Crystal structure of diaquatris(benzohydrazide-κ2 N,O)(isophthalato-κO)samarium(III) nitrate

The first benzohydrazide complex of a lanthanide is reported. The SmIII ion is nine-coordinated in a distorted tricapped trigonal–prismatic geometry by three oxygen atoms and three nitrogen atoms from three benzhydrazide (bzz) ligands, one oxygen atom from the isophthalate (itp2−) ligand, and two oxygen atoms from coordinated water molecules. The crystal structure features extensive hydrogen bonding as well as C—H⋯π and π–π interactions.

The first benzohydrazide complex of a lanthanide is reported. In the title compound, [Sm(C 8 H 4 O 4 )(C 7 H 8 N 2 O) 3 (H 2 O) 2 ]NO 3 , systematic name diaquatris(benzohydrazide-2 N,O)(isophthalato-O)samarium(III) nitrate, the Sm III ion is nine-coordinated in a distorted tricapped trigonal-prismatic geometry by three oxygen atoms and three nitrogen atoms from three benzhydrazide (bzz) ligands, one oxygen atom from the isophthalate (itp 2À ) ligand, and two oxygen atoms from coordinated water molecules. The nitrate group is disordered over two sets of sites with occupancy factors of 0.310 (17) and 0.690 (17). In the crystal, adjacent molecules are linked into chains via pairs of O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds between the carboxylate acceptor and the coordinated water and amine NH 2 donors. Molecules are further stacked by interactions involving the benzene ring of the itp 2À ligands, forming double chains that extend in the b-axis direction. These double chains are further linked into a three-dimensional supramolecular network via hydrogen bonds (O-HÁ Á ÁO, N-HÁ Á ÁO and C-HÁ Á ÁO) between the complex molecule and the nitrate groups along with C-HÁ Á Á andinteractions involving the benzene rings of the bzz and itp 2À ligands.

Chemical context
Research on lanthanide-based coordination compounds is one of the most active fields in chemistry and materials science. Distinct from transition metal centers, lanthanide ions often demonstrate high and variable coordination numbers as well as diverse coordination geometries, which can lead to versatile structures and topologies (Cotton & Raithby, 2017). They are also very attractive luminescent centers for the high colour purity and relatively long lifetimes arising from electronic transitions within the partially filled 4f orbitals, which make them potential candidates for applications in lighting, photonics and as luminescent probes and sensors (Parker, 2000;Bü nzli & Piguet, 2005;Cui et al., 2018). Besides the metal ions, the organic ligands also have significant effects on the construction of novel lanthanide coordination compounds and their potential applications (Lu et al., 2012;Xu et al., 2016;You et al., 2018). It is well-known that lanthanide ions have a high affinity for and prefer to bind to hard donor atoms such as oxygen-containing organic ligands, for instance aromatic carboxylic acids. Terephthalic acid and its derivatives have thus been widely employed in the synthesis of novel lanthanide-based coordination compounds with interesting architectures and photoluminescence properties (Karmakar et al., 2016;Park & Oh, 2016). These ligands can exhibit various ISSN 2056-9890 coordination modes when coordinated to the metal centers, as well as serving as antennas or sensitizers to absorb light and transfer energy to the excited states of the central lanthanide ions (Bü nzli & Piguet, 2005). Aromatic organic compounds containing the hydrazide group have been used widely as chemical receptors for sensing anions (Ran et al., 2017;, but have received less attention as metal chelators. In a search for new structural chemistry, we employed benzhydrazide (bzz) and isoterephthalic acid (H 2 itp) as ligands to react with Sm(NO 3 ) 3 Á6H 2 O under hydrothermal conditions, and the crystal structure determination of the title compound is reported herein.

Structural commentary
The molecular structure of the title compound is shown in Fig. 1. The asymmetric unit comprises one Sm III ion, three benzhydrazide (bzz) ligands, one completely deprotonated isophthalate (itp 2À ) ligand, two coordinated water molecules, and one disordered NO 3 À ion. The hydrazide group of the bzz ligand adopts a bidentate 2 -1 : 1 chelating coordination mode, whereas the carboxylate groups of the fully deprotonated itp 2À ligand display a 1 -1 : 0 monodentate coordina-tion fashion. The Sm III ion is nine-coordinated by three oxygen atoms (O1, O2, O3) and three nitrogen atoms (N1, N3, N5) of three different bzz ligands, one oxygen atom (O4) from the completely deprotonated itp 2À ligand, and other two oxygen atoms (O8, O9) from the coordinated water molecules. The central metal Sm III atom can be described as having a distorted tricapped trigonal-prismatic geometry, Fig. 2, with the Sm-N and the Sm-O bond lengths in the ligand ranging from 2.633 (2) to 2.694 (2) Å and 2.340 (2) to 2.478 (2) Å , respectively, and the N/O-Sm-N/O bond angles fall in the range 60.97 (6) to 145.24 (6) . These values are comparable to other reported values for oxygen/nitrogen-coordinated Sm III complexes (Alipour et al., 2016;An et al., 2016 View of the distorted tricapped trigonal-prismatic coordination geometry of the central Sm III atom.

Figure 1
Molecular structure of the title compound, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level. Table 1 Hydrogen-bond geometry (Å , ).

Supramolecular features
As can be seen in Fig. 3, one carboxylate group of the itp 2À ligand adopts a monodentate coordination mode to the Sm III ion, while the other acts as an acceptor of hydrogen-bonding interactions (Table 1) involving the water molecules and the amine NH 2 group of the bzz ligand of an adjacent complex molecules. This arrangement gives rise to chains extending along the b-axis direction by offsetinteractions between the benzene rings of symmetry-related itp 2À ligands, Fig. 4, with a centroid to centroid distance of Cg4Á Á ÁCg4 i = 3.692 (2) Å and a dihedral angle = 0.0 (2) [Cg4 is the centroid of the C23-C29 ring; symmetry code: (i) 2 À x, 1 À y, 1 À z). Fig. 5 shows the crystal packing of the title compound along the a axis. The three-dimensional supramolecular architecture of the crystal is sustained by numerous O-HÁ Á ÁO, N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds between the complex molecules and the nitrate groups along with weak C-HÁ Á Á interactions between the aromatic C-H bonds and the benzene rings of the bzz ligands, Table 1. Furthermore, weak aromaticstacking interactions involving the bzz ligands [Cg1Á Á ÁCg1 ii = 3.882 (2) Å , dihedral angle = 0.0 (5) ; Cg1 is the centroid of the C2-C7 ring; symmetry code: (ii) 1 À x, Ày, 2 À z;] , and the bzz and itp 2À ligands [Cg2Á Á ÁCg4 iii = 3.715 (3) Å , dihedral angle = 4.7 (9) ; Cg2 is the centroid of the C9-C14 ring; symmetry code: (iii) 1 À x, 1 À y, 1 À z], are also observed, which help further to stabilize the crystal structure.
research communications View of a supramolecular chain formed by O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds.

Figure 4
View of a supramolecular double chain sustained by O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonding along withstacking interactions.

Figure 5
The crystal packing of the title compound, viewed along the a axis. The nitrate molecules are shown with a space-filling model.

Database survey
A search of the Cambridge Structural Database (CSD, version 5.39, last update August 2018; Groom et al., 2016) gave 20 hits for the benzohydrazide complexes with transition metal ions, but none of them involves a lanthanide ion. The most typical coordination mode of benzohydrazide ligands in structures appears to be a bidentate chelating mode with metal centers through nitrogen and oxygen donor atoms (BOHYCU, Nyburg et al., 1971;EKAMIM, Odunola et al., 2003;EZARED, EZARIH, Patel et al., 2011;XUQYUD01, Thiam et al., 2009). In these complexes, the nitrogen atoms of the hydrazide group serve as donors for hydrogen bonding.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were located in difference maps. The H atoms bonded to C atoms were treated as riding atoms in geometrically idealized position with C-H distances of 0.93 Å and with U iso (H) = 1.2U eq (C). The H atoms bonded to O and N atoms were located in a difference-Fourier map, but were refined with distance restraints of O-H = 0.84 AE 0.01 Å and N-H = 0.88 AE 0.01 Å , and with U iso (H) = 1.5U eq (O) and 1.2U eq (N). The nitrate group is disordered over two sets of sites, with occupancy factors of 0.310 (17)   Data collection: APEX3 (Bruker, 2016); cell refinement: SAINT (Bruker, 2016); data reduction: SAINT (Bruker, 2016); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Diaquatris(benzohydrazide-κ 2 N,O)(isophthalato-κO)samarium(III) nitrate
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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (