Crystal structure, dielectric, piezoelectric and elastic properties of (±)-tris(ethylenediamine)cobalt(III) nitrate, (±)–[Co(H2N(CH2)2NH2)3](NO3)3

Abstract

Abstract Large single crystals of optical quality of (±)-tris(ethylenediamine)cobalt(III) nitrate have been grown from aequeous solutions. An X-ray structure analysis yielded space group Pca21, a 1 = 15.441(3) Å, a 2 = 8.607(2) Å, a 3 = 12.328(2) Å, Z = 4, ϱ calc = 1.724 g cm−3, ϱ obs = 1.730 g cm−3. The structure is built up from [Co(H2N(CH2)2NH2)]3+ cations and nitrate anions which are linked by Coulomb interactions and by a three-dimensional network of hydrogen bonds. Two ligands of the cationic chelate complex are disordered. Its probable conformation is Δδλλ or the enantiomorphic Λδδλ. Pyroelectric, dieletric, piezoelectric and elastic constants have been determined at room temperature. Additionally, we have studied the coefficients of thermal expansion and the thermoelastic constants in the range between 270 K and 350 K. The structure exhibits a nearly trigonal symmetry around the [unk]2-axis. The physical properties obey qualitatively this symmetry. The maximum longitudinal piezoelectric effect surmounts d 111 of α-quartz by a factor 10. The largest piezoelectric constant is d 113 ≈ 14d 111 of α-quartz. Dielectric and elastic constants appear only slightly anisotropic, contrary to a strongly anisotropic thermal expansion.