氢原子在Ni(111)次表面和Ni(211)、(533)台阶面上的吸附与振动

应用原子与表面簇合物相互作用的五参数Morse势(5-MP)方法对氢原子在Ni(111)表面和次表面以及Ni(211), (533)台阶面进行了系统研究, 得到了氢原子在上述各面的吸附位、吸附几何、结合能和本征振动频率. 计算结果表明, 在Ni(111)面上, 氢原子优先吸附在三重位, 随着覆盖度的增加会吸附在次表面八面体位和四面体位. Ni(211), (533)的最优先吸附位都是四重位, 当氢原子的覆盖度增大时占据(111)平台的三重吸附位. 靠近台阶面的吸附位受台阶和平台高度的影响很大. 此外, 我们计算了氢原子在各表面的不同吸附位的扩散势垒, 获得氢原子在各表面的最低能量扩散通道.     

The synthesis and crystal structure of [NiL(NCS)2] (L=3-hydroxyethyl-1,3,5,8,12-pentaazacyclotetradecane)

The reaction of H2CO and H2NCH2CH2OH with the nickel(II) complex of 1,9-diamino-3,7-diazanonane (2,3,2-tet) in the presence of Et3N gives the nickel(II) complex of the macrocycle 3-hydroxyethyl-1,3,5,8,12-pentaazacyclotetradecane (L), which can be readily isolated as the perchlorate salt. The reaction of KCNS with the perchlorate salt in aqueous solution gives [NiL(NCS)2] and the crystal structure of this complex has been determined. The complex is octahedral and trans with the two N-bonded thiocyanates in the axial sites with Ni-NCS bond lengths of 2.106 and 2.145AÅ. The equatorial sites are occupied by N2, N5, N8 and N12 with Ni-N bond distances of 2.053 to 2.076AÅ, which are typical for octahedral nickel(II) complexes. The ligand has a trans III configuration of the sec-NH centres, leading to chair six-membered rings and gauche five-membered rings. The hydroxyethyl group on N3 is axial. There is no evidence for hydrogen-bonding interactions involving the hydroxyethyl group in the crystal lattice.     

Layered cobalt hydroxysulfates with both rigid and flexible organic pillars: synthesis, structure, porosity, and cooperative magnetism.

The synthesis and characterization of two members of a family of porous magnetic materials is described. The structures of Co4(SO4)(OH)6(C2N2H8)0.5*3H2O and Co4(SO4)(OH)6(C6N2H12)0.5*H2O and their thermal stability can be tailored via the choice of organic pillar. The interactions between the pillaring agent and the compositionally complex inorganic layer are discussed. The influences of two pillaring agents i.e., the flexible ethylenediamine and the relatively rigid 1,4-diazabicyclo[2,2,2]octane, on thermal stability, rigidity upon guest loss, and magnetic behavior of the pillared solids are compared. The magnetism of the pillared layered cobalt hydroxides is complex due to the influences of multiple metal sites, inter- and intralayer exchange, spin-orbit coupling, and geometrical frustration. The wide variety of potential pillars, oxyanions, and possible metal substitutions at the octahedral and tetrahedral sites offers the possibility of tailoring the magnetic and porous properties of these materials.     

Electron paramagnetic resonance, scanning electron microscopy with energy dispersion X-ray spectrometry, X-ray powder diffraction, and NMR characterization of iron-rich fired clays

The aim of this study is to clarify the structure of an iron-rich clay and the structural changes involved in the firing process as a preliminary step to get information on ancient ceramic technology. To this purpose, illite-rich clay samples fired at different temperatures were characterized using a multitechnique approach, i.e., by electron paramagnetic resonance, scanning electron microscopy with electron dispersion X-ray spectrometry, X-ray powder diffraction, magic angle spinning and multiple quantum magic angle spinning NMR. During firing, four main reaction processes occur: dehydration, dehydroxylation, structural breakdown, and recrystallization. When the results are combined from all characterization methods, the following conclusions could be obtained. Interlayer H2O is located close to aluminum in octahedral sites and is driven off at temperatures lower than 600 degrees C. Between 600 and 700 degrees C dehydroxylation occurs whereas, between 800 and 900 degrees C, the aluminum in octahedral sites disappears, due to the breakdown of the illite structure, and all iron present is oxidized to Fe3+. In samples fired at 1000 and 1100 degrees C iron clustering was observed as well as large single crystals of iron with the occurrence of ferro- or ferrimagnetic effects. Below 900 degrees C the aluminum in octahedral sites presents a continuous distribution of chemical shift, suggesting the presence of slightly distorted sites. Finally, over the whole temperature range, the presence of at least two tetrahedral aluminum sites was revealed, characterized by different values of the quadrupolar coupling constant.     

Structure and magnetism of new hybrid cobalt hydroxide materials built from decorated brucite layers

The structure, synthesis and magnetic properties of three new complex cobalt hydroxyl oxalates are presented, showing a modification of the 2-D double layer hydroxide structure. Co(12)(OH)(18)(ox)(3)(pip) [ox = oxalate, C(2)O(4)(2-); pip = piperazine, C(4)N(2)H(10)] (1), is essentially built from brucite-like layers with a one ninth depletion of the octahedral sites and a preservation of a trigonal crystallographic symmetry. ACo(28)(OH)(43)(ox)(6)Br(2)(H(2)O)(2) [A = Na (2), K (3)] are similarly composed of a brucite-like layer with three nineteenths depletion of octahedral sites, again preserving a trigonal symmetry. Both 2 and 3 show a small degree of structural disorder within the framework. All of these compounds have alternating layers of a mineral-like metal hydroxide structure and a metal oxalate coordination network, with the depletion in the hydroxyl layers being templated by the coordination network. Magnetic studies of 1 reveal a metamagnetic character, with the onset of an antiferromagnetic phase below T(c) = 23.5 K (H = 0 G), and a first order antiferromagnet to metamagnet transition at H(c) = 500-1000 G (T = 20-6 K). Compound 3 shows a more conventional ferrimagnetic ordering below 33(±1) K with a small coercive field of 107(±5) G at 10 K.     

The effect of ligand charge on the coordination geometry of an Fe(III)ion: five- and six-coordinate Fe(III) complexes of tris(2-benzimidazolylmethyl)amine

By using the tripodal tetradentate ligand tris(2-benzimidazolylmethyl)amine (H(3)ntb), which can have several charge states depending on the number of secondary amine protons, mononuclear octahedral and dinuclear trigonal bipyramidal Fe(III) complexes were prepared. The reaction of mononuclear octahedral [Fe(III)(H(3)ntb)Cl(2)]ClO(4), 1, with 3 equiv of sec-butylamine in methanol led to the formation of mononuclear cis-dimethoxo octahedral Fe(III)(H(2)ntb)(OMe)(2), 2. One equivalent of the sec-butylamine was used to generate the monoanionic H(2)ntb(-) ligand where one of the three amines in the benzimidazolyl groups was deprotonated. The remaining 2 equiv were used to generate two methoxides that were coordinated to the octahedral Fe(III) ion in a cis fashion as demonstrated by the chlorides in 1. Reaction of 1 with excess (7 equiv) sec-butylamine generated the doubly deprotonated dianionic Hntb(2-) that stabilized the dinuclear mu-oxo Fe(III)(2)O(Hntb)(2), 3, adopting a five-coordinate trigonal bipyramidal geometry. The magnetic data for 3 are consistent with the antiferromagnetically coupled Fe(III) (S = 5/2) sites with the coupling constant J = -127 cm(-1).     

Chemical modification of zinc hydroxide nitrate and Zn-Al-layered double hydroxide with dicarboxylic acids

A zinc hydroxide nitrate (ZHN), Zn5(OH)8(NO3)2.2H2O, and a layered double hydroxide (LDH), Zn/Al-NO3 were doped with 0.2 mol% of Cu2+ during alkaline chemical precipitation. Both compounds were intercalated with adipate ((-)OOC(CH2)4COO(-)), azelate ((-)OOC(CH2)7COO(-)), and benzoate (C6H5COO(-)) ions through ion exchange reactions. Solid state 13C nuclear magnetic resonance spectroscopy showed only one signal of carboxylic carbon for adipate and azelate intercalated into LDH, indicating that the carboxylic ends of both acids were equivalent, whereas the signal split when the intercalation was into the ZHN matrix. The electron paramagnetic resonance (EPR) spectrum of copper in octahedral cation sites of LDH layers showed a Hamiltonian parameter ratio g ||/A ||=170 cm and, after intercalation of adipate, the change was not significant: g ||/A ||=174 cm. This result indicates that the carboxylate ions did not coordinate with copper centers. Nonetheless, the intercalation of azelate increased the ratio to g ||/A ||=194 cm, similar to the spectra of ZHN modified with adipate, g ||/A ||=199 cm, and azelate, g ||/A ||=183 and 190 cm, which are associated with the coordination of copper by weak carboxylate anion ligands. Copper occupies octahedral or tetrahedral sites in ZHN layers, and the EPR spectra indicate that the dicarboxylate anions reacted preferentially with octahedral sites, whereas benzoate reacted with both sites.     

Placement of H atoms in the crystal lattice of cubic titanium oxyhydride: Simulation and diffraction experiment

Possible models for the arrangement of hydrogen atoms in the sites of the cubic lattice of titanium oxyhydride TiO_yH_p with vacancies in the metallic and nonmetallic sublattices are considered for the first time. It has been established that interstitial H atoms in oxyhydrides occupy vacant octahedral sites 4(b) of the oxygen sublattice. No displacement of H atoms in tetrahedral sites 8(c) is observed.     

Dynamical Equilibrium between Brønsted and Lewis Sites in Zeolites: Framework-Associated Octahedral Aluminum

While the structures of Brønsted acid sites (BAS) in zeolites are well understood, those of Lewis acid sites (LAS) remain an active area of investigation. Under hydrated conditions, the reversible formation of framework-associated octahedral aluminum has been observed in zeolites in the acidic form. However, the structure and formation mechanisms are currently unknown. In this work, combined experimental ²⁷Al NMR spectroscopy and computational data reveal for the first time the details of the zeolite framework-associated octahedral aluminium. The octahedral LAS site becomes kinetically allowed and thermodynamically stable under wet conditions in the presence of multiple nearby BAS sites. The critical condition for the existence of such octahedral LAS appears to be the availability of three protons: at lower proton concentration, either by increasing the Si/Al or by ion-exchange to non-acidic form, the tetrahedral BAS becomes thermodynamically more stable. This work resolves the question about the nature and reversibility of framework-associated octahedral aluminium in zeolites.     

催化甘油脱水反应的酸活化蒙脱石负载WOx催化剂的研究

甘油是一种可由生物资源生产、可持续的、可降解的平台化学品,是生物柴油、肥皂化工等工业生产过程中的主要副产物.催化甘油脱水反应生产丙烯醛,有望能替代丙烯等石油裂解产物合成丙烯醛的传统工业路线.丙烯醛是一种重要的化工中间体,被用于合成蛋氨酸、丙烯酸、3-甲基吡啶和1,3-丙二醇,并被广泛地应用于农药、医药、高分子材料等领域.随着全球可持续能源发展,生物柴油生产迅速发展,将产生大量的副产物甘油.利用甘油为原料,通过合适的催化剂的催化脱水反应生成丙烯醛,是近十多年来国内外工业催化的研究热点之一.用于催化甘油脱水合成丙烯醛的酸催化剂有杂多酸、金属氧化物、沸石与酸性粘土矿物等.钨磷杂多酸(H3PW12O40)负载的催化剂虽然具有较强的酸性,有利于催化甘油脱水,但容易导致结焦,而且热稳定差,容易失活.钨磷杂多酸负载于SiO2,TiO2,Al2O3,SiO2-Al2O3,K-10蒙脱石上表现出不同的催化活性,表明催化剂和载体的表面酸性和孔结构影响催化性能.近来研究发现,负载于ZrO2,Al2O3的钨氧化物(WOx)催化剂热稳定性好、酸性高,在甘油脱水反应生成丙烯醛中表现出良好的催化性能.但有关钨氧化物(WOx)结构、催化活性受载体组成、酸性影响的本质和规律一直不清楚.本文采用20 wt%的硫酸、盐酸、磷酸和乙酸对蒙脱石进行酸改性,并在磷酸改性的蒙脱石上负载W含量为4–16 wt%的WOx作为催化剂,用于甘油气相脱水反应.X-射线衍射(XRD)、热重-差热法(TG-DTG)、氨程序升温脱附(NH3-TPD)、红外光谱(FT-IR)和紫外漫反射可见光谱(DR UV-vis)等表征,探讨了酸改性和负载WOx的蒙脱石对催化剂催化性能的影响.蒙脱石经过20wt%的硫酸、盐酸、磷酸和乙酸的活化,酸性增加.四种酸改性的蒙脱石对甘油气相脱水反应均有催化活性,这是因为在蒙脱石酸活化过程中,H+经过阳离子交换反应进入蒙脱石层间,同时蒙脱石八面体中的部分Al3+被浸出,使层板上出现不饱和Al3+,为催化剂提供了L酸位,蒙脱石硅氧四面体上的Si?OH以及[AlO4]上吸附的H3O+提供了B酸位.XRD分析表明,负载WOx的蒙脱石表面存在WO2.72,WO2.9和WO3三种不同类型的WOx,当钨负载量从12 wt%增至16 wt%,孤立的单斜晶系WO3晶粒增多.NH3-TPD和DR UV-vis结果表明,WOx负载在蒙脱石表面以[WO5/WO6](B酸位)、[WO4]和单斜晶系WO3相(L酸位)形式存在.蒙脱石上负载WOx能够调节催化剂的酸强度、酸量和酸位.随着钨负载量从4 wt%增至12 wt%,丙烯醛收率从40.9%增加到67.3%;进一步增加钨负载量到16 wt%,丙烯醛收率降为50.7%.结果发现,随着钨负载量的增加,催化活性组分含量增加,[WO5/WO6](B酸位)增加,使催化活性增加;当W负载量达到16 wt%时,WOx分散性降低,且在催化剂表面形成孤立的单斜晶系WO3相(L酸位),不利于提高丙烯醛选择性.当反应温度为320 oC,甘油水溶液浓度为15 wt%时,磷酸活化蒙脱石负载12 wt%W的催化剂上甘油转化率为89.6%,丙烯醛收率达到73.3%.     

New cobalt(II) and zinc(II) coordination frameworks incorporating a pyridyl-pyrazole ditopic ligand

The metal-directed assembly of new molecular frameworks incorporating 4-(4-pyridyl)pyrazole (L), containing non-linear coordination vectors, is presented. Three metallo-arrays of types [Co(LH)2(NO3)4], [Co(LH)2(H2O)4][NO3]4.H2O and [Zn2(L-H)2Cl2].2EtOH are reported. The cobalt(II) in [Co(LH)2(NO3)4] displays distorted octahedral geometry, with the two protonated pyridyl-pyrazole ligands coordinated through their pyrazole nitrogen atoms in a trans-orientation; the remaining four coordination sites are occupied by nitrate anions. Two internal hydrogen bonds occur between each pyrazole NH and the oxygens of adjacent coordinated nitrato ligands. Short intermolecular hydrogen bonds also occur between the two pyridinium hydrogens and bound nitrate ligands on different molecules to yield a two-dimensional hydrogen-bonded array. Two of these arrays interpenetrate to form an extended two dimensional layer; such layers stack throughout the crystal structure. A second product of type [Co(LH)2(H2O)4][NO3]4.H2O exists as two crystallographically independent, but chemically similar, forms. In each form, the two protonated pyridyl-pyrazole ligands occupy trans positions about the cobalt, with the remaining four coordination sites being filled by water molecules to yield a distorted octahedral coordination geometry. Intramolecular hydrogen-bonding is observed between the two non-coordinated pyrazoyl nitrogen atoms and bound water oxygen atoms. The third complex, [Zn2(L-H)2Cl2].2EtOH, contains dimer units consisting of two zinc(II) ions bridged by two pyrazoylate groups in which the coordination geometry of each zinc approximates a tetrahedron. Each zinc is bound to two deprotonated pyridine-pyrazole ligands (L-H), one pyridyl group (from a different dimeric unit) and one chloro ligand. Each pyridyl nitrogen thus connects each of these zinc dimers to an adjacent dimer unit, forming a three-dimensional network containing small voids. The latter are occupied by ethanol molecules which form hydrogen bonds to the chloro ligands.     

Fe3+ concentration dependence of photoacoustic absorption spectroscopy on ZnGa2O4 ceramic powders

In this paper we present the photoacoustic spectroscopy of ZnGa2O4 with 5 and 10% of Fe3+. The ZnGa2O4 is a normal spinel, with Zn2+ ions in tetrahedral sites and Ga3+ ions in octahedral sites. It is expected for these hosts that Fe3+ ions occupy Ga3+ sites. Therefore, the optical properties would be associated to an octahedral symmetry. The energy levels were identified and the crystal field and electronic interaction parameters calculated with Tanabe-Sugano matrices for d5 configuration. We have also studied the dependence of the photoacoustic signal amplitude on the excitation light modulation frequency. Our results indicate that thermal expansion is the predominant phenomenon for the photoacoustic signal generation.     

[RuCl2{PPh2(2,6-Me2C6H3)}2]: A Neutral 14-Electron Ruthenium(II) Complex with Two Agostic Interactions

“Bidentate” ligand behavior is shown by (2,6-dimethylphenyl)diphenylphosphane in the title compound: In the nearly octahedral environment of the ruthenium atom two coordination sites are occupied by methyl groups of the two xylyl substituents. NMR investigation and an X-ray analysis (see picture) reveal that the methyl groups act as weak donors to form two strong agostic Ru⋅⋅⋅C−H interactions.     

EXAFS studies on adsorption-desorption reversibility at manganese oxide-water interfaces. II. Reversible adsorption of zinc on delta-MnO2

Microscopic structures of Zn(II) adsorbed at delta-MnO(2)-water interfaces were studied using extended X-ray absorption fine structure (EXAFS) spectroscopy. In a 0.1 M NaNO(3) solution of pH 5.50, hydrous Zn(II) was adsorbed onto the solid surface in the form of octahedral coordination. Adsorbed octahedral Zn(II) was located above and below the vacancy sites of delta-MnO(2). Each Zn was coordinated on one side to H(2)O molecules forming an H(2)O sheet and on the other side to oxygen atoms shared with layer MnO(6) octahedra forming a corner-sharing octahedral interlayer complex. The average Zn-O and Zn-Mn distances were 2.07+/-0.01 and 3.52+/-0.01 A, respectively. Macroscopic adsorption-desorption isotherms showed that, in contrast to that of the Zn-gamma-MnOOH system, adsorption of Zn(II) on delta-MnO(2) was highly reversible. EXAFS results indicated that the highly reversible adsorption was due to the weak adsorption mode of the corner-sharing linkage between the adsorbate and adsorbent polyhedra.     

Application of solid-state early-transition metal clusters as catalysts

Metal cluster compounds are expected to be catalysts for new reactions because of synergistic effect of the metal atoms. In solid-state halide clusters and sulfide clusters, metal cluster frameworks are linked in two- or three-dimensions to form a cluster network. Halogen- or sulfur-deficient metal sites in an octahedral metal cluster framework are retained intact and act as catalytically active sites even at high temperatures of 400–700?°C. This review reports recent advances in the development of coordinatively unsaturated metal atoms on solid-state clusters with an octahedral metal framework and their application to organic catalytic reactions.     

Hydrothermal synthesis and structure of a three-dimensional cobalt(II) triazolate magnet

The reaction of CoCl2.6H2O, 1,2,4-triazole, and H(2)O at 200 degrees C for 96 h yields purple rods of [Co2(trz)3Cl] (1; trz = 1,2,4-triazolate) in 90% yield. The structure of 1 consists of {Co(trz)3}n(n-) chains of Co(II) sites linked through tetrahedral sites of {CoN(3)Cl} geometry into a three-dimensional framework. The competing antiferromagnetic interactions of the octahedral and tetrahedral Co(II) centers result in weak ferromagnetic behavior below Tc = 9 K.     

利用程序升温还原方法研究钴,钌,钼加氢脱硫催化剂氧化态的还原过程

钴或镍在加氢脱硫(HDS)催化剂中的助剂作用文献已有很多的讨论。近年来,研究结果发现,少量的钌加入到Mo/Al_2O_3和Co-Mo/Al_2O_3催化剂上可以显著地提高其加氢脱硫活性,可是关于钌的助剂作用前人研究的较少。因此对比研究钴和钌的的助剂作用有助于认识各种不同类型的助剂在加氢脱硫催化剂中的功能。本文应用程序升温还原方法对钴和钌在加氢脱硫催化剂的前身态氧化物还原过程中的助剂作用进行了考察。     

Cation distribution in co-doped ZnAl2O4 nanoparticles studied by X-ray photoelectron spectroscopy and 27Al solid-state NMR spectroscopy

Co(x)Zn(1-x)Al(2)O(4) (x = 0.01-0.6) nanoparticles were synthesized by the citrate sol-gel method and were characterized by X-ray powder diffraction and transmission electron microscopy to identify the crystalline phase and determine the particle size. X-ray photoelectron spectroscopy and (27)Al solid-state NMR spectroscopy were used to study the distribution of the cations in the tetrahedral and octahedral sites in Co(x)Zn(1-x)Al(2)O(4) nanoparticles as a function of particle size and composition. The results show that all of the as-synthesized samples exhibit spinel-type single phase; the crystallite size of the samples is about 20-50 nm and increases with increasing annealing temperature and decreases with Co-enrichment. Zn(2+) ions are located in large proportions in the tetrahedral sites and in small proportions in the octahedral sites in Co(x)Zn(1-x)Al(2)O(4) nanoparticles. The fraction of octahedral Zn(2+) increases with increasing Co concentration and decreases with increasing particle size. Besides the tetrahedral and octahedral coordinations, the presence of the second octahedrally coordinated Al(3+) ions is observed in the nanoparticles. The change of the inversion parameter (2 times the fraction of Al(3+) ions in tetrahedral sites) with Co concentration and particle size is consistent with that of the Zn fraction in octahedral sites. Analysis of the absorption properties indicates that Co(2+) ions are located in the tetrahedral sites as well as in the octahedral sites in the nanoparticles. The inversion degree of Co(2+) decreases with increasing particle size.     

Tetrahedral Co(II) coordination in alpha-type cobalt hydroxide: Rietveld refinement and X-ray absorption spectroscopy

We report a Rietveld refinement analysis and X-ray absorption study on a green-color Cl(-)-intercalated alpha-type cobalt hydroxide phase. The refinement clearly demonstrated that one-fifth to one-sixth of the Co(II) at octahedral sites was replaced by pairs of tetrahedrally coordinated Co(II) on each side of the hydroxide plane, represented by a structural formula of [Co(octa)(0.828)Co(tetra)(0.348)(OH)2](0.348+)Cl(0.348).0.456H2O. X-ray absorption spectroscopy also indicated that the divalent cobalt were in local neighboring environments of both octahedral and tetrahedral coordination. Furthermore, UV-vis spectroscopic measurements elucidate the typical green/blue color of an alpha-type cobalt hydroxide.     

Equilibrium studies in solution involving nickel(II) complexes of flexidentate Schiff base ligands: isolation and structural characterization of the planar red and octahedral green species involved in the equilibrium

Three new flexidentate 5-substituted salicylaldimino Schiff base ligands (L1-OH-L3-OH) based on 1-(2-aminoethyl)piperazine (X=H, L1-OH; X=NO2, L2-OH; and X=Br, L3-OH) and their nickel(II) complexes (1a, 1b, 2, and 3) have been reported. The piperazinyl arm of these ligands can in principle have both boat and chair conformations that allow the ligands to bind the Ni(II) center in an ambidentate manner, forming square-planar and/or octahedral complexes. The nature of substitution in the salicylaldehyde aromatic ring and the type of associated anion in the complexes have profound influences on the coordination geometry of the isolated products. With the parent ligand L1-OH, the product obtained is either a planar red compound [Ni(L1-O)]+, isolated as tetraphenylborate salt (1a), or an octahedral green compound [Ni(L1-NH)(H2O)3](2+), isolated with sulfate anion (1b); both have been crystallographically characterized. In aqueous solution, both these planar (S=0) and octahedral (S=1) forms are in equilibrium that has been followed in the temperature range 298-338 K by 1H NMR technique using the protocol of Evans's method. The large exothermicity of the equilibrium process [Ni(L1-O)]+ + 3H2O + H+<=>[Ni(L1-NH)(H2O)3](2+) (DeltaH degrees=-46 +/- 0.2 kJ mol(-1) and DeltaS degrees=-133 +/- 5 J K(-1) mol(-1)) reflects formation of three new Ni-OH2 bonds in going from planar to the octahedral species. With the 5-nitro derivative ligand L2-OH, the sole product is an octahedral compound 2, isolated as a sulfate salt while with the bromo derivative ligand L3-OH, the exclusive product is a planar molecule 3 with associated tetraphenylborate anion. Both 2 and 3 have been structurally characterized by X-ray diffraction analysis.