Structure-property correlations in novel spin crossover materials

In complexes where the energy difference between the high and low spin state of the metal is of the order of k(_b)T, temperature can be used to induce a spin crossover transition (SC). In some cases, at very low temperatures, irradiation can induce excitation to a meta-stable high spin state. At low temperatures, this Light-Induced Excited Spin-State Trapped (LIESST) state is generally long lived, enabling structural examination. The results presented herein refer to a wide range of iron(II) spin crossover materials which have been structurally studied in both thermal and light induced states. These fall into three categories; mononuclear, dinuclear and polymeric. The mononuclear complexes studied include FeL[H(_2)B(Pz)(_2)](_2) L = 2,2'-bipyridine (1) and 1,10-phenanthroline (2), of which 2 was found to undergo a change in symmetry in addition to the change in spin state, leading to a novel light induced polymorphism that has not been previously seen. Two dinuclear compounds with step transitions have been examined. While {[N(CN)(_2)](FeBpl)(_2)}(PF(_6))(_3) undergoes a gradual transition, the transitions in [Fe(Btz)(NCS)(_2)](_2)Bpmd are abrupt and the latter also undergoes LIESST but with a rapid relaxation that has not been observed previously with any other technique. While the origin of this relaxation is uncertain, the structure of this excited state has been studied under constant irradiation. The largest structural study of three dimensional SC materials has been carried out, including bimetallic polymers with [Au(CN)(_2)], [Ag(CN)(_2)]-, [Ag(_2)(CN)(_3)]- and [Pd(CN)(_4)](^2-) bridging ligands. These anionic bridges have been shown to enhance cooperativity between iron centres leading to abrupt transitions and hysteresis. These materials have been shown to undergo LIESST, crystalline state allosterism, and thermo-chromism. Such multi-property materials have a high potential for technological applications

Chiral selection in the formation of borates from racemic binaphthols and related diols

A series of racemic or stereochemically labile chiral borate anions based on the 2,2′-biphenol motif was investigated. All borates were homochiral in the solid state, although in some cases the heterochiral diastereomers were computed to be thermodynamically preferred (DFT). The crystallographic preference for the homochiral diastereomer was attributed to its lower bulk, higher molecular symmetry, and the therewith associated better packing ability

Charge-ice dynamics in the negative thermal expansion material Cd(CN)2_2

We use variable-temperature (150--300\,K) single-crystal X-ray diffraction to re-examine the interplay between structure and dynamics in the ambient phase of the isotropic negative thermal expansion (NTE) material Cd(CN)$_2$. We find strong experimental evidence for the existence of low-energy vibrational modes that involve off-centering of Cd$^{2+}$ ions. These modes have the effect of increasing network packing density---suggesting a mechanism for NTE that is different to the generally-accepted picture of correlated Cd(C/N)$_4$ rotation modes. Strong local correlations in the displacement directions of neighbouring cadmium centres are evident in the existence of highly-structured diffuse scattering in the experimental X-ray diffraction patterns. Monte Carlo simulations suggest these patterns might be interpreted in terms of a basic set of `ice-rules' that establish a mapping between the dynamics of Cd(CN)$_2$ and proton ordering in cubic ice VII.Comment: 5 pages, 5 figures, submitted to PR

Methyl 6-amino-6-oxohexanoate

The title compound, C7H13NO3, adopts an approximately planar conformation. The torsion angles in the aliphatic chain between the carbonyl group C atoms range from 172.97 (14) to 179.38 (14)° and the r.m.s. deviation of all non-H atoms is 0.059 Å. The crystal packing is dominated by two strong N—H⋯O hydrogen bonds involving the amide groups and forming R 2 2(8) rings and C(4) chains. Overall, a two-dimensional network parallel to (100) is formed. A weak inter­molecular C—H⋯O inter­action is also present

3-Meth­oxy-3-oxopropanaminium chloride

In the title compound, C4H10NO2 +·Cl−, the central ethyl­ene bond of the cation adopts a gauche conformation. The three H atoms of the –NH3 + group are engaged in strong and highly directional inter­molecular N—H⋯Cl hydrogen bonds, which result in a tape-like arrangement along [010] of the respective ion pairs. In addition, weak inter­molecular C—H⋯Cl and C—H⋯O inter­actions are present

Exploring a practice‐based approach to elementary preservice science teacher preparation

The science methods course model presented here, called an immersed methods course (IMC), engaged preservice elementary teachers in reform‐based science instructional approaches within authentic classroom settings and with elementary students in a guided format. Questions guiding the study were: (1) Did participation in the IMC model impact preservice teachers (PTs') science teaching self‐efficacy? (2) Which science methods course model activities/experiences did PTs identify as the most impactful on their science teaching? (3) How did participation in the IMC model impact PTs' understandings of science teaching? Participants were 138 elementary PTs from a Southeastern United States university. Data were collected from seven course sections over 3 years and included pre/post science teaching self‐efficacy survey data, post written responses, and interviews. Member checking approaches were also used to refine and establish the validity of findings. Researchers completed qualitative data analysis, which was complimented by quantitative statistical analysis. Findings across data sources suggest participation positively influenced PTs' science teaching self‐efficacy and beliefs about the effectiveness of the instructional approaches. Participation also helped PTs apply theories to practice and develop competency using the practices. Findings highlight how the IMC model mitigates constraints associated with current science teacher preparation approaches

Conformational studies on substituted ε-caprolactams by X-ray crystallography and NMR spectroscopy

The synthesis and conformational analysis of ε-caprolactams containing a -COOMe group at the C-6 position is described. The influence of different C-2, C-6 and N substituents on ring conformation was studied using X-ray crystallography and NMR spectroscopy. The results provide evidence that all the analysed caprolactams adopt a chair type conformation with a planar lactam. In the 6-substituted caprolactam, the -COOMe residue prefers to reside in an equatorial position, but can be induced to occupy an axial orientation by the introduction of a bulky tert-butyloxycarbonyl (BOC) group on the lactam nitrogen or by C-2/C-3 ring desaturation. The BOC protected caprolactam was found to undergo exchange between two chair forms as detected by solution NMR, one with the C-6 ester equatorial (30%) and the other with it in the axial position (70%); the latter was observed by X-ray crystallography. For the C-2 dithiocarbamate substituted C-6 methyl ester seven-membered rings, a single chair form is observed for cis-isomers with both substituents equatorial. The analogous trans-isomers, however, exist as two chair forms in a 1 : 1 equilibrium ratio of 1,NC4 and 4C1,N conformers, where either substituent can occupy axial or equatorial positions. This journal i

Masked alkynes for synthesis of threaded carbon chains

Polyynes are chains of sp1 carbon atoms with alternating single and triple bonds. As they become longer, they evolve towards carbyne, the 1D allotrope of carbon, and they become increasingly unstable. It has been anticipated that long polyynes could be stabilized by supramolecular encapsulation, by threading them through macrocycles to form polyrotaxanes—but, until now, polyyne polyrotaxanes with many threaded macrocycles have been synthetically inaccessible. Here we show that masked alkynes, in which the C≡C triple bond is temporarily coordinated to cobalt, can be used to synthesize polyrotaxanes, up to the C68 [5]rotaxane with 34 contiguous triple bonds and four threaded macrocycles. This is the length regime at which the electronic properties of polyynes converge to those of carbyne. Cyclocarbons constitute a related family of molecular carbon allotropes, and cobalt-masked alkynes also provide a route to [3]catenanes and [5]catenanes built around cobalt complexes of cyclo[40]carbon and cyclo[80]carbon, respectively