B. Kulicka

Structure and properties of [2-NH2C5H4NH][SbCl4] and [2-NH2C5H4NH][SbBr4]

The crystal structures of [2-NH 2 C 5 H 4 NH][SbCl 4 ] (2-APyHSbCl 4 ) and [2-NH 2 C 5 H 4 NH][SbBr 4 ] (2-APyHSbBr 4 ) are determined at 100 K. Both compounds crystallize in the monoclinic space group: P2 1 /c. The structure is composed of SbX - 4 (X = Cl, Br) ions which form infinite chains through the crystal via halogen linkages. The structural phase transformations are detected by the differential scanning calorimetry and dilatometric techniques: at 402 K, close to continuous, and at 412 K, clearly discontinuous, in 2-APyHSbCl 4 and 2-APyHSbBr 4 , respectively. Dielectric relaxation studies in the frequency range between 1 kHz and 25 MHz indicate reorientations of the 2-aminopyridinium (2-APyH) cations in both compounds in the low temperature phases. The proton NMR second moment, M 2 , and spin-lattice relaxation time, T 1 , for 2-APyHSbCl 4 and 2-APyHSbBr 4 measured between 78 and 430 K reveal the in-plane reorientation of the 2-APyH cations. The possible mechanism of the phase transitions in the title crystals is discussed on the basis of the results presented.

Structure and properties of [4-NH2C5H4NH][BiCl4]

The halogenoantimonates(III) and halogenobismuthates(III) of the general formula RaMbX3b+a (where R denotes organic cations, X = Cl, Br, I and M = Sb, Bi) form a large group of ferroelectric crystals [1]. The title crystal [4-NH2C5H4NH][BiCl4] (abbreviation – 4APCB) is closely related to the recently found antimonate(III) analog [4-NH2C5H4NH][SbCl4] [2] , which reveals interesting ferroelectric properties with intermediate incommensurate phases. 4APCB undergoes at 252 K structural phase transition (PT) of first order. The room temperature structure (phase I) is monoclinic, space group Cc with a = 13.229, b = 13.505 c = 7.350 A and β = 120.31. The structure is composed of BiCl4 ions which form infinite chains through the crystals via chloride linkages. Each bismuth lies in a distorted octahedral environment. The 4-aminopyridinium cation reveals substantial disorder. The low temperature phase (II) is monoclinic, space group P21\c with a = 11.1660(7), b = 13.5857(8), c = 7.2750(4) A and β = 93.777(5). Over the phase II the organic cations are fully ordered. The structural analysis, calorimetric (DSC) and spectroscopic studies (IR) show that the PT is governed by the dynamics of the 4-aminopyridinium cations.