Kinetics and mechanism for the formation of o‐carboxy(N‐methyl)‐benzohydroxamic acid in the cleavage of ethyl N‐[o‐(N‐methyl‐N‐hydroxycarbamoyl)‐benzoyl]carbamate in N‐methylhydroxylamine,acetate, and phosphate buffers

The rate of cleavage of ethyl N‐[o‐(N‐methyl‐N‐hydroxycarbamoyl)benzoyl]‐ carbamate (ENMBC) in the buffer solutions containing N‐methylhydroxylamine, acetate + N‐methylhydroxylamine, and phosphate + N‐methylhydroxylamine followed an irreversible consecutive reaction path: ENMBC where A and B represent N‐hydroxyl group cyclized product of ENMBC and o‐(N‐methyl‐N‐hydroxycarbamoyl)benzoic acid, respectively. Both rate constants k_{1 obs} and k_{2 obs} showed the presence of buffer catalysis, but buffer catalysis turned out to be weak in the presence N‐methylhydroxylamine buffer, while it was strong in the presence of acetate and phosphate ones. Buffer‐independent rate constants k₁₀ and k₂₀ increased linearly with the increase in a_OH with definite intercepts. The values of molar absorption coefficient of A , obtained under varying total buffer concentrations at a constant pH, showed the presence of a fast equilibrium: A + CH₃NHOH ? C , where C represents N‐[o‐(N‐methyl‐N‐hydroxycarbamoyl)methyl]benzohydroxamic acid. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 427–437, 2003     

Effects of CH3OH‐H2O and CH3OH solvents on rate of reaction of phthalimide with piperidine

Pseudo‐first‐order rate constants (k_obs) for the cleavage of phthalimide in the presence of piperidine (Pip) vary linearly with the total concentration of Pip ([Pip]_T) at a constant content of methanol in mixed aqueous solvents containing 2% v/v acetonitrile. Such linear variation of k_obs against [Pip]_T exists within the methanol content range 10%–∼80% v/v. The change in k_obs with the change in [Pip]_T at 98% v/v CH₃OH in mixed methanol‐acetonitrile solvent shows the relationship: k_obs = k[Pip]_T + k[Pip], where respective k and k represent apparent second‐order and third‐order rate constants for nucleophilic and general base‐catalyzed piperidinolysis of phthalimide. The values of k_obs, obtained within [Pip]_T range 0.02–0.40 M at 0.03 M NaOH and 20 as well as 50% v/v CH₃OH reveal the relationship: k_obs = k₀/(1 + {k_n[Pip]/k_OX[⁻OX]_T}), where k₀ is the pseudo‐first‐order rate constant for hydrolysis of phthalimide, k_n and k_OX represent nucleophilic second‐order rate constants for the reaction of Pip with phthalimide and for the XO⁻‐catalyzed cyclization of N‐piperidinylphthalamide to phthalimide, respectively, and [⁻OX]_T = [NaOH] + [⁻OX_re], where [⁻OX_re] = [⁻OH_re] + [CH₃O_re⁻]. The reversible reactions of Pip with H₂O and CH₃OH produce ⁻OH_re and CH₃O_re⁻ ions. The effects of mixed methanol‐water solvents on the rates of piperidinolysis of PTH reveal a nonlinear decrease in k with the increase in the content of methanol. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 29–40, 2001     

Incorporating glycidyl methacrylate into block copolymers using poly(methacrylate‐ran‐styrene) macroinitiators synthesized by nitroxide‐mediated polymerization

Methyl methacrylate/styrene (MMA/S), ethyl methacrylate/styrene (EMA/S) and butyl methacrylate/styrene (BMA/S) feeds (>90 mol % methacrylate) were copolymerized in 50 wt % p‐xylene at 90 °C with 10 mol % of additional SG1‐free nitroxide mediator relative to unimolecular initiator (BlocBuilder^®) to yield methacrylate rich copolymers with polydispersities _w/ _n = 1.23–1.46. k_pK values (k_p = propagation rate constant, K = equilibrium constant) for MMA/S copolymerizations were comparable with previous literature, whereas EMA/S and BMA/S copolymerizations were characterized by slightly higher k_pK's. Chain extensions with styrene at 110 °C initiated by the methacrylate‐rich macroinitiators (number average molecular weight _n = 12.9–33.5 kg mol^?1) resulted in slightly broader molecular weight distributions with _w/ _n = 1.24–1.86 and were often bimodal. Chain extensions with glycidyl methacrylate/styrene/methacrylate (GMA/S/XMA where XMA = MMA, EMA or BMA) mixtures at 90 °C using the same macroinitiators resulted frequently in bimodal molecular weight distributions with many inactive macroinitiators and higher _w/ _n = 2.01–2.48. P(XMA/S) macroinitiators ( _n = 4.9–8.9 kg mol^?1), polymerized to low conversion and purified to remove “dead” chains, initiated chain extensions with GMA/MMA/S and GMA/EMA/S giving products with _w/ _n ～ 1.5 and much fewer unreacted macroinitiators (<5%), whereas the GMA/BMA/S chain extension was characterized by slightly more unreacted macroinitiators (～20%). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2574–2588, 2009     

Combining Modular Ligation and Supramolecular Self‐Assembly for the Construction of Star‐Shaped Macromolecules

A well‐defined random copolymer of styrene (S) and chloromethylstyrene (CMS) featuring lateral chlorine moieties with an alkyne terminal group is prepared (P(S‐co‐CMS), = 5500 Da, PDI = 1.13). The chloromethyl groups are converted into Hamilton wedge (HW) entities (P(S‐co‐HWS), = 6200 Da, PDI = 1.13). The P(S‐co‐HWS) polymer is subsequently ligated with tetrakis(4‐azidophenyl)methane to give HW‐functional star‐shaped macromolecules (P(S‐co‐HWS))₄, = 25 100 Da, PDI = 1.08). Supramolecular star‐shaped copolymers are then prepared via self‐assembly between the HW‐functionalized four‐arm star‐shaped macromolecules ( P(S‐co‐HW )) ₄ and cyanuric acid (CA) end‐functionalized PS (PS–CA, = 3700 Da, PDI = 1.04), CA end‐functionalized poly(methyl methacrylate) (PMMA–CA, = 8500 Da, PDI = 1.13) and CA end‐functionalized polyethylene glycol (PEG–CA, = 1700 Da, PDI = 1.05). The self‐assembly is monitored by ¹H NMR spectroscopy and light scattering analyses.     

Direct Cyclodextrin‐Mediated Ring Opening Polymerization of ϵ‐Caprolactone in the Presence of Yttrium Trisphenolate Catalyst

Unmodified β‐cyclodextrin has been directly used to initiate ring‐opening polymerization of ϵ‐caprolactone in the presence of yttrium trisphenolate. Well‐defined cyclodextrin (CD)‐centered star‐shaped poly(ϵ‐caprolactone)s have been successfully synthesized containing definite average numbers of arms (N_arm = 4–6) and narrow polydispersity indexes (below 1.10). The number‐average molecular weight ( ) and average molecular weight per arm ( ) are controlled by the feeding molar ratio of monomer to initiator. The prepared star‐PCL with of 2.7 × 10³ is in fully amorphous and that with of 13.3 × 10³ is crystallized. In addition, the obtained poly(e‐caprolactone) (PCL) stars with various molecular weights have different solubilities in methanol and tetrahydrofuran, which can be applied for further modifications.     

Determination of Propagation Rate Coefficient of Acrylates by Pulsed‐Laser Polymerization in the Presence of Intramolecular Chain Transfer to Polymer

Unusual difficulties are faced in the determination of propagation rate coefficients (k_p) of alkyl acrylates by pulsed‐laser polymerization (PLP). When the backbiting is the predominant chain transfer event, the apparent k_p of acrylates determined in PLP experiments for different frequencies should range between k_p (propagation rate coefficient of the secondary radicals) at high frequency and k at low frequency. The k value could be expressed from kinetic parameters: , where k_fp is the backbiting rate coefficient, k_p2 is the propagation rate coefficient of mid‐chain radicals, and [M] is the monomer concentration.

Apparent propagation rate coefficients determined for different frequencies by simulating the PLP of n‐butyl acrylate at 20 °C. Horizontal full lines show the values of k_p and k.     

The kinetics of the reaction: Br + C3H6 ⇌ HBr + C3H5

Studies of the reaction of Br + propylene to produce HBr and allyl radical were made using VLPR (Very Low Pressure Reactor) over the range 263–363 K. Apparent bimolecular rate constants k were found to vary in an inverse manner with the initial concentration of bromine atoms introduced into the reactor. Plots of k against [Br] give straight lines whose intercepts were taken to be the true bimolecular, metathesis rate constant k₁. The reaction scheme is where k₂ ? k₁ and k_?1 [HBr] is negligibly small under our conditions. Arrhenius parameters for k₁ were assigned for linear and bent transition states and shown to give excellent fits to the observed intercepts. where θ = 2.303 RT (kcal mol^?1). The dependence of k on [Br] is accounted for in terms of the reactivity of Br* (²P_1/2) produced in the microwave discharge. The activation energy for the metathesis reaction of Br* with propylene is shown to be very small.     

SP–PLP–EPR Investigations into the Chain‐Length‐Dependent Termination of Methyl Methacrylate Bulk Polymerization

Termination kinetics of methyl methacrylate (MMA) bulk polymerization has been studied via the single pulsed laser polymerization–electron paramagnetic resonance method. MMA‐d₈ has been investigated to enhance the signal‐to‐noise quality of microsecond time‐resolved measurement of radical concentration. Chain‐length‐dependent termination rate coefficients of radicals of identical size, k, are reported for 5–70 °C and up to i = 100. k decreases according to the power‐law expression . At 5 °C, k_t for two MMA radicals of chain‐length unity is k = (5.8 ± 1.3) · 10⁸ L · mol⁻¹ · s⁻¹. The associated activation energy and power‐law exponent are: E_A(k) ≈ 9 ± 2 kJ · mol⁻¹ and α ≈ 0.63 ± 0.15, respectively.

     

Selective Detection of Ascorbic Acid Using Octacyanomolybdate‐Doped‐Glutaraldehyde‐Cross‐Linked Poly‐L‐Lysine Film Modified Glassy Carbon Electrode

The present work describes oxidation of ascorbic acid (AA) at octacyanomolybdate‐doped‐glutaraldehyde‐cross‐linked poly‐L ‐lysine (PLL‐GA‐Mo(CN) film modified glassy carbon electrode in 0.1 M H₂SO₄. The modified electrode has been successfully prepared by means of electrostatically trapping Mo(CN) mediator in the cationic film of glutaraldehyde‐cross‐linked poly‐L ‐lysine. The dependence of peak current of modified electrode in pure supporting indicates that the charge transfer in the film was a mixed process at low scan rates (5 to 200 mV s^?1), and kinetically restrained at higher scan rates (200 to 1000 mV s^?1). Cyclic voltammetry and rotating disk electrode (RDE) techniques are used to investigate the electrocatalytic oxidation of ascorbic acid and compared with its oxidation at bare and undoped PLL‐GA film coated electrodes. The rate constant of catalytic reaction k obtained from RDE analysis was found to be 9.5×10⁵ cm³ mol^?1 s^?1. The analytical determination of ascorbic acid has been carried out using RDE technique over the physiological interest of ascorbic acid concentrations with a sensitivity of 75 μA mM^?1. Amperometric estimation of AA in stirred solution shows a sensitivity of 15 μA mM^?1 over the linear concentration range between 50 and 1200 μM. Interestingly, PLL‐GA‐Mo(CN) modified electrode facilitated the oxidation of ascorbic acid but not responded to other electroactive biomolecules such as dopamine, uric acid, NADH, glucose. This unique feature of PLL‐GA‐Mo(CN) modified electrode allowed for the development of a highly selective method for the determination of ascorbic acid in the presence of interferents.     

Amphiphilic Poly(4‐acryloylmorpholine)/Poly[2‐(N‐carbazolyl)ethyl acrylate] Random and Block Copolymers Synthesized by NMP

A series of random copolymers and block copolymers containing water‐soluble 4AM and fluorescent VAK are synthesized by NMP. The homopolymerizations of 4AM and VAK and 4AM/VAK random copolymerization are performed in 50 wt% DMF using 10 mol% SG1, resulting in a linear increase in versus conversion, and final polymers with narrow molecular weight distributions ( < 1.4). Reactivity ratios r_VAK = 0.64 ± 0.52 and r_4AM = 0.86 ± 0.66 are obtained for the 4AM/VAK random copolymerization. In addition, a poly(4AM) macroinitiator is used to initiate a surfactant‐free suspension polymerization of VAK. After 2.5 h, the resulting amphiphilic block copolymer has = 12.6 kg · mol^?1, = 1.48, molar composition F_VAK = 0.38 with latex particle sizes between 270 and 475 nm.

     

Arrhenius parameters for the gas‐phase reactions of O3 with two butenes and two methyl‐substituted butenes over the temperature range of 295–351 K

Gas‐phase reactions of ozone with two butenes (1‐butene and isobutene) and two methyl‐substituted butenes (2‐methyl‐1‐butene and 3‐methyl‐1‐butene) have been studied in an indoor chamber at 295–351 K. The O₃ concentrations were monitored by Model 49C‐Ozone analyzer. The butene concentrations were measured by gas chromatography–flame ionization detector. The Arrhenius expressions of k=3.50×10^?15e^{(?1756±84)/T} cm³ molecule^?1 s^?1, k=3.39×10^?15e^{(?1697±52)/T} cm³ molecule^?1 s^?1, k=6.18×10^?15e^{?(1822±80)/T} cm³ molecule^?1 s^?1, and k=7.24×10^?14e^{?(2741±139)/T} cm³ molecule^?1 s^?1 were obtained for the ozonolysis reactions of 1‐butene, isobutene, 2‐methyl‐1‐butene, and 3‐methyl‐1‐butene, respectively. Both the reaction rate constant and activation energy obtained in this work are in good agreement with those reported by using different techniques in the literature. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 238–246, 2011     

Ein neues Selten‐Erd‐Metall(III)‐Fluorid‐Oxoselenat(IV): YF[SeO3]

A New Rare‐Earth Metal(III) Fluoride Oxoselenate(IV): YF[SeO₃] Just two representatives of the rare‐earth metal(III) fluoride oxoselenates(IV) with the formula type MF[SeO₃] (M = La and Lu) exist so far, whereas for the intermediate lanthanoids only M₃F[SeO₃]₄‐type compounds (M = Gd and Dy) were accessible. Because of the similar radius of Y³⁺ to the radii of the heavier lanthanoid cations, a missing link within the MF[SeO₃] series could be synthesized now with the example of yttrium(III) fluoride oxoselenate(IV). Contrary to LuF[SeO₃] with its triclinic structure, YF[SeO₃] crystallizes monoclinically in space group P2₁/c (no. 14, a = 657.65(7), b = 689.71(7), c = 717.28(7) pm, β = 99.036(5)° and Z = 4). A single Y³⁺ cation occupying the general site 4e is surrounded by six oxide and two fluoride anions forming [YO₆F₂]^11? polyhedra (d(Y–O) = 228–243 plus 263 pm, d(Y–F) = 219–220 pm). These are linked via common O···O edges to chains running along [010] and adjacent chains get tied to each other by sharing common O3···O3 and O3···F edges which results in sheets parallel to (100). The Se⁴⁺ cations connect these sheets as ψ¹‐tetrahedral [SeO₃]^2? anions (d(Se–O) = 168–174 pm) for charge balance via all oxygen atoms. Despite the different coordination numbers of seven and eight for the rare‐earth metal(III) cations the structures of LuF[SeO₃] and YF[SeO₃] appear quite similar. The chains containing pentagonal bipyramids [LuO₅F₂]^9? are connected to layers running parallel to the (100) plane again. In fact it is only necessary to shorten the partial structure of the straight chains along [001] to achieve the angular chains in YF[SeO₃]. As a result of this shortening one oxide anion at a time moves into the coordination sphere of a neighboring Y³⁺ cation and therefore adds up the coordination number for Y³⁺ to eight. For the synthesis of YF[SeO₃] yttrium sesquioxide (Y₂O₃), yttrium trifluoride (YF₃) and selenium dioxide (SeO₂) in a molar ratio of 1 : 1 : 3 with CsBr as fluxing agent were reacted within five days at 750 °C in evacuated graphitized silica ampoules.     

Metal Complexes with Macrocyclic Ligands. Part XXI. A nonlinear relationship between the stability of Cu2+ complexes and their complexation rate with 1,4,8,11-tetraazacyclotetradecane

The kinetics of the reaction (1) between 1,4,8,11-tetraazacyclotetradecane (Cy) and a series of Cu(II) complexes CuL (L) = glycolate, malonate, succinate, picolinate, glycinate, iminodiacetate, nitrilotriacetate, N-(2-hydroxyethyl)ethylenediaminetriacetate, ethyienediamine, 1,3-diaminopropane, diethylenetriamine and N,N-bis(3-aminopropylamine) were studied spectrophotometrically at 25° and I = 0.5 (KNO₃). From the analysis of the log k_obs/log [L] profiles obtained at different pH values the resolved bimolecular rate constants k (Table 3) were obtained by a nonlinear curve-fitting procedure. For nearly all systems studied, the rate constant k, describing the reaction between the 1:1 complex CuL and the monoprotonated form of the macrocycle CyH, was obtained. The nonlinear relationship between log k and log K_CuL and its nature is discussed. It is shown that the inverse relationship between reactivity and stability described by others is only a special case of the more general Eqn. 3 described here.     

Controlled Synthesis of a Chitosan‐Based Graft Copolymer Having Polysarcosine Side Chains Using the NCA Method with a Carboxylic Acid Additive

Summary: A novel chitosan derivative with polysarcosine side chains, i.e., chitosan‐graft‐polysarcosine [chitosan‐graft‐poly(N‐methylglycine)], was synthesized by ring‐opening polymerization of sarcosine N‐carboxyanhydride (NCA) with chitosan as a macroinitiator in the presence of carboxylic acids in dimethyl sulfoxide at 27 °C. Degree of substitution ( ) for polysarcosine side chains introduced to chitosan was controlled successfully by the feed amount of the additive nicotinic acid ( = 0.21–0.71). Independent of control, degree of polymerization ( ) for polysarcosine side chains was controlled by adjusting feed ratios of NCA monomer to chitosan ( = 14–43). Kinetic analysis of the propagation of sarcosine NCA was conducted by measuring CO₂ evolution. Apparent k_p values decreased with increased feed amounts of nicotinic acid, supporting the theory that propagation of NCA in the presence of nicotinic acid proceeds via equilibrium between active amine and dormant ammonium species.

Propagation mechanism of carboxylic acid‐mediated polymerization of sarcosine N‐carboxyanhydride.     

Methyl‐, Ethenyl‐, and Ethynyl‐Bridged Cationic Digold Complexes Stabilized by Coordination to a Bulky Terphenylphosphine Ligand

Reactions of the gold(I) triflimide complex [Au(NTf₂)(PMe₂Ar )] ( 1 ) with the gold(I) hydrocarbyl species [AuR(PMe₂Ar )] ( 2 a – 2 c ) enable the isolation of hydrocarbyl‐bridged cationic digold complexes with the general composition [Au₂(μ‐R)(PMe₂Ar )₂][NTf₂], where Ar =C₆H₃‐2,6‐(C₆H₃‐2,6‐iPr₂)₂ and R=Me ( 3 ), CH?CH₂ ( 4 ), or C?CH ( 5 ). Compound 3 is the first alkyl‐bridged digold complex to be reported and features a symmetric [Au(μ‐CH₃)Au]⁺ core. Complexes 4 and 5 are the first species of their kind that contain simple, unsubstituted vinyl and acetylide units, respectively. In the series of complexes 3 – 5 , the bridging carbon atom systematically changes its hybridization from sp³ to sp² and sp. Concomitant with this change, and owing to variations in the nature of the bonding within the [Au(μ‐R)Au]⁺ unit, there is a gradual decrease in aurophilicity, that is, the strength of the Au???Au bonding interaction decreases. This change is illustrated by a monotonic increase in the Au–Au distance by approximately 0.3 Å from R=CH₃ (2.71 Å) to CH?CH₂ (3.07 Å) and C?CH (3.31 Å).     

Molecular Characteristics of Poly(N‐isopropylacrylamide) Separated from Nanocomposite Gels by Removal of Clay from the Polymer/Clay Network

The extraordinary mechanical and swelling/deswelling properties of nanocomposite (NC) gels are attributed to their unique organic (polymer)/inorganic (clay) network structure. In this study, poly(N‐isopropylacrylamide) (PNIPA) was successfully separated from an NC gel network by decomposing the clay (hectorite) using hydrofluoric acid (HF). A very low HF concentration (0.2 wt.‐%) was adequate for the decomposition of the clay without causing any damage to PNIPA. The separated PNIPA had a high (=5.5 × 10⁶ g · mol⁻¹). Also, was almost constant regardless of the clay concentration (C_clay = 1–25 × 10⁻² mol · l⁻¹), even though the properties of the NC gel varied widely over this C_clay range. Comparisons of NC gels, PNIPA, and SiO₂‐NC gels indicated that the clay platelets specifically play an important role in NC gels.

     

Primary radical termination and unimolecular termination in the heterogeneous polymerization of acrylamide initiated by a fluorinated azo‐derivative initiator: A kinetic study

Acrylamide was polymerized in acetonitrile at 82 °C with a perfluorinated azo‐derivative initiator. The polymerization proceeded heterogeneously. Varying amounts of initiator and monomer were used. The activation energy was deduced from three experiments carried out at 59, 71, and 82 °C. The following kinetic law, deviating a great deal from the classical law, was obtained: R ∼ [I₂][M](0.05% < [I₂]_o/[M]_o < 1.00%) and R ∼ [I₂][M](1% < [I₂]_o/[M]_o < 7%). These results can be interpreted in light of the contribution of primary radical termination and the emergence of occlusion. The development of a new kinetic relationship allowed us to confirm the existence of both of these termination reactions. The calculation of the k_prt /k_i · k_p ratio was also achieved. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1834–1843, 2000     

Mechanism of the azide–bromine reaction in aqueous medium

Results on the oxidation of N by Br₂ in neutral and acid media are presented. The rate of the reaction is found to be proportional to [N] and [Br₂]. The gaseous product of oxidation is found to be pure nitrogen. The stoichiometry of the reaction is The reaction shows a positive salt effect. It is found that the addition of Br^? stabilizes the complex BrN₃, which decomposes into Br^? and N₂: The spectroscopic measurements also support the kinetic observation. The equilibrium constant K, the rate constants and the thermodynamic parameters were calculated. It is observed that H⁺ ion inhibits the reaction. The mechanism is discussed in terms of the kinetic results.     

Structure and Bonding of the Hexameric Platinum(II) Dichloride,Pt6Cl12 (β‐PtCl2)

The crystal structure of Pt₆Cl₁₂ (β‐PtCl₂) was redetermined ( a_h = 13.126Å, c_h = 8.666Å, Z = 3; a_rh = 8.110Å, α = 108.04°; 367 hkl, R = 0.032). As has been shown earlier, the structure is in principle a hierarchical variant of the cubic structure type of tungsten (bcc), which atoms are replaced by the hexameric Pt₆Cl₁₂ molecules. Due to the 60° rotation of the cuboctahedral clusters about one of the trigonal axes, the symmetry is reduced from to ( ). The molecule Pt₆Cl₁₂ shows the (trigonally elongated) structure of the classic M₆X₁₂ cluster compounds with (distorted) square‐planar PtCl₄ fragments, however without metal‐metal bonds. The Pt atoms are shifted outside the Cl₁₂ cuboctahedron by Δ = +0.046Å ( (Pt—Cl) = 2.315Å; (Pt—Pt) = 3.339Å). The scalar relativistic DFT calculations results in the full symmetry for the optimized structure of the isolated molecule with d(Pt—Cl) = 2.381Å, d(Pt—Pt) = 3.468Å and Δ = +0.072Å. The electron distribution of the Pt‐Pt antibonding HOMO exhibits an outwards‐directed asymmetry perpendicular to the PtCl₄ fragments, that plays the decisive role for the cluster packing in the crystal. A comparative study of the Electron Localization Function with the hypothetical trans‐(Nb₂Zr₄)Cl₁₂ molecule shows the distinct differences between Pt₆Cl₁₂ and clusters with metal‐metal bonding. Due to the characteristic electronic structure, the crystal structure of Pt₆Cl₁₂ in space group is an optimal one, which results from comparison with rhombohedral Zr₆I₁₂ and a cubic bcc arrangement.     

Towards Clathrates: Frozen States of Hydration of tert‐Butylamine

The dilution of tert‐butylamine (tBA) with water and subsequent cooling leads to a large series of different crystalline hydrates by an in situ IR laser melting‐zone procedure. The crystal structures were determined for tBA?n H₂O, with n=0, , 1, 7 , 7 , 9 , 11, and 17. For the two lower hydrates (n= , 1), one‐ and two‐dimensional hydrogen‐bonded networks are formed, respectively. The higher hydrates (n>1) exhibit a clathrate‐like three‐dimensional water framework with the tBA molecules as part of, or sitting inside, the cages. In all cases, tBA is hydrogen‐bonded to the H₂O framework. In the intermediate range (1相似文献