A new co-crystal dinuclear/trinuclear ZnII–ZnII/ZnII–SmIII–ZnII complex with a salen-type Schiff base ligand

In the pentanuclear title complex, [SmZn2(C22H18N2O4)2(NCS)2(C3H7NO)2][Zn2(C22H18N2O4)(NCS)3]·C3H7NO·0.32H2O, a dinuclear unit and a trinuclear unit co-exist. In the crystal, the trinuclear cationic units and dinuclear anionic units are assembled into infinite layers.

In the pentanuclear title complex, [SmZn 2 (C 22  ;2 2 N,N-dizinc(II) dimethylformamide monosolvate 1.32-hydrate, a dinuclear unit and a trinuclear unit co-exist. One of the Zn II centers in the dinuclear unit as well as the two Zn II centers in the trinuclear unit are located in the inner N 2 O 2 cavity of the ligand and are coordinated to the nitrogen atom of one thiocyanate moiety, giving rise to a square-pyramidal geometry. The second Zn II center in the dinuclear unit is coordinated to the two phenolate oxygen atoms of the ligand and to two thiocyanate groups via the nitrogen atom in a tetrahedral geometry. The Sm III ion is eight-coordinated by four phenolate O atoms from the two ligand molecules, two methoxy O atoms from the two ligand molecules and two O atoms from the DFM solvent molecule. In the dinuclear unit, the two methoxy oxygen atoms remain uncoordinated while in the trinuclear unit, for each ligand one methoxy oxygen is coordinated and the other one remains uncoordinated. In the crystal, the trinuclear cationic units and dinuclear anionic units are assembled into infinite layers. These layers are held together via electrostatic interactions, forming a three-dimensional structure. In the dinuclear unit, the C and S atoms of one of the thiocyanate groups are disordered over two sets of sites in a 0.680 (4)(4):0.320 (4) ratio.

Chemical context
Over recent years, polyheteronuclear complexes of 3d and 4f metals have been studied with increasing interest by chemists (Cristó vã o et al., 2017;Cristó vã o & Miroslaw, 2013;Ding et al., 2015;Tian et al., 2012;Wu & Hou, 2010). The various structures obtained (Rossi et al., 2018;Zhou et al., 2015;Ghosh & Ghosh, 2016), the physicochemical properties (Cristó vã o et al., 2017) and the potential applications in fields such as luminescence (Zhao et al., 2014;Zhu et al., 2018), magneto chemistry (Chesman et al., 2012;Klokishner & Reu, 2012), electrochemistry (Yin et al., 2017) and catalysis (Lan et al., 2018) have made this chemistry very attractive. These compounds are obtained from Schiff bases, which are organic compounds having several donor sites, which are used to assemble stable structures with transition metal or lanthanide ISSN 2056-9890 ions. Both the nature of the ligand and the nature of the metal strongly influence the properties of the compound obtained. The Schiff bases obtained by condensation between a diamine and a well-selected keto-precursor may have two cavities of different dimensions, which can accommodate metal ions of different sizes (Andruh, 2011;Gao et al., 2012). The salen-type Schiff base obtained by the condensation of 1,2-diaminobenzene and ortho-vanillin has two cavities of different sizes, viz. N 2 O 2 and O 2 O 2 . The smaller inner N 2 O 2 cavity consists of two imino nitrogen atoms and two phenolato oxygen atoms and can encapsulate 3d metal ions. The larger outer O 2 O 2 cavity consists of two phenolato oxygen atoms and two oxygen atoms from methoxy groups and can encapsulate 3d ions or lanthanide ions that have a larger ionic radius and prefer oxygen because of their hard-acid characters. By controlling the ratio of the ligand-3d metal-4f metal, it is possible to synthesize 3d-3d and 3d-4f-3d complexes. It is in this context that we used the ligand N,N 0 -bis(3-methoxysalicylidene)phenylene-1,2-diamine (H 2 L) to synthesize the Zn-Zn/Zn-Sm-Zn co-crystal whose structure is described herein.
In the dinuclear unit, all of the methoxy oxygen atoms remain uncoordinated, whereas in the trinuclear unit, for each of the two metalloligands, one of the methoxy atoms remains uncoordinated (O1 and O34) while the others (O4 and O31) are coordinated to the Sm III atom. The longest bond distances around the Sm III ion are for Sm-O4 [2.6707 (13) Å ] and Sm-O31 [2.6934 (13) Å ]. The Sm-O phenoxy distances are in the range 2.3348 (12)-2.4417 (12) Å and are comparable to those found for the Zn 2 Sm complex (Gao et al., 2012) in which the mean Sm-O phenoxy distance is 2.332 Å . The Sm-O DMF distances are longer than those found in a samarium complex (Kou et al., 1998) with Sm-O91 and Sm-O101 values of 2.3831 (13) and 2.3476 (13) Å , respectively (Table 1). The octacoordinated polyhedron around the Sm III atom is best An ORTEP view of the asymmetric unit of the title compound, showing the atom-numbering scheme. Displacement ellipsoids are plotted at the 50% probability level. In the trinuclear unit, the Zn(di--phenoxo) 2 Sm bridging fragments show a difference between the Zn-O and Sm-O binding lengths whose mean values are 2.0204 (su?) and 2.3860 (su?) Å , respectively. The four Zn-O phenoxo -Sm angles have different values with an averages of 106.54 (su?) and 107.16 (su?) , respectively, for those involving the Zn1 and Zn31 atoms. The sum of the angles in the Zn1(di-phenoxo) 2 Sm1 and Zn31(di--phenoxo) 2 Sm1 arms are 359.58 and 359.89 , respectively, indicating regular planar geometries. The dihedral angle between Zn1/O2/Sm1/O3 and Zn31/O32/ Sm1/O33 plane normals is 76.01 (3) with the displacement of the respective constituent atoms not exceeding 0.046 and 0.023 Å . In the trinuclear unit, the dihedral angles between the planes O2/Sm1/O3 and O2/Zn1/O3 and the plane normals O32/Sm1/O33 and O32/Zn1/O33 are 6.04 (6) and 3.10 (6) , respectively. In the dinuclear unit, the dihedral angle between the O62/Zn61/O63 and O62/Zn62/O63 planes is 21.31 (10) .
In the dinuclear unit, the Zn61 atom is tetracoordinated while the Zn62 atom is pentacoordinated. The values of the angles around Zn61, which fall in the range 76.86 (6)-119.03 (8) , are indicative of a distorted tetrahedral environment. The geometry around the Zn62 atom is best described as a distorted square pyramidal, as indicated by the value of 0.105 for the Addison parameter . The apical position is occupied by the nitrogen atom N141 of the thiocyanate group with the basal plan occupied by atoms N51, N52, O62 and O63 from the ligand molecule. The angles between the N141 atom in the apical position and each of the four basal plane atoms fall in the range 106.67 (6)-111.37 (7) and are far from the ideal value of 90 . The deformation of the basal plane around the Zn62 atom is indicated by the values of the transoid [138.41 (6) and 144.96 (7) ] and cisoid angles [88.34 (6) and 88.94 (6) ], which are different from the ideal values of 180 and 90 for a square-planar geometry ( Table 1). The anionic thiocyanate ions are N donors and bind to the zinc atoms in a unidentate fashion. The Zn-N-CS bond angles in the dinuclear and trinuclear units are in the range 170.9 (5)-176.12 (18) , indicating a quasi-linear alignment. The N-C-S angles vary between 177.7 (2) and 179.4 (2) , showing that these three atoms adopt an almost linear alignment.

Synthesis and crystallization
The complex [(ZnL)Á(H 2 O)] was prepared according to a literature method  with slight modification. To a solution of 1,2-diaminobenzene (0.250 g, 2.31 mmol) in 10 mL of acetonitrile was added a solution of o-vanillin (0.705 g, 4.62 mmol) in 10 mL of acetonitrile. The resulting orange mixture was refluxed for 60 min, affording the organic H 2 L ligand. After cooling, a solution of Zn(CH 3 COO) 2 Á2H 2 O (0.507 g, 2.31 mmol) in 10 mL of acetonitrile was added. The mixture was heated under reflux for 60 min. On cooling, the orange precipitate was filtered off, washed with 3 Â 10 mL of ether and dried in air, yielding a compound formulated as

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were positioned geometrically (C-H = 0.95-0.98 Å ) and refined using a riding model with U iso (H) = 1.2U eq (C) or 1.5U eq (C methyl , O). One of the thiocyanate groups was found to be partially disordered such that the C and S atoms 136 of this group were distributed over two positions. In the dinuclear unit, the C and S atoms of one of the thiocyanate groups are disordered over two sets of sites in a 0.680 (4):0.320 (4) ratio. The water molecule is partially occupied [0.32 (4)].  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 1.48 e Å −3 Δρ min = −1.13 e Å −3 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. One of the thiocyanate ligands is partially disordered. Atoms C161 and S161 are modelled over two positions using thermal parameter restraints. Water molecule O171 partially occupies its site. Its occupancy was refined to 32%, linked to the minor component of the partially disordered thiocyanate.