Studies of reaction heats and structure of complexes formed between strong N-bases and phenols

The heats of reactions between various phenols and two strong N-bases of guanidine-like character in acetonitrile, are determined. The values can be used as a measure of self-assembly abilities of the phenol molecules in the interactions with strong N-bases, playing a very important role in biological systems. In the case of TBD complexes with corresponding nitrophenols, the protonated N-base is hydrogen-bonded to the nitro group excluding the self-assembly process of the phenols. In the case of other phenols, the self-assembly abilities are dependent on pK_a values of phenols. With increasing acidity of phenols their ability to form the hydrogen-bonded chains decreases. The maximum of length of the chains is observed for 4-methylphenol, which has a similar pK_a value to that in the tyrosine residue in biological systems.     

SnCl4 and SbCl5 promoted aromatization of enamines

Aromatic amines have been synthesized efficiently from enamines using SnCl₄ and SbCl₅ in CH₂Cl₂ at room temperature.     

An amino acid bioconjugate of an organoplatinum tris(pyrazolyl)borate complex: Synthesis and structure of [p-(BuO-Phe-CO)C6H4Tp]PtMe3

The platinum trimethyl complex of a benzoic acid-functionalized hydrido-tris(pyrazolyl)borate (Tp) ligand [p-(HO₂C)C₆H₄Tp]PtMe₃4 has been synthesized from the corresponding p-bromo complex [p-BrC₆H₄Tp]PtMe₃3. Compound 4 may be readily coupled to biomolecules such as amino acids as exemplified by coupling to l-phenylalanine-tert-butylester to provide [p-(^tBuO-Phe-CO)C₆H₄Tp]PtMe₃5. Compound 5 has been structurally characterized in the solid state by X-ray diffraction. It constitutes the first example of a tris(pyrazolyl)borate bioconjugate.     

Intramolecular Hindrances to CCl3 Reorientations in CCl3PCl4 and (CCl3)2PCl3 Crystals

The trigonal bipyramidal structure of trichloromethyl-tetrachlorophosphorane CCl₃PCl₄ and bis(trichloromethyl)trichlorophosphorane (CCl₃)₂PCl₃ molecules with apical CCl₃ groups is responsible for steric hindrances to reorientations of these groups around the C–P bond. The intramolecular barriers to CCl₃ reorientations calculated for the two phosphoranes (Hartree–Fock method using the 6-31G(d) basis set) are 105.9 kJ/mole and 106.6 kJ/mole, respectively. These internal barriers are high enough to block the reorientational motion of the CCl₃ groups, as found previously by ³⁵Cl NQR for the stated crystals.     

Polymer-supported calix[4]arenes for sensing and conversion of NO2/N2O4

The use of simple calix[4]arenes 1a,b for NO₂/N₂O₄ sensing and conversion is demonstrated, both in solution and in the solid state. Upon reacting with these gases, compounds 1a,b encapsulate reactive NO⁺ cations within their cavities with the formation of deeply colored (λ_max∼570 nm) charge-transfer complexes 2a,b. Further functionalization of the calix[4]arene platform is reported for attachment to solid supports. Polymer-supported calixarene material 3 was prepared, which reversibly traps NO₂/N₂O₄ with the formation of nitrosonium storing polymer 4. Material 4 was effectively used for nitrosation of amides.     

Synthesis, crystal structures and luminescence properties of the Eu-doped yttrium oxotellurates(IV) Y2Te4O11 and Y2Te5O13

Y₂Te₄O₁₁:Eu³⁺ and Y₂Te₅O₁₃:Eu³⁺ single crystals in sub-millimeter scale were synthesized from the binary oxides (Y₂O₃, Eu₂O₃ and TeO₂) using CsCl as fluxing agent. Crystallographic structures of the undoped yttrium oxotellurates(IV) Y₂Te₄O₁₁ and Y₂Te₅O₁₃ have been determined and refined from single-crystal X-ray diffraction data. In Y₂Te₄O₁₁, a layered structure is present where the reticulated sheets consisting of edge-sharing [YO₈]¹³⁻ polyhedra are interconnected by the oxotellurate(IV) units, whereas in Y₂Te₅O₁₃ only double chains of condensed yttrium-oxygen polyhedra with coordination numbers of 7 and 8 are left, now linked in two crystallographic directions by the oxotellurate(IV) entities. The Eu³⁺ luminescence spectra and the decay time from different energy levels of the doped compounds were investigated and all detected emission levels were identified. Luminescence properties of the Eu³⁺ cations have been interpreted in consideration of the now accessible detailed crystallographic data of the yttrium compounds, providing the possibility to examine the influence of the local symmetry of the oxygen coordination spheres.     

Preparation and molecular structures of some complexes containing C5 chains

Complexes containing a Co₃ cluster linked to SiMe₃, Au(PPh₃), W(CO)₃Cp and Fc groups by a C₅ chain have been prepared by elimination of AuBr(PR₃) (R=Ph, tol) in the reactions between Co₃(μ₃-CBr)(μ-dppm)(CO)₇ and {(R₃P)Au}CCCCX [X=SiMe₃, W(CO)₃Cp] or {(OC)₇(μ-dppm)Co₃}CCC{Au(PPh₃)} and FcCCI (X=Fc). Subsequent auro-desilylation of the SiMe₃ compound affords {(OC)₇(μ-dppm)Co₃}CCCCC{Au[P(tol)₃]}. Single-crystal X-ray structures of the W(CO)₃Cp, Au{P(tol)₃} and Fc complexes are reported. The C₅ chain shows little departure from a formal CCCCC fragment.     

Chlorination of V2O5 by CCl4. Adsorption and steady state reaction

The adsorption of CCl₄ on V₂O₅ as well as the steady state kinetics of the chlorination reaction in this system have been studied by volumetric and thermogravimetric methods. Though the adsorption observable below 420 K is of physical character, it can be suggested that an unmeasurable, dissociative type adsorption also occurs. The apparent activation energy of the chlorination process is 77±5 kJ mol^–1, while the reaction order is 0.5 in CCl₄.

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CCl₄ V₂O₄ . 420 , , CCl₄ . 77±5 . ^–1, 0,5 CCl₄.

     

Hydroxy- and boronic-acid-functionalized carbosilanes: Synthesis and solid state structure of Si(C6H4-4-SiMe2((CH2)3OH))4

Consecutive synthesis methodologies for the preparation of carbosilanes (Ph)(Me)Si((CH₂)₃B(OH)₂)₂ (2), Si(C₆H₄-4-SiMe₂((CH₂)₃B(OH)₂))₄ (5), (Ph)(Me)Si((CH₂)₃OH)₂ (3), and Si(C₆H₄-4-SiMe_3−n((CH₂)₃OH)_n)₄ (6a, n = 1; 6b, n = 2; 6c, n = 3) are reported. Boronic acids 2 and 5 are accessible by treatment of (Ph)(Me)Si(CH₂CHCH₂)₂ (1) or Si(C₆H₄-4-SiMe₂(CH₂CHCH₂))₄ (4a) with HBBr₂·SMe₂ followed by addition of water, while 3 and 6 are available by the hydroboration of 1 or Si(C₆H₄-4-SiMe_3−n(CH₂CHCH₂)_n)₄ (4a, n = 1; 4b, n = 2; 4c, n = 3) with H₃B·SMe₂ and subsequent oxidation with H₂O₂.The single molecular structure of 6a in the solid state is reported. Representative is that 6a crystallized in the chiral non-centrosymmetric space group P2₁2₁2₁ forming 2D layers due to intermolecular hydrogen bond formation of the HO functionalities along the crystallographic a and c axes.     

Second-sphere coordination in hexaamminecobalt(III) salt with organic sulphonate anion: Synthesis, characterisation and X-ray crystal structure of [Co(NH3)6](CH3SO3)3

Reaction of hexaamminecobalt(III) chloride with the silver salt of methanesulphonic acid in aqueous medium (1:3 molar ratio) forms hexaamminecobalt(III) methanesulphonate, [Co(NH₃)₆](CH₃SO₃)₃, in high yield. This cobalt(III) complex has been characterized by spectroscopic techniques (UV/visible, IR and NMR) and its solubility product determined. The X-ray crystal structure shows that the [Co(NH₃)₆]³⁺ cations interact at the second sphere by sharing edges with the anions, via N–H  O hydrogen bonds. The structure is related to that of [Co(NH₃)₆]Cl(CH₃SO₃)₂, but is modified to accommodate additional anions in place of Cl⁻.     

Supramolecular structures containing ‘isolated’ pentaborate anions and non-metal cations: Crystal structures of [Me3NCH2CH2OH][B5O6(OH)4] and [4-MepyH, 4-Mepy][B5O6(OH)4]

The solid-state structures of two non-metal pentaborates [Me₃NCH₂CH₂OH][B₅O₆(OH)₄] (1) and [4-MepyH, 4-Mepy][B₅O₆(OH)₄] (2) have been determined by single-crystal X-ray diffraction methods. Structures 1 and 2 both contain supramolecular pentaborate frameworks held together by extensive H-bond interactions. The framework of 1 exists essentially as planes of pentaborate anions linked via three pairwise ‘planar’ β → α interactions, with a fourth β → β interaction crosslinking the planes. The framework of 2 is very similar except that one of the three pairwise linkages within the plane is replaced by pairwise ‘step-like’ bifurcated H-bonds to both α sites of a neighboring anion. The cations in 1 and the cations and neutral 4-Mepy ligands in 2 are present in the framework cavities and channels, with additional H-bond interactions existing between cations and anions.     

Ruthenium-based bioconjugates: Synthesis and X-ray structure of the mixed ligand sandwich compound RuCp(p-(CO2H)C6H4Tp) and labelling of amino acids and the neuropeptide enkephalin

Four differently substituted mixed ligand sandwich complexes CpRu(p-BrC₆H₄)Tp (3), CpRu(p-BrC₆H₄)Tp^Me (4), Cp^∗Ru(p-BrC₆H₄)Tp (5), Cp^iPrRu(p-BrC₆H₄)Tp (6), incorporating cyclopentadienyl (Cp) and functionalized tris(pyrazolyl)borate (Tp) ligands, have been synthesized and characterized. Air-stable 6 has been converted to benzoic acid-functionalized Cp^iPrRu(p-(CO₂H)C₆H₄)Tp (7), which has been structurally characterized in the solid state by X-ray diffraction. Compound 7 may be readily coupled to biomolecules as exemplified by the coupling to phenylalanine-methylester to give Cp^iPrRu(p-(CO-Phe-OMe)C₆H₄Tp) (8). In a solid phase peptide synthesis (SPPS), 7 has been coupled to the pentapeptide Enkephalin, to provide Cp^iPrRu(p-(CO-Tyr-Gly-Gly-Phe-Leu-OH)C₆H₄Tp) (9) as the first example of a mixed ligand sandwich ruthenium bioconjugate.     

Unexpected product formed by the reaction of [2,6-(MeOCH2)2C6H3]Li with SbCl3: Structure of Sb-O intramolecularly coordinated organoantimony cation

Reaction of [2,6-(MeOCH₂)₂C₆H₃]Li (1) with SbCl₃ in 1:1 molar ratio yielded except the intended product [2,6-(MeOCH₂)₂C₆H₃]SbCl₂ (2) unexpected complex 3 consisting of antimony anion [Sb₆Cl₂₂]⁴⁻ compensated by four intramolecularly coordinated organoantimony cations [2,6-(MeOCH₂)₂C₆H₃]₂Sb⁺. Compound 3 is labile in CH₂Cl₂(CHCl₃) solution and decomposes to compound 2 and SbCl₃. Both compounds were characterized by the help of ¹H and ¹³C NMR spectroscopy, ESI-mass spectrometry and in the case of 3 by single crystal X-ray diffraction techniques.     

B(C6F5)3 catalyzed dehydrocarbon polycondensation of PhSiH3 with (MeO)4Si as model polyfunctional comonomers in new route to hydrophobic silicone TQ resins

Highly branched methoxy substituted phenylsilsesquioxane-silicate copolymers were obtained by dehydrocarbon polycondensation of phenylsilane (PhSiH₃) with tetramethoxysilane (TMOS) in toluene solution catalyzed by tris(pentafluorophenyl)borane [B(C₆F₅)₃]. This model reaction represents a new non-hydrolytic route to TQ silicone resins, which do not contain reactive and hydrophilic silanol groups and therefore, should be more stable and have better miscibility with some organic polymers. The soluble siloxane copolymers, which do not contain volatile oligomers, were obtained using the PhSiH₃:TMOS molar ratios below 0.9. The dehydrocarbon condensation is accompanied by metathetic exchange of hydrosilyl and methoxysilyl functions, which is responsible for the formation of links between units originating from the same comonomer. Competition between the dehydrocarbon condensation and metathesis is consistent with a mechanism involving the transient formation of a tertiary oxonium ion intermediate. ²⁹Si NMR analysis of the copolymer product proves that extensive cyclization occurs during the polycondensation, most likely leading to a significant proportion of ladder and cage like structures.     

Synthesis, crystal and band structures, and properties of a new supramolecular complex (Hg2As)2(CdI4)

A new quaternary supramolecular complex (Hg₂As)₂ (CdI₄) (1) has been prepared by the solid-state reaction and structurally characterized by single crystal X-ray diffraction analysis. Compound 1 crystallizes in the space group P2₁ of the monoclinic system with two formula units in a cell: a=7.945(4), b=12.934(6), c=8.094(4) Å, β=116.898°(1), V=741.7(6) Å³. The structure of 1 is characterized by a tridymite-like three-dimensional cationic framework, which is composed of mercury and arsenic atoms, with the channels being occupied by discrete CdI₄²⁻ tetrahedral guest-anions. The optical properties were investigated in terms of the diffuse reflectance and Fourier transform infrared spectra. The electronic band structure along with density of states (DOS) calculated by DFT method indicates that the present compound is a semiconductor with a direct band gap, and that the optical absorption is mainly originated from the charge transitions from I-5p and As-4p to Cd-5s and Hg-6s states.     

An easy electrochemical procedure for tailoring thin films containing the [Fe(bpy)2(CH3CN)2] and/or [Fe(bpy)3]-like cores (bpy=2,2-bipyridine). Application to the design of a modified electrode with a supramolecular structure

A simple electrochemical procedure to tailor thin polymeric films containing the [Fe^II(bpy)₂(CH₃CN)₂]²⁺ and/or [Fe^II(bpy)₃]²⁺-like cores have been described (bpy=2,2^′-bipyridine). The procedure is based on the electroreductive precipitation of soluble polymers prepared in situ in CH₃CN by mixing Fe³⁺ ions and a bis bipyridyl ligand, (chiragen: chir). In the resulting [Fe^II(chir)(CH₃CN)₂]_n²⁺ films, the two labile S ligands can be easily replaced by a bidentate ligand. This method has been applied with success to design a modified electrode with a supramolecular structure.     

Syntheses and X-ray structural studies of the novel complexes [Ni(en)2(3-pyt)2] and [Cu(en)2](3-pyt)2 based on 5-(3-pyridyl)-1,3,4-oxadiazole-2-thione

Two novel mononuclear mixed-ligand complexes [Ni(en)₂(3-pyt)₂] (1) and [Cu(en)₂](3-pyt)₂ (2), derived from potassium [N′-(pyridine-3-carbonyl)-hydrazinecarbodithioate [K⁺(H₂L)⁻] and containing en as a co-ligand, have been synthesized. The [K⁺(H₂L)⁻] undergoes cyclization in the presence of ethylenediamine (en) and is converted to 5-(3-pyridyl)-1,3,4-oxadiazole-2-thione (3-pyt)⁻. [Ni(en)₂(3-pyt)₂] and [Cu(en)₂](3-pyt)₂ have been characterized with the aid of elemental analyses, IR, UV–Vis, magnetic susceptibility and single crystal X-ray studies. The complexes 1 and 2 crystallize in the orthorhombic and monoclinic systems with space groups Pca2(1) and C2/c, respectively. The single crystal X-ray diffraction studies of both complexes indicate that (3-pyt)⁻ adopts a thione form in 1 but is present as a thiolato form in 2.     

Synthesis of palladium and platinum donor complexes and study of their participation in self-assembly reactions. X-ray crystal structure of [Pt(C6H4CCC5H4N)2(dppp)] (dppp = 1,3-bis(diphenylphosphino)propane)

Novel square-planar compounds [M(NC₅H₄CCH)₂(dppp)](OTf)₂ (M = Pd (1), Pt (2)), [Pt(CCC₆H₄CN)₂(dppp)] (3) and [Pt(C₆H₄CCC₅H₄N)₂(dppp)] (4) (dppp = 1,3-bis(diphenylphosphino)propane) were prepared and characterised. Their potential as building blocks in the generation of heterobimetallic squares was studied. The reaction of 4 and the ditopic acceptor species [Pd(H₂O)₂(dppf)](OTf)₂ enabled a tetrametallic metallocycle containing two platinum and two palladium atoms to be obtained. The crystal X-ray structure of 4 shows that the Pt?N vectors are nearly perpendicular, and confirm the suitability of the compound to act as a corner unit for the construction of molecular squares.     

A study of electronic structure of SbCl5.L and SnCl4.L2 complexes by the PM3 method

Electronic structures of SbCl₅.L and SnCl₄.L₂ complexes were studied by the semiempirical PM3 method. The results were compared with the data from ³⁵Cl NQR and ¹²¹Sb NQR studies and Mössbauer spectra.

A good correlation was obtained between the calculated and experimental values of quadrupole coupling constants. The calculated energies of the donor-acceptor bond formation were compared with the degree of electron density transfer. The derived correlation dependences between the above two parameters suggest different properties for cis and trans complexes.     

A study of electronic structure of SbCl5.L and SnCl4.L2 complexes by the PM3 method

Electronic structures of SbCl₅.L and SnCl₄.L₂ complexes were studied by the semiempirical PM3 method. The results were compared with the data from ³⁵Cl NQR and ¹²¹Sb NQR studies and Mössbauer spectra.

A good correlation was obtained between the calculated and experimental values of quadrupole coupling constants. The calculated energies of the donor-acceptor bond formation were compared with the degree of electron density transfer. The derived correlation dependences between the above two parameters suggest different properties for cis and trans complexes.