Crystal structures and magnetic properties of two low-dimensional materials constructed from [Mn(III)(salen)H2O]+ and [M(CN)8](3-/4-) (M = Mo or W) precursors

The syntheses, X-ray structures, and magnetic behaviors of two new cyano-bridged assemblies, the molecular [Mn(III)(salen)H2O]3[W(V)(CN)8].H2O (1) and one-dimensional [Mn(salen)(H2O)2]2[[Mn(salen)(H2O)][Mn(salen)]2[Mo(CN)(8)]].0.5ClO4.0.5OH.4.5H2O (2), are presented. Compound 1 crystallizes in the monoclinic system, has space group P2(1)/c, and has unit cell constants a = 13.7210(2) A, b = 20.6840(4) A, c = 20.6370(2) A, and Z = 4. Compound 2 crystallizes in the triclinic system, has space group P, and has unit cell dimensions a = 18.428(4) A, b = 18.521(3) A, c = 18.567(4) A, and Z = 2. The structure of 1 consists of the asymmetric V-shaped Mn-NC-W-NC-Mn-O(phenolate)-Mn molecules, where W(V) coordinates with [Mn(salen)H2O] and singly phenolate-bridged [Mn(salen)H2O]2 moieties through the neighboring cyano bridges. The [W(V)(CN)8]3- ion displays distorted square-antiprism geometry. The structure of 2 consists of the cyano-bridged [Mn3(III)Mo(IV)]n- repeating units linked by double phenolate bridges into one-dimensional zigzag chains. The Mn(III) centers are bound to Mo(IV) of square-antiprism geometry through the neighboring cyano bridges. The magnetic studies of 1 reveal the antiferromagnetic intramolecular interactions through the CN and phenolate bridges and the relatively weak intermolecular interactions. Compound 1 becomes antiferromagnetically ordered below TN = 4.6 K. The presence of the magnetic anisotropy is documented with the MH measurements carried out for both polycrystalline and single-crystal samples. At T = 1.9 K, the spin-flop transition is observed in the field of 18 kOe applied parallel to the bc plane, which is the easy plane of magnetization. Field dependence of magnetization of 1 shows field-induced metamagnetic behavior from the antiferromagnetic ground state of ST = 3/2 to the state of ST = 5/2. The magnetic properties of 2 indicate a weak antiferromagnetic interaction between Mn(III) centers in double-phenolate-bridged [Mn(III)(salen)]2 dinuclear subunits and a very weak ferromagnetic interaction between them through the diamagnetic [Mo(IV)(CN)8]4- spacer.     

The first structurally characterized nonorganometallic titanium(III) alkoxo-bridged dinuclear complexes

The reaction of [Ti4(OMe)14Cl2] (1) with an excess of AlMe3 gave the cocrystallite [Ti2(mu-OMe)2(mu-Cl)Cl3(thf)3].[Ti2(mu-OMe)3Cl3(thf)3] (2.3) species in a 1:1 ratio. Similar to 2, [Ti2(mu-OEt)2(mu-Cl)Cl3-(thf)3] (4) was obtained in the reaction of an equimolar mixture of TiCl4 and Ti(OEt)4 with Al/AlMe3. The short distance [2.543(1)av A in 2.3 and 2.599(1) A in 4] between "Ti(+3)" atoms, their diamagnetism, and ELF analysis indicate the presence of a Ti-Ti bond.     

Cucurbit[6]uril pseudorotaxanes: distinctive gas-phase dissociation and reactivity

Cucurbit[6]uril forms a doubly charged complex with 1,4-butanediammonium cation that is observed using electrospray ionization Fourier transform mass spectrometry. Such 1:1 complexes are not observed for the smaller cucurbit[5]uril, which forms a 2:1 ammonium:cucurbituril complex instead. The 1:1 complex with cucurbit[6]uril is difficult to fragment via collisional activation; when it does fragment, both breakup of the cucurbituril cage and loss of the amine are observed. Further, the complex reacts with tert-butylamine via slow adduction. In contrast, nonrotaxane analogues (such as doubly charged 2:1 complexes of either protonated 1,4-butanediamine or protonated ethylenediamine with cucurbit[6]uril) fragment via easy loss of the intact amine upon collisional activation and react with tert-butylamine via rapid displacement of the original amine. On the basis of stoichiometry, fragmentation behavior, and reactivity, we conclude that the doubly charged complex of cucurbit[6]uril with 1,4-butanediammonium is a gas-phase pseudorotaxane.     

Selection of reversed-phase liquid chromatographic columns with diverse selectivity towards the potential separation of impurities in drugs

To select appropriate stationary phases from the continuously expanding supply of potentially suitable HPLC columns, the properties of 28 frequently applied stationary phases were determined by measuring several chromatographic parameters. From these results, based on chromatographic expertise, eight stationary phases with different properties and selectivities were selected. The aim of this study is to apply chemometric tools to evaluate the initially selected set of columns, i.e. a more systematic approach for making such a selection is examined. Starting from the information obtained on the 28 stationary phases, the re-evaluation was performed independently based on the chemometric techniques Pareto-optimality, principal component analysis (PCA), and Derringer's desirability functions. The aim was to select a set of efficient columns exhibiting large selectivity differences. The chemometrically selected stationary phases were divided in groups based on hydrophobicity, a critical retention-determining property in reversed-phase chromatography. This allowed to further reducing the selection to three columns. It is demonstrated that the selection by the chemometric approaches in general is fairly comparable with the initial selection.     

Analysis of First-Order Reactions with Distributed Parameters

Simple methods of analysis of first-order kinetic processes controlled by distributions of parameters (activation energies and/or frequency factors) are presented. Both the isothermal and nonisothermal regimes are considered. The procedures make use of numerically calculated time derivatives of the concentrations of decaying species (reactants in the case of chemical reactions). They do not require any adjustable initial or boundary values of parameters (like concentration at the infinite time) being thus more accurate and reliable than earlier methods in which kinetic parameters were determined from the concentration, and not from its time derivative. The methods were successfully employed in analysis of the thermally driven cis–trans isomerization of a photochromic crown ether containing the azobenzene moiety incorporated in the crown.     

Synthesis of mesoporous carbons using ordered and disordered mesoporous silica templates and polyacrylonitrile as carbon precursor

Mesoporous carbons were synthesized from polyacrylonitrile (PAN) using ordered and disordered mesoporous silica templates and were characterized using transmission electron microscopy (TEM), powder X-ray diffraction, nitrogen adsorption, and thermogravimetry. The pores of the silica templates were infiltrated with carbon precursor (PAN) via polymerization of acrylonitrile from initiation sites chemically bonded to the silica surface. This polymerization method is expected to allow for a uniform filling of the template with PAN and to minimize the introduction of nontemplated PAN, thus mitigating the formation of nontemplated carbon. PAN was stabilized by heating to 573 K under air and carbonized under N2 at 1073 K. The resulting carbons exhibited high total pore volumes (1.5-1.8 cm3 g(-1)), with a primary contribution of the mesopore volume and with relatively low microporosity. The carbons synthesized using mesoporous templates with a 2-dimensional hexagonal structure (SBA-15 silica) and a face-centered cubic structure (FDU-1 silica) exhibited narrow pore size distributions (PSDs), whereas the carbon synthesized using disordered silica gel template had broader PSD. TEM showed that the SBA-15-templated carbon was composed of arrays of long, straight, or curved nanorods aligned in 2-D hexagonal arrays. The carbon replica of FDU-1 silica appeared to be composed of ordered arrays of spheres. XRD provided evidence of some degree of ordering of graphene sheets in the carbon frameworks. Elemental analysis showed that the carbons contain an appreciable amount of nitrogen. The use of our novel infiltration method and PAN as a carbon precursor allowed us to obtain ordered mesoporous carbons (OMCs) with (i) very high mesopore volume, (ii) low microporosity, (iii) low secondary mesoporosity, (iv) large pore diameter (8-12 nm), and (v) semi-graphitic framework, which represent a desirable combination of features that has not been realized before for OMCs.     

Cationic polymerization of 1,4,6-trioxaspiro [4,4]-nonane

Cationic polymerization of 1,4,6-trioxaspiro [4,4]-nonane ( 1 ) with (CH₃)₃O⁺SbF₆^?(2) and CH₃OSO₂CF₃(3) initiators has been investigated. Although the observed rates of initiation and propagation are relatively slow, they consist of rapid reversible elementary reactions. In ¹H-NMR spectra, a broadening of the monomer signal was observed, indicating a fast exchange between “free” monomer and monomer engaged in the active species. The variety of orthoester bonds were observed in the polymer formed at the early stages of monomer conversion. The final polymer has, however, structure of a linear poly(ester–ether) including two subsequent ester or ether linkages. To account for these new facts, the mechanism of polymerization was proposed, consisting of a rapid reversible opening of one of the rings in the monomer molecule involved in the growing species, followed by the slower opening of the second ring with formation of the ester linkages. It appears that the rings originally present in the chains rearrange into the linear units intramolecularly.     

Ordinary and strong density continuity of complex analytic functions

In the paper we prove that the complex analytic functions are (ordinarily) density continuous. This stays in contrast with the fact that even such a simple function asG:²²,G(x,y)=(x,y ³ ), is not density continuous [1]. We will also characterize those analytic functions which are strongly density continuous at the given pointa . From this we conclude that a complex analytic functionf is strongly density continuous if and only iff(z)=a+bz, wherea, b andb is either real or imaginary.     

Some remarks on the theorem of Möbius

H.S.M. Coxeter in his book Introduction to Geometry quotes a theorem of Möbius. In the paper two counterexamples are given. A corrected version of the theorem is stated and proved.     

Simple formula for nuclear charge radius

A new formula for the nuclear charge radius is proposed, dependent on the mass numberA and neutron excessN-Z in the nucleus. It is simple and it reproduces all the experimentally available mean square radii and their isotopic shifts of even-even nuclei much better than other frequently used relations.This work is partly supported by the Polish Committee of Scientific Research under contract No. 203119101