Dielectric relaxation in cyano complexes of the K4Me11(CN)6·3 H2O type. I. Ferroelectric behaviour

Several K₄Me¹¹ (CN)₆·3 H₂O type cyano complexes belonging to the C_2h crystal class were studied to examine their ferroelectricity and the dielectric-relaxation process. Isomorphous substances obtained through replacing the Fe^2? ion by Ru²⁺, Os²⁺ and Mn²⁺ ions show ferroelectric behaviour and dielectric relaxation, in both the ferro- and para-electric phases. It was found, through a careful analysis of the shape of the dielectric-absorption band, that a polydispersive nature appears in the whole temperature range explored and becomes very pronounced in the immediate vicinity of the transition temperature. The distribution of the relaxation times has been described by means of the Williams-Watts decay function.     

Structural investigation on hexasubstituted benzene derivatives. Part 2: The structure of metadinitrotetramethylbenzene and molecular mechanics analysis on meta and ortho derivatives

C₁₀H₁₂N₂O₄ (M r=224.2) crystallizes in the monoclinic system, space groupP2₁/mwitha=15.462(4),b=7.926(3),c=8.972(3) Å;=90.2(1)°;V=1099.5(6) ų;Z=4;D _c=1.35 gcm^–3;(Cu-K)=8.6 cm^–1; =1.5418 Å;F(000)=472. The position of the molecule on a crystallographic mirror plane forces the NO₂ plane to be normal to the benzene ring. The-electron-withdrawing character of the NO₂ groups induces a deformation on the geometry of the benzene.     

Structural investigation on hexasubstituted benzene derivatives. Part 1. The structure of ortho-dinitrotetramethylbenzene

C₁₀H₁₂N₂O₄ (M _r =224.2) crystallizes in the triclinic system, space groupP¯1 witha=8.327(3),b=8.734(3),c=8.453(3) Å;a=63.6(1),=97.0(1), =100.4(1)°;V=541.0(6) ų,Z=2,D _c =1.38 g cm^–3,(Cu-K)=8.7 cm^–1, =1.5418 Å, F(000)=236. Deviation from theoretic geometry of the benzene ring and from planarity is observed in accordance with the-electron-withdrawing character of the NO₂ groups and the high steric hindrance of the substituents.     

Dielectric relaxation in cyano complexes of the K4Me11(CN)6·3H2O type. II. Isotopic effect

The dielectric relaxation of deuterated K₄Me¹¹(CN)₆·3H₂O doped with NH₄¹ has been investigated in the vicinity of the transition temperature. In all cases the dielectric band appeared to be non-symmetrical and may be described by means of the Williams-Watts empirical decay function ?(Φ) ? exp[?(?/τ_-)]. A mechanism for the asymmetry of the dielectric absorption due to fluctuation of the “Glarum defects” is proposed. Also, the nature of the dielectric absorption in the crystals is discussed.     

Dipole moments of (CH3)3MX compounds with bonds between halogens and group IV a elements: evidence for pX → dM bonding

The electric dipole moments of the two series of molecules (CH₃)₃MX with M  C, Si, Ge, Sn and Pb, and X  Cl and Br have been determined. The two carbon compounds show behaviour different from that of the others, and this is interpreted as indicating that p_X → d_M back-bonding is present for the other elements of the series, and it is suggested that the extent of this back-bonding decreases with an increase in the atomic number of M.