Problems of unusual hydrogen bonds between proton donors and transition metal hydrides and borohydrides

The results of experimental and theoretical studies of intermolecular MH...HX and BH...HX hydrogen bonds with the hydride hydrogen atom acting as a proton accepting site are analyzed. Spectral (IR and NMR) criteria for their formation are presented. The spectral, structural, and thermodynamic characteristics of these unusual hydrogen bonds obey the regularities found for classical hydrogen bonds. It was shown that the MH...HX bonds participate in the proton transfer with the formation of nonclassical cationic hydrides and the |M(η²-H₂|⁺ hydrogen bonds are formed in low-polarity media. Problems arising in this new line of investigations are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 846–851, May, 1998.     

Synthesis and Thermal Decomposition Behaviors of Magnesium Borohydride Ammoniates with Controllable Composition as Hydrogen Storage Materials

An ammonia‐redistribution strategy for synthesizing metal borohydride ammoniates with controllable coordination number of NH₃ was proposed, and a series of magnesium borohydride ammoniates were easily synthesized by a mechanochemical reaction between Mg(BH₄)₂ and its hexaammoniate. A strong dependence of the dehydrogenation temperature and purity of the released hydrogen upon heating on the coordination number of NH₃ was elaborated for Mg(BH₄)₂?x NH₃ owing to the change in the molar ratio of H^δ+ and H^δ?, the charge distribution on H^δ+ and H^δ?, and the strength of the coordinate bond N:→Mg²⁺. The monoammoniate of magnesium borohydride (Mg(BH₄)₂?NH₃) was obtained for the first time. It can release 6.5 % pure hydrogen within 50 minutes at 180 °C.     

Binary Polyazides of Cadmium and Mercury

Following our interest in binary element–nitrogen compounds we report here on the synthesis and comprehensive characterization (M.p., IR/Raman, elemental analysis, ¹⁴N/¹³³Cd/¹⁹⁹Hg NMR) of tri‐ and tetraazido cadmate and mercurate anions [E(N₃)_(2+n)]^n? (E=Cd, Hg; n=1, 2) in a series of [Ph₄P]⁺ and [PNP]⁺ ([PNP]⁺=bis(triphenylphosphine)iminium) salts. The azide/chloride exchange in CH₂Cl₂ as well as the formation of tetrazolate salts in CH₃CN solutions of the polyazido mercurates were investigated. Single crystal X‐ray structures of all new compounds, and for comparison [Ph₄P][Cd₂(N₃)₅(H₂O)], were determined. Moreover, the synthesis of anhydrous cadmium(II) azide and its DMSO adduct is presented for the first time. For a better understanding of structure and bonding in E(N₃)₂, [E(N₃)₃]^? and [E(N₃)₄]^2?, theoretical calculations at the M06‐2X/aug‐cc‐pVDZ level were carried out.     

Adjustment of twist angles in pseudo-helical lanthanide complexes by the size of metal ions

Control of self-assembled nanostructures is a promising technique for nanotechnology. We have examined as to whether nanostructures could be controlled by the size of the central metal ion. Lanthanides are a natural choice for such a study as the size of their trivalent ions changes with atomic number gradually. For this investigation, a series of rare earth complexes ([LaL(1)], [CeL(1)], [SmL(1)], [TbL(1)], [YL(1)], and [LuL(1)]) with a tripodal heptadentate ligand L(1) were synthesized, and their X-ray crystallographic analysis was performed. Although the structures of the ligand (H(3)L(1)) and of the metal complex ([ML(1)]) were quite different, all complexes were almost isostructural pseudohelices. The result of the crystallographic studies demonstrated that the twist angles of helices in the complexes depend on the ionic size of the central metal. A detailed analysis helped determine which portion of the helical strand contributed to the total helicity, and the major cause for the difference in helicity among the lanthanides is discussed. Moreover, this result is the first example showing that La(I) (II) and Lu(I) (II) complexes with the same tripodal heptadentate ligand are isostractural.     

Novel modification of anhydrous transition metal oxalates from powder diffraction

The known metal–C₂O₄ structures may be divided into two modifications, α and β. The α‐modification has an order–disorder struxture, revealing one‐dimensional disordering of the metal–oxalate chains, and the β‐modification is ordered. The crystal structures of orthorhombic γ‐MnC₂O₄ {poly[μ‐oxalato‐manganese(II)]; space group Pmna , a = 7.1333 (1), b = 5.8787 (1), c = 9.0186 (2) Å, V = 378.19 (1) ų, Z = 4 and D_x = 2.511 Mg m⁻³} and γ‐CdC₂O₄ {poly[μ‐oxalato‐cadmium(II)]; space group Pmna , a = 7.3218 (1), b = 6.0231 (1), c = 9.2546 (2) Å, V = 408.13 (1) ų, Z = 4 and D_x = 3.262 Mg m⁻³} have been obtained from powder diffraction patterns. The structures are isostructural. Each metal atom in each structure is coordinated by seven O atoms which belong to five oxalate ions. The crystal packing, which contains noticeable cavities in the [101] and [001] directions, is not close packed and essentially differs from the known disordered α‐ and ordered β‐modifications of transition metal oxalates. This modification seems to be metastable. It was found that a spontaneous γ→β phase transition takes place for γ‐CdC₂O₄.     

Hydrogen storage in borohydrides Comparison of hydrolysis conditions of LiBH<Subscript>4</Subscript>, NaBH<Subscript>4</Subscript> and KBH<Subscript>4</Subscript>

The hydrogen storage capabilities of alkaline borohydrides through a hydrolyzing process were determined by taking into consideration the hydration of the end products. Comparison of LiBH₄, NaBH₄ and KBH₄ showed their storage capacities to be dependent on the composition of the metaborate formed. This composition is ruled by the hydrolysis conditions, especially the temperature reached during the reaction and the stability of the hydrates. The borohydride with the highest hydrogen content in the solid state, LiBH₄, could be less efficient than KBH₄ if the hydrolysis is performed at 120°C.     

Heavy alkaline earth metal pyrazolates: synthetic pathways, structural trends, and comparison with divalent lanthanoids

Two series of heavy alkaline earth metal pyrazolates, [M(Ph(2)pz)(2)(thf)(4)] 1 a-c (Ph(2)pz=3,5-diphenylpyrazolate, M=Ca, Sr, Ba; THF=tetrahydrofuran) and [M(Ph(2)pz)(2)(dme)(n)] (M=Ca, 2 a, Sr, 2 b, n=2; M=Ba, 2 c, n=3; DME=1,2-dimethoxyethane) have been prepared by redox transmetallation/ligand exchange utilizing Hg(C(6)F(5))(2). Compounds 1 a and 2 b were also obtained by redox transmetallation with Tl(Ph(2)pz). Alternatively, direct reaction of the alkaline earth metals with 3,5-diphenylpyrazole at elevated temperatures under solventless conditions yielded compounds 1 a-c and 2 a-c upon extraction with THF or DME. By contrast, [M(Me(2)pz)(2)(Me(2)pzH)(4)] 3 a-c (M=Ca, Sr, Ba; Me(2)pzH=3,5-dimethylpyrazole) were prepared by protolysis of [M[N(SiMe(3))(2)](2)(thf)(2)] (M=Ca, Sr, Ba) with Me(2)pzH in THF and by direct metallation with Me(2)pzH in liquid NH(3)/THF. Compounds 1 a-c and 2 a-c display eta(2)-bonded pyrazolate ligands, while 3 a,b exhibit eta(1)-coordination. Complexes 1 a-c have transoid Ph(2)pz ligands and an overall coordination number of eight with a switch from mutually coplanar Ph(2)pz ligands in 1 a,b to perpendicular in 1 c. In eight coordinate 2 a,b the pyrazolate ligands are cisoid, whilst 2 c has an additional DME ligand and a metal coordination number of ten. By contrast, 3 a,b have octahedral geometry with four eta(1)-Me(2)pzH donors, which are hydrogen-bonded to the uncoordinated nitrogen atoms of the two trans Me(2)pz ligands. The application of synthetic routes initially developed for the preparation of lanthanoid pyrazolates provides detailed insight into the similarities and differences between the two groups of metals and structures of their complexes.     

金属皂的晶体结构

钠、钾以外金属的高级脂肪酸盐通称金属皂。它们兼具金属盐和脂肪酸的特性,在工业上广泛用作为塑料助剂(热稳定剂、润滑剂等)、油漆催干剂、增稠剂、防水剂、脱模剂,爽滑剂等[1]。金属皂的许多特性随脂肪链长度和金属种类的不同而变化。稀土、碱土和锌、镉、铅等金属皂是重要的PVC热稳定剂和润滑剂[2,3]。前文[4,5]已报道了稀土金属皂结构的红外光谱和X 射线衍射谱,本文报道镁、钙、锶、钡、锌、镉、铅与棕榈酸、肉豆蔻酸、月桂酸、癸酸锌、辛酸形成金属皂结构的X 射线衍射谱。1　实验部分1 1　金属皂合成采用复分解法[1]合成,产物均…     

Structure determination of homoleptic AuI, AgI, and CuI aryl/alkylethynyl coordination polymers by X-ray powder diffraction

This article describes the structure determination of five homoleptic d(10) metal-aryl/alkylacetylides [RC triple bond CM] (M=Cu, R=tBu 1, nPr 2, Ph 3; R=Ph, M=Ag 4; Au 5) by using X-ray single-crystal and powder diffraction. Complex 1.C6H6 reveals an unusual Cu20 catenane cluster structure that has various types of tBuC triple bond C-->Cu coordination modes. By using this single-crystal structure as a starting model for subsequent Rietveld refinement of X-ray powder diffraction data, the structure of the powder synthesized from CuI and tBuC triple bond CH was found to have the same structure as 1. Complex 2 has an extended sheet structure consisting of discrete zig-zag Cu4 subunits connected through bridging nPrC triple bond C groups. Complex 3 forms an infinite chain structure with extended Cu-Cu ladders (Cu-Cu=2.49(4)-2.83(2) A). The silver(I) congener 4 is iso-structural to 3 (average Ag-Ag distance 3.11 A), whereas the gold(I) analogue 5 forms a Au...Au honeycomb network with PhC triple bond C pillars (Au-Au=2.98(1)-3.26(1) A). Solid-state properties including photoluminescence, nu(C triple bond C) stretching frequencies and thermal stability of these polymeric systems are discussed in the context of the determined structures.     

Activation of Small Molecules by Phosphorus Biradicaloids

The reactivity of biradicaloid [P(μ‐NTer)]₂ was employed to activate small molecules bearing single, double, and triple bonds. Addition of chalcogens (O₂, S₈, Se_x and Te_x) led to the formation of dichalcogen‐bridged P₂N₂ heterocycles, except from the reaction with molecular oxygen, which gave a P₂N₂ ring featuring a dicoordinated P^III and a four‐coordinated P^V center. In formal [2πe+2πe] addition reactions, small unsaturated compounds such as ethylene, acetylene, acetone, acetonitrile, tolane, diphenylcarbodiimide, and bis(trimethylsilyl)sulfurdiimide are readily added to the P₂N₂ heterocycle of the biradicaloid [P(μ‐NTer)]₂, yielding novel heteroatom cage compounds. The synthesis, reactivity, and bonding of the biradicaloid [P(μ‐NTer)]₂ were studied in detail as well as the synthesis, properties, and structural features of all addition products.     

Prospects for the combination of mechanochemistry and flow applied to catalytic transformations

The urge of developing modern alternatives regarding industrial production has led to the creation of novel techniques that help overcome critical disadvantages from traditional batch mechanochemistry. One promising strategy includes the merging of flow processes with mechanochemistry. Two technologies are herein highlighted: twin-screw extrusion (TSE) and Impact (induction) in Continuous flow HEated Mechanochemistry (I-CHEM) allowing not only the industrial production of polymers but also active pharmaceutical ingredients, synthesis of (nano)materials, and the obtention of high-added value products from biomass and wastes valorization.     

Polymorph Identification and Crystal Structure Determination by a Combined Crystal Structure Prediction and Transmission Electron Microscopy Approach

Electron diffraction offers advantages over X‐ray based methods for crystal structure determination because it can be applied to sub‐micron sized crystallites, and picogram quantities of material. For molecular organic species, however, crystal structure determination with electron diffraction is hindered by rapid crystal deterioration in the electron beam, limiting the amount of diffraction data that can be collected, and by the effect of dynamical scattering on reflection intensities. Automated electron diffraction tomography provides one possible solution. We demonstrate here, however, an alternative approach in which a set of putative crystal structures of the compound of interest is generated by crystal structure prediction methods and electron diffraction is used to determine which of these putative structures is experimentally observed. This approach enables the advantages of electron diffraction to be exploited, while avoiding the need to obtain large amounts of diffraction data or accurate reflection intensities. We demonstrate the application of the methodology to the pharmaceutical compounds paracetamol, scyllo‐inositol and theophylline.     

在温和条件下合成金属有机骨架与多酸复合材料及其性能研究

本文利用机械球磨法成功将三种多金属氧簇H3PW12O40、H4SiW12O40和H3PMo12O40负载入ZIF-8纳米晶材料中,并采用粉末衍射(PXRD)、紫外可见吸收光谱(UV-Vis)、傅里叶-红外光谱(FT-IR)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等测试方法对复合材料进行了一系列表征.结果表明,复合材料结构稳定,合成方法具有操作简单、反应时间短、产量高等特点.此外,得到的复合材料对重金属离子Cu2+、Pd2+和Cd2+等均表现出良好的吸附性能.