| Abstrakt: |
The compound [TiO(acac)2] (acac 4;= 4;acetylacetonate) reacts with N-hydroxyiminodiacetic acid (H3hida) or (R,R)-2,2′-(hydroxyimino)dipropionic acid (R,R-H3hidpa) to yield [Ti(hida)2]2– or [Ti(R,R-hidpa)2]2–, respectively. The anion [Ti(R,R-hidpa)2]2– has been obtained from H2O in the presence of Ca2+ as [Ca(H2O)4][Ca(H2O)5]3[Δ-Ti(R,R-hidpa)2]4·2H2O 3 which crystallises in the space group P21 (no. 4) with a 4;= 4;14.258(2), b 4;= 4;16.516(3), c 4;= 4;19.169(3) Å, β 4;= 4;110.907(9)°; least-squares refinement of 6082 reflections and 1126 variables converged with agreement factors of R 4;= 4;0.069 and R′ 4;= 4;0.054. The anions possess the co-ordination geometry identified for other Amavadin-style complexes, viz. eight-co-ordination achieved by the ligation of two mutually trans and staggered η2-NO groups and four unidentate carboxylate oxygen atoms; Ti–N(NO) 2.04(1)–2.10(1), Ti–O(NO) 1.962(9)–2.001(9), Ti–O(CO2) 2.024(9)–2.100(9), N–O 1.38(1)–1.44(1) Å. The lattice of compound 3 comprises of parallel zigzag strands of alternating [Δ-Ti(R,R-hidpa)2]2– and [Ca(H2O)x]2+ (x 4;= 4;4 or 5) linked interstrand by CaII binding to carboxylato-oxygen atoms and intra- and inter-strand by hydrogen bonding from the H2O molecules to the oxygen atoms of the anions. The anions are obtained exclusively in the Δ-helical form and this has enabled 1H and 13C NMR studies to follow epimerisation at the TiIV centre to produce a mixture of the Δ- and Λ-helical forms. Carbon-13 NMR spectroscopy has been used to investigate the interaction of the carboxylato groups of [Ti(hida)2]2– with solvents. |
