Metal‐stabilized rare tautomers: N4 metalated cytosine (M = Li+, Na+, K+, Rb+ and Cs+), theoretical views

Ab initio calculations indicate that metalation of the exocyclic amino group of cytosine by the elements of Group IA (Li, Na, K, Rb and Cs) induces protonation of a nucleobase ring nitrogen atom, and hence causes a proton shift from an exocyclic to an endocyclic nitrogen atom. Thus, this metal‐assisted process leads to the generation of rare nucleobase tautomers. The calculations suggest that this kind of metalation increases the protonation energies of the aromatic ring of the nucleobase. The present study reports the quantum chemistry analysis of the metal‐assisted tautomerization. The calculations clearly demonstrate that metalation of the exocyclic amino group of the nucleobase significantly increases the protonation energy of the aromatic rings of the nucleobase. Also, absolute anisotropy shift, molecular orbital and natural bond orbital calculations are compatible with these results. Copyright © 2003 John Wiley & Sons, Ltd.     

Über Tetrabromothallate MTlBr4 (M = K,Rb, Cs,NH4)

On the Tetrabromothallates MTlBr₄ (M = K, Rb, Cs, NH₄) The tetrabromothallates MTlBr₄ (M = K, Rb, Cs, NH₄) were obtained by dehydratisation of the appropriate hydrates MTlBr₄ · nH₂O and by the reaction of TlBr, MBr, and Br₂ in closed glass tubes at 400°C. KTlBr₄ and NH₄TlBr₄ crystallize orthorhombic in the Ga[GaCl₄]-type with the following lattice constants a = 795.2(3), b = 1036.0(4), c = 1042.1(5) pm (KTlBr₄), and a = 812.6(3), b = 1070.1(13), c = 1110.6(10) pm (NH₄TlBr₄), respectively.     

Structure of (BEDT-TTF)-Based Organic Metals with Photochromic Nitroprusside Anion (BEDT-TTF)4M[FeNO(CN)5]2, where M = Na+, K+, NH+4, Tl+, Rb+, and Cs+

The crystal and molecular structures of a family of three-component radical cation salts bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF), (BEDT-TTF)₄M[NP]₂, where M = Na⁺, K⁺, NH⁺ ₄, Tl⁺, Rb⁺, and Cs⁺and NP is the nitroprusside anion [FeNO(CN)₅]^2–, are studied by X-ray structure analysis. These salts are isostructural and behave as stable metals down to helium temperatures. Their structures are characterized by radical cation layers of the "-type alternating with layers of complex anions [M⁺(NP^2–)₂]^3–. The conducting radical cation system and photochromic nitroprusside anion in the crystals were shown to affect each other. On the one hand, this changes the geometric parameters of the nitroprusside anion as compared to those of the Na₂[NP] · 2H₂O crystals in the ground state and, on the other hand, makes the geometries of the two crystallographically independent BEDT-TTF molecules with a different number of shortened contacts with the anion different. Based on the data of crystallochemical analysis of the (BEDT-TTF)₄M[FeNO(CN)₅]₂structures, we suggest their possible routes of chemical modification with the purpose of changing their physical properties.     

CTAB-promoted prussian blue-modified electrode and its cation transport characteristics for K+, Na+, Li+, and NH4+ ions

A Prussian blue (PB) film was deposited on a glassy carbon (GC) electrode by cyclic voltammetry in the presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB). The electrode thus formed showed 4-fold enhancements in redox current and charge values in pure KCl electrolyte as well as greater stability than an electrode prepared in the absence of CTAB. This improved performance of a PB+CTAB electrode versus a PB electrode was further demonstrated using SEM, XRD, and electrochemical impedance spectroscopy (EIS) measurements. A comparative study was undertaken on the cation transport characteristics of PB and PB+CTAB electrodes for Na+, Li+, and NH4+ ions. We obtained a CV pattern for a CTAB-promoted PB film, which showed ideal Nernstian behavior at all scan rates from 5 to 140 mV s(-1). Conditions for the formation and preservation of these ideal and stable PB films are discussed. Possible mechanisms for the beneficial effects of CTAB are proposed.     

Über die Dihydrogenphosphide der Alkalimetalle,MPH2 mit M ≙ Li,Na, K,Rb und Cs

Dihydrogenphosphides of Alkali Metals, MPH₂ (M ? Li, Na, K, Rb, Cs) The dihydrogenphosphides from lithium to cesium were obtained by the reaction of PH₃ with the corresponding solutions of the metals or the metal amides in ammonia. The compounds were examined by X-ray, IR-spectroscopic, and thermochemical techniques. LiPH₂ is not stable at room temperature, while evolving PH₃ it decomposes to yellow products. NaPH₂ is a stable, white compound; above 393 K it decomposes associated with discolouring. KPH₂ and RbPH₂ exist in the region from 110 K to ～400 K in three crystalline forms. Its high-temperature modification is of the sodium chloride-type structure; a monoclinic deformation occurs with decreasing temperature. DSC-measurements revealed a further low temperature form. CsPH₂ crystallizes in the CsCl-type structure between 110 K and ～400 K.     

Comparative analysis of solubility in CuCl-MCl-H2O systems at 25°C (M+ = Li+, Cs+, NH 4 + )

Solubility in the ternary system CuCl-NH₄Cl-H₂O at 25°C was determined by the method of isothermal lifting of oversaturation. A comparative analysis of solubility in this system and the previously studied systems CuCl-MCl-H₂O (M⁺ = Li⁺, Na⁺, K⁺, Cs⁺) was made. The results obtained were interpreted in terms of competition between hydration, association, and complexation processes in water-salt systems.     

Synthese und Charakterisierung von Tetrabromoferraten(III) AFeBr4 mit einwertigen Kationen A  Cs,Rb, Tl,NH4, K,Na, Li,Ag

Preparation and Characterization of Tetrabomoferrates(III) AFeBr₄ with Monovalent Cations A ? Cs, Rb, Tl, NH₄, K, Na, Li, Ag Tetrabromoferrates(III) AFeBr₄ of the monovalent cations A ? Cs, Rb, Tl, NH₄, Na, Ag, Li have been prepared in closed ampoules by reaction of the appropriate bromides with iron and an excessive amount of bromine. The dark red compounds were characterized by DTA, Raman spectroscopy and X-ray powder diffraction. Their crystal structures have been assigned to five structure types, containing FeBr₄ anions. The coordination number runs from 12 (Cs⁺, Rb⁺) over 10 (NH₄⁺) and 8 (K⁺), to 6 (Na⁺, Ag⁺, Li⁺). Lattice parameters for all compounds see “Inhaltsübersicht”. CsFeBr₄ and RbFeBr₄ crystallize orthorhombic in the BaSO₄-type, NH₄FeBr₄ monoclinic in the KAlBr₄-type, KFeBr₄ orthorhombic in the GaGaCl₄-type, NaFeBr₄ monoclinic in the NaGaBr₄-type, AgFeBr₄ and LiFeBr₄ monoclinic in the LiAlCl₄-type, while the structure of TlFeBr₄ is still unknown.     

Raman spectra of the double-anion salts M3ZnCl4NO3 (M+ = K+, Rb+, NH4)

Recently characterized K3ZnCl4NO3 and (NH4)3ZnCl4NO3, and newly prepared Rb3ZnCl4NO3 constitute a limited series of isomorphous double-anion salts (space group Pnma, Z = 4). Room-temperature (295 K) Raman spectra from polycrystalline samples of the compounds are reported and interpreted on the basis of the Cs site symmetry of the ZnCl4(2-) and NO3- ions with reference to the D2h factor group of the unit cell. The spectra are compared with Raman spectra of the corresponding M2ZnCl4 and MNO3 single-anion salts. Relative positions and frequencies of the ZnCl4(2-) modes vary considerably among the M3ZnCl4NO3 compounds, despite the isomorphism. The NO3- modes are more similar in all three compounds. The NO3- doubly degenerate v3 and V4 modes are split into two distinct bands as a result of the decent in symmetry from D3h for the free ion to Cs at the crystallographic site. The unequal intensities of the v3 bands observed for K3ZnCl4NO3 and Rb3ZnCl4NO3 and the equal intensities of the v4 bands observed for all three compounds suggest the same factor-group assignments as the high-temperature phase NH4NO3(III). The free-ion Raman-inactive planar deformation mode, v2, is evident in all three compounds, but with lesser intensity than its overtone 2v2. In K3ZnCl4NO3 and Rb3ZnCl4NO3, the symmetric stretching band, in addition to the very strong component for v1, shows a weak, low-frequency band found in many ionic nitrates, which has been attributed to thermally disordered nitrate ions or hot bands. This feature is not found in the spectrum of (NH4)3ZnCl4NO3. The 12 NH4+ ions in the unit cell of (NH4)3ZnCl4NO3, which occupy C1 and Cs sites in a 2:1 ratio, give rise to extremely broad bands that show no evidence of the individual symmetry distinctions of the cations. The broad band from NH4+ v4 obscures the region in which NO3- v3 bands are expected, but the NO3- overtone 2v2 is evident as a sharp peak above a similarly broad band from NH4+ v2.     

Polarographic study of Tl+, Li+, Na+, K+, and Cs+ complexes with monensin anion in dipolar aprotic solvents

Summary The stability constants,K _sof monensin complexes with Li⁺, Na⁺, K⁺ and Cs⁺ ions were studied by a competitive polarographic method using the Tl⁺/Tl(Hg) redox couple as a sensitive electrochemical probe. TheK _svalues are strongly influenced by the solvents (acetonitrile, propionitrile, acetone, N,N-dimethylformamide, N-methyl pyrolidinone, N,N-dimethylacetamide, dimethylsulfoxide, N,N-diethylformamide and N,N-diethylacetamide were used in experiments) and vary inversely with the Gutmann donicity scale. Molecular mechanics computations revealed the probable structures of the complexes.

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Polarographische Untersuchung von Tl⁺-, Li⁺-, Na⁺- und Cs⁺-Komplexen mit Monesin-Anion in dipolaren aprotischen Lösungsmitteln

Zusammenfassung Es wurden die StabilitätskonstantenK _svon Monesin-Komplexen mit Li⁺-, Ma⁺- und Cs⁺-Ionen mittels einer competitiven polarographischen Methode unter Verwendung der Tl⁺/Tl(Hg)-Redoxelektrode als sensitiver elektrochemischer Sonde bestimmt. DieK _s-Werte werden stark vom Lösungsmittel (Acetonitril, Propionitril, Aceton, N,N-Dimethylformamid, N-Methylpyrrolidinon, N,N-Dimethylacetamid, Dimethylsulfoxid, N,N-Diethylformamid und N,N-Diethylacetamid) beeinflußt, wobei sie invers zurGutmann schen Donizitätsskala variieren. Die wahrscheinliche Struktur der Komplexe wurde mittels molekularmechanischer Berechnungen ermittelt.

     

M+(12-crown-4) supramolecular cations (M+ = Na+, K+, Rb+, and NH4+) within Ni(2-thioxo-1,3-dithiole-4,5-dithiolate)2 molecular conductor

Monovalent cations (M+ = Na+, K+, Rb+, and NH4+) and 12-crown-4 were assembled to new supramolecular cation (SC+) structures of the M+(12-crown-4)n (n = 1 and 2), which were incorporated into the electrically conducting Ni(dmit)2 salts (dmit = 2-thioxo-1,3-dithiole-4,5-dithiolate). The Na+, K+, and Rb+ salts are isostructural with a stoichiometry of the M+(12-crown-4)2[Ni(dmit)2]4, while the NH4+ salt has a stoichiometry of NH4+(12-crown-4)[Ni(dmit)2]3(CH3CN)2. The electrical conductivities of the Na+, K+, Rb+, and NH4+ salts at room temperature are 7.87, 4.46, 0.78, and 0.14 S cm-1, respectively, with a semiconducting temperature dependence. The SC+ structures of the Na+, K+, and Rb+ salts have an ion-capturing sandwich-type cavity of M+(12-crown-4)2, in which the M+ ion is coordinated by eight oxygen atoms of the two 12-crown-4 molecules. On the other hand, the NH4+ ion is coordinated by four oxygen atoms of the 12-crown-4 molecule. Judging from the M(+)-O distances, thermal parameters of oxygen atoms, and vibration spectra, the thermal fluctuation of the Na+(12-crown-4)2 structure is larger than those of K+(12-crown-4)2 and Rb+(12-crown-4)2. The SC+ unit with the larger alkali metal cation gave a stress to the Ni(dmit)2 column, and the SC+ structure changed the pi-pi overlap mode and electrically conducting behavior.     

Reaktivität von Monophosphan-Platin(0)-Verbindungen gegenüber Schwefeldioxid

Reactivity of Monophosphine Platinum(0) Complexes with SO₂ . The addition reaction of (PPh₃)Pt(ViSi) (ViSi = {η²-H₂C?CHSiMe₂}₂O) ( 1 ) with SO₂ gives within 30 min the red SO₂ complex (PPh₃)Pt(η²-H₂C?CHSiMe₂- OSiMe₂CH?CH₂)(SO₂) ( 2 ). A reaction time of 24 h with SO₂ leads to the elimination of the ViSi ligand, and the unstable monomeric intermediate (PPh₃)Pt(SO₂) cyclo- trimerizes to the stable cluster [Pt(PPh₃)(SO₂)]₃ ( 3 ). 3 is also obtained within 30 min by the reaction of (PPh₃)Pt(C₂H₄)₂ ( 4 ) with SO₂. The crystal structure of 3 has been determined; space group P2₁/n, Z = 4, a = 1 606.1(3), b = 1 019.3(1), c = 3 624.6(5) pm, β = 93.67°, R/R_w = 0.102/0.121.     

Ein neues Oxouranat(VI): K2Li4[UO6]. Mit einer Bemerkung über Rb2Li4[UO6] und Cs2Li4UO6

A New Oxouranate(VI): K₂Li₄[UO₆]. With a Remark about Rb₂Li₄[UO₆] and Cs₂Li₄[UO₆] For the first time K₂Li₄UO₆ has been prepared by an exchange reaction of α-Li₆UO₆ with K₂O [K:U = 2.0:1, sealed au-tube; 750°C; 30 d single crystals; 680°C, 10 d powder]. The irregular shaped single crystals, which are of yellow color and sensitive to moisture crystallize in P3 m1 (Z = 1) with a = 619.27(5), c = 533.76(6) pm. The structure determination (PW 1100, AgKα R = 4.80%, R_w = 4.81% for 220 unique reflexions) reveals a new type of structure. The characteristic elements are the isolated group [UO₆] and the C.N. = 12 for K⁺. While Li(1) has a nearly regular square of 4 O^2? as coordination polyhedron, Li(2) is octahedrally surrounded. The Madelung Part of Lattice Energy (MAPLE) is calculated and discussed. In addition to K₂Li₄[UO₆] the new oxides Rb₂Li₄[UO₆] and Cs₂Li₄[UO₆] are prepared as pale yellow powders which are little sensitive to moisture (both: au-tube, 680°C, 10 d). According to powder datas both compounds are isotypic with K₂Li₄[UO₆] [Rb₂Li₄[UO₆]: a = 622.91(5), c = 535.93(6) pm; Cs₂Li₄[UO₆]: a = 626.70(6), c = 539.92(6) pm].     

Ladungsverteilung und Struktur der Komplexe MeIGaCl4, MeIGa2Cl7 und KAl2Br7 (MeI = Na+, K+, Rb+, Cs+, Ga+). Eine NQR-Untersuchung (35C1,69Ga,81Br)

Ohne Zusammenfassung     

A joint experimental and theoretical study of cation-pi interactions: multiple-decker sandwich complexes of ferrocene with alkali metal ions (Li+, Na+, K+, Rb+, Cs+)

A systematic study of cation-pi interactions between alkali metal ions and the cyclopentadienyl ring of ferrocene is presented. The alkali metal (Li+, Na+, K+, Rb+, Cs+) salts of the ditopic mono(pyrazol-1-yl)borate ligand [1,1'-fc(BMe2pz)2]2- crystallize from dimethoxyethane as multiple-decker sandwich complexes with the M+ ions bound to the pi faces of the ferrocene cyclopentadienyl rings in an eta5 manner (fc = (C5H4)2Fe; pz = pyrazolyl). X-ray crystallography of the lithium complex reveals discrete trimetallic entities with each lithium ion being coordinated by only one cyclopentadienyl ring. The sodium salt forms polyanionic zigzag chains where each Na+ ion bridges the cyclopentadienyl rings of two ferrocene moieties. Linear columns [-CpR-Fe-CpR-M+-CpR-Fe-CpR-M+-](infinity) (R = [-BMe2pz]-) are established by the K+, Rb+, and Cs+ derivatives in the solid state. According to DFT calculations, the binding enthalpies of M+-eta5(ferrocene) model complexes are about 20% higher as compared to the corresponding M+-eta6(benzene) aggregates when M+ = Li+ or Na+. For K+ and Rb+, the degree of cation-pi interaction with both aromatics is about the same. The binding sequence along the M+-eta5(ferrocene) series follows a classical electrostatic trend with the smaller ions being more tightly bound.