Crystal structure of (7-{[bis(pyridin-2-ylmethyl)amino-κ3 N,N′,N′′]methyl}-5-chloroquinolin-8-ol)dibromidozinc(II)

In the title compound, the ZnII atom has a distorted square-pyramidal coordination environment. The molecular structure exhibits an intramolecular O—H⋯N hydrogen bond. In the crystal, the molecules are linked by intermolecular C—H⋯Br hydrogen bonds, generating ribbon structures. These ribbons are linked though intermolecular C—H⋯Br hydrogen bonds, forming a two-dimensional network sheet.

In the title compound, [ZnBr 2 (C 22 H 19 ClN 4 O)], the Zn II atom adopts a distorted square-pyramidal coordination geometry, formed by two bromido ligands and three N atoms of the bis(pyridin-2-ylmethyl)amine moiety in the pentadentate ligand containing quinolinol. The Zn II atom is located well above the mean basal plane of the square-based pyramid. The apical position is occupied by a Br atom. The O and N atoms of the quinolinol moiety in the ligand are not coordinated to the Zn II atom. An intramolecular O-HÁ Á ÁN hydrogen bond, generating an S(5) ring motif, stabilizes the molecular structure. In the crystal, the molecules are linked by intermolecular C-HÁ Á ÁBr hydrogen bonds, generating ribbon structures containing alternating R 2 2 (22) and R 2 2 (14) rings. These ribbons are linked through an intermolecular C-HÁ Á ÁBr hydrogen bond, forming a twodimensional network sheet.

Chemical context
8-Quinolinol (Hq) is a notable bidentate ligand and an excellent analytical reagent for the determination of the concentration and separation of metal ions (Medlin, 1960;Eguchi et al., 2019). Hq derivatives and their metal complexes have wide applications in diverse areas such as pharmaceuticals (Lai et al., 2009) and organic light-emitting diodes (Li et al., 2020). Bis(pyridin-2-ylmethyl)amine [di(2-picolyl)amine, dpa] is a well-known tridentate ligand and highly selective for Zn II . Its derivatives are utilized as chemosensors for detecting Zn II at low concentration in biological samples (Lin et al., 2013) . In addition, some Zn II complexes with dpa derivatives comprise a binding site for polyphosphates such as diphosphate and adenosine triphosphate, and can act as respective anion sensors (Aoki et al., 2020;Bazany-Rodríguez et al., 2020). We, hence, developed the pentadentate ligand, 7-{[bis-(pyridin-2-ylmethyl)amino]methyl}-5-chloroquinolin-8-ol (HClqdpa) containing Hq and dpa moieties (Kubono et al., 2015). Subsequently, reactions between HClqdpa and Zn II salts were carried out in order to develop fluorescent anion sensors. In the course of these studies, a crystalline complex was obtained from the reaction with zinc(II) bromide. Here, the crystal structure of the respective title compound is reported.

Structural commentary
The molecular structure of the title compound is shown in Fig. 1. The Zn II atom adopts a distorted square-pyramidal geometry and coordinates two bromido ligands (Br1 and Br2) and three N atoms (N7, N8 and N9) of the dpa moiety in HClqdpa forming the ZnBr 2 (dpa) unit. The Hq moiety of the pentadentate ligand (HClqdpa) is not coordinated to the Zn II center. The five-coordinate geometry parameter, = ( À )/ 60, derived from the two largest angles ( < ) in a structure has ideal values of 0 for square-pyramidal and of 1 for trigonal-bipyramidal geometry (Addison et al., 1984). In the title compound it is equal to 0.138. The Zn II atom is located 0.5574 (3) Å above the mean basal plane (Br2/N8/N7/N9) of the square-based pyramid. The dpa moiety is meridionally bound to the Zn II atom. The apical position is occupied by the Br1 atom with the apical bond being slightly elongated to 2.4419 (4) Å compared to the equatorial Br2-Zn3 bond length of 2.4085 (4) Å . The Zn-N bond lengths in the title compound are 2.1455 (18) and 2.1497 (18) Å for the pyridyl atoms (N8, N9), and 2.2670 (18) Å for the tertiary atom N7. In comparison, the Zn-N bond lengths in the crystal structure of a related complex with a mesityl methylene-appended dpa derivative are 2.093 (3), 2.066 (3), and 2.521 (3) Å (MUDWEQ; Acharya et al., 2020). The bond lengths for the pyridyl N atoms are, hence, shorter and the bond length for the tertiary N atom is longer than those in the title compound. The dihedral angle between the two pyridine rings in the title compound is 15.84 (13) . In a related complex (MUDWEQ; Acharya et al., 2020), this dihedral angle between two pyridine rings is widened to 23.53 (18) , concomitant with an increased parameter of 0.211. The phenolic oxygen O5 of the Hq moiety is bound to hydrogen atom H5, which was found and refined freely. The proton, therefore, does not dissociate and no phenoxy function is formed. There is an intramolecular hydrogen bond, O5-H5Á Á ÁN6, generating an S(5) ring motif ( Fig. 1 and Table 1). The quinoline ring system is slightly bent with an r.m.s. deviation of 0.018 (3) Å . In the quinoline ring system, the largest deviation from the mean plane is 0.020 (4) Å for carbon atom C15. The quinoline plane subtends dihedral angles of 24.14 (11) and 36.65 (11) with the two pyridine rings.

Figure 2
A portion of the crystal packing of the title compound showing the ribbon structure motif built from alternating R 2 2 (22) and R 2 2 (14) rings. The C-HÁ Á ÁBr hydrogen bonds between the dimers and the intramolecular hydrogen bonds are shown as dashed lines. H atoms not involved in the interactions were omitted for clarity.

Figure 1
The molecular structure of the title compound, with atom labeling. Displacement ellipsoids are drawn at the 50% probability level. H atoms are represented by spheres of arbitrary radius. The intramolecular O-HÁ Á ÁN hydrogen bond is shown as a dashed line. (Fig. 3). The ribbon structures are, therefore, linked through the intermolecular C22-H22Á Á ÁBr2 ii hydrogen bonds and form a two-dimensional network sheet parallel to [222] (Fig. 3).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The hydroxy H atom was located in a difference-Fourier map and freely refined. The C-bound H atoms were positioned geometrically and refined using a riding model: C-H = 0.95-0.99 Å with U iso (H) = 1.2U eq (C). One outlier reflex (002) was omitted from the refinement.

Funding information
Funding for this research was provided by: JSPS KAKENHI (grant No. JP20K05565).

(7-{[Bis(pyridin-2-ylmethyl)amino-κ 3 N,N′,N′′]methyl}-5-chloroquinolin-8-ol)dibromidozinc(II)
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. Refinement was performed using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F 2 . R-factor (gt) are based on F. The threshold expression of F 2 > 2.0 sigma(F 2 ) is used only for calculating Rfactor (gt).

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