An unsymmetrical dinuclear scandium complex comprising salophen ligands [H2salophen = N,N′-bis(salicylidene)-1,2-phenylenediamine]

Scandium nitrate tetrahydrate reacts with H2salophen [N,N′-bis(salicylidene)-1,2-phenylenediamine] in ethanol to give the unsymmetrical dinuclear complex Sc(NO3)2(μ-salophen)Sc(salophen)(EtOH).

Scandium complexes comprising salen-type Schiff-base ligands are fairly rare, with the majority of such compounds having been reported by Anwander and co-workers (Meermann et al., 2006(Meermann et al., , 2009. Access to these complexes was achieved via treatment of the scandium silylamide precursor Sc[N(SiHMe 2 ) 3 ] 3 (THF) with substituted H 2 salen precursors under anaerobic conditions. We report here the straightforward formation and structural characterization of a dinuclear scandium complex comprising salophen ligands using scan-dium nitrate tetrahydrate as the starting material. Treatment of a diluted solution of Sc(NO 3 ) 3 Á4H 2 O in ethanol with an ethanolic solution of the protonated ligand H 2 salophen (Bonnaire et al., 1981) resulted in the rapid formation of a yellow precipitate which was identified as the title complex Sc(NO 3 ) 2 (-salophen)Sc(salophen)(EtOH). The analytically pure material could be isolated in 70% yield. The title compound was fully characterized through the usual set of elemental analysis and spectroscopic methods (IR, NMR, MS). The NMR spectra in DMSO-d 6 solution showed only one set of salophen 1 H and 13 C signals, and only one 45 Sc signal, and consequently the dimeric structure seems to be split into a monomeric species in DMSO. The mass spectrum did not display the molecular ion, but other high-molecular-mass peaks attributable to dimeric species, e.g. [M À CH 3 ] + at m/z 863, [M À EtOH] + at m/z 843, and [M À EtOH À NO 3 ] + at m/z 780.

Structural commentary
The asymmetric unit of the title compound recrystallized from ethanol contains two scandium atoms, two nitrate moieties, two salophen ligands, and one EtOH molecule (Fig. 1). Both Sc atoms are situated in the tetradentate coordination pocket of a salophen ligand. Sc1 is coordinatively saturated by two chelating nitrate anions, resulting in a somewhat square-antiprismatic coordination. Sc2 is connected to the two oxygen atoms of the other Sc(salophen) unit, thus connecting the two parts of the molecule. An irregular seven-coordination of Sc2 is completed by an EtOH ligand. This asymmetrical structure is stabilized by an intramolecular O-HÁ Á ÁO hydrogen bond between EtOH and a nitrate ligand [O6Á Á ÁO11 2.787 (3) Å , O6Á Á ÁH approx. 2.01 Å ; Table 1].

Figure 2
Illustration of intra-and intermolecularstacking interactions. The association of the complex molecules results in a supramolecular chain structure, which extends along the a-axis direction.

Figure 1
Molecular structure of the title compound in the crystalline state, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms attached to C atoms are omitted for clarity.
1.014 (1) Å . Both values are considerably larger than those observed in related complexes (Meermann et al., 2006(Meermann et al., , 2009, which can again be traced back to the higher coordination numbers of scandium. Both salophen ligands deviate markedly from planarity, as the two salicylidene arms are twisted out of the particular phenylene-diamine plane around the C-N single-bonds. The (phenylene)C C-N C(imide) torsion angles (which would be 0 in the case of perfect planarity) are 15.7 (4) and 24.6 (4) for the salophen ligand at Sc1, and 30.0 (4) and 34.7 (4) for the salophen ligand at Sc2. The corresponding angles between the salicylidene C 6 rings are 12.9 (2) for Sc1 and 53.5 (1) for Sc2, being in the same range as in the reference compounds (Meermann et al., 2006(Meermann et al., , 2009. Intramolecularstacking interactions between the two salophen ligands may contribute to the stabilization of the dimeric structure. The two phenylene-diamine moieties are oriented almost parallel to each other with an angle of 11.8 (1) between the C 6 rings, and the closest interatomic contact between the rings is 3.401 (4) Å (C2Á Á ÁC23). The same is true for the two salicylidene moieties, with an angle of 14.4 (1) and the closest contact being 3.247 (4) Å (C17Á Á ÁC35). The remaining two salicylidene moieties are not in a proper orientation for efficientstacking [angle between C 6 rings = 37.1 (2) ].

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms attached to C atoms were fixed geometrically and refined using a riding model. All C-H distances within the salophen ligands were constrained to 0.95 Å . For the EtOH ligand, the C-H distances within the CH 2 group were constrained to 0.99 Å , the C-H distances within the CH 3 group were constrained to 0.98 Å , and the CH 3 research communications  group was allowed to rotate freely around the C-C vector. The oxygen-bound EtOH hydrogen atom was located in the difference-Fourier map and refined freely, the corresponding O-H distance was restrained to 0.84 (2) Å . The U iso (H) values were set at 1.2U eq (X) (X = C, O). The reflections 020 and 021 disagreed strongly with the structural model and were therefore omitted from the refinement. ; program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: publCIF (Westrip, 2010).