction with three equivalents of [Pd(bipy)](NO3)2 to form a macrotricycle closed by palladium coordination unexpectedly afforded the mononuclear species [Pd(1)(bipy)]2+ and [Pd(2)(bipy)]2+. These complexes show fluxional behavior on the 1H NMR timescale, the [Pd(bipy)]2+ fragment hopping between the pyrimidinyl coordinating moieties. The ΔGc‡’s estimated by the coalescence method are temperature independent, which means that ΔSc‡ = 0. This indicates that the “merry-go-round” process of [Pd(bipy)]2+ occurs intramolecula…
Structural and metallo selectivity in the assembly of [2 × 2] grid-type metallosupramolecular species: Mechanisms and kinetic control
2011
An unsymmetrical bis(tridentate) ligand LH in which one binding site can be readily deprotonated forms a kinetically inert [Co(III)L(2)](+) complex which can be used as a "corner" species for the "Coupe du Roi" assembly of trans,trans-[Co(2)M(2)L(4)](6+) metallogrids (M = Fe(II), Co(II), Cu(II), Zn(II)). In the mixed Co(III)/Co(II) species, the oxidation states appear to be localised. In solution, the ligand LH forms octacationic, homometallic [2 × 2] grids with the individual labile metal ions Fe(II), Co(II), Cu(II), Zn(II), seemingly as mixtures of all possible isomers arising from the unsymmetrical nature of the ligand. In the solid state, however, [Zn(4)L(4)](CF(3)SO(3))(8)·4CH(3)CN cry…
Cytosine Nucleobase Ligand: A Suitable Choice for Modulating Magnetic Anisotropy in Tetrahedrally Coordinated Mononuclear CoII Compounds
2017
A family of tetrahedral mononuclear CoII complexes with the cytosine nucleobase ligand is used as the playground for an in-depth study of the effects that the nature of the ligand, as well as their noninnocent distortions on the Co(II) environment, may have on the slow magnetic relaxation effects. Hence, those compounds with greater distortion from the ideal tetrahedral geometry showed a larger-magnitude axial magnetic anisotropy (D) together with a high rhombicity factor (E/D), and thus, slow magnetic relaxation effects also appear. In turn, the more symmetric compound possesses a much smaller value of the D parameter and, consequently, lacks single-ion magnet behavior.
Supramolecular Assembly of Organophosphonate Diesters Using Paddle-Wheel Complexes: First Examples in Porphyrin Series
2014
The reactions of dicopper tetrapivalate complex Cu2(μ-OOC-t-Bu)4(NCMe)2 (1) with triphenylphosphine oxide and diethyl phosphite allow paddle-wheel (PW) copper(II) complexes with phosphorus-containing axial ligands (2, 3) to be obtained. When meso-bis(diethoxyphosphoryl)porphyrins 4M were employed in this ligand exchange reaction, a series of one-dimensional (1D) homo- and heterometallic coordination polymers 5M composed of PW subunits and organophosphonate diesters were prepared and characterized by means of single crystal X-ray analysis. Planar porphyrinate 4Pd and nonplanar metalloporphyrinates 4Cu and 4Ni proved to be appropriate molecular structural blocks for assembly of coordination p…
Asymmetric Vinylogous Mannich-Type Addition of α,α-Dicyanoalkenes to α-Fluoroalkyl Sulfinyl Imines
2018
Abstract. The asymmetric vinylogous Mannich reaction (AVMR) of alfa,alfa-dicyanoalkenes with alfa-fluoroalkyl sulfinyl imines has been successfully accomplished. This transformation is unprecedented with fluorinated imines at the same time as the use of dicyanoalkenes in AVMR has been scarcely reported. Several fluorinated sulfinyl imines are compatible with the process, which gaves access to a family of chiral fluorinated amines with excellent level of stereocontrol. Interestingly, the selectivity found in our protocol is reverse to that encountered in analogous AVMR previously reported. Additionally, the synthetic applicability of the addition products has been exemplified with several tr…
Isomerization of perchlorohexatriene in three consecutive rearrangements to perchloro-2-vinylbutadiene
2017
Perchlorohexatriene isomerizes in three subsequent rearrangements to perchloro-2-vinylbutadiene. A radical-induced Z-E-equilibration of linear perchlorohexatrienes is followed by cyclization to a methylenecyclopentene. Under flash-vacuum pyrolysis conditions, a ring contraction to 1,2-dimethylenecyclobutane occurs. In the condensed phase, a radical-induced ring opening generates the branched perchloro-vinylbutadiene. All compounds are converted to hexachlorobenzene, but only at very high temperatures.
Synthesis and solid state structure for a series of poly(1-pyrrolylmethyl)benzene derivatives. Control of the interplaying π–π and C–H⋯π interactions?
2006
The syntheses of new hexa- and 1,2,4,5-tetra-1-pyrrolylmethyl-benzene (1 and 2, respectively) compounds and their crystal structures, along with those for the related disubstituted o-, m- and p-di-1-pyrrolylmethyl-benzene (3–5) derivatives are reported. The arrangements of molecules in the 1-D structure for 2–5 are controlled by the interplay of two different weak interactions: π–π and C–H⋯π (Ph) interactions. The absence of such interactions in the packing of 1 seems to be related to the arrangement of the pyrrolylmethyl arms with respect to the benzene core, which prevents the π cloud of the aromatic ring to be part of any intermolecular interaction. In addition, C–H⋯π (pyrrolyl) interact…