Redetermination of diaquatris(4-oxopent-2-en-2-olato-κ2 O,O′)lanthanum(III)

The structure of the title compound, [La(C5H7O2)3(H2O)2], has been redetermined to modern standards with anisotropic displacement parameters for all non-H atoms and the hydrogen-bonding pattern unambiguously established [for the previous study, see Phillips et al. (1968 ▶). Inorg. Chem. 7, 2295–2299]. The La3+ ion is coordinated by three O,O′-bidentate acetylacetate (acac−) ligands and two water molecules, resulting in a fairly regular square-antiprismatic LaO8 coordination geometry, with both aqua ligands part of the same square face. In the crystal, the neutral complex molecules are linked into [110] chains by O—H⋯O hydrogen bonds.

The molecular geometry of the compound I was almost identical to previous report. The La III is ligated from three acetylacetonate ligands and two aqua ligands which are forming 8-coordinate structure around La III (Figure 1). The average distance of oxygen atoms of acetylacetonate (O1-O6) and La III is 2.489 (30) Å while the original structure showed the average distance of 2.473 (24) Å. The two aqua ligands also align at parpendicular position each other in which O7-La1 -O8 angle of 75.20 (5) o . Similar coordination structures are seen in Ho III (acac) 3 (H 2 O) 2 by Kooijman et al. (2000) and Yb III (acac) 3 (H 2 O) by Watkins et al. (1969). Both complexes have three acac ligands and the former one has nearly identical structure in which two aqua ligands ligate to the central ion and complete 8-coordinated square antiprismatic structure. The longest bond lengths between the central lanthanide ion and the oxygen atoms of acac ligands were observed for the compound I due to difference in their ionic radii. The compound I in the crystal are connected by four hydrogen bonding, O7-O1 i (symmetry codes: (i) 2 -x, 2 -y, 1 -z), O7-O3 i , O8-O4 ii (symmetry codes: (ii) 1 -x, 1 -y, 1 -z) and O8-O6 ii , which are forming a one dimensional hydrogen bonding network ( Figure 2) propagating in the [110] direction.

Experimental
An water suspension (10 ml) of acetylacetone (161.9 mg, 1.62 mmol) and LaCl 3 . 7H 2 O (200.0 mg, 0.54 mmol) were stirred under room temperature. Quantitative amount of NaOH (64.7 mg, 1.62 mmol) was added to the suspension. A white precipitate was immediately generated. The precipitate was filtered and recrystallized from CH 2 Cl 2 and methanol in the presence of small amount of water (ca. 3%). Colorless blocks of the title compound were obtained in a few days and mounted on a glass capillary. Yield: 77.9 mg, (31%

Refinement
H atoms except two aqua ligands were placed in geometrically idealized positions and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (C-H). H atoms attached to O7 (H1W and H2W) and O8 (H3W and H4W) were found in a difference Fourier map. Any restraints were not needed for a stable refinement. All hydrogen atoms were included in the structure factor calculation.

Figure 1
An ORTEP view of the title compound, with displacement ellipsoids drawn at the 50% probability level.

Figure 2
Part of a [110] hydrogen-bonded chain in the title compound. The blue broken lines show the hydrogen bonds. Symmetry  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.