Syntheses and crystal structures of three [M(acac)2(TMEDA)] complexes (M = Mn, Fe and Zn)

Syntheses and crystal structures of three metal complexes [M(acac)2(TMEDA)] [M = Mn (1), Fe (2) and Zn (3)] with acetylacetonate and N,N,N′,N′-tetramethylethylenediamine are discussed.


Structural commentary
Compounds 1-3 crystallize in the monoclinic system, space group P2 1 /n with Z = 4. However, despite the similarity of the lattice parameters and the analogous molecular structures, complexes 1-3 are not isotypic. The crystal structures consist of discrete complex molecules [M(acac) 2 TMEDA] in which the central metal atoms are coordinated nearly octahedrally by four oxygen atoms of two acac ligands and two nitrogen atoms of the TMEDA ligand ( Figs. 1-3  Molecular structure of complex 2 showing the labeling scheme. Displacement ellipsoids drawn at 50% probability level, H atoms are omitted.

Figure 3
Molecular structure of complex 3 showing the labeling scheme. Displacement ellipsoids drawn at 50% probability level, H atoms are omitted.  Ni et al., 2005].
In general, the above-mentioned [M(hfa) 2 (TMEDA)] (M = Mn, Fe, Zn) complexes exhibit shorter M-N distances than the corresponding [M(acac) 2 (TMEDA)] complexes. This effect is probably due to the electron-withdrawing effect of the CF 3 groups of the hfa ligands.
Each of the complexes 1-3 exhibits nearly planar sixmembered acac-M chelate rings. The maximum deviation from planarity, as indicated by the dihedral angle between the M/O1/O2 (M/O3/O4) plane of the chelate ring and the best plane through O1/C2/C3/C4/O2 (O3/C7/C8/C9/O4), is 6.2 (1) in the case of the zinc complex 3. PLATON (Spek, 2009) was used to calculate the dihedral angles. The five-membered M-TMEDA ring adopts a twist conformation with approximate C 2 symmetry. As a result of the centrosymmetric crystal structure, both types of the enantiomeric chelate rings with and conformations are present.

Supramolecular features
The packing of the [M(acac) 2 (TMEDA)] units is dominated by van der Waals interactions. The mutual arrangement of the complex units 1-3 is similar but not identical . In the case of the iron compound 2 there is also a contribution from weak C-HÁ Á ÁO hydrogen bridges (Table 4). As a result, the complexes are associated by R 2 2 (8) type motifs, forming centrosymmetric dimers (Fig. 5).    Hydrogen-bond geometry (Å , ) for 2. (18) 2002; Zeller et al., 2004;Halbach et al., 2012). However, none of these complexes is isotypic with the three title compounds.

Synthesis and crystallization
TMEDA (7.5 ml, 5.8 g, 50 mmol) was added to a suspension of [M(acac) 2 (H 2 O) 2 ] (25 mmol, M = Mn: 9.71 g, Fe: 9.73 g, Zn: 9.97 g) in toluene (30 ml). The suspension was stirred at 323 K for 2 h. After removal of the solvent under reduced pressure, n-hexane (25 ml) was added and insoluble parts were filtered off. The filtrates were kept at 248 K to obtain the products as yellow (1), red-brown (2) and colourless (3)  Crystal structure of compound 2, viewed along the b axis. The intermolecular C-HÁ Á ÁO hydrogen bonds are shown as dashed lines.

Figure 6
Crystal structure of compound 3, viewed along the b axis.

Figure 4
Crystal structure of compound 1, viewed along the b axis.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 5. All hydrogen atoms were positioned geometrically and refined using a riding model with U iso (H) = 1.2(CH and CH 2 ) or 1.5(CH 3 ) times U eq (C  program(s) used to refine structure: SHELXL2014/7 (Sheldrick, 2015b); molecular graphics: DIAMOND (Brandenburg, 2019); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Bis(acetylacetonato-κ 2 O,O′)(N,N,N′,N′-tetramethylethylenediamine-κ 2 N,N′)manganese(II) (1)
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Bis(acetylacetonato-κ 2 O,O′)(N,N,N′,N′-tetramethylethylenediamine-κ 2 N,N′)iron(II) (2)
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.