Crystal structure packing efficiency

Solv=MeOH, EtOH and PrOH), and l,4-bis(4-pyridyl-butadiyne) (bpb, n= 0.5, Solv=MeOH). Like the btr derivative, compressed [FeN6] pseudo-octahedral sites define the knots of the square- or rhombus-shaped windows, which constitute the layered grid structure of the three compounds. Stacking of these layers in the crystal defines their most important structural differences, which are determined by the ligand size and crystal packing efficiency. In principle, the 2D grids are organised in a fashion similar to that described for the [Fe(btr)2(NCX)2]-H20 system the parallel layers are alternated so that the iron atoms of one layer lie vertically above and below the centres of the squares formed by the iron atoms of the adjacent layers. 

The tris and bis complexes of acetylacetone (2,4-pentanedione) (167) with chromium(III) have been known for many years (168,169).739 The tris compound is generally prepared by the reaction of an aqueous suspension of anhydrous chromium(III) chloride with acetylacetone, in the presence of urea.740 Recently a novel, efficient synthesis of tris(acetylacetonato)chromium-(III) from Cr03 in acetylacetone has been reported.741 The crystal structure of the tris complex has been determined.744 A large anisotropic motion was observed for one of the chelate rings, attributed to thermal motion, rather than a slight disorder in the molecular packing. 

The relatively large number of crystal structure analyses of hydrates is, of course, a consequence of the use of water as the least expensive and most common solvent. The water molecules are small enough that they can stabilize crystal structures by filling voids between molecules for more efficient packing, while also contributing to the lattice energy by additional hydrogen bonds. 

Figure 4.9. Schematic representations of the crystal structures of the salts of enantiopure 5 with / -substiluted 1-arylethylamines in success, (a) Less soluble salts, in which the formation of a stable supramolecular hydrogen-bond sheet, the realization of efficient CII—ti interaction, and the close packing of the sheets are achieved, (b) More soluble salts, in which efficient CH n interaction is not realized and the close packing of the supramolecular sheets a stable supramolecular hydrogen-bond sheet is not formed, (c) More soluble salts, in which a stable supramolecular hydrogen-bond sheet is formed and the close packing of the supramolecular sheets is achieved, while efficient interaction is not realized.

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