Di-μ-chlorido-bis{chlorido[(R)/(S)-1,5-diphenyl-3-(2-pyridyl-κN)-2-pyrazoline-κN 2]zinc(II)}

In the centrosymmetric binuclear title compound, [Zn2Cl4(C20H17N3)2], the coordination geometry of the ZnII ion can be described as a distorted ZnN2Cl3 trigonal bipyramid (τ = 0.89), arising from the N,N′-bidentate ligand, a terminal chloride ion and two bridging chloride ions. The N atoms occupy one axial and one equatorial site and the terminal chloride ion occupies an equatorial site. The dihedral angle between the pyridine and pyrazole rings is 12.8 (2)°. In the crystal, aromatic π–π stacking [centroid–centroid separations = 3.812 (3) and 3.848 (3) Å] and C—H⋯Cl and C—H⋯π interactions help to establish the packing.

In the centrosymmetric binuclear title compound, [Zn 2 Cl 4 -(C 20 H 17 N 3 ) 2 ], the coordination geometry of the Zn II ion can be described as a distorted ZnN 2 Cl 3 trigonal bipyramid ( = 0.89), arising from the N,N 0 -bidentate ligand, a terminal chloride ion and two bridging chloride ions. The N atoms occupy one axial and one equatorial site and the terminal chloride ion occupies an equatorial site. The dihedral angle between the pyridine and pyrazole rings is 12.8 (2) . In the crystal, aromaticstacking [centroid-centroid separations = 3.812 (3) and 3.848 (3) Å ] and C-HÁ Á ÁCl and C-HÁ Á Á interactions help to establish the packing.
Cg1 is the centroid of the C51-C56 ring.  A comparison between the previously described ligand (Barceló-Oliver et al., 2010) and its Zn II complex permits to observe a conformational modification related to the pyridine-pyrazoline moiety, where the s-trans conformation found in the ligand changes to a s-cis disposition in the complex (See Fig. 1). This feature is common in 2,2'-bipyridyl ligands.
supplementary materials sup-2 The dimer is formed through two bridged chlorido anions linked with long (Zn1-Cl2) and short (Zn1-Cl2 i ) distances to the Zn II metal ions (see Fig. 2 and Table 1). Moreover, pyridine (Zn1-N32) and imino (Zn1-N2) nitrogen atoms and a monodentate chloride ligand (Zn1-Cl1) are coordinated to both metal ions. The geometry around the metallic ion is described by means a distorted trigonal bipyramid [τ = 0.89 (Addison et al., 1984)]. The bite distance between the two bonding nitrogen atoms is 2.716 (7) Å and the dihedral angle between the pyridyl and the pyrazolyl planes is 12.8°.
Within the dimeric complex unit, some hydrogen bonds are found with the chlorine atoms as acceptors: C5 from the pyrazoline ring interacts with Cl1 i , C12 from the phenyl ring bonded to N1 is in contact with Cl1 and C33 from the pyridine ring interacts with Cl2 (see Table 2 for more details). More in detail, the second hydrrogen bond (C12-H12···Cl1) forces the twist of the phenyl ring respect to the pyrazoline mean plane (N1-C11 bond): the structure of the ligand ( Barceló-Oliver et al., 2010) presents an angle between mean planes of 3.47° while this value is 19.63° in the Zn II complex.
On the other hand, two pyrazoline ligands of adjacent complex units form a centrosymmetric couple along the b direction of the crystal by means of two C-H···π interactions between pyridine rings, with C34 as donors, and phenyl rings bounded to C5, corresponding to two different molecules (Table 3 and Fig. 3). This interaction yields a one-dimensional chain throrugh the crystal which is also reinforced with intramolecular π-π interactions (

Refinement
All H atoms were placed in geometrically calculated positions and refined using a riding model, with C-H = 0.95-1.00 Å and U iso (H) = 1.2Ueq(C).
supplementary materials sup-3 Figures  Fig. 1. Reaction scheme where the s-trans conformation on the ligand is depicted by a bold blue line and the s-cis conformation found after coordination to the Zn II ion is depicted also with bold red lines. Fig. 2. View (50% probability) of the asymmetric unit of (I). The other half of the complex is related by an inversion center, sharing the two Cl2 atoms.

Table 3
Centroid-centroid interactions (Å, °) Cg2 and Cg3 are the centroids of the C311/N32/C33-C36 and C11-C16 rings, respectively. As defined in PLATON (Spek, 2009), α is the dihedral angle between planes I and J, β is the angle between the CgI->CgJ vector and the normal to the plane I, γ is the angle between the CgI->CgJ vector and the normal to the plane J, CgI-Perp is the perpendicular distance of CgI from ring J, CgJ-Perp is the perpendicular distance of CgJ from ring I, and the slippage S is the distance between CgI and the perpendicular projection of CgJ on ring I. Symmetry codes: (i) 1-x, -1/2+y, 1/2-z; (ii) 1-x, 1-y, 1-z supplementary materials sup-9