Dimers In Solid State Research Articles

The 1:1 co-crystallization of enantiomers of an arene-tethered and ortho-metallated N-heterocyclic carbene ruthenium(II) half-sandwich complex: Synthesis, structural characterization and theoretical study

The reaction of [RuCl 2( p-cymene)] 2 with in situ deprotonated NHC precursor 1,3-bis(biphenyl-2-yl)imidazolinium chloride was carried out in p-xylene at 140 °C to produce ▪ 2, in which the NHC moiety acts as a tridentate C,C′,C′′-ligand. The complex 2 was characterized by NMR spectroscopy and X-ray crystallographic study. Crystallographic analysis combined with computational study regarding the compound, 1-[η 6-(2′-biphenyl)]-3-[2-phenyl-1,2-phenylene]imidazolidin-2-ylidenechlororuthenium(II), 2, reveals that its metal-centered enantiomers are co-crystallized in 1:1 ratio and NHC frame possessing a tridentate coordination mode consists of σ-donation of the carbene carbon, η 6-arene tethering of terminal biaryl and η 1-coordination of the biphenyl ring at 2-position. Enantiomers of the complex are packed as asymmetric dimers in solid state formed by C–H⋯Cl type weak H-bonds and C–H⋯π type interactions giving rise to asymmetric chains. Both interactions serve to stabilization of the extended structure.

Template-Controlled Face-to-Face Stacking of Olefinic and Aromatic Carboxylic Acids in the Solid State

A rigid 1,8-dipyridylnaphthalene template for supramolecular organization of unsaturated dicarboxylic acids in the solid state has been developed. Self-assembly of the template and aromatic dicarboxylic acids generates nondistorted paracyclophane and pyridinophane architectures with perfectly superimposed pi-systems. The dipyridyl template can be used to promote stereoselective solid-state dimerization of olefinic dicarboxylic acids.

Resonance Stabilized Bisdiselenazolyls as Neutral Radical Conductors

An efficient and versatile synthetic route to resonance stabilized bisselenathiazolyl and bisdiselenazolyl radicals 3 and 4 is described. Structural analysis of 3 and 4 confirm that lattice and pi-delocalization energies are sufficient to offset solid-state dimerization of the radicals and that the two selenium-containing radicals are isostructural with the all-sulfur based system 1. Variable temperature conductivity measurements indicate that sequential replacement of sulfur by selenium leads to a progressive increase in conductivity and reduction in thermal activation energy.

Equilibria and Structure of the Lanthanide(III)-2-hydroxy-1,3-diaminopropane-N,N,N‘,N‘-tetraacetate Complexes: Formation of Alkoxo-Bridged Dimers in Solid State and Solution

The complex formed between 1,3-diamino-2-hydroxypropane-N,N,N',N'-tetraacetic acid (H4L-OH) and Nd3+ at pH 7.5 was found to be a dinuclear dimer in the solid state by X-ray crystallography. In the complex K4[Nd2(L-O)2(H2O)2].14H2O each ligand is coordinated to both Nd3+ atoms with an iminodiacetate group (the Nd3+-Nd3+ distance is 3.9283(8) A). The alcoholic OH groups are deprotonated, and the alkoxo oxygens are coordinated to both Nd3+ in a bridging position. The Nd3+ ions are nine-coordinated with one water molecule per Nd(III) ion in the inner sphere. The complex K4[Nd2(L-O)2(H2O)2].14H2O has an inversion center, and the space group is P1. Two of the K+ counterions are six-coordinated, while the other two K+ ions are eight-coordinated; polar polymeric water-K+ layers are formed between the apolar ligand layers via the bridging water molecules. The dinuclear dimer complexes are also present in aqueous solution. The proton relaxivities of the Gd3+ complex decrease with the increase of pH, and at pH > 6, the low relaxivity values indicate the probable absence of H2O in the inner sphere and the predominance of the eight-coordinated dimer species [Gd2(L-O)2].4- The results of ESI-TOF MS studies of the complexes of La3+, Nd3+, and Lu3+ proved the formation of dinuclear dimers in dilute (0.25 mM) solutions. pH-potentiometric titrations indicate the formation of complexes with 1:1 (Ln(L-OH)-, Ln(HL-OH), and Ln2(L-O)24-) and 2:1 (Ln2(L-O)+) metal-to-ligand ratios. The stability constants of the Ln(L-OH)- species increase from La3+ (log K = 10.19) to Lu3+ (log K = 14.08). The alcoholic OH group of the Ln(L-OH)- species dissociates at unusually low pH values. The pH range of dissociation shifts to lower and lower pH's with the increasing atomic number of the lanthanides. This pH range is about 4-7 for the La3+ complex and 1-4 for the Lu3+ complex. The results of 1D and 2D 1H and 13C NMR studies of the La3+ complex, the number and multiplicity of signals, and the values of coupling constants are in agreement with the dinuclear dimer structure of the complex in solution.

The structural characteristics of organozinc complexes incorporating N,N′-bidentate ligands

Dimethylzinc reacts with an excess of N-2-pyridylaniline 6 to give the homoleptic species, Zn[PhN(2-C(5)H(4)N)](2) 8. Single crystal X-ray diffraction reveals a solid-state dimer based on an 8-membered (NCNZn)(2) core motif. Zn[CyN(2-C(5)H(4)N)]Me (Cy =c-C(6)H(11)) 10, prepared by the combination of ZnMe(2) with the corresponding cyclohexyl-substituted pyridylamine, is also dimeric in the solid state but reveals a central (ZnN)(2) metallacycle. Employment of (p-Tol)NH(2-C(5)H(4)N)(p-Tol = 4-MeC(6)H(4)) 11 yielded the tris(zinc) adduct Zn(3)[(p-Tol)N(2-C(5)H(4)N)](4)Me(2) 12, which incorporates a central chiral molecule of 'Zn[(p-Tol)N(2-C(5)H(4)N)](2)' 12a, that bridges two 'Zn[(p-Tol)N(2-C(5)H(4)N)]Me' 12b units. A similar trimetallic structure is noted when the pyridylaniline substrate 11 is replaced with the bicyclic guanidine 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH), affording Zn(3)(hpp)(4)Me(2) 13. Spectroscopic studies point to retention of the solid-state structure of in hydrocarbon solution. Reaction of 13 with dimesityl borinic acid, Mes(2)BOH (Mes = mesityl), affords Zn(3)(hpp)(4)(OBMes(2))(2) 14 in which the trimetallic core is retained. This reactivity is in contrast to the closely related reaction of dimeric Zn[Me(2)NC[N(i)Pr](2)]Me 15 with Mes(2)BOH, which yielded Zn[Me(2)NC[N(i)Pr](2)][OBMes(2)].Me(2)NC[N(i)Pr][NH(i)Pr] 16 as a result of protonation at the guanidine ligand in addition to the Zn-Me bond.

Synthesis and crystal structures of mono-potassium salts of calix[4]arene and p- tert-butylcalix[4]arene

The mono-potassium salts obtained by the action of K 2CO 3 on calix[4]arene and p- tert-butylcalix[4]arene are found to possess very similar solid-state dimer structures that differ only in the presence of a cation–π interaction in the former. The mono-potassium salt obtained by the action of KOSiMe 3 on p- tert-butylcalix[4]arene, on the other hand, is found to possess a monomeric structure.

Crystal structure of a novel synthetic inhibitor of HIV-1 protease

The crystal structure of a novel non-peptidic HIV-1 protease inhibitor derived by simple solid-state dimerization of 4-aryl-1,4-dihydropyridines, reveals a strained central cage and the conformation of its phenyl, benzyl, and hydroxymethylene substituents. The polycyclic cage includes two nearly flat cyclobutane rings and four fused piperidine rings in boat conformations. The cage geometry reveals two unexpected features, namely marked distortions of the valence angles in every second piperidine and a shortening of one of the cyclobutane bonds. The molecule displays exact centrosymmetry, but the central cage and the hydroxymethylene substituents also approximate the C 2-symmetry of the target enzyme. The two independent hydroxyl groups are involved in intermolecular hydrogen bonding, one as a donor, the other as an acceptor. The disposition of the hydroxyl groups in the molecular framework is compatible with the dual role of the inhibitor in the active-site cavity of HIV-1 protease, whereby one OH group is hydrogen-bonded to the catalytic aspartates, whereas another one provides an interface to the locked flaps of the enzyme.

Solid-state photodimerization of cholest-4-en-3-one.

Crystalline cholest-4-en-3-one undergoes solid-state dimerization by UV radiation to give two ring A - ring A connected dimers. No dimerization occurs in solution. The first dimer, characterized by a cyclobutane ring, is formed by connection of C-2 and C-3 of a moiety with C-5' and C-6' of another moiety, respectively. The latter dimer has a six-membered ketal ring formed by connection of C-2 with C-5' and of O, linked to C-3, with C-3'. The structures have been determined by spectroscopic means. X-ray analysis of title compound evidences the proximity of the axial H-2 of a molecule to the C-4' of a molecule in the upper layer. The transfer of the hydrogen and the connection between C-2 and C-5' might be the driving force of dimerization.

Porous Siloxane Linked Phenylacetylene Nitrile Silver Salts from Solid State Dimerization and Low Polymerization

Three 3-fold symmetric rigid backbone phenylacetylene nitrile molecules have been prepared to which one to six hydroxy side chains have been attached. These molecules were cocrystallized with silver(I) trifluoromethanesulfonate (triflate) to form microcrystalline porous solids. X-ray powder data show that all three crystal structures are isotypic to the crystal structures found in previous single crystal studies on related systems. Structural models based on these earlier single crystal structures have theoretical powder patterns in reasonable agreement with the experimentally observed patterns. These crystalline materials were allowed to react with silyl triflates. 1H NMR and X-ray powder studies show that the silyl triflate groups react with the alcohol terminated side chains to form siloxane linkages with retention of the initial crystal structure. In the case of 1,3,5-tris(4-((4-cyanophenyl)ethynyl)-2-((4-hydroxybutoxy)methyl)phenylethynyl)benzene, a phenylacetylene nitrile molecule with three alcohol...

Crystal structures of dimeric manganese(III) complexes of tetradentate Schiff-base ligands with ancillary axial donors

[ N,N′-Ethylenebis(salicylideneaminato)]manganese(III) benzoate ([Mn(salen)(O 2CC 6H 5)] crystallized to form a solid-state dimer in which the Mn(salen) moiety is linked to its neighbor by two shared phenolate oxygen atoms, in striking contrast to the linear polymeric structure formed with bridging acetate ligands. A substantial cavity between the two manganese atoms was then produced by the weak coordination of the phenolate oxygen to the neighboring manganese bearing benzoate in a monodentate mode.

Effect of carbonate salts on the kinetics of acid-catalyzed dimerization of adefovir dipivoxil.

The chemical stability and product(s) distribution of adefovir dipivoxil (ADV) was examined in the presence of soluble and insoluble carbonate salts. Chemical stability of ADV in the solid state at 60 degrees C/30% RH was examined. Stability was also examined in the presence of excess formaldehyde vapor at 23 degrees C/53% RH. ADV and its degradation product(s) were determined by reverse phase HPLC. Addition of aqueous soluble carbonate salts, such as sodium carbonate, compromised the stability of ADV in solid state. However, aqueous insoluble carbonates, such as calcium carbonate and magnesium carbonate, enhanced the stability of ADV as compared to the control formulation. Pivalic acid, a degradation product of ADV, was shown to accelerate the degradation rate of ADV in solid state. The de-stabilizing effect of this acid on ADV stability was diminished in the presence of magnesium carbonate. Pivalic acid also increased the rate at which ADV dimers were formed in the presence of formaldehyde vapor. Addition of insoluble carbonates reduced the rate of formaldehyde-catalyzed dimerization of ADV. Addition of insoluble carbonate salts decreased the rate of degradation of ADV by minimizing the extent of formaldehyde-catalyzed dimerization in solid state.

Phosphine-substituted porphyrins as supramolecular building blocks

A route to alkyne-phosphine-substituted metalloporphyrins is presented. The X-ray structure of the methanol adduct of a diphenylphosphine Zn(II) porphyrin reveals solid state dimerisation accompanied by proton transfer from coordinated methanol to phosphine in a process reminiscent of carbonic anhydrase. The ability of the phosphine-substituted porphyrins to form non-covalent arrays with a Ru(II) porphyrin was explored using 1H/31P NMR and UV/vis spectroscopy as well as MALDI-TOF mass spectrometry.

A Theoretical Study of the Pressure-Induced Dimerization of C60 Fullerene

We present a theoretical study of the solid-state dimerization of C60 fullerene, which occurs under pressure through [2+2] cycloaddition of double bonds. The possible crystal packings of (C60)2 molecules are calculated by minimization of the lattice energy with a bond charge intermolecular potential model proved successful in the previous C60 studies. The set of dimer lattices that were derived from the fcc lattice was used to construct the initial structures for minimization. The final structures found this way, although belonging to various space-group symmetries, retain approximately fcc arrangement of the constituting C60 cages. On the other hand, the structure obtained from the dimer motif observed in the o-dichlorobenzene solvate of (C60)2 exhibits a hcp-like C60 arrangement. The more energetically stable hcp-type dimer seems not to form due to the high potential barrier separating the fcc and hcp structures. The relative stability of the predicted structures changes significantly under pressure. Some of the dimer structures are remarkably similar to the respective theoretical monomeric and polymeric C60 structures studied previously. On this basis we propose that the respective structures are connected states in the possible conversion paths from pristine C60 to its various polymerization products. One of the dimer structures is geometrically favorable for the formation of the higher C60 chain oligomers as well as of the infinite polymer.

Monte-Carlo simulations of chemical reactions in molecular crystals

Chemical reactions in molecular crystals, yielding new entities (dimers, trimers,…, polymers) in the original structure, are simulated for the first time by stochastic Monte Carlo methods. The results are compared with those obtained by deterministic methods. They show that numerical simulation is a tool for understanding the evolution of these mixed systems. They are in kinetic and not in thermodynamic control. Reactive site distributions, x-ray diffuse scattering, and chain length distributions can be simulated. Comparisons are made with deterministic models and experimental results obtained in the case of the solid state dimerization of cinnamic acid in the beta phase and in the case of the solid state polymerization of diacetylenes.

Structure and conformation of tri- O-acetyl-D-glucal dimer in solid state and in solution

X-Ray crystallography and 1 H NMR spectroscopy indicate that the conformations of both rings A and B and the relative orientation of the rings in the C-linked disaccharide 1,3,4,6-tetra- O -acetyl-2- C -(4,6-di- O -acetyl-2,3-dideoxy-α-D- erythro -hex-2- enopyranosyl)-2-deoxy-β-D-glucopyranose in solution are virtually identical to the crystalline structure.

Ab Initio Studies of the Contrasting Butadiene Cheletropic and Diels−Alder Cycloaddition Reactivities Observed for “Carbenic” Phosphorus (Phosphenium) and Arsenic (Arsenium) Cations

Quantum-chemical studies (UMP2/6-311G*//UHF/6-311G*) on a series of phosphenium and arsenium derivatives confirm singlet ground states and reveal an unexpected model for the bonding in their lowest triplet state. Models of the novel solid-state dimer structures that are experimentally observed for some arsolanium cations reveal large positive dimerization energies (P, 3, 277 kJ/mol; As, 7, 207 kJ/mol), implying that the observed dimers are imposed by crystal-packing phenomena. The surprising contrast observed in the butadiene cycloaddition reactivities for phosphenium and arsenium cations are understood in terms of the calculated absolute energies of the observed structural arrangements for the cycloadducts in each case; the cheletropic adduct 4 is 52 kJ/mol more stable than the Diels−Alder adduct for the phospholanium cation, while in the case of the arsolanium cation the Diels−Alder adduct 9 is favored by 59 kJ/mol.

Modeling of fluorescence quantum yields of supported dyes Aluminium carboxyphthalocyanine on cellulose

Aggregation equilibrium and the fluorescence properties of hydroxoaluminium tricarboxymonoamidephthalocyanine adsorbed on microgranular cellulose have been studied at different dye loadings. Up to a concentration of nearly 3 × 10−6 mol phthalocyanine (g cellulose)−1 diffuse reflectance spectra may be interpreted on the basis of a simple monomer–dimer equilibrium. Monomer and dimer spectra are similar to the spectra of the monomeric dye in solution. The solid-state dimer spectrum is red-shifted with respect to that of the monomer and this is attributed to the coplanarity of dimers. Fluorescence spectra and quantum yields show typical effects of re-absorption and re-emission of light. In particular, the observed fluorescence quantum yields depend on concentration and span the range 0.29–0.07. To account for these effects as well as the effect of aggregation on fluorescence quantum yields and to obtain corrected fluorescence spectra a model based on the Kubelka–Munk theory of diffuse reflectance is developed. The application of this model to the case under study yields a true fluorescence quantum yield ϕ = 0.46 ± 0.02 in the whole range of concentrations, which is slightly higher than the value found for the same dye in dimethyl sulfoxide solution.

Alane– and gallane–sulfur donor chemistry: synthesis of AlH3·NMe(CH2CH2)2S, {AlH2[µ-N(CH2CH2)2S]}2and MH(SCH2CH2NEt2)2(M = Al or Ga)

Reaction of N-methylthiomorpholine hydroiodide with LiAlH4 in OEt2 yielded the Lewis-base adduct of alane, AlH3·NMe(CH2CH2)2S 1, which is monomeric in benzene as the N-donor species. Thiomorpholine with H3Al·NMe3 also in OEt2 afforded the metallated species {AlH2[µ-N(CH2CH2)2S]}22; in the solid-state dimers arising from bridging amido centres are weakly associated via intermolecular Al ⋯ S interactions at 3.22(3)A. Treatment of 2-diethylaminoethanethiol hydrochloride with LiMH4(M = Al or Ga) in OEt2 or tetrahydrofuran generated the five-co-ordinate species MH(SCH2CH2NEt2)2(M = Al 3 or Ga 4), authenticated by X-ray crystallography as isostructural, chiral five-co-ordinate species in the solid, the N-donor groups occupying apical positions of trigonal-bipyramidal metal centres.

Photodimerization of α,ω-diarylbutadienes. I. Crystal and molecular structures of trans,trans-1-(2′-methoxyphenyl)-4-(4′-nitrophenyl)-1,3-butadiene and its photodimer

X-ray crystallographic studies showed that orange crystals of the title diarylbutadiene 1 undergo a topochemically controlled [2 + 2] photocycloaddition when exposed to visible light to produce the cyclobutane dimer 2, which is yellow. The conformation of molecule 1 is planar with a maximum deviation from an all-atom mean plane, including substituents, of ≤ 0.28 Å. The crystal structure of 1 displays pairs of molecules packed in a head-to-tail arrangement across inversion centers that allows π orbital overlap between nearest neighbor butadiene double bonds. Intermolecular distances and angles between these photoreactive atoms are [Formula: see text], 3.517(2) Å and [Formula: see text], 92.0(2)°; and the dihedral angle between the plane of the four photoreactive atoms and the plane of the butadiene in one molecule is 72.9°. Molecule 2 lies on a crystallographic inversion centre, which constrains the cyclobutane ring to absolute planarity with C—C distances of 1.558(2) and 1.569(2) Å and C—C—C angle of 90.61(1)°. The dihedral angles between the cyclobutane ring and the two phenyl rings are 81.2° for the p-nitrophenyl and 54.0° for the o-methoxyphenyl. From the crystal structures of 1 and 2, the displacement of each of the four photoreactive atoms during the solid-state dimerization can be estimated to be ca. 1.00 Å. Crystals of 1 are orthorhombic, Pbca, a = 7.471(1), b = 14.283(1), c = 25.940(1) Å, Z = 8, and those of 2 are monoclinic, P21/c, a = 11.5396(5), b = 16.129(1), c = 7.9035(3) Å, β = 90.264(3)°, Z = 4. Both structures were solved by direct methods and refined to final values of R = 0.0481 and 0.0512 using 2788 and 2333 observed (I > 3 σ(I)) reflections, for 1 and 2, respectively.

Probing polymorphism and reactivity in the organic solid state using 13C NMR spectroscopy: Studies of p-Formyl- trans-cinnamic acid

p-Formyl- trans-cinnamic acid (p-FCA) is known to exist in two different crystal phases (denoted β and γ). When crystals of the β phase of p-FCA are exposed to UV radiation, a solid state dimerization reaction occurs to produce 4,4′-diformyl-β-truxinic acid. In contrast, crystals of the γ phase of p-FCA are photostable. It is shown in this paper that high resolution solid state 13C NMR spectroscopy is a sensitive technique for distinguishing the β and γ phases of p-FCA, and can be used to investigate, in detail, the chemical transformation that occurs upon UV irradiation of the β phase. Specifically, the 13C NMR spectra presented here were recorded using the TOSS (total suppression of sidebands) pulse sequence; this is based upon the standard 13C CPMAS (cross polarization/magic angle sample spinning/high power 1H decoupling) method, but has the additional feature that all orders of spinning sidebands are eliminated from the spectrum. The photoproduct obtained from UV irradiation of β-p-FCA contains a significant noncrystalline component (assessed via powder X-ray diffraction), and our NMR studies suggest that this noncrystalline component of the photoproduct contains some amount of the γ phase of the monomer p-FCA. A mechanism is proposed to explain the fact that UV irradiation of β-p-FCA can generate, in addition to the expected photodimer, an impurity amount of the γ phase of p-FCA.