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

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

Formation of a σ-alkane complex and a molecular rearrangement in the solid-State : [Rh(Cyp2PCH2CH2PCyp2)(η2:η2-C7H12)][BArF 4]

Addition of H2 to the precursor [Rh(Cyp2PCH2CH2PCyp2)(η2:η2- C7H8)][BArF 4] gives the σ-alkane complex [Rh(Cyp2PCH2CH2PCyp2)(η2:η2- C7H12)][BArF 4] by a single-crystal to single-crystal reaction, as characterized by Xray crystallography, SSNMR spectroscopy, and periodic DFT. An unexpected rearrangement of the {Rh(L2)}+ fragment is revealed

On the Spin content of the Nucleon

A QCD sum rule calculation of Balistky and Ji on the spin content of the nucleon is done with a different approach to the evaluation of the bilocal contributions and to the extraction of the nucleon pole residues. The result obtained is much more numerically stable which puts their conclusion that about half of the nucleon spin is carried by gluons on firmer ground.Comment: 7 pages, two (eps) figure, minor corrections and one figure adde