Crystal structure of dichloridobis{μ-2-methoxy-6-[(methylimino)methyl]phenolato}{2-methoxy-6-[(methylimino)methyl]phenolato}cadmium(II)cobalt(III) monohydrate

Heterometallic Co/Cd solvatomorphs, which differ by half of the solvent water molecule, show a remarkable variation in the cadmium coordination sphere.

The title compound, [CoCd(C 9 H 10 NO 2 ) 3 Cl 2 ]ÁH 2 O, is a solvatomorph of the corresponding hemihydrate recently published by us . Appl. Cat. A, 560, 171-184]. The current structure reveals different cell parameters and space group compared with the published one while both are monoclinic with almost the same cell volume. The title compound is formed of discrete neutral dinuclear molecules with no crystallographically imposed symmetry and water molecules of crystallization. The overall geometry about the cobalt(III) ion is octahedral with an N 3 O 3 environment; each ligand acts as a meridional ONO donor. The Cd II coordination sphere approximates an irregular square pyramid with a chlorine atom at the apex. There is significant shortening of a Cd-O bond length to the oxygen atom of the methoxo group on one of the ligands [2.459 (3) Å ] compared to the corresponding distance in the published structure [2.724 (7) Å ], while other Cd-Cl/N/O bonds remain roughly the same. In the crystal lattice, the heterometallic molecules, which are related by the crystallographic n-glide plane and interlinked by weak hydrogen bonds to solvent water molecules, form columns along [101]. Adjacent columns lie antiparallel to each other.

Chemical context
The title compound, [CoCd(C 9 H 10 NO 2 ) 3 Cl 2 ]ÁH 2 O, (1) is a solvatomorph of the corresponding hemihydrate recently published by us (CSD refcode TEZKER; Nesterova et al., 2018). We have studied the heterometallic hemihydrate [CoCdL 3 Cl 2 ]Á0.5H 2 O (2) with a Schiff base ligand {HL is 2-methoxy-6-[(methylimino)methyl]phenol} and its related complex [CoL 3 ]ÁDMF (DMF is N,N 0 -dimethylformamide) in alkanes oxidation reactions. Complexes of transition metals have proved to be efficient catalysts for a broad range of organic reactions, including direct C-H functionalization (Pototschnig et al., 2017;. At the same time, the catalytic properties of heterometallic compounds, and those combining catalytically active and non-active metals in particular, in stereospecific sp 3 C-H oxidation with m-chloroperbenzoic acid have received significantly less attention. A comparison of the catalytic behaviours of the hetero-and monometallic analogues provided further insight into the origin of stereoselectivity of the oxidation of C-H bonds . ISSN 2056-9890 While the hemihydrate (2) was prepared by direct synthesis  employing Co powder and cadmium chloride as starting materials, for the synthesis of the title compound two metal acetate salts were reacted with the Schiff base formed in situ from the condensation between o-vanillin and CH 3 NH 2 ÁHCl in water/ethanol in a 1:1:3 molar ratio. Remarkably, the isolated plate-like crystals of (1) were brown-red, not brown-green, and appeared non-isostructural with the prismatic hemihydrate (2) while both are monoclinic with almost the same cell volume [2923.10 (10) Å 3 in (1) and 2931.3 (7) Å 3 in (2)]. The previously published structure was solved and refined in the standard setting P2 1 /c whereas the current structure is in P2 1 /n [a, b, c, : 9.4036 (2), 21.1588 (4), 15.0319 (3) Å , 102.221 (2) , respectively in (1) and 14.090 (2), 16.887 (2), 13.179 (2) Å , 110.84 (2) in (2)]. Another striking difference is a significantly shorter Cd-O bond length to the oxygen atom of the methoxo group on one of the ligands [2.459 (3) Å ] compared to the corresponding distance in (2) [2.724 (7) Å ], while other Cd-Cl/N/O bonds remain roughly the same. The reason for such a discrepancy could be the incorporation of a whole water molecule in (1) instead of a half-molecule in (2), which slightly changes the hydrogen bonding and packing motifs in the former compound.

Structural commentary
The heterometallic complex (1) is built up from discrete CoCdL 3 Cl 2 molecules and water molecules of crystallization. The molecular structure of (1) closely resembles that of the hemihydrate . The complex molecule has no crystallographically imposed symmetry (Fig. 1). The ligand moieties are deprotonated at the phenol O atom and octahedrally coordinate the Co III ion through the three azomethine N and three phenolate O atoms in a mer configuration. The three crystallographically non-equivalent salicylaldimine ligands have Co-O and Co-N bond lengths in the ranges 1.871 (4)-1.932 (3) and 1.933 (4)-1.961 (5) Å , respectively, (Table 1). Average Co-O and Co-N bond lengths in (1) and (2)   The molecular structure of the title compound, showing the atomnumbering scheme. Non-H atoms are shown with displacement ellipsoids at the 30% probability level. The nearest coordination geometry of the cadmium centre in (1) is strictly comparable to that for (2). The cadmium atom has two quite short bonds with the bridging phenolato oxygen atoms, O11 and O31 [2.235 (3), 2.286 (3) Å ], of the two deprotonated Schiff bases and two longer bonding distances to the chlorine atoms [Cl1: 2.4091 (14), Cl2: 2.4222 (12) Å ] in a distorted tetrahedral geometry. The angles at the metal atom vary from 68.33 (12) to 127.90 (10) ( Table 1). In addition, Cd1 is weakly bonded to the oxygen atom O12 at 2.459 (3) Å , which implies that the Cd1 coordination sphere approximates an irregular square pyramid with Cl1 atom at the apex. There is a marked decrease in the Cd-O12 bond length when (1) is compared to (2) [2.724 (7) Å ] and the cobalt-cadmium separation [3.286 Å in (1) versus 3.315 Å in (2)], providing a rare structural example of variations in the metal coordination sphere to accommodate changes possibly caused by a different number of solvent molecules in the crystal lattice.

Supramolecular features
The heterometallic molecules related by the crystallographic n-glide plane are stacked along [101] with adjacent columns lying antiparallel to each other (Fig. 2). The dinuclear units show no significant intermolecular interactions in the solid state: the minimum CoÁ Á ÁCd separation between the neighbouring CoCdL 3 Cl 2 molecules within a column is 8.372 Å . There are weak hydrogen bonds between the solvent water molecule and the oxygen atoms on one of the ligands (O21, O22) and also to the Cl1 atom of the molecule related by the crystallographic n-glide plane (Fig. 2, Table 2). Very weak C-HÁ Á ÁCl/O hydrogen-bonding interactions between the complex molecules lead to a consolidation of the crystal packing.

Database survey
A search of the Cambridge Structural Database (CSD; Groom et al., 2016) via the WebCSD interface in September 2018 returned 43 hits for the crystal structures of metal complexes with HL and the ligand itself. Almost half of the complexes are heptanuclear homometallic assemblies (M = Mn, Co, Ni, Zn) with planar hexagonal disc-like cores and varying anions and solvent molecules. The metal centres in the cores are in distorted octahedral geometries with the six 3 -bridging OH À or MeO À ions linking the central metal atom to the six peripheral ones; the metal-to-ligand ratio M II :L is 7:6. The ligand molecules are singly deprotonated at the phenolate site and adopt a chelating bridging mode, forming five-and sixmembered rings similar to those in (1). The rest of the complexes are mainly mononuclear compounds with molecular (Mn, Co and Pt) or polymeric (Mn) arrangements in the crystal lattice and metal-to-ligand ratios M II/III :L of 1:2 and 1:3. There are also dimeric (Cu) and tetrameric (Co, Mn) complexes with the teranuclear cores additionally supported by other bridging ligands. The heterometallic examples with HL are limited to the four Na/M (M = Fe, Ni) 1s-3d structures of 4 and 5 nuclearity and [CoCdL 3 Cl 2 ]Á0.5H 2 O (2) already mentioned.

Synthesis and crystallization
2-Hydroxy-3-methoxy-benzaldehyde (0.23 g, 1.5 mmol) and methylamine hydrochloride (0.10 g, 1.5 mmol) were added to ethanol (10 ml) and stirred magnetically for 10 min. Cd(CH 3 COO) 2 Á2H 2 O (0.13 g, 0.5 mmol) and Co(CH 3 COO) 2 Á-4H 2 O (0.12 g, 0.5 mmol) both dissolved in 2 ml water were added to the light-yellow solution of the Schiff base formed in situ. The resultant red-brown solution was stirred at room temperature for an hour, then filtered and left to stand at room temperature. Brown-red plate-like crystals of (1) suitable for crystallographic characterization were formed over several days in a mixture with yellow flakes. They were collected by filter-suction, washed with ethanol and finally dried in air.
choice for (1) as this leads to a smaller angle. The P2 1 /c setting of the current structure can be determined by the transformation [1 0 0, 0 1 0, 1 0 1] to give the unit cell a = 9.404, b = 21.159, c = 15.954 Å , = = 90, = 112.95 . It is clear that the unit cells of (1) and (2) are different even if both are compared in the standard P2 1 /c settings. The water molecule hydrogen atoms in (1) were located and refined with geometries restrained to ideal values. All remaining hydrogen atoms were added at calculated positions and refined by use of a riding model with isotropic displacement parameters based on those of the parent atom (C-H = 0.95 Å , U iso (H) = 1.2U eq C for CH, C-H = 0.98 Å , U iso (H) = 1.5U eq C for CH 3 ).  (Rigaku OD, 2015); cell refinement: CrysAlis PRO (Rigaku OD, 2015); data reduction: CrysAlis PRO (Rigaku OD, 2015); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 1999) and Mercury (Macrae et al., 2006); software used to prepare material for publication: WinGX (Farrugia, 2012).

Dichloridobis{µ-2-methoxy-6-[(methylimino)methyl]phenolato}{2methoxy-6-[(methylimino)methyl]phenolato}cadmium(II)cobalt(III) monohydrate
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. Refinement. The water molecule hydrogen atoms were located and refined with geometries restrained to ideal values. The largest peak is 0.80 Angstroms from Cd1; the deepest hole is 0.73 Angstroms from Cd1.