Triclinic behaviour

Figure 55 shows the cyclic voltammetric behaviour of [Nin(OEP)] (OEP = 2,3,7,8,12,13,17,18-octaethylporphyrin) in CH2C12 solution,96 together with its solid-state molecular structure (in the planar triclinic... 

Figure 8.69 Space-filling representation of the three polymorphic forms of ferrocene (a) triclinic, (b) monoclinic, and (c) orthorhombic. (Reprinted with permission from [3] 1998 American Chemical Society) (d) Phase behaviour of ferrocene.

The air-stable reduced porphyrin ay-dimethyl-aY-dihydro-octaethylporphinato-nickel(n) contains a planar NiN4 grouping with the porphyrin having a folded and ruffled core.483 The triclinic form of l,2,3,4,5,6,7,8-octaethylporphinatonickel(n) has very short Ni—N distances (1.929 A) compared with the tetragonal form (1.957 A).485 The behaviour of tetra-(4-N-methylpyridyl)porphinatonickel(n) in aqueous acetone shows it to be four-co-ordinate and planar, but it adds pyridine or imidazole... 

Tautomerization of porphyrins in crystals exhibits diverse patterns of behaviour. There are polymorphic crystal structures of tetraphenylporphyrin (TPP) [19] the tetragonal and the triclinic forms (Silvers and Tlilinsky, 1967 Codding and Tulinsky, 1972 Tblinsky, 1973). In the tetragonal form. X-ray... 

Fig. 10.5 (TMTSF)2PF6 a phase diagram for the transition temperature as a function of the applied pressure. The data points are due to different authors. At low temperatures and low applied pressures, one observes the behaviour of an insulator with spin-density waves. At low temperature and high pressure, the substance is superconducting at higher temperature it is metallic. Crystallographic data triclinic, a = 7.29 A, b = 7J A,c= 13.52 A, = 83.39°, = 86.27°,... 

If the fibres are uniaxial, there is still some symmetry in the material, and the number of parameters needed to describe the elastic behaviour is smaller than 21, the value for a triclinic lattice. If the fibres are directed, but their positions in space are irregular or arranged on a hexagonal lattice, the material is transversally isotropic i. e., its properties are the same in all directions perpendicular to the fibre direction. In this case, there are five independent elastic constants (see section 2.4.6). If the fibres are uniaxial and arranged on a rectangular lattice, the material is orthotropic, and the number of independent elastic components is nine (see section 2.4.5). 

---