Übergangsmetall—methylen-komplexe: LXI. Übergangsmetall—vinyliden-komplexe: Neuartige synthese aus diazoalken-vorstufen

The diazoolefines of composition N₂CCR₂ (R/R = CH₃/CH₃ and(-CH₂-)₅) are suitable precursors of the corresponding vinylidene ligands CCR₂. Thus, treatment of the RhRh complex [(η⁵-C₅Me₅)Rh(μ-CO)]₂ (1) with the N-nitrosourethanes 2a and 2b, resp., in the presence of lithium t-butoxide yields the otherwise inaccessible μ-vinylidene complexes (μ-CCR₂)[(η⁵-C₅Me₅)Rh(CO)]₂ (R = CH₃ (3a), R,R = (-CH₂-)₅ (3b)). The analogous cobalt compound (μ-CCMe₂)[(η⁵-C₅Me₅)Co(CO)]₂ (5a) is obtained similarly. This procedure extends the well-documented diazoalkane method for the synthesis of μ-alkylidene complexes to the less stable diazoalkenes. A single-crystal X-ray diffraction study of the dimethylvinylidene derivative 3a shows the CMe₂ ligand to adopt an almost symmetrically metal-bridging position (d(RhC) 197.8(1) and 204.3(1) pm), with a rhodium-rhodium single bond completing a three-membered Rh₂C-metallacycle (d(RhRh) 268.4(0) pm) analogous with cyclopropane.     

Determination of bismuth, indium and lead in geological samples by electrothermal AAS Part 2. Comparative study of palladium and molybdenum containing chemical modifiers*

A comparative and systematic study has been carried out of the effects of palladium and molybdenum containing chemical modifiers, such as Pd + Rh, Pd + Pt, Pd + Ru, Pd + Rh + Pt, Pd + Rh + Ru, Mo + Pd, Mo + Rh, Mo + Ru and Mo + Pt and additionally tartaric acid (TA) as a reducing agent together with mixed modifiers for the thermal stabilization of Bi, In and Pb in a Zeeman electrothermal atomic absorption spectrometer (ETAAS). The effect of the mass ratios of the mixed modifier components on the maximum pretreatment temperature for the analytes has been determined. The modifier mixtures of Pd + Rh + Pt, Mo + Pd + TA and Mo + Pt + TA were found to be especially powerful for the determination of Bi, In and Pb. These mixed modifiers could increase the ashing temperatures of the analytes up to 1250–1400° C. They were applied to the determination of Bi and Pb in dissolved geological reference samples and accuracy and precision of the method were thereby enhanced. The percent relative error was decreased from 20.0 to 0.4 for Bi and from 10.5 to 0.3 for Pb, depending on the sample type. Received: 9 May 1997 / Revised: 19 August 1997 / Accepted: 20 August 1997     

The sorption behavior of a nickel-insolubilized humic acid system in a column arrangement

The sorption characteristics of insolubilized humic acid (IHA) were investigated for Ni (II) in a column arrangement. The sodium form of the IHA (INaA) was used as a solid phase. Column operations were performed with five steps and all of them were monitored continuously by a flowthrough cell-adapted UV-Vis spectrophotometer. Thus, all solid-phase extraction (SPE) steps were visualized by breakthrough curves and analyses progress were evaluated. However, all calculations and evaluations were focused on the atomic absorption spectrophotometric (AAS) analyses of the solutions collected during the stripping steps. There was a high correlation (r(2), 0.972) between peak area and AAS data of stripping steps. The effect of concentration and pH of the loading solution onto sorption of Ni (II) by INaA was investigated. Sorption characteristics were evaluated by using Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) adsorption isotherms, as well as by Scatchard plot analysis. Multilayer sorption was found to be agreeable for Ni (II). From the D-R isotherm the mean free energy of sorption (E) was calculated (6.65 kJ mol(-1)) and attributed to the multilayer sorption. Finally, the sorption characteristic of the INaA-Ni (II) system was compared with that of the INaA-Cu (II) system, and possible separation of two ions in a binary mixture system is discussed.     

Two new isoflavanoids from the rhizomes of Iris soforana

Two new isoflavones 1 and 2 along with eleven known compounds 3-13, have been isolated for the first time from the rhizomes of Iris soforana. The structures of these compounds were determined on the basis of spectroscopic methods and found to be 5,3'-dihydroxy-4'-methoxy-6,7-methylenedioxyisoflavone (1) (Soforanarin A), and 5,7,5'-trimethoxy-6,3',4'-trihydroxyisoflavone (2) (Soforanarin B).     

Monoclinic and triclinic concomitant polymorphs of di‐μ‐pyridazine‐1κ2N:2κ2N′‐bis­[(saccharinato)silver(I)]

Crystallization of the title compound, di‐μ‐pyridazine‐1κ²N:2κ²N′‐bis­[(2,3‐dihydro‐3‐oxobenzisosulfonazolato‐κN)silver(I)], [Ag₂(C₇H₄NO₃S)₂(C₄H₄N₂)₂], from acetonitrile yields both monoclinic, (I), and triclinic, (II), polymorphs. In both forms, the silver(I) ions have a slightly distorted trigonal AgN₃ coordination geometry and are doubly bridged by two neutral pyridazine (pydz) ligands, generating a centrosymmetric dimeric structure. The saccharinate (sac) ligands are N‐coordinated. The dihedral angles between the sac and pydz rings are 8.43 (7) and 7.94 (8)° in (I) and (II), respectively, suggesting that the dimeric mol­ecule is nearly flat. The bond geometry is similar in both polymorphs. In (I), the dimers inter­act with each other via aromatic π_sac–π_pydz stacking inter­actions, forming two‐dimensional layers, which are further crosslinked by weak C—H⋯O inter­actions. Compound (II) exhibits similar C—H⋯O and π–π inter­actions, but additional C—H⋯π and π⋯Ag inter­actions help to stabilize the packing of the dimers.     

C−H?Pd interactions and cyano-bridged heteronuclear polymeric complexes

Three new heterometallic complexes, [Cu(N-Meim)₄Pd(μ-CN)₂(CN)₂]_n (1), [Zn(N-Meim)₃Pd(μ-CN)₂(CN)₂]_n (2) and [Cd(N-Meim)₂Pd(μ-CN)₄]_n (3), have been isolated from the reactions of M[Pd(CN)₄] (M = Cu(II), Zn(II) or Cd(II)) and N-Meim (N-methylimidazole) with in different molar ratios. All complexes have been characterized by X-ray analyses, vibrational (FT-IR and Raman) spectra, thermal and elemental analyses. The crystallographic analysis reveals that the crystal structures of 1 and 2 are 1D coordination polymer, while 3 presents a 2D network. In the Cu(II) and Zn(II) complexes, two cyanide groups of [Pd(CN)₄]²⁻ coordinated to the adjacent M(II) ions and distorted octahedral and square pyramidal geometries of complexes are completed by four and three nitrogen atoms of N-Meim ligands, respectively. The Cd(II) ion is six-coordinate, completed with the two nitrogen atoms of N-Meim ligands in the axial positions and the four nitrogen atoms from bridging cyano groups in the equatorial plane. The most striking features of complexes 1-3 are the presence of obvious C-H?Pd hydrogen-bonding interactions between the Pd(II) and hydrogen atoms of N-Meim ligand. This weak hydrogen bonding plays a crucial role in the architecture of the network polymers. The adjacent chains are held together by C-H?Pd, C-H?π or π?π interactions, forming three-dimensional network.     

Two-dimensional supramolecular networks generated from weak AgCpy interactions: Synthesis, structural, thermal and fluorescence studies of silver(I) complexes of 5,5-diethylbarbiturato with pyridine-2-ylmethanol and 2,6-dimethoxypyridine

Two new silver(I) complexes [Ag(barb)(pym)]·H₂O (1) and [Ag(barb)(dmpy)]·1.5H₂O (2) (barb = 5,5-diethylbarbiturate, pym = pyridine-2-ylmethanol and dmpy = 2,6-dimethoxypyridine) have been synthesized and characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffraction. In both complexes, the silver(I) ions are linearly coordinated by the N atoms of a barb anion and a pym or a dmpy ligand, forming mononuclear species. The molecules of 1 and 2 are doubly bridged by N–HO hydrogen bonds involving the barb moieties and these hydrogen-bonded dimers are assembled into two-dimensional layered networks through weak AgC_py (η¹) interactions of ca. 3.3 Å. Additionally, the thermal and fluorescent properties of these complexes are also investigated.     

2‐[(4‐Hydroxyphenyl)iminomethyl]­thiophene

The molecular structure of the title compound, C₁₁H₉NOS, has three planar moieties, two of which are rings, namely the hydroxy­phenyl and the thio­phene, with an angle of 20.76 (10)° between them. The crystal structure is stabilized by an O—H?N hydrogen bond and by C—H?O intermolecular interactions. The C?O intermolecular contact distance is 3.443 (2) Å.