Marek Nečas

Bambus[6]uril

A macrocyclic hexamer, the structure of which is reminiscent of part of the bamboo-plant stem (see picture), was directly prepared by the condensation of a glycoluril derivative and formaldehyde. The macrocycle bound halide anions with high affinity and selectivity.

Displacement of triphenylphosphine from Cu(PPh3)2NO3 and Co(PPh3)2Cl2 by a diselenoimidodiphosphinato ligand. X-ray crystal structure of (PPh3)Cu[Ph2P(Se)NP(Se)Ph2] and Co[Ph2P(Se)NP(Se)Ph2]2 containing the novel CuSe2P2N and CoSe2P2N inorganic metallocycles

The reaction of Cu(PPh3)2NO3 with K[Ph2P(Se)-N-P(Se)Ph2] produced a tricoordinate copper(I) complex, Cu(PPh3)[Ph2P(Se)-N-P(Se)Ph2], containing the novel inorganic (carbon-free) CuSe2P2N metallocycle. The same diselenium reagent gave with Co(PPh3)2Cl2 a spirobicyclic compound Co[Ph2P(Se)-N-P(Se)Ph2]2, containing the novel inorganic CoSe2P2N metallocycle. The crystal structure of the two compounds was investigated by X-Ray diffraction. In both compounds the inorganic metallocycles are nonplanar and display strongly distorted twisted boat conformations.

Electron density shift in imidazolium derivatives upon complexation with cucurbit[6]uril.

In this study, we have investigated the supramolecular interaction between series of 1-alkyl-3-methylimidazolium guests with variable alkyl substituent lengths and cucurbit[6]uril (CB6) in the solution and the solid state. Correct interpretation of (1)H NMR spectra was a key issue for determining the binding modes of the complexes in solution. Unusual chemical shifts of some protons in the (1)H NMR spectra were explained by the polarization of the imidazolium aromatic ring upon the complexation with the host. The formation of 1:1 complex between 1-ethyl-3-methylimidazolium and CB6 is in disagreement with previously reported findings describing an inclusion of two guest molecules in the CB6 cavity.

Reaction of large-bite ligands with various tellurium compounds: Synthesis and structural characterization of [Te2(μ-Cl)2{(SPPh2)2N}2], [(4-MeOC6H4TeCl3)2{μ-Ph2P(S)CH2CH2P(S)Ph2}] and [Te2(μ-Ph2PS2)2] representing novel types of tellurium complexes

Abstract The three title compounds have been synthesized and their structures determined by X-ray crystallography. [Te2(μ-Cl)2{(SPPh2)2N}2], 1, is a dinuclear square planar Te(II) complex where each Te atom is coordinated to the two sulfur atoms of the bidentate dithiolate ligand and to the two bridging chloride ligands. The Te–S bond lengths are 2.4980(8) and 2.5054(8) A, while the Te–Cl bond lengths are 2.9065(9) and 2.9230(9) A. In [(4-MeOC6H4TeCl3)2{μ-Ph2P(S)CH2CH2P(S)Ph2}], 2, the dithio ligand is neutral and adds a molecule of [4-MeOC6H4TeCl3] at each sulfur atom, thus bridging the two Te(IV) atoms. The coordination of both tellurium atoms is ψ-octahedral with the anisyl group and a lone pair of electrons in axial positions. The Te–S bonds, 2.7747(6) and 2.8198(5) A, are surprisingly weak while the Te–Cl bonds lie in the range 2.4247(5) to 2.5343(6) A, those trans to Te–S being shortest. [Te2(μ-Ph2PS2)2], 3, is a binuclear Te(I) complex, mainly held together by a Te–Te bond of 2.7298(5) A. Both anisobidentate diphenyldithiophosphinate ligands bridge the two tellurium atoms. The resulting coordination around each tellurium is best described as T-shaped with the Te–Te bond along the stem. In the asymmetric near linear S–Te–S system, the short Te–S bonds are 2.487(2) and 2.495(2) A while the long bonds are 2.947(2) and 3.033(2) A, respectively. The strongly different trans influences of the dithio ligands of 1 and 2 are discussed and it is suggested that they are dependent upon the basicity of the sulfur atoms.

Remarkable Salt Effect on Stability of Supramolecular Complex between Modified Cucurbit[6]uril and Methylviologen in Aqueous Media

The supramolecular complex formed by partial inclusion of methylviologen in MeCB6 was described both in solution and in the solid state. The association constant of the complex was determined using (1)H NMR and UV-vis spectrophotometric titration. An extraordinary 2000-fold drop in the association constant of the complex was observed when pure water was replaced by 50 mM NaCl solution.

New fused heterocycles by combined intra-intermolecular criss-cross cycloaddition of nonsymmetrical azines ☆

Thermally induced intra-intermolecular criss-cross cycloaddition of nonsymmetrical azines in the presence of phenyl isocyanate is described. This one-pot reaction gives heterocyclic compounds containing three fused five-membered rings. The molecular and crystal structure of the products is reported and discussed.

Luminescence properties of “double-stranded staircase” copper(I) halide coordination polymers with N-containing ligands

A set of CuIXL coordination polymers (X = Cl, Br, I; L = derivatives of pyrazine and bipyridine) with double-stranded staircase structures was analyzed by X-ray crystallography and luminescence spectroscopy to find a relationship between the structure and luminescence properties of the polymers. Our measurements have proved that luminescence emission wavelengths varied between 500–750 nm, after the polymers were irradiated by light with a wavelength of 370 nm. Although each coordination polymer has shown different emission maximum, we observed several interesting trends related to the structure of the compounds. There is a clear correlation between the emission maxima and the halide size and/or Cu–X distance, respectively. On the other hand, the substitution of the ligand L (pyrazine derivatives, 4,4′-bipyridine) has no significant contribution to the emission spectra. This observation supports the theory that the halide to metal charge transfer (XMCT) plays a key role in the photoluminescence of staircase polymers.

The synthesis and characterisation of bis(diisopropylphosphoryl)ferrocene Fe[(η5-C5H4)P(O)iPr2]2, bis(diisopropylthiophosphoryl)ferrocene Fe[(η5-C5H4)P(S)iPr2]2, and bis(diisopropylselenophosphoryl)ferrocene Fe[(η5-C5H4)P(Se)iPr2]2, the oxidised derivatives of bis(diisopropylphosphino)ferrocene

Abstract The synthesis and spectroscopic characterisation of three chalcogenophosphoryl ligands derived from ferrocene is reported. The synthesis was based on the oxidation of Fe[(η5-C5H4)PiPr2]2 by elementary sulfur and selenium, and hydrogen peroxide, respectively. All new compounds were characterised by X-ray crystallography and comparison with their aryl analogues was made. Contrary to Fe[(η5-C5H4)P(E)Ph2]2 (E=O, S, Se), the prepared compounds are not centrosymmetric, with the iso-propyl groups showing more flexibility than the phenyl substituents.

The synthesis and characterization of N-(diphenylthiophosphinyl)-P-phenyl-thiophosphonamidic acid phenyl ester and related compounds chiral at phosphorus

The synthesis and spectroscopic characterization of three novel phosphorus(V) compounds, chiral at phosphorus, are reported. All three compounds were characterized by X-ray crystallography, and for one compound a 1H-31P HETCOR experiment was performed.

Bambusuril as a One-Electron Donor for Photoinduced Electron Transfer to Methyl Viologen in Mixed Crystals

Methyl viologen hexafluorophosphate (MV2+·2PF6-) and dodecamethylbambus[6]uril (BU6) form crystals in which the layers of viologen dications alternate with those of a 1:2 supramolecular complex of BU6 and PF6-. This arrangement allows for a one-electron reduction of MV2+ ions upon UV irradiation to form MV+• radical cations within the crystal structure with half-lives of several hours in air. The mechanism of this photoinduced electron transfer in the solid state and the origin of the long-lived charge-separated state were studied by steady-state and transient spectroscopies, cyclic voltammetry, and electron paramagnetic resonance spectroscopy. Our experiments are supported by quantum-chemical calculations showing that BU6 acts as a reductant. In addition, analogous photochemical behavior is also demonstrated on other MV2+/BU6 crystals containing either BF4- or Br- counterions.