TWO NEW PSEUDO-ISOTYPIC ZIRCONIUM NITRILOTRIACETATES OF GUANIDINIUM AND NICKEL. E. Haussühl, G. Giester and E. Tillmanns, Institut für Mineralogie und Kristallographie, Universität Wien, Althanstr. 14, A-1090 Wien, Austria
Crystals of nitrilotriacetic acid, H3NTA' (NTA'=N(CH2COO)3) and several of its salts show surprisingly large nonlinear optical effects. Similar strong polar effects were detected in crystals of the type X2Zr(NTA')2.y H2O. Large single crystals of NiZr(NTA')2.8 H2O (I) and (C(NH2)3)2Zr(NTA')2.H2O (II) have been obtained from aqueous solutions by controlled cooling from 296 to 291 K over a period of about two months. The raw materials were produced by reacting the carbonates of guanidinium and nickel, respectively, with the stoichiometric quantities of an aqueous solution of ZrCl4 and nitrilotriacetic acid.
Crystals of the two species exhibit a similar morphology (point symmetry 222). Their crystal structures (space group C2221, Z = 4) show close relationships. Lattice constants at 293 K are:
(I) a = 10.009 Å, b = 20.710 Å, c = 11.514 Å and
(II) a = 11.279 Å, b = 20.258 Å, c = 10.346Å
The tensors of thermal expansion, dielectricity, piezoelectricity and elasticity determined with the use of large single crystals show strong anisotropy in both species. Piezoelectric effects more than 25 times larger than d111 of [[alpha]]-quartz are observed. (II) undergoes phase transitions between 287.5 and 289.6 K which appear to be of the third order.
Isolated Zr(NTA')2 molecules are similarly arranged in both structures and form sheets parallel to the plane (010). The large cations guanidinium and nickel occupy positions between these sheets with one octahedral Ni2+(H2O)6 complex in a special position in (I) replacing two guanidinium1+ ions in a general position in (II). Hydrogen bonds are formed between Ni(H2O)6 octahedra in (I) or guanidinium ions and water molecules in (II), respectively, and oxygen atoms of the acetate groups.