Thiolates, selenolates, and tellurolates of the s-block elements

The potential of alkali and alkaline earth metal chalcogenolates in synthetic chemistry and various technical applications has sparked the recent interest in the chemistry of alkali and alkaline earth metal thiolates, selenolates and tellurolates. As a result, an increasing body of work concerned with exploring synthetic routes to the target compounds, analyzing the influence of metal, ligand and donor on the structural chemistry, and correlating structure and function has appeared in the literature, most of which during the last few years. This article describes recent trends in this area of alkali and alkaline earth chemistry, by discussing synthetic access routes, analyzing structure determining factors such as metal, donor and ligand influence, comparing structural similarities and disparities in alkali and alkaline earth chemistry, and discussing structure–function relationships.     

When VSEPR Fails: Experimental and Theoretical Investigations of the Behavior of Alkaline‐Earth‐Metal Acetylides

The synthesis, structural, and spectral characterization as well as a theoretical study of a family of alkaline‐earth‐metal acetylides provides insights into synthetic access and the structural and bonding characteristics of this group of highly reactive compounds. Based on our earlier communication that reported unusual geometry for a family of triphenylsilyl‐substituted alkaline‐earth‐metal acetylides, we herein present our studies on an expanded family of target derivatives, providing experimental and theoretical data to offer new insights into the intensively debated theme of structural chemistry in heavy alkaline‐earth‐metal chemistry.     

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.     

Recent advances in tailoring the aggregation of heavier alkaline earth metal halides, alkoxides and aryloxides from non-aqueous solvents

This overview on one of the subjects treated in our group deals with the synthesis and study of low-dimensional polymer and molecular solid state structures formed with alkaline earth metal ions in non-aqueous solvents. We have chosen several synthetic approaches in order to obtain such compounds. The first concept deals with the "cutting out" of structural fragments from a solid state structure of a binary compound, which will be explained with reference to BaI2. Depending on the size and concentration of oxygen donor ligands, used as chemical scissors on BaI2, three-, two-, one- and zero-dimensional derived adducts of BaI2 are obtained, comparable to a structural genealogy tree for BaI2. A second part deals with the supramolecular approach for the synthesis of low dimensional polymeric compounds based on alkaline earth metal iodides, obtained by the combination of metal ion coordination with hydrogen bonding between the cationic complexes and their anions. Certain circumstances allow rules to be established for the prediction of the dimensionality of a given compound, contributing to the fundamental problem of structure prediction in crystal engineering. A third section describes a synthetic approach for generating pure alkaline earth metal cage compounds as well as alkali and alkaline earth mixed metal clusters. A first step deals with different molecular solvated alkaline earth metal iodides which are investigated as a function of the ligand size in non-aqueous solvents. These are then reacted with some alkali metal compound in order to partially or totally eliminate alkali iodide and to form the targeted clusters. These unique structures of ligand stabilized metal halide, hydroxide and/or alkoxide and aryloxide aggregates are of interest as potential precursors for oxide materials and as catalysts. Approaches to two synthetic methods of the latter, sol-gel and (MO)CVD (metal-organic chemical vapour deposition), are investigated with some of our compounds. (D. C. Bradley, Chem. Rev., 1989, 89, 1317-22; K. G. Caulton and L. G. Hubert-Pfalzgraf, Chem. Rev., 1990, 90, 969-95; T. P. Hanusa, Coord. Chem. Rev., 2000, 210, 329-367; T. P. Hanusa, in Comprehensive Coordination Chemistry II, ed. J. A. McCleverty and T. J. Meyer, Elsevier, Amsterdam, 2004, vol. 3, 1-92). 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 chemistry in this field.     

Zur Kenntnis der sogenannten «Erdalkalicarbonyle»

The alkaline earth metals in liquid ammonia react with carbon monoxide to form the so-called ‘alkaline earth metal carbonyls’. These products which according to older literature are formulated as M(CO)₂(M = Ca, Sr, Ba) contain only 65–70% of the expected amount of carbon monoxide. As can be seen from the nitrogen content of the compounds the solvent ammonia participates in the reaction. By hydrolysis leading to a variety of compounds it is demonstrated that the ‘alkaline earth metal carbonyls’ are mixtures of substances such as metal acetylenediolates, metal methoxides, and ammonium carbonate. These mixtures are different from the ‘alkali carbonyls’ as for instance can be seen from the low acetylenediolate content of the ‘alkaline earth metal carbonyls’.     

Rare‐Earth‐Metal Methylidene Complexes

Transition‐metal carbene complexes have been known for about 50 years and widely applied as reagents and catalysts in organic transformations. In contrast, the carbene chemistry of the rare‐earth metals is much less developed, but has attracted the research interest in the recent years. In this field rare‐earth‐metal alkylidene, especially methylidene, compounds are an emerging class of compounds with a high synthetic potential for organometallic chemistry and maybe in the future also for organic chemistry.     

Crystal structure evolution of complex metal aluminum hydrides upon hydrogen release

Complex aluminum hydrides have been widely studied as potential hydrogen storage materials but also,for some time now, for electrochemical applications. This review summarizes the crystal structures of alkali and alkaline earth aluminum hydrides and correlates structure properties with physical and chemical properties of the hydride compounds. The crystal structures of the alkali metal aluminum hydrides change significantly during the stepwise dehydrogenation. The general pathway follows a transformation of structures built of isolated [AlH4]~- tetrahedra to structures built of isolated [Al H6]~(3-) octahedra.The crystal structure relations in the group of alkaline earth metal aluminum hydrides are much more complicated than those of the alkali metal aluminum hydrides. The structures of the alkaline earth metal aluminum hydrides consist of isolated tetrahedra but the intermediate structures exhibit chains of cornershared octahedra. The coordination numbers within the alkali metal group increase with cation sizes which goes along with an increase of the decomposition temperatures of the primary hydrides. Alkaline earth metal hydrides have higher coordination numbers but decompose at slightly lower temperatures than their alkali metal counterparts. The decomposition pathways of alkaline metal aluminum hydrides have not been studied in all cases and require future research.     

Review: the multicolored coordination chemistry of violurate anions

This review provides a comprehensive overview on the coordination chemistry of violuric acid, C₄H₃N₃O₄ (= H₃Vio), and its derivatives (e.g. 1,3-diorganovioluric acids and thiovioluric acid). The most remarkable property of these colorless compounds is the formation of brightly colored (pantochromic/polychromic) salts with colorless cations such as alkali metal and alkaline earth metal ions and organoammonium ions. These magnificent colors have fascinated chemists for more than a century. Only in recent years it has been fully recognized that the structural chemistry of violurates is rather interesting and diverse. Violurate anions are excellent building blocks for new supramolecular assemblies in the crystalline state. Various organoammonium violurates and transition metal violurate complexes have been structurally characterized through single-crystal X-ray diffraction. Highly characteristic for these structures is the formation of 1D, 2D, or 3D hydrogen-bonded assemblies in the crystalline state. This review provides a comprehensive overview on the multicolored coordination chemistry of violurate anions, with the focus being on structurally characterized species.     

Alkaline Earth Metallocenes Coordinated with Ester Pendants: Synthesis,Structural Characterization,and Application in Metathesis Reactions

A variety of ester‐substituted cyclopentadiene derivatives have been synthesized by one‐pot reactions of 1,4‐dilithio‐1,3‐butadienes, CO, and acid chlorides. Direct deprotonation of the ester‐substituted cyclopentadienes with Ae[N(SiMe₃)₂]₂ (Ae=Ca, Sr, Ba) efficiently generated members of a new class of heavier alkaline earth (Ca, Sr, Ba) metallocenes in good to excellent yields. Single‐crystal X‐ray structural analysis demonstrated that these heavier alkaline earth metallocenes incorporated two intramolecularly coordinated ester pendants and multiply‐substituted cyclopentadienyl ligands. The corresponding transition metal metallocenes, such as ferrocene derivatives and half‐sandwich cyclopentadienyl tricarbonylrhenium complexes, could be generated highly efficiently by metathesis reactions. The multiply‐substituted cyclopentadiene ligands bearing an ester pendant, and the corresponding heavier alkaline earth and transition‐metal metallocenes, may have further applications in coordination chemistry, organometallic chemistry, and organic synthesis.     

Recent Developments in the Organic Chemistry of Calcium – An Element with Unlimited Possibilities in Organometallic Chemistry?

The organocalcium chemistry developed vastly during the last decade. The preparation of the organocalcium compounds via direct synthesis (insertion of Ca into a C‐X bond of phenyl halides, Grignard reaction) affords skilful procedures due to the inertia of the calcium metal and the extreme reactivity of the organocalcium derivatives. Further suitable preparative methods include metathesis reactions of CaX₂ with KR or LiR, metallation reactions of H‐acidic substrates, metal‐halogen exchange reactions, and transmetallation of heavy main group atoms in their compounds with calcium metal. Possibilities to stabilize organocalcium compounds include steric shielding by bulky ligands at the periphery and electronic reduction of the nucleophilicity of the calcium‐bound carbanions. Selected applications in catalysis such as hydrophosphination are also mentioned. Very recent developments and challenges in the preparation of alkaline earth metal(I) compounds are presented as well. Concepts to overcome the rather large atomization energies of the metals are discussed.     

Fluorometric sensing of alkali metal and alkaline earth metal cations by novel photosensitive monoazacryptand derivatives in aqueous micellar solutions

Novel monoazacryptand-type fluorescent chemosensors, (derived from an 18-crown-6) and (derived from a 15-crown-5) both with a pyrene ring as their photoresponsive moiety, were synthesized. Their fluorescence properties for alkali metal and alkaline earth metal cations in water were then examined. The detection of metal cations was accomplished by a change in the fluorescence intensity of the host compounds, based on a photoinduced electron transfer (PET) mechanism. In aqueous solution, showed little fluorescence upon the addition of Ba2+ because of the very weak complexation with Ba2+, but the presence of micelles of polyoxyethylene(10) isooctylphenyl ether (Triton X-100) enabled to show highly sensitive and selective Ba2+ detection among alkali metal and alkaline earth metal cations. With respect to the selective fluorescent detection of important metal cations (Na+, K+, Mg2+, Ca2+) relevant to living organisms, was found to detect K+ with high selectivity in aqueous micellar solutions of polyoxyethylene(20) sorbitan monostearate (Tween-60). The selectivity for metal cations was mainly dependent on the goodness of fit of the host cavity and the metal cation size. In the presence of anionic surfactants, detected alkaline earth metal cations more effectively than alkali metal cations.     

Discriminating detection between Mg2+ and Ca2+ by fluorescent signal from anthracene aromatic amide moiety

Novel fluorescent reagents 1 and 2 were synthesized. In the absence of metal ions, the fluorescence emissions of these compounds were quite weak, but their intensities were much greater in the presence of alkaline earth metal ions. The peak shape and maximum wavelength of the emission of the complex with Mg2+ differed from those of Ca2+ and other alkaline earth metal ions. The peak wavelength difference was 30 nm.     

Bulky Amido Ligands in Rare Earth Chemistry — Syntheses,Structures, and Catalysis

The amido metal chemistry of the rare earth elements is a rapid developing area in coordination chemistry. Especially bulky mono and bidentate amido and amidinates have been introduced as ligands in rare earth chemistry. Due to these sterically demanding ligands, the coordination numbers of the rare earth elements are significantly reduced. This article focuses on two of these bulky ligand systems: bis(trimethylsilyl)amide and aminotroponiminates. The homoleptic bis(trimethylsilyl)amides of rare earth elements, [Ln{N(SiMe₃)₂}₃], are well established compounds in synthetic chemistry. Therefore, this article reviews recent progress in the catalytic application of these compounds. In the second part of this research report, it is shown that N, N′‐disubstituted aminotroponiminates and mono bridged bisaminotroponiminates can be used as cyclopentadienyl alternatives. Achiral and chiral aminotroponiminates have been used. The structural properties, reactivities as well as the catalytic and synthetic applications of the aminotroponiminates complexes will be outlined in this article.     

From monomers to solids: controlled hydrolysis to form novel, heteroleptic hydroxide-containing complexes

Four novel alkaline earth metal tetranuclear aryloxide/pyrazolate hydroxides of the general formula M4(ligand)6(OH)2(donor)n have been prepared by either adding stoichiometric quantities of water to preformed alkaline earth metal aryloxides or in a direct metalation regime combining metal, ligand (alcohol, pyrazole), and donor with stoichiometric amounts of water. The compounds are considered as potential intermediates in the sol-gel process. A nonhydrolyzable magnesium aryloxide has also been obtained using the same reaction scheme. Unexpectedly, a dimeric strontium complex with further association of a second dimer via hydrogen bonding from the solvent of crystallization, ethylenediamine, has been isolated by the treatment of strontium metal with a mixture of alcohol and water. All compounds were characterized using X-ray crystallography, 1H and 13C NMR, and IR spectroscopy.     

Generation of organo-alkaline earth metal complexes from non-polar unsaturated molecules and their synthetic applications

Organomagnesium compounds, represented by the Grignard reagents, are one of the most classical yet versatile carbanion species which have widely been utilized in synthetic chemistry. These reagents are typically prepared via oxidative addition of organic halides to magnesium metals, via halogen–magnesium exchange between halo(hetero)arenes and organomagnesium reagents or via deprotonative magnesiation of prefunctionalized (hetero)arenes. On the other hand, recent studies have demonstrated that the organo-alkaline earth metal complexes including those based on heavier alkaline earth metals such as calcium, strontium and barium could be generated from readily available non-polar unsaturated molecules such as alkenes, alkynes, 1,3-enynes and arenes through unique metallation processes. Nonetheless, the resulting organo-alkaline earth metal complexes could be further functionalized with a variety of electrophiles in various reaction modes. In particular, organocalcium, strontium and barium species have shown unprecedented reactivity in the downstream functionalization, which could not be observed in the reactivity of organomagnesium complexes. This perspective will focus on the newly emerging protocols for the generation of organo-alkaline earth metal complexes from non-polar unsaturated molecules and their applications in chemical synthesis and catalysis.

In this perspective, we highlight the recent development of metallation protocols of non-polar unsaturated molecules for the generation of organo-alkaline earth metal compounds and their applications in chemical synthesis and catalysis.     

Proton di-ionizable p-tert-butylcalix[4]arene-crown-6 compounds in cone, partial-cone and 1,3-alternate conformations: synthesis and alkaline earth metal cation extraction

Novel proton di-ionizable p-tert-butylcalix[4]arene-crown-6 compounds in cone, partial-cone and 1,3-alternate conformations are synthesized to compare the efficiency and selectivity with which they extract alkaline earth metal ions. In these ligands, a crown-6 polyether unit links alternate aromatic rings of the calix[4]arene framework. To the remaining lower-rim positions are attached oxyacetic acid or N-(X)sulfonyl oxyacetamide groups. Changing the conformation varies the spatial relationship between a polyether-complexed divalent metal ion and the ionized side arms of the ligands. This is found to markedly affect the efficiency and selectivity in competitive solvent extraction of alkaline earth metal ions from aqueous solutions into chloroform by the di-ionizable calix[4]arene-crown-6 ligands.     

Structure and Bonding in Organometallic Anions of Heavy Group 14 and 15 Elements

Alkali metal organometallic complexes (containing C–metal bonds) and the frequently structrually related alkali metal amides and alkoxides have been investigated extensively both in the solid state and in solution in the past two decades. However, until recently, the related complexes containing the heavier metallic and semi-metallic p block elements and the alkali and alkaline earth metals had rarely been studied in their own right. Recent solid-state structural studies have illustrated the immense structural diversity and bonding modes to be found within these species. One of the principal focuses of recent studies has been complexes containing organometallic anions of p block metals (e.g., triorganostannates, containing R₃Sn^?) in which metal–metal bonds occur between the heavy p block metal and the alkali or alkaline earth metal and the investigation of the nature of this bonding. The development of new synthetic routes has also allowed the preparation of a variety of anionic ligands with p block metal centers which promise new opportunities in coordination chemistry. In addition, the synthesis of a family of homologous anionic π complexes has given a fresh direction in the chemistry of p block metal metallocene complexes.     

Accurate enthalpies of formation of alkali and alkaline earth metal oxides and hydroxides: assessment of the correlation consistent composite approach (ccCA)

Computing the enthalpies of formation for alkali metal and alkaline earth metal oxides (M(x)O) and hydroxides [M(OH)(n)] using the Gaussian-n (Gn) and Weismann-n (Wn) ab initio model chemistries is difficult due to an improper treatment of core-valence electron correlation effects. Using a new model chemistry called the correlation consistent Composite Approach (ccCA), enthalpies of formation were determined for eight different alkali/alkaline earth metal oxides and hydroxides. Unlike the Gn and Wn model chemistries, which must be modified to properly account for core-valence electron correlation, the standard implementations of the ccCA provide acceptable results, and all enthalpies of formation obtained with the ccCA are within the accepted range of recommended values.     

Synthesis of classes of ternary metal oxide nanostructures

Nanoscale structures, such as nanoparticles, nanorods, nanowires, nanocubes, and nanotubes, have attracted extensive synthetic attention as a result of their novel size-dependent properties. Ideally, the net result of nanoscale synthesis is the production of structures that achieve monodispersity, stability, and crystallinity with a predictable morphology. Many of the synthetic methods used to attain these goals have been based on principles derived from semiconductor technology, solid state chemistry, and molecular inorganic cluster chemistry. We describe a number of advances that have been made in the reproducible synthesis of various ternary oxide nanomaterials, including alkaline earth metal titanates, alkali metal titanates, bismuth ferrites, ABO(4)-type oxides, as well as miscellaneous classes of ternary metal oxides.     

Analogy of the coordination chemistry of alkaline earth metal and lanthanide Ln(2+) ions: the isostructural zoo of mixed metal cages [IM(OtBu)4{Li(thf)}4(OH)] (M=Ca, Sr, Ba, Eu), [MM'6(OPh)8(thf)6] (M=Ca, Sr, Ba, Sm, Eu, M'=Li, Na), and their derivatives with 1,2-dimethoxyethane

As previously shown, alkali and alkaline earth metal iodides in nonaqueous, aprotic solvents behave like transition metal halides, forming cis- and trans-dihalides with various neutral O-donor ligands. These compounds can be used as precursors for the synthesis of new mixed alkali/alkaline earth metal aggregates. We show here that Ln2+ ions form isostructural cluster compounds. Thus, with LiOtBu, 50% of the initial iodide can be replaced in MI2, M=Ca, Sr, Ba, Eu, to generate the mixed-metal alkoxide aggregates [IM(OtBu)4{Li(thf)}4(OH)], for which the M--OH contacts were investigated by theoretical methods. With M'OPh (M'=Li, Na), a new mixed-metal aryloxide cluster type [MM'6(OPh)8(thf)6] is obtained for M=Ca, Sr, Ba, Sm, Eu. Their stability versus DME (DME=1,2-dimethoxyethane) as bidentate ligand is studied.