Solid state structures group

A transition-state structure was proposed on the basis of the solid-state structure of [Ni((R,R)-DBF0X)(H20)3](C104)2 (Fig. 1.8). The catalyst-dienophUe complex is thought to be a square-bipyramidal structure containing an octahedral nickel ion. The dienophile adopts an s-cis conformation with the si face shielded by a phenyl group. 

Syntheses and Solid State Structures of Group 13-Distibine... 

Wells et al. characterized group 13-stibine adducts by single crystal X-ray structure analyses first in 1997 [35]. The solid state structures of three borane-stibine adducts of the type X3B—Sb(Tms)3 (X = Cl 6, Br 7, I 8), obtained by reaction of boron trihalides BX3 and Sb(Tms)3 in n-pentane, were determined. 

Reliable information on the thermodynamic stability of group 13/15 adducts is usually obtained by gas phase measurements. However, due to the lability of stibine and bismuthine adducts in the gas phase toward dissociation, temperature-dependent H-NMR studies are also useful for the determination of their dissociation enthalpies in solution [41b], We focussed on analogously substituted adducts t-BusAl—E(f-Pr)3 (E = P 9, As 10, Sb 11, Bi 12) since they have been fully characterized by single crystal X-ray diffraction, allowing comparisons of their thermodynamic stability in solution with structural trends as found in their solid state structures. 

Up to now, fifteen group 13-stibine R3AI—SbR and four group 13-bismuthine adducts R3AI—BiR3 have been structurally characterized by single crystal X-ray diffraction studies. Their central structural parameters are summarized in Table 5. Structures 1-4 show the solid state structures of four representative adducts. 

Structures 5 and 6 display the solid state structures of two representative distibine and dibismuthine adducts. The ligands bound to the central Sb and Bi atoms adopt a staggered conformation in relation to one another, with the bulky M(t-Bu)3 groups arranged in a trans-position. This is likely due to repulsive steric interactions. The central Sb—Sb [281.1(1) 32 283.9(1) pm 35] and Bi—Bi bond distances [298.3(1) 36 and 298.4(1) pm 37] are almost unchanged compared to the uncomplexed distibines and dibismuthines, as can be seen... 

Sohnel, T, Hermann, H.L. and Schwerdtfeger, P. (2001) Towards the Understanding of Solid State Structures From Cubic to Chain-Like Arrangements in Group 11 Halides. Angewandte Chemie International Edition, 40, 4381-4385. 

The solid state structure of complex 7b is shown in Figure 25.1. Similar to parent chelating ether complex [9b], the solid-state structure of 7b shows a distorted square-pyramidal structure with the benzylidene moiety at the apical position. The N-aryl ring is located above the benzylidene moiety resulting in the relatively close contact of the benzylidene proton with the 7r-aromatic system of the mesityl group. 

We also performed a single-crystal X-ray structure analysis of this lead compound. The solid state structure of this compound depicted in Fig. 3-15 shows a half-boat-like ( sofa ) conformation with the 9-phenanthryl group in a quasi-axial or r/Mf/.v/-flagpole position, and the a, 3-unsaturated exocyclic ester in a s-cis conformation. This cleft-like conformation is advantageous for the creation of centers with a high recognition ability, since one enantiomer fits in better than the other thus leading to selectivity. 

Bis(trimethylsilyl)arsine reacts with diethyl- or dimethylzinc to form different arsenide complexes with the structure dependent on the steric demands of the alkyl group. In the presence of both methyl and ethyl groups alkylzinc bis(trimethylsilylarsenide) forms which has a trimeric solid state structure (37) with a six-membered Zn3As3 and Zn-As distances with an average of 2.48 A.322... 

Figure 3 Solid-state structure and partial labeling scheme of tetrameric [(2-pyridyl)CSiMe3Zn]4 9. The trimethylsilyl groups have been truncated to the silicon atoms. Here and in all following figures the hydrogen atoms are not shown, and the carbon atoms are not labeled.

The reaction of 2equiv. of a pyrrole-substituted cyclopentadiene with Zn[N(SiMe3)2]2 (Scheme 19) afforded the dicyclopentadienylzinc complex 23.52 A solid-state structure of this compound was not obtained, but room-temperature 1H NMR spectroscopic studies showed two equivalent cyclopentadienyl groups, whose signals broadened on cooling. 

Figure 29 The solid-state structure of Li2[ZnMe4]. The grey spheres represent the methyl groups.

The solid-state structure of 68c, Figure 36, shows that the zinc atom is surrounded in a trigonal-planar fashion by one methyl group and two 2,4,6-trisilacyclohexyl ligands, of which one has a chair conformation, while the other one has a boat conformation. 

In general, high-resolution NMR of solids is found to be very much complementary to diffraction techniques in the investigation of solid-state structures. The applications may be classified into three very general groupings ... 

Thanks to the pioneering works of many research groups, solid-state NMR is now a well established spectroscopy for the study of biological solids, particularly for those with inherent structural disorder such as amyloid fibrils. We have provided an overview of a rather complete set of NMR techniques which have developed for samples prepared by chemical synthesis or protein expression. There are many different ways to present the materials discussed in this review. We hope that the way we have chosen can give a snapshot of some facets of the very exciting discipline of biological solid-state NMR spectroscopy. In spite of the success of solid-state NMR as a tool in biological study, it is not yet a mature technique and there is much room for further development. Below we will speculate on a few possibilities from our own perspective. 

---