Metal Imides Research Articles

Thermochemical production of ammonia via a two-step metal nitride cycle - materials screening and the strontium-based system.

Ammonia synthesis via the catalytic Haber-Bosch process is characterized by its high pressures and low single-pass conversions, as well as by the energy-intensive production of the precursors H2 and N2 and their concomitant greenhouse gas emissions. Alternatively, thermochemical cycles based on metal nitrides stand as a promising pathway to green ammonia production because they can be conducted at moderate pressures without added catalysts and be further driven by concentrated solar energy as the source of high-temperature process heat. The ideal two-step cycle consists of the nitridation of a metal to form a metal nitride, followed by the hydrogenation of the metal nitride to synthetize NH3 and reform the metal. Here, we perform a combined theoretical and experimental screening of mono-metallic nitrides for several candidates, namely for Sr, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, W, Li, and Al. For the theoretical screening, Ellingham diagrams and chemical equilibrium compositions are examined with thermodynamic data derived from density function theory computations. For the experimental screening, thermogravimetric runs and mass balances supported by on-line gas analyses are performed for both steps of the cycle at ambient pressure and over the temperature ranges 100-1000 °C for nitridation and 100-500 °C for hydrogenation. The strontium-based cycle is selected as a reference for detailed examination and shown to synthetize NH3 at 1 bar by effecting the nitridation at 407 °C (at peak rate) and the hydrogenation at 339 °C (at peak rate). The co-formation of metal hydrides (SrH2) and metal imides (Sr2HN) are shown to help close the material cycle.

Characterization of the "Absent" Vanadium Oxo V(═O){N(SiMe3)2}3, Imido V(═NSiMe3){N(SiMe3)2}3, and Imido-Siloxy V(═NSiMe3)(OSiMe3){N(SiMe3)2}2 Complexes Derived from V{N(SiMe3)2}3 and Kinetic Study of the Spontaneous Conversion of the Oxo Complex into Its Imido-Siloxy Isomer.

The synthesis and characterization of V(═O){N(SiMe3)2}3 (1), V(═NSiMe3){N(SiMe3)2}3 (2), and V(═NSiMe3)(OSiMe3){N(SiMe3)2}2 (3) are described. Prior attempts to synthesize the vanadium(V) oxo complex 1 via salt metathesis of VOCl3 with the lithium or sodium silylamide salt had yielded either the putative rearranged species V(═NSiMe3)(OSiMe3){N(SiMe3)2}2 (3) or the oxo-bridged, dimetallic {(μ-O)2V2[N(SiMe3)2]4}. We now show that complex 1 is available by treatment of the vanadium(III) tris(silylamide) V{N(SiMe3)2}3 with iodosylbenzene. The imido complex 2 was obtained by treatment of V{N(SiMe3)2}3 with trimethylsilyl azide. Sublimation of 1 formed complex 3, which was determined to be V(═NSiMe3)(OSiMe3){N(SiMe3)2}2, on the basis of infrared, electronic, and 1H and 51V NMR spectroscopies. Crystallographic disorder precluded a complete structural characterization of 3, although a four-coordinate V atom, as well as severely disordered ligands, were apparent. Comparison of the vibrational spectra of 1 and 2 allowed an unambiguous assignment of the V-O (995 cm-1) and V-Nimide (1060 cm-1) stretching bands. The vibrational spectrum of complex 3 displayed strong absorbances at 1090 and 945 cm-1, indicative of its metal imide and metal siloxide moieties. The 1H NMR spectrum of 1 in deuterated benzene showed overlapping signals for the ligand protons proximal and distal to the oxo moiety at 0.52 and 0.38 ppm. The 1H NMR spectrum of 2 in deuterated methylene chloride displayed distinct signals for the imido (0.41 ppm) and amido (0.35 ppm) protons, whereas 1H NMR spectroscopy of 3 showed three signals in an intensity ratio consistent with the formula V(═NSiMe3)(OSiMe3){N(SiMe3)2}2. 51V NMR spectra of 1-3 revealed singlet resonances at -119 ppm (1), -24 ppm (2), and -279 ppm (3). The electronic spectra of 1-3 displayed single absorbances in the charge transfer region, consistent with their d0 electron configurations. Kinetic studies of the spontaneous conversion of complex 1 to 3 were used to determine the rate constants (ca. 0.0002 s-1 (63 °C), 0.0006 s-1 (73 °C), 0.002 s-1 (83 °C)) and activation energy (ca. 20 kcal/mol) of this first-order process.

Electronic structure and bonding of the ScNH and YNH molecules

We report the results of multi-reference configuration interaction calculations of the electronic and geometric structures of the X2Σ+, B2Σ+, Ã2Πi, Ã2Πr &2Δ states of the transition metal imides, ScNH and YNH, and compare with the available experimental data. The metal is bonded to the NH group by a double bond in the π system for all states. There are 4 π electrons in the X2Σ+, B2Σ+, Ã2Πr &2Δ states and 3 in the Ã2Πi. The atomic orbital composition in the 4π states is remarkably similar, the average being 75%2pπ+21%dπ+4%pπ while in the 3π state we have 88%2pπ+10%dπ+2%pπ.

Coinage Metal (Bisfluorosulfonyl)imide Complexes: Preparation, Characterization, and Catalytic Applications

Triflate (–OTf) and triflimide (–NTf2) represent two most widely used weakly coordinating counteranions in transition metal catalysis, yet their high price hinders large‐scale application. Herein, we report the preparation, characterization, and catalytic applications of silver(I), gold(I), and copper(II) (bisfluorosulfonyl)imide (–FSI) complexes, showing –FSI as a low cost alternative of –OTf and –NTf2. These complexes, including AgFSI·2MeCN (1), AgFSI·MeCN (2), AgFSI·H2O (3), (AgFSI)6·(H2O)4 (4), AgFSI (5), LAuFSI (6a–6e), and CuFSI2·4H2O (7), are prepared conveniently starting from KFSI, an inexpensive chemical, and shown interesting structural features and some unprecedented coordination modes. In comparison with the corresponding coinage metal triflimides, the FSI complexes have exhibited comparable or better catalytic performance in a series of the model chemical transformations.

Editorial

Editorial

Donald Charlton Bradley. 7 November 1924—20 December 2014

Don Bradley was a twentieth-century pioneer of inorganic chemistry. He opened up the field of metal alkoxides and defined the parameters controlling the aggregative and volatility properties of this class of compounds that later dictated their use as precursors for fabrication of metal oxide thin films. His legacy also included seminal contributions to our knowledge of structure and bonding in the compound classes of metal amides and metal imides. He made highly innovative contributions in the field of metal organic chemical vapour deposition (MOCVD) fabrication of III/V semiconductor thin films, both through synthesis of single source precursors and through synthesis of molecular vehicles for safe storage and delivery of pyrophoric precursors. A modest, witty and gentle man of great intellectual depth and generosity, he nurtured and encouraged the fledgling talent of his students and co-workers and enthusiastically incorporated new developments in terms of experimental and theoretical tools to provide ever deeper understanding. He was relentless in giving his time and effort to support his college, Queen Mary, and the University of London as well as scientific organizations such as the Royal Society, Royal Institution and Royal Society of Chemistry, performing a range of society- or divisional-level official roles at various times, and he even made time for board of governor roles in schools. Don was held in the highest of esteem by his friends and family, students, colleagues and fellow scientists from across the world.

Taking the pressure off

Ammonia holds promise as a clean energy carrier, but its synthesis requires high pressures and large production scales that are ill-matched to renewable, decentralized energy production. Now, researchers use metal imides to mediate ammonia production in a chemical looping process that operates under mild conditions.

Production of ammonia via a chemical looping process based on metal imides as nitrogen carriers

Ammonia is a promising carbon-free energy carrier, but is currently synthesized industrially under harsh conditions. Synthesizing ammonia using lower temperatures and pressures could therefore improve its prospects as a chemical means to store and transport energy. Here we report that alkali and alkaline earth metal imides function as nitrogen carriers that mediate ammonia production via a two-step chemical looping process operating under mild conditions. Nitrogen is first fixed through the reduction of N2 by alkali or alkaline earth metal hydrides to form imides and, subsequently, the imides are hydrogenated to produce NH3 and regenerate the metal hydrides. The oxidation state of hydrogen therefore switches between −1 (hydride), 0 (H2) and +1 (imide and NH3). Late 3d metals accelerate the reaction rates of both steps. The chemical loop mediated by BaNH and catalysed by Ni produces NH3 at 100 °C and atmospheric pressure. Reducing the severity of the conditions required to synthesize ammonia would increase the viability of its use as a carbon-free energy carrier. Here the authors use metal imides to mediate ammonia production via a two-step chemical looping process that operates under mild conditions.

5d Metal(IV) Imide Complexes. The Impact (or Lack Thereof) of d-Orbital Occupation on Methane Activation and Functionalization.

This research evaluates 5d metal imide complexes, (OH)2M═NMe (M = W, Re, or Os), and their reactions with methane to form dimethylamine. Each is calculated to follow a consistent reaction pathway regardless of the metal's d-orbital occupation, whereby the methane C-H bond undergoes oxidative addition (OA) to the metal and then the methyl migrates from the metal to the nitrogen to form an amide. Finally, hydrogen migrates to the nitrogen before dissociating to form amine products. While homolytic M-imide, M-amide M-H, and M-CH3 bond dissociation free energies (BDFEs) were analyzed, the BDFEs of neither hexavalent nor tetravalent metal moieties reflect the oxidative addition kinetics. Instead, a strain theory approach, supported by electron density analysis for the OA transition state, is found to be explanatory. Notably, the rate-determining step, the hydrogen migration transition state, has a consistent jump in free energy versus the preceding intermediate, (OH)2MIV(H)-N(CH3)Me, for all metals evaluated. Thus, the height of the RDS is largely reflective of the stability of the MIV-amide intermediate, suggesting a strategy for viable catalysis.

Demonstrating hydrogen production from ammonia using lithium imide – Powering a small proton exchange membrane fuel cell

Abstract Accessing the intrinsic hydrogen content within ammonia, NH3, has the potential to play a very significant role in the future of a CO2-free sustainable energy supply. Inexpensive light metal imides and amides are effective at decomposing ammonia to hydrogen and nitrogen (2NH3 → 3H2 + N2), at modest temperatures, and thus represent a low-cost approach to on-demand hydrogen production. Building upon this discovery, this paper describes the integration of an ammonia cracking unit with a post-reactor gas purification system and a small-scale PEM fuel cell to create a first bench-top demonstrator for the production of hydrogen using light metal imides.

Methane C–H Bond Activation by “Naked” Alkali Metal Imidyl and Alkaline Earth Metal Imide Complexes. The Role of Ligand Spin and Nucleophilicity

High accuracy correlation consistent Composite Approach (ccCA) calculations have been used to investigate methane C-H bond activation with alkali metal imidyl and alkaline earth metal imide complexes. Alkali metals (Li, Na) and alkaline earth metals (Be, Mg) are used in this research given their redox innocence, namely, M(+) and M(2+), respectively. The ccCA calculations for methane activation by imidyl radical NH(•-) and triplet nitrene NH(••) show a thermodynamic (ΔΔH = 13.2 kcal/mol) and kinetic (ΔΔH(‡) = 15.9 kcal/mol) preference for the former. Methane activation by LiNH(•) and MgNH proceeds via hydrogen atom abstraction (HAA) and [2 + 2] transition states; only HAA pathways are isolated for NaNH and BeNH. The ccCA computed enthalpies lead to the hypothesis that the nucleophilicity of the nitrogen of the activating ligand (NR) is the key ingredient in activating the strongest sp(3) C-H bonds like that of methane.

C–H Activation by Multiply Bonded Complexes with Potentially Noninnocent Ligands: A Computational Study

Second- and third-row (typically precious metals) transition metal complexes are known to possess certain electronic features that define their structure and reactivity and are usually not observed in their first-row (base metal) congeners. Can these electronic features be conferred onto first-row transition metals with the aid of noninnocent and/or very high-field ligands? In this research, the impact upon methane C-H bond activation was modeled using the dipyridylazaallyl (smif) supporting ligand for late, first-row transition metal (M) imide, oxo, and carbene complexes (M = Fe, Co, Ni, or Cu; E = O, NMe, or CMe2). Density functional theory calculations suggest that the combination of smif with iron and the oxo activating ligand is the most energetically favorable complex for methane C-H activation. A change in the preferred transition state for methane C-H activation from [2+2] addition to hydrogen atom abstraction was observed upon going from Fe to Cu and for Fe as compared to precious metals. Contrary to expectations, it was the imide ligand rather than the dipyridylazaallyl ligand that was found to possess redox "noninnocent" characteristics.

A Ru(I) Metalloradical That Catalyzes Nitrene Coupling to Azoarenes from Arylazides

Unusual N-N coupling of aryl azides to yield azoarenes is demonstrated by the Ru(I) metalloradical, [SiP(iPr)(3)]Ru(N(2)) (4) ([SiP(iPr)(3)] = (2-iPr(2)PC(6)H(4))(3)Si(-)). The yield of the azoarene is dependent on the substituent on the aryl azide, and the reaction is catalytic for p-methoxy and p-ethoxy phenyl azides, while no azoarene is observed for p-trifluoromethylphenyl azide. Studies aimed at probing the viability of a bimolecular coupling mechanism of metal imide species, as shown in the related [SiP(iPr)(3)]Fe system, have led to the isolation of several structurally unusual complexes including the ruthenium(IV) imide, 7-OMe, as well as the Ru(II) azide adduct 8-OMe. One electron reduction of 7-OMe complex led to the isolation of the formally Ru(III) imide complex, [SiP(iPr)(3)]Ru(NAr) (Ar = p-MeOC(6)H(4), 5-OMe). EPR spectroscopy on 5-OMe suggests that the complex is electronically similar to the previously reported imide complex, [SiP(iPr)(3)]Ru(NAr) (Ar = p-CF(3)C(6)H(4,)5-CF(3)), and features radical character on the NAr moiety, but to a greater degree. The stability of 5-OMe establishes that bimolecular coupling of 5-OMe is kinetically inconsistent with the reaction. Further studies rule out mechanisms in which 5-OMe reacts directly with free aryl azide or a transient Ru(I) azide adduct. Together, these studies show that 5-OMe is likely uninvolved in the catalytic cycle and demonstrates the influence of the metal center on the mechanism of reaction. Instead, we favor a mechanism in which free aryl nitrene is released during the catalytic cycle and combines with itself or with free aryl azide to yield the azoarene.

Vibrational Spectroscopy and Analysis of Pseudo-tetrahedral Complexes with Metal Imido Bonds

A number of assignments have been previously posited for the metal-nitrogen stretch (nu(M-NR)), the N-R stretch (nu(MN-R)), and possible ligand deformation modes associated with terminally bound imides. Here we examine mononuclear iron(III) and cobalt(III) imido complexes of the monoanionic tridentate ligand [PhBP3] ([PhBP3] = [PhB(CH2PPh2)3]-) to clarify the vibrational features for these trivalent metal imides. We report the structures of [PhBP3]FeNtBu and [PhBP3]CoNtBu. Pseudo-tetrahedral metal imides of these types exhibit short bond lengths (ca. 1.65 A) and nearly linear angles about the M-N-C linkages, indicative of multiple bond character. Furthermore, these compounds give rise to intense, low-energy visible absorptions. Both the position and the intensity of the optical bands in the [PhBP3]MNR complexes depend on whether the substituent is an alkyl or aryl group. Excitation into the low-energy bands of [PhBP3]FeNtBu gives rise to two Raman features at 1104 and 1233 cm(-1), both of which are sensitive to 15N and 2H labeling. The isotope labeling suggests the 1104 cm(-1) mode has the greatest Fe-N stretching character, while the 1233 cm(-1) mode is affected to a lesser extent by (15)N substitution. The spectra of the deuterium-labeled imides further support this assertion. The data demonstrate that the observed peaks are not simple diatomic stretching modes but are extensively coupled to the vibrations of the ancillary organic group. Therefore, describing these complexes as simple diatomic or even triatomic oscillators is an oversimplification. Analogous studies of the corresponding cobalt(III) complex lead to a similar set of isotopically sensitive resonances at 1103 and 1238 cm(-1), corroborating the assignments made in the iron imides. Very minimal changes in the vibrational frequencies are observed upon replacement of cobalt(III) for iron(III), suggesting similar force constants for the two compounds. This is consistent with the previously proposed electronic structure model in which the added electron resides in a relatively nonbonding orbital. Replacement of the tBu group with a phenyl ring leads to a significantly more complicated resonance Raman spectrum, presumably due to coupling with the vibrations of the phenyl ring. Polarization studies demonstrate that the observed modes have A(1) symmetry. In this case, a clearer resonance enhancement of the signals is observed, supporting a charge transfer designation for the electronic transitions. A series of isotope-labeling experiments has been carried out, and the modes with the greatest metal-nitrogen stretching character have been assigned to peaks at approximately 960 and approximately 1300 cm(-1) in both the iron and cobalt [PhBP3]MNPh complexes. These results are consistent with a multiple M-N bond for these metal imides.

Hydrogen storage of metal nitrides by a mechanochemical reaction

Mechanochemical reaction of metal nitrides (Li 3N, Ca 3N 2, h-BN, Mg 3N 2, Si 3N 4, AlN, TiN, VN, ZrN) was performed in a planetary ball mill. We demonstrated that hydrogen (H 2) can be stored by the ball milling of their respective metal nitrides in a H 2 atmosphere at 1 MPa and room temperature. The H 2 content of ball-milled metal nitrides was 0.2–5.0 wt.%. This reaction did not occur at ambient conditions without a mechanochemical reaction mechanism. Infrared absorption showed that the N–H stretching vibrations of the ball-milled light metal nitrides occurred at 3100–3500 cm −1. The N–H force constant of the metal imides in the ball-milled metal nitrides decreased with the metal ionic radius and the electronegativity. These results indicated that the size of the metal ion and the charge transfer from the metal to nitrogen play important roles for the force constant.

Hydrogen storage of metal nitride by a mechanochemical reaction.

Metal imides (Li(2)NH, CaNH), a metal amide (LiNH(2)) and metal hydrides (LiH, CaH(2)) were synthesized by ball milling of their respective metal nitrides (Li(3)N, Ca(3)N(2)) in a H(2) atmosphere at 1 MPa and at room temperature.

Rearrangement of a mesylate tropane intermediate in nucleophilic substitution reactions. Synthesis of aza-bicyclo[3.2.1]octane and aza-bicyclo[3.2.2]nonane ethers, imides, and amines.

Nucleophilic substitution of 2beta-mesyloxymethyl-N-methyl-3beta-p-tolyl-tropane intermediate with alkoxides, metal imides, or amines was found to lead not only to the expected bicyclo[3.2.1]octane (tropane) ether, imide, and amine derivatives but also to unexpected bicyclo[3.2.2]nonane derivatives. When alkoxides were used as nucleophile, only the rearranged bicyclo[3.2.2]nonane structure was obtained, whereas the use of amines or imides as nucleophile afforded a mixture of the two structures. The bicyclo[3.2.2]nonane structure was assigned by NMR analysis.

Novel double substrate insertion versus isocyanate extrusion in reactions of imidotitanium complexes with CO2: critical dependence on imido N-substituents †

Reaction of the cyclopentadienyl–amidinate supported imidotitanium complexes [Ti(η-C5Me5){MeC(NiPr)2}(NR)] (R = tBu 1a or Ar 1b where Ar = 2,6-C6H3Me2) with CO2 proceed via initial cycloaddition reactions, but depending on the imido N-substituent go on to yield products of either isocyanate extrusion or double CO2 insertion, the latter forming [Ti(η-C5Me5){MeC(NiPr)2}{O(CO)N(Ar)(CO)O}] 4; the double CO2 insertion reaction leading to 4 is the first example for any transition metal imide.

Transition metal imide/organic imine metathesis reactions: unexpected observations

Mixtures of [Ti(NBut)Cl2(py)3] 1 and PhC(NAr)H (Ar = C6H3Me2-2,6 or C6H4Me-4) gave quantitative conversion to [Ti(NAr)Cl2(py)3] and PhC(NBut)H, the products of TiNBut/CNAr transition metal imide/organic imine meta-thesis; examination of the kinetics for Ar = C6H4Me-4 showed that the rate limiting step for this process is zero order in [1], demonstrating that these reactions do not involve metal imide particiption in the rate limiting step.

Reactions between primary amines and magnesium or zinc dialkyls: intermediates in metal imide formation

The reactions of several different primary amines with diorganomagnesium or dialkylzinc compounds are reported. Treatment of Mg(η 5-C 5H 5) 2 with t-BuNH 2 or DippNH 2 (Dipp = 2,6- i- Pr 2 C 6 H 3−) leads to the adduct Mg(η 5-C 5H 5)(η 2-C 5H 5) {NH 2(t-Bu)}THF ( 1a) or the amide Mg(η 5-C 5H 5)(NHDipp)THF ( 1b). Reaction between Mg(t-Bu) 2 or commercially available Mg‘Bu’ 2 (‘Bu’ = statistical mixture of n-Bu and s-Bu groups) gave the dimeric amide species [t-BuMg{NH(t-Bu)}THF] 2 ( 2a) or [‘Bu’Mg{NH(t-Bu)}THF] 2 ( 2b). In contrast reaction of Mg‘Bu’ 2 with MesNH 2 or TriphNH 2 (Mes = 2,4,6-Me 3 C 6 H 2−, Triph = 2,4,5-Ph 3C 6H 2−) gave, after suitable workup, the bisamides Mg{(NHMes) 2{OP(NMe 2}) 3} 2 ( 3a) or Mg(NHTriph) 2(THF) 2·THF ( 3b ·THF). A bisamide, the dimer {Mg(NCy 2) 2} 2 ( 4), was isolated in almost quantitative yield by the reaction of dibutylmagnesium with 2 equiv. of HNCy 2 (Cy = cyclohexyl) whereas the trimetallic amide Mg 3(μ-NHDipp) 4N(SiMe 3) 2 2 ( 5) was isolated from the transamination reaction between DippNH 2 and [MgN(SiMe 3) 2 2] 2. A unique product with a rare dodecameric ring structure, (EtMgNHDipp) 12 ( 6), was observed when MgEt 2 reacts with DippNH 2. Reaction between ZnEt 2 or Zn(CH 2SiMe 3) 2 and a variety of primary amines afforded a selection of structurally diverse products. The compounds isolated were: {EtZn(NHPh)THF} 3 (7), {EtZn(NHMes)THF} 2·0.5THF ( 8·0.5THF), Et 2Zn 4(NHDipp) 4(OEt) 2 ( 9), {EtZnNH(t-Bu)} 3 ( 10) and (Me 3SiCH 2ZnNHDipp) 2 ( 11). Crystal data: 1a, a = 10.863(2), b = 9.299(2), c = 17.787(5) A ̊ , β = 98.56(2)° , monoclinic, space group P2 1/ c, Z = 4, R = 0.048 for 2337 ( I>2 σ(1)) data; 2a, a = 8.922(2), b = 16.101(4), c = 11.132(2) A ̊ , β = 111.18(2)° , monoclinic, space group P2 1/ n, Z = 2, R = 0.081 for 2076 ( I>2 σ(1)) data; 3a, a = 11.174(2), b = 18.161(4), c = 18.808(6) A ̊ , β = 92.34(3)° , monoclinic, space group P2 1/ n, Z = 8, R = 0.145 for 4945 ( I>2 σ( I)) data; 4, a = 22.828(5), b = 10.768(2), c = 21.350(4) A ̊ , β = 117.74(3)° , monoclinic, space group P2 1/ c, Z = 4, R = 0.067 for 6264 ( I>2 σ( I)) data; 5, a = 21.754(5), b = 15.214(2), c = 20.657(4) A ̊ , orthorhombic, space group Pbcn, Z = 4, R = 0.063 for 2338 ( I > 2 σ( I)) data; 6, a = 26.063(5), b = 35.332(4), c = 24.535(4) A ̊ , orthorhombic, space group Pnma, Z = 4, R = 0.178 for 10408 ( I > 2 σ( I)) data; 7, a = 12.715; (3), b = 13.606(3), c = 22.339(5) A ̊ , α = 90.53(3) , β = 96.20(3), γ = 93.85(3)°, triclinic, space group P 1, Z = 4, R = 0.143 for 4483 (I > 2σ(I)) data; 8·0.5THF, a = 43.58(2), b = 8.724(2), c = 38.90(1) A ̊ , β = 117.49(2)° ; monoclinic, space group C2/ c, Z = 16, R = 0.058 for 5587 ( I>2 σ( I)) data; 9, a = 10.875(2), b = 11.669(2), c = 11.968(2) A ̊ , α = 76.17(2), β = 86.52(2), γ = 69.69(2)° , triclinic, space group P 1, Z = 1, R = 0.043 for 2733 (I > 2σ(I)) data; 10, a = 11.281(3), b = 14.891(4), c = 15.103(5) A ̊ , β = 90.88(2)° , monoclinic, space group P2 1/ n, Z = 4, R = 0.060 for 2363 ( I>2 σ( I)) data; 11, a = 10.147(2), b = 11.640(2), c = 17.521(2) A ̊ , α = 71.23(1), β = 77.50(1), γ = 69.78(1)° , triclinic, space group P 1, Z = 2, R = 0.065 for 4752 ( I > 2 σ( I)) data.