Perhydroxylated 1,7-Dioxaspiro[5.5]undecanes (“Spiro Sugars”): Synthesis,Stereochemistry, and Structure

As spiro sugars is an apt way of considering perhydroxylated 1,7-dioxaspiro[5.5]undecanes–a class of compounds which has not been found in nature up to now. The crystal structure of such a spiroacetal, in which the two pyran rings show the β-D -manno configuration, is depicted. Note that the all-trans arrangement of C-6, C,-5, O_pyr, C_spiro, O_pyr^′, C-5′, and C-6′ does not allow any of the stereoelectronic effects that are typical of carbohydrates.     

NMR Spectroscopic Structural Determination of Organozinc Reagents: Evidence for “Highly Coordinated” Zincates

The structures of ¹³ C-labeled methylzinc reagents have been studied by NMR spectroscopy. Analysis of the spectra gives information on the number of chemically equivalent methyl groups that are attached to the metal centers. Shown is the structure of trimethylzincate with the spin couplings that form the basis of the spin system used in the calculation.     

Strain-Induced “Band Flips” in Cyclodecaamylose and Higher Homologues

The cavity of the larger molecule has less space for guests! Unlike the structure of the smaller annular cyclodextrins, that of the higher homologues of cycloamyloses (CAs) with more than ten glucose units contains a 90° kink between adjacent glucose residues within one half of the molecule and a 180° band flip between adjacent units in different halves (see depicted section of the CA14 structure) to yield butterfly-shaped structures with narrow, groovelike cavities.     

Synthesis and Structure of (CH3Si)6(NH)9: A Si–N Cage Made from Methyltrichlorosilane and Ammonia

No bulky substituents are bonded to the silicon centers of the cagelike title compound 1 , which is readily formed by reaction of methyltrichlorosilane with ammonia and sodium. According to X-ray structure analysis, 1 consists of two Si₃N₃ rings in the chair conformation that are bridged through the silicon centers by NH groups. The result is a cage in which three bars are missing, as can be seen on the right.     

Preparation of “Si‐Centered” Chiral Silanes by Direct α‐Lithiation of Methylsilanes

The direct α‐lithiation of methyl‐substituted silanes as an efficient method for the preparation and elaboration of Si‐chiral compounds is reported. Deprotonation of chiral oligosilanes occurs selectively and with high yields at the methyl group of the stereogenic silicon center, even in the presence of multiple methylsilyl or methylgermyl substituents. Computational studies have confirmed this preference as a consequence of pre‐coordination of the lithiating agent by the amino side‐arm and repulsion effects in the corresponding transition state. This complexation is also obvious from X‐ray structure analyses of the α‐lithiated silanes, which exhibit intriguing structure formation patterns differing in the type of aggregation and the amount of alkyllithium used. An alternative route to Si‐chiral compounds is also presented, which involves desymmetrization of dimethylsilanes mediated by a chiral side‐arm. Structure analyses and computational studies have shown that the diastereoselectivity of this α‐lithiation is influenced by the selectivity of the formation of the stereogenic nitrogen upon complexation of the alkyllithium.     

Versatile Reactivity of Cyclic 1,2‐Dimethylhydrazinodiphosphines

A versatile reactivity from the cage compound P(NMeNMe)₃P is presented. The Staudinger reaction with Me₃SiN₃ is carried out. The crystal structure of the compound issued from the reaction on both sides (Me₃SiN=P(NMeNMe)₃P=NSiMe₃) is reported. When the reaction occurs on only one side, the remaining free phosphorus atom is complexed with RuCl₂(p‐cymene). P(NMeNMe)₃P reacts with PCl₃, leading to the heterocyclic compound ClP(NMeNMe)₂PCl. This heterocycle also displays a versatile reactivity. Substitution reaction with HNiPr₂ leads to iPr₂NP(NMeNMe)₂PNiPr₂. Very complex ¹H and ¹³C NMR spectra suggest that the cis isomer is the largely major isomer of this compound. The cis structure is confirmed by X‐ray diffraction. Besides the reaction on the P–Cl functions, the reaction on the lone pair of ClP(NMeNMe)₂PCl is carried out, leading to the complex (p‐cymene)Cl₂RuPCl(NMeNMe)₂ClPRuCl₂(p‐cymene). Characterization of this compound by X‐ray diffraction displays a cis isomer for this compound also.     

Self-Assembly of a Three-Dimensional [Ga6(L2)6] Metal–Ligand “Cylinder”

A near trigonal antiprism with metal–metal distances in the nanometer regime is formed by the six metal ions in the crystalline, homochiral [Ga₆(L²)₆] (see structure). This metal–ligand “cylinder” is based on a threefold symmetric, β-diketone ligand, and represents a new geometry for metal–ligand clusters.     

The First Six-Membered “True” Heterocycle – Hydrogen-Bond-Assisted Ladder Formation in a KOCNPS Ring System

A ladder of alternating K₂S₂ and K₂O₂ rings exists in K[Ph₂P(S)NC(O)Ph]⋅MeOH, the first six-membered “true” heterocycle, in the solid state (see picture). A simple P–N bond-forming reaction between benzamide and Ph₂PCl gives the precursor Ph₂P(S)NHC(O)Ph, from which the potassium salt can be generated by reaction with KOtBu.     

“Cage‐like” Carboxyl Bridged Octaphenyltetraantimony Compounds (SbPh2)4(μ‐O)4(μ‐OH)2(μ‐O2CR)2: Synthesis and Structural Characterization

The metal‐directed self‐assembly of biphenylantimony trichloride and homocarboxylic acids LH [L = 2‐CHO‐C₆H₄COO^– ( 1 ), 2, 3‐2F‐C₆H₄COO^– ( 2 ), 4‐CF₃–C₆H₄COO^– ( 3 )] provided three novel tetranuclear organoantimony(V) complexes, which were characterized by elemental analysis, FT‐IR, ¹H, and ¹³C NMR spectroscopy as well as melting point, and X‐ray single crystal analysis. In the molecular structure, four hexacoordinate antimony atoms are linked into a [Sb₂(μ‐O)₂]₂(μ‐O)₂ “cage” architecture by oxo‐bridges which are terminally bridged by two carboxyl groups.     

Ce16Si15O6N32—An Oxonitridosilicate with Silicon Octahedrally Coordinated by Nitrogen

A rarity in solid‐state chemistry is octahedrally coordinated silicon. Ce₁₆Si₁₅O₆N₃₂ is the first nitridosilicate with this structural motif. Most oxosilicates containing octahedrally coordinated silicon are high‐pressure phases. In contrast to that Ce₁₆Si₁₅O₆N₃₂ has been synthesized under ambient pressure. An SiN₆ octahedron that is surrounded by two parallel rings formed from six Si(O,N)₄ tetrahedra is depicted.     

Sandwich Double‐Decker Lanthanide(III) “Intracavity” Complexes Based on Clamshell‐Type Phthalocyanine Ligands: Synthesis,Spectral, Electrochemical,and Spectroelectrochemical Investigations

Phthalocyanine compounds of novel type based on a bridged bis‐ligand, denoted “intracavity” complexes, have been prepared. Complexation of clamshell ligand 1,1′‐[benzene‐1,2‐diylbis(methanediyloxy)]bis[9(10),16(17),23(24)‐tri‐tert‐butylphthalocyanine] (^clam,tBuPc₂H₄, 1 ) with lanthanide(III) salts [Ln(acac)₃] ? n H₂O (Ln=Eu, Dy, Lu; acetylacetonate) led to formation of double‐deckers ^clam,tBuPc₂Ln ( 2 a – c ). Formation of high molecular weight oligophthalocyanine complexes was demonstrated as well. The presence of an intramolecular covalent bridge affecting the relative arrangement of macrocycles was shown to result in specific physicochemical properties. A combination of UV/Vis/NIR and NMR spectroscopy, MALDI‐TOF mass‐spectrometry, cyclic voltammetry, and spectroelectrochemistry provided unambiguous characterization of the freshly prepared bis‐phthalocyanines, and also revealed intrinsic peculiarities in the structure–property relationship, which were supported by theoretical calculations. Unexpected NMR activity of the paramagnetic dysprosium complex 2 b in the neutral π‐radical form was observed and examined as well.     

Preparation and Crystal Structure of the Clathrate‐I Cs8–xGe44+y□2–y

The clathrate‐I phase Cs_8–xGe_44+y□_2–y (space group Pm$\bar{3}$ n) was prepared by high‐pressure high‐temperature reactions of Cs₄Ge₄ and α‐Ge. Different reaction conditions were found to have a strong influence on the lattice parameter of the clathrate‐I phase ranging from 10.8070(2) Å to 10.8493(3) Å. A single crystal with composition Cs₈Ge_44.40(2)□_1.60(2) was obtained from a sample with a = 10.8238(2) Å (niobium ampoule, p = 3.4 GPa, T_max = 1400 °C). Structure analysis based on X‐ray single crystal data shows unambiguously an excess of germanium atoms with respect to the electron balanced composition Cs₈Ge₄₄□₂ on basis of the Zintl concept.     

Recent Advances in the Chemistry of “Clusters” and Coordination Polymers of Alkali,Alkaline Earth Metal and Group 11 Compounds

This contribution gives an overview on the different subjects treated in our group. One of our fundamental interests lies in the synthesis and study of low‐dimensional polymer and molecular solid state structures. We have chosen several synthetic approaches in order to obtain such compounds. Firstly, the concept of cutting out structural fragments from a solid state structure of a binary compound will be explained on behalf of BaI₂. Oxygen donor ligands, used as chemical scissors on BaI₂, allow obtaining three‐, two‐, one‐ and zero‐dimensional derived compounds depending on their size and concentration. Thus, a structural genealogy tree for BaI₂ can be established. This method, transferred to alkali halides using crown ethers and calix[n]arenes as delimiting ligands, leads us to the subject of one‐dimensional ionic channels. A second chapter deals with the supramolecular approach for the synthesis of different dimensional polymer structures derived from alkaline earth metal iodides, and based on the combination of metal ion coordination with hydrogen bonding between the cationic complexes and their anions. Under certain circumstances, rules can be established for the prediction of the dimensionality of a given compound, thus contributing to the fundamental problem of structure prediction in crystal engineering. A third part describes a fundamentally new synthetic pathway for generating pure alkaline earth metal cage compounds as well as alkali and alkaline earth mixed metal clusters. In a first step, different molecular precursors, such as solvated alkaline earth metal halides are investigated as a function of the ligand size and reactivity. They are then reacted with some alkali metal compound in order to partially eliminate alkali halide and to form the clusters. The so obtained unique structures of ligand stabilized metal halide, hydroxide and/or alkoxide and aryloxide aggregates are of interest as potential precursors for oxide materials. Approaches to two synthetic methods of the latter, sol‐gel and (MO)‐CVD, are investigated with our compounds. In order to generate single source precursors for oxide materials, we started to investigate transition metal ions, especially Cu and Ag, using multitopic ligands. This has led us into the fundamental problematic of “crystal engineering” and solid state structure prediction and we found ourselves confronted to numerous interesting cases of polymorphism and pseudo‐polymorphism. Weak interactions, such as π‐stacking, H‐bonding and metal‐metal interactions, and solvent, counter ion and concentration effects seem to play important roles in the construction of such low‐dimensional structures. Finally, the physical properties of some of our compounds are described qualitatively in order to show the wide spectrum of possibilities and potential applications for the chemistry in this field.     

Stoichiometrically Controlled Revocable Self‐Assembled “Spiro” versus Quadruple‐Stranded “Double‐Decker” Type Coordination Cages

The simple combination of Pd^II with the tris‐monodentate ligand bis(pyridin‐3‐ylmethyl) pyridine‐3,5‐dicarboxylate, L , at ratios of 1:2 and 3:4 demonstrated the stoichiometrically controlled exclusive formation of the “spiro‐type” Pd₁L₂ macrocycle, 1 , and the quadruple‐stranded Pd₃L₄ cage, 2 , respectively. The architecture of 2 is elaborated with two compartments that can accommodate two units of fluoride, chloride, or bromide ions, one in each of the enclosures. However, the entry of iodide is altogether restricted. Complexes 1 and 2 are interconvertible under suitable conditions.     

Interfaces between Molecular and Polymeric “Metals”: Electrically Conductive,Structure-Enforced Assemblies of Metallomacrocycles

The design, synthesis, characterization, and understanding of new molecular and macro-molecular substances with “metal-like” electrical properties represents an active research area at the interface of chemistry, physics, and materials science. An important, long-range goal in this field of “materials by design” is to construct supermolecular assemblies which exhibit preordained collective phenomena by virtue of “engineered” interactions between molecular building blocks. In this review, such a class of designed materials is discussed which, in addition, bridges the gap between molecular and polymeric conductors: assemblies of electrically conductive metallomacrocycles. It is seen that efforts to rationally construct stacked metal-like molecular arrays lead logically to structure-enforced macromolecular assemblies of covalently linked molecular subunits. Typical building blocks are robust, chemically versatile metallophthalocyanines. The electrical optical, and magnetic properties of these metallomacrocyclic assemblies and the fragments thereof, provide fundamental information on the connections between local atomic-scale architecture, electronic structure, and the macroscopic collective properties of the bulk solid.