Oxidation‐induced nanostructures on Cu{100}, Cu(Ag) and Ag/Cu{100} studied by photoelectron spectroscopy

Initial surface oxidation and nanoscale morphology on Cu{100}, Cu(Ag) and Ag/Cu{100} have been investigated in situ by X‐ray photoelectron spectroscopy (XPS), X‐ray induced Auger electron spectroscopy (XAES) and the inelastic electron background analysis as a function of oxygen exposure at 3.7 × 10^?2 and 213 mbar pressures at a surface temperature of 373 K. Relative Cu₂O concentrations have been quantified by analysis of the peak shape of the XAES Cu LMM transition. The surface morphology of Cu₂O islands and the Ag layer has been characterized by inelastic electron background analysis of XAES O KLL and Ag 3d transitions. Oxygen‐induced segregation of Cu, as well as the subsequent Cu₂O island formation on Cu(Ag) and Ag/Cu{100} surfaces, has been investigated quantitatively. Our results indicate that Ag has a clear inhibitive effect on the initial oxidation and Cu₂O island formation on Cu(Ag) and Ag/Cu{100} surfaces. The Cu₂O islands are also observed to remain highly strained on Ag/Cu{100} even at higher O₂ exposures. The results suggest that strained Cu₂O islands eventually penetrate through the buried Ag layer, and in conjunction with segregating Cu atoms enable the oxidation to proceed at a similar rate to or even faster than on the unalloyed Cu surface. Copyright © 2007 John Wiley & Sons, Ltd.     

Diselenophosphate‐Induced Conversion of an Achiral [Cu20H11{S2P(OiPr)2}9] into a Chiral [Cu20H11{Se2P(OiPr)2}9] Polyhydrido Nanocluster

A polyhydrido copper nanocluster, [Cu₂₀H₁₁{Se₂P(OiPr)₂}₉] ( 2_H ), which exhibits an intrinsically chiral inorganic core of C₃ symmetry, was synthesized from achiral [Cu₂₀H₁₁{S₂P(OiPr)₂}₉] ( 1_H ) of C_3h symmetry by a ligand‐exchange method. The structure has a distorted cuboctahedral Cu₁₃ core, two triangular faces of which are capped along the C₃ axis, one by a Cu₆ cupola and the other by a single Cu atom. The Cu₂₀ framework is further stabilized by 9 diselenophosphate and 11 hydride ligands. The number of hydride, phosphorus, and selenium resonances and their splitting patterns in multinuclear NMR spectra of 2_H indicate that the chiral Cu₂₀H₁₁ core retains its C₃ symmetry in solution. The 11 hydride ligands were located by neutron diffraction experiments and shown to be capping μ₃‐H and interstitial μ₅‐H ligands (in square‐pyramidal and trigonal‐bipyramidal cavities), as supported by DFT calculations on [Cu₂₀H₁₁(Se₂PH₂)₉] ( 2_H′ ) as a simplified model.     

Site Preference in Multimetallic Nanoclusters: Incorporation of Alkali Metal Ions or Copper Atoms into the Alkynyl‐Protected Body‐Centered Cubic Cluster [Au7Ag8(C≡CtBu)12]+

The synthesis, structure, substitution chemistry, and optical properties of the gold‐centered cubic monocationic cluster [Au@Ag₈@Au₆(C≡C^tBu)₁₂]⁺ are reported. The metal framework of this cluster can be described as a fragment of a body‐centered cubic (bcc) lattice with the silver and gold atoms occupying the vertices and the body center of the cube, respectively. The incorporation of alkali metal atoms gave rise to [M_nAg_8?nAu₇(C≡C^tBu)₁₂]⁺ clusters (n=1 for M=Na, K, Rb, Cs and n=2 for M=K, Rb), with the alkali metal ion(s) presumably occupying the vertex site(s), whereas the incorporation of copper atoms produced [Cu_nAg₈Au_7?n(C≡C^tBu)₁₂]⁺ clusters (n=1–6), with the Cu atom(s) presumably occupying the capping site(s). The parent cluster exhibited strong emission in the near‐IR region (λ_max=818 nm) with a quantum yield of 2 % upon excitation at λ=482 nm. Its photoluminescence was quenched upon substitution with a Na⁺ ion. DFT calculations confirmed the superatom characteristics of the title compound and the sodium‐substituted derivatives.     

One Electron Makes Differences: From Heme {FeNO}7 to {FeNO}8

The first X‐ray single‐crystal structure of a {FeNO}⁸ porphyrin complex [Co(Cp)₂][Fe(TFPPBr₈)(NO)], and the structure of the {FeNO}⁷ precursor [Fe(TFPPBr₈)(NO)] are determined at 100 K. The two complexes are also characterized by FTIR and UV/Vis spectroscopy. [Fe(TFPPBr₈)(NO)]^? shows distinct structural features in contrast to a nitrosyl iron(II) porphyrinate on the Fe? N? O^? moiety, which include a much more bent Fe? N? O^? angle (122.4(3)°), considerably longer Fe? NO^? (1.814(4)) and N? O^? (1.194(5) Å) bond distances. These and the about 180 cm^?1 downshift ν_N‐O stretch (1540 cm^?1) can be understood by the covalently bonding nature between the iron(II) and the NO^? ligand which possesses a two‐electron‐occupied π* orbital as a result of the reduction. The overall structural features of [Fe(TFPPBr₈)(NO)]^? and [Fe(TFPPBr₈)(NO)] suggest a low‐spin state of the iron(II) atom at 100 K.     

Two New Silver(I) Ammine Complexes by Displacement Reaction Between [Ag(NH3)2]+ Ions and Different Pyridine‐4,5‐Imidazoledicarboxylic Acids

[Ag(NH₃)₂]⁺ ions are chosen as an initial reaction precursor because of its simple displacement reaction and intrinsic arrangement as well as specific coordination directionality. Two new silver(I) ammine complexes, Ag₂(NH₃)HL² ( 2 ) and Ag₂(NH₃)₂HL³ ( 3 ), were obtained by a simple substitution reaction between [Ag(NH₃)₂]⁺ ions and pyridine‐4,5‐imidazoledicarboxylic acid [H₃L² = 2‐(3′‐pyridyl) 4,5‐imidazoledicarboxylic acid and H₃L³ = 2‐(4′‐pyridyl) 4,5‐imidazoledicarboxylic acid]. Silver dimers are connected into a 2D layer and 1D chain in complexes 2 and 3 , respectively. In complex 2 two kinds of displacement reactions (mono‐substituting and bis‐substituting) occurred between the ammine molecules in [Ag(NH₃)₂]⁺ ions and H₃L², however, only the mono‐substituting reaction occurs in complex 3 .     

Bis(dimethylamino)trifluoromethylsulfonium Salze: [CF3S(NMe2)2]+[Me3SiF2]‐, [CF3S(NMe2)2]+[HF2]‐ und [CF3S(NMe2)2]+[CF3S]‐

Bis(dimethylamino)trifluoro sulfonium Salts: [CF₃S(NMe₂)₂]⁺[Me₃SiF₂]^‐, [CF₃S(NMe₂)₂]⁺ [HF₂]^‐ and [CF₃S(NMe₂)₂]⁺[CF₃S]^‐ From the reaction of CF₃SF₃ with an excess of Me₂NSiMe₃ [CF₃(NMe₂)₂]⁺[Me₃SiF₂]^‐ (CF₃‐BAS‐fluoride) ( 5 ), from CF₃SF₃/CF₃SSCF₃ and Me₂NSiMe₃ [CF₃S(NMe₂)₂]⁺‐ [CF₃S]^‐ ( 7 ) are isolated. Thermal decomposition of 5 gives [CF₃S(NMe₂)₂]⁺ [HF₂]^‐ ( 6 ). Reaction pathways are discussed, the structures of 5 ‐ 7 are reported.     

{nBuMg(OR)}2 und {Mg(OR)2}2 (R = 2, 4, 6‐tBu3C6H2) – sterisch überfrachtete Magnesiumalkoholate

Reaction of 2, 4, 6‐tri‐tert‐butylphenol ( 1 ) with di‐n‐butylmagnesium in the molar ratio 1:1 allows the synthesis of {(nBu)Mg(μ‐OR)₂Mg(nBu)} ( 2 ) (R = 2, 4, 6‐tBu₃C₆H₂), which reacts with excess 1 to give the homoleptic alcoholate complex {(RO)Mg(μ‐OR)₂Mg(OR)} ( 3 ) (R = 2, 4, 6‐tBu₃C₆H₂). The structures of 2 and 3 were determined by X‐ray crystallography.     

A Novel Octahedral Hexasilver（I） Cluster： Ag[SSCN（n—C4H9）2]6

The first crystal structural report of a AgDTC complex (DTC-dialkyldithiocarbamate,R=n-butyl)presented in this paper shows that it is a hexanuclear species.The structural arrangement for the DDP(dialkyldithiophosphate)ligands is different from that of Cu6(DDP)6,but is the same as that of Ag6-[SSP(O-i-Pr)2]6.     

Hypervalent Organoselenium(II) Compounds with Organophosphorus Ligands. Crystal and Molecular Structure of [2‐(iPr2NCH2)C6H4]Se[S2PR′2] (R′ = Ph,OiPr)

Redistribution reactions between diorganodiselenides of type [2‐(R₂NCH₂)C₆H₄]₂Se₂ [R = Et, iPr] and bis(diorganophosphinothioyl disulfanes of type [R′₂P(S)S]₂ (R = Ph, OiPr) resulted in the hypervalent [2‐(R₂NCH₂)C₆H₄]SeSP(S)R′₂ [R = Et, R′ = Ph ( 1 ), OiPr ( 2 ); R = iPr, R′ = Ph ( 3 ), OiPr ( 4 )] species. All new compounds were characterized by solution multinuclear NMR spectroscopy (¹H, ¹³C, ³¹P, ⁷⁷Se) and the solid compounds 1 , 3 , and 4 also by FT‐IR spectroscopy. The crystal and molecular structures of 3 and 4 were determined by single‐crystal X‐ray diffraction. In both compounds the N(1) atom is intramolecularly coordinated to the selenium atom, resulting in T‐shaped coordination arrangements of type (C,N)SeS. The dithio organophosphorus ligands act monodentate in both complexes, which can be described as essentially monomeric species. Weak intermolecular S ··· H contacts could be considered in the crystal of 3 , thus resulting in polymeric zig‐zag chains of R and S isomers, respectively.     

Kristallstrukturen der iso‐Thiocyanatoberyllate (Ph4P)2[Be(NCS)4] und (Ph4P)4[{Be2(NCS)4(μ‐NCS)2}{Be2(NCS)6(μ‐H2N2C2S2)}]

Bis(tetraphenylphosphonium) hexachloridodiberyllate, (Ph₄P)₂[Be₂Cl₆], reacts with excess trimethylsilyl‐iso‐thiocyanate to give a mixture of colourless single crystals of (Ph₄P)₂[Be(NCS)₄] ( 1 ) and (Ph₄P)₄[{Be₂(NCS)₄(μ‐NCS)₂}{Be₂(NCS)₆(μ‐H₂N₂C₂S₂)}] ( 2 ), which can be separated by selection. Both complexes were characterized by X‐ray diffraction. Compound 1 can be prepared without by‐products by treatment of (Ph₄P)₂[BeCl₄] with excess Me₃SiNCS in dichloromethane solution. 1 : Space group I4₁/a, Z = 4, lattice dimensions at 100(2) K: a = b = 1091.2(1), c = 3937.1(3) pm, R₁ = 0.0474. The [Be(NCS)₄]^2– ion of 1 forms tetragonally distorted tetrahedral anions with Be–N distances of 168.4(2) pm and weak intermolecular S ··· S contacts along [100] and [010]. 2 ·4CH₂Cl₂: Space group P , Z = 1, lattice dimensions at 100(2) K: a = 919.5(1), b = 1248.3(1), c = 2707.0(2) pm, α = 101.61(1) °, β = 95.08(1) °, γ = 94.52(1) °, R₁ = 0.103. Compound 2 contains two different anionic complexes in the ratio 1:1. In {Be₂(NCS)₄(μ‐NCS)₂}^2–, the beryllium atoms are connected by (NCS)^– bridging groups forming centrosymmetric eight‐membered Be₂(NCS)₂ rings with distances Be–N of 168(1) pm and Be–S of 235.2(9) pm. The second anion {Be₂(NCS)₆(μ‐H₂N₂C₂S₂)}^2– consists of two {Be(NCS)₃}^– units, which are linked by the nitrogen atoms of the unique dimeric cyclo‐addition product of HNCS with Be–N distances of 179(1) pm.     

Nickel(II)–Lanthanide(III) Magnetic Exchange Coupling Influencing Single‐Molecule Magnetic Features in {Ni2Ln2} Complexes

Four isostructural [Ni₂Ln₂(CH₃CO₂)₃(HL)₄(H₂O)₂]³⁺(Ln³⁺=Dy ( 1 ), Tb ( 2 ), Ho ( 3 ) or Lu ( 4 )) complexes and a dinuclear [NiGd(HL)₂(NO₃)₃] ( 5 ) complex are reported (where HL=2‐methoxy‐6‐[(E)‐2′‐hydroxymethyl‐phenyliminomethyl]‐phenolate). For compounds 1 – 3 and 5 , the Ni²⁺ ions are ferromagnetically coupled to the respective lanthanide ions. The ferromagnetic coupling in 1 suppresses the quantum tunnelling of magnetisation (QTM), resulting in a rare zero dc field Ni–Dy single‐molecule magnet, with an anisotropy barrier U_eff of 19 K.     

Silver–Ethene Complexes [Ag(η2‐C2H4)n][Al(ORF)4] with n=1, 2, 3 (RF=Fluorine‐Substituted Group)

Compounds including the free or coordinated gas‐phase cations [Ag(η²‐C₂H₄)_n]⁺ (n=1–3) were stabilized with very weakly coordinating anions [A]^? (A=Al{OC(CH₃)(CF₃)₂}₄, n=1 ( 1 ); Al{OC(H)(CF₃)₂}₄, n=2 ( 3 ); Al{OC(CF₃)₃}₄, n=3 ( 5 ); {(F₃C)₃CO}₃Al‐F‐Al{OC(CF₃)₃}₃, n=3 ( 6 )). They were prepared by reaction of the respective silver(I) salts with stoichiometric amounts of ethene in CH₂Cl₂ solution. As a reference we also prepared the isobutene complex [(Me₂C?CH₂)Ag(Al{OC(CH₃)(CF₃)₂}₄)] ( 2 ). The compounds were characterized by multinuclear solution‐NMR, solid‐state MAS‐NMR, IR and Raman spectroscopy as well as by their single crystal X‐ray structures. MAS‐NMR spectroscopy shows that the [Ag(η²‐C₂H₄)₃]⁺ cation in its [Al{OC(CF₃)₃}₄]^? salt exhibits time‐averaged D_3h‐symmetry and freely rotates around its principal z‐axis in the solid state. All routine X‐ray structures (2θ_max.<55°) converged within the 3σ limit at C?C double bond lengths that were shorter or similar to that of free ethene. In contrast, the respective Raman active C?C stretching modes indicated red‐shifts of 38 to 45 cm^?1, suggesting a slight C?C bond elongation. This mismatch is owed to residual librational motion at 100 K, the temperature of the data collection, as well as the lack of high angular data owing to the anisotropic electron distribution in the ethene molecule. Therefore, a method for the extraction of the C?C distance in [M(C₂H₄)] complexes from experimental Raman data was developed and meaningful C?C distances were obtained. These spectroscopic C?C distances compare well to newly collected X‐ray data obtained at high resolution (2θ_max.=100°) and low temperature (100 K). To complement the experimental data as well as to obtain further insight into bond formation, the complexes with up to three ligands were studied theoretically. The calculations were performed with DFT (BP86/TZVPP, PBE0/TZVPP), MP2/TZVPP and partly CCSD(T)/AUG‐cc‐pVTZ methods. In most cases several isomers were considered. Additionally, [M(C₂H₄)₃] (M=Cu⁺, Ag⁺, Au⁺, Ni⁰, Pd⁰, Pt⁰, Na⁺) were investigated with AIM theory to substantiate the preference for a planar conformation and to estimate the importance of σ donation and π back donation. Comparing the group 10 and 11 analogues, we find that the lack of π back bonding in the group 11 cations is almost compensated by increased σ donation.     

X‐Ray and Electron Diffraction Study of Poly(p‐dioxanone)

Summary: Solution‐grown lamellar crystals of poly(p‐dioxanone) (PPDX) have been crystallized isothermally from butane‐1,4‐diol at 100 °C. The crystal structure of PPDX has been determined by interpretation of X‐ray fiber diagrams of PPDX fibers and electron diffraction diagrams of lozenge‐shaped chain‐folder lamellar crystals. The unit cell of PPDX is orthorhombic with space group P2₁2₁2₁ and parameters: a = 0.970 nm, b = 0.742 nm, and c (chain axis) = 0.682 nm. There are two chains per unit cell, which exist in an antiparallel arrangement.

Transmission electron micrograph of PPDX chain‐folded lamellar crystals obtained by isothermal crystallization and its electron diffraction diagram.     

Neue [{Cp(CO)2Mo}2ESbCl]‐Cluster mit tetraedrischem Mo2SbE‐Gerüst (E = S,Se)

Reaction of [{Cp(CO)₃Mo}₂SbCl] with S₈ or Se₈ leads to the formation of cluster compounds [{Cp(CO)₂Mo}₂ESbCl] (E = S, Se). [{Cp(CO)₂Mo}₂SSbCl] crystallizes monoclinic, space group P2₁/n with a = 812.28(3), b = 855.65(4), c = 2441.01(9) pm and β = 90.149(3)°; [{Cp(CO)₂Mo}₂SeSbCl] · CH₂Cl₂ crystallizes triclinic, space group P$\bar{1}$ with a = 828.82(9), b = 1002.8(1), c = 1340.0(2) and α = 109.24(1), β = 100.87(1), γ = 96.81(1)°. For both compounds X‐ray crystal structure analysis reveals tetrahedral Mo₂SbE cluster cores with Sb–E bond lengths of 256.8(1) pm (E = S) and 265.3(1) (E = Se). According to the 18 electron rule the [{Cp(CO)₂Mo}₂ESbCl] clusters can be regarded as complexes of the 4 electron donator ESbCl that is coordinated “side‐on” to a {Cp(CO)₂Mo}₂ fragment.     

[Cu32(H)20{S2P(OiPr)2}12]: The Largest Number of Hydrides Recorded in a Molecular Nanocluster by Neutron Diffraction

An air‐ and moisture‐stable nanoscale polyhydrido copper cluster [Cu₃₂(H)₂₀{S₂P(OiPr)₂}₁₂] ( 1_H ) was synthesized and structurally characterized. The molecular structure of 1_H exhibits a hexacapped pseudo‐rhombohedral core of 14 Cu atoms sandwiched between two nestlike triangular cupola fragments of (2×9) Cu atoms in an elongated triangular gyrobicupola polyhedron. The discrete Cu₃₂ cluster is stabilized by 12 dithiophosphate ligands and a record number of 20 hydride ligands, which were found by high‐resolution neutron diffraction to exhibit tri‐, tetra‐, and pentacoordinated hydrides in capping and interstitial modes. This result was further supported by a density functional theory investigation on the simplified model [Cu₃₂(H)₂₀(S₂PH₂)₁₂].     

Nitridorhenium(V)‐Komplexe mit Dimercaptobernsteinsäuredimethylester. Präparation,Charakterisierung und Kristallstruktur von [Re{NC(CH3)2PPhMe2}(DMSMe2)2]

Nitridorhenium(V) Complexes with Dimercapto Succinic Acid Dimethylester. Preparation, Characterization, and Crystal Structure of [Re{NC(CH₃)₂PPhMe₂}(DMSMe₂)₂] Reaction of [ReNCl₂(Me₂PhP)₃] 1 with two equivalents of dimercaptosuccinic acid dimethylester (DMSMe₂) results in the formation of a neutral, diamagnetic rhenium(V)‐DMSMe₂ complex with a phenyldimethylphosphinoisopropyl group at the nitrido ligand as a consequence of a nucleophilic attack of the coordinated nitrido ligand on the solvent molecule. The formed complex 2 of the composition [Re{NC(CH₃)₂(Me₂PhP)}(DMSMe₂)₂] crystallizes in the triclinic space group P 1, a = 12.334(7), b = 12.412(7), c = 12.414(8) Å; α = 60.14(3)°, β = 67.98(3)°, γ = 80.63(6)°; Z = 2. Rhenium is located in a square‐pyramidal configuration of the donor atoms. The two meso‐DMSMe₂ ligands are in a syn‐endo conformation. The rhenium‐nitrogen bond (1.697(12) Å) is only slightly longer than typical Re–N bonding distances in nitrido complexes and comparable with other Re–N–C bonding distances. The addition of a solvent molecule is observed in acetone ( 2 ) as well as in methylethylketone ( 3 ). Moreover, a reaction of the nitrido group with the condensation product of ketone is found by mass spectrometry ([ReN{C(CH₃)(C₂H₅)CH₂C(O)C₂H₅(Me₂PhP)}(DMSMe₂)₂] 4 ).     

Synthesis and Structures of N‐Alkyl‐1,13‐dimethoxychromeno‐ [2,3,4‐kl]acridinium Salts: The Missing Azaoxa[4]helicenium

Helical structures are interesting due to their inherent chirality. Helicenium ions are triarylmethylium structures twisted into configurationally stable helicenes through the introduction of two heteroatom bridges between the three aryl substituents. Of the configurationally stable [4]helicenium ions, derivatives with sulfur, oxygen and nitrogen bridges have already been synthesised. However, one [4]helicenium ion has proven elusive, until now. We present herein the first synthesis of the 1,13‐dimethoxychromeno[2,3,4‐kl]acridinium (DMCA⁺) [4]helicenium ion. A series of six differently N‐substituted DMCA⁺ ions as their hexafluorophosphate salts are reported. Their cation stability was evaluated and it was found that DMCA⁺ is ideally suited as a phase‐transfer catalyst with a pK_R+ of 13.0. The selectivity of nucleophilic addition to the central carbon atom of DMCA⁺ has been demonstrated with diastereotopic ratios of up to 1:10. The single‐crystal structures of several of the DMCA⁺ salts were determined, and structural differences between N‐aryl‐ and N‐alkyl‐substituted cations were observed. The results of a comparative study of the photophysics of the [4]helicenium ions are presented. DMCA⁺ is found to be a potent red‐emitting dye with a fluorescence quantum yield of 20 % in apolar solvents and a fluorescence lifetime of 12 ns. [4]Helicenium ions, including DMCA⁺, all suffer from solvent‐induced quenching, which reduces the fluorescence quantum yields significantly (?_fl<5 %) in polar solvents. A difference in photophysical properties is observed between N‐aryl‐ and N‐alkyl‐substituted DMCA⁺, which has tentatively been attributed to a difference in molecular conformation.