Orthorhombic polymorph

In this interpretation, the persistence of the orthorhombic polymorph must be imputed to metastability associated to low reaction kinetics. At subsolidus temperatures, characteristic of most metamorphic regimes (including the granu-... 

Cix-RuClj(dmso) is made from RuClj and DMSO as yellow crystals [937], from RuClj, and DMSO [938] or from mer-RuCl3((dmso)3Cl3 and (dppe) with DMSO, this last method giving the orange orthorhombic polymorph [939], X-ray crystal structures on the monoclinic and orthorhombic polymorphs (cf. the brief review in ref. [939]) show essentially the same structures (Fig. 1.43). The orthorhombic form has cis chloro ligands, with one O- and three S-bonded (dmso)... 

The [C4Qlm]+ cations in the two polymorphs were found predominantly to differ with respect to conformation The structural results showed that the polymorphism is due to a rotational isomerism of the butyl group of fhe [C4Qlm]+ cation around C7-C8, as defined in Figure 12.1. In the monoclinic polymorph, the butyl chain is in anti (or trans) conformation around C7-C8, and in the orthorhombic polymorph it is gauche around C7-C8. The conformational difference reveals itself in fhe rofafion of the butyl chain... 

Figure 21. Molecular structure of Mn(S2CO-i-Pr)2(2,2 -bpy), orthorhombic polymorph the molecule has twofold symmetry.

The structure of each polymorph has been determined by X-ray crystallography. The colorless polymorph crystallizes in the monoclinic space group P2i/c, while the yellow polymorphs forms in the orthorhombic space group P2i2i2i. Figure 7 shows a drawing of the chain of cations that are found in the colorless, monoclinic polymorph, and Fig. 8 presents a view of the more complex chains present in the yellow, orthorhombic polymorph. In these two... 

PROP Colorless, deliquescent needles, or orthorhombic crystals. Undergoes transition to high temp orthorhombic polymorph at 4°. Mp 415°, bp 520°, d 1.899 25°, vap press 1 mm 291° (subl). Very sol in H2O, EtOH, Et20, or Py sltly sol in CgHg,... 

Nichols, G. and Frampton, C. S. (1998). Physicochemical characterization of the orthorhombic polymorph of paracetamol crystallized from solution. J. Pharm. ScL, 87, 684-93. [113, 144f]... 

The usual maroon form of this oxide has the rutile structure, the mean distance of Pb to the six octahedral neighbours being 218 A. At 300 under 40 kbar pressure this converts to a black orthorhombic polymorph, the structure of which has been described in the discussion of close-packed structures in Chapter 4. 

A new unsolvated form of pyrazine-2,3-dicarboxylic acid 100 was subjected to X-ray crystallography <04AX(E)1305>, as was an orthorhombic polymorph of A,A -bis(2-pyridyimethyl)pyrazine-2,3-dicarboxamide 101 <04AX(E)210> and two triclinic polymorphs of... 

Views of the molecular packing for the triclinic and orthorhombic polymorphs of p-(N-chlorobenzylidene)-p-chloroanihne. (The figure is adapted from data presented in Ref. 32.)... 

When polymorphs are not interconvertible, the crystal forms are said to be monotropic graphite and diamond are monotropic forms of carbon. The term isopolymorphism is used when each of the polymorphous forms of one substance is isomorphous with the respective polymorphous form of another substance. For instance, the regular and orthorhombic polymorphs of arsenious oxide, AS2O3, are respectively isomorphous with the regular and orthorhombic polymorphs of antimony trioxide, Sb203. These two oxides are thus said to be isodimorphous. 

D.L. Bryce, K. Eichele, R.E. Wasyhshen, An O NMR and quantum chemical study of monoclinic and orthorhombic polymorphs of triphenylphosphine oxids, Inorg. Chem. 42 (2003) 5085. 

Mechanochemical co-crystallisation has also been exploited in the synthesis of readily compressible and thermodynamically stable forms of the API paracetamol (Figure 8.8(b)). While tablet formation using the thermodynamically stable polymorph of paracetamol is difficult, the metastable orthorhombic polymorph yields tablets much more readily due to its layered crystal structure. Consequently, it was expected that co-crystals of paracetamol with a similar layered structure would also be readily compressible. Screening by LAG revealed four co-crystals of paracetamol with improved ability to compress into tablets. Structural characterisation and Density Functional Theory (DFT) calculations revealed that enhanced compressibility was related to the formation of a sheet-like structure reminiscent of the second polymorph of paracetamol (Figure 8.8(c)-(e)). ... 

Two orthorhombic polymorphic forms I THXMAMll and II THXMAM13 (room temp.). Third cubic (high temperature > 409 K) polymorph THXMAM12 (no coordinates). 

In contrast with the work by Shimada [74] Grande and Co. [76] observed that amorphous GeSe2 at T= 250 - 300 °C partly crystallized in two phases when compressed, the first at 3.0 GPa and the second at 7.7GPa. Also, during quenching performed at 7.7 GPa an orthorhombic polymorph of GeSc2 was found at 500 C. 

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