Crystal structure of polymeric bis(3-amino-1H-pyrazole)cadmium dibromide

The title compound {[CdBr2(3-apz)2]} n consists of a Cd2+ cation, bromide anions balancing the charge and bridging 3-aminopyrazole (3-apz) molecules. The Cd2+ cations are coordinated by two bromide anions and two 3-apz ligands, generating trans-CdN4Br2 octahedra, and are linked into chains by pairs of the bridging ligands. In the crystal, the 3-apz ligands and bromide anions of neighboring chains are linked through interchain hydrogen bonding into a two-dimensional supramolecular network.


Chemical context
Inorganic-organic coordination polymers, an active field of investigation in chemistry, attract attention for their intriguing structures and applications.Inorganic components may introduce magnetic, optical, and mechanical attributes, while organic ligands offer versatility and luminescence.Combining these attributes yields novel materials with diverse properties such as catalysis, separation, luminescence, spin transition and more (Seredyuk et al., 2015;Pin ˜eiro-Lo ´pez et al., 2021).The formation of a coordination polymer involves the selfassembly of organic ligands and metal ions, driven by strong and directional interactions such as metal-ligand coordination bonds, as well as weaker hydrogen bonds, �-� stacking, halogen-halogen, and C-H� � �X interactions (X = O, N, halogen, etc.).Engineering polymeric networks is a challenge that demands further exploration of metal-organic interactions.
The pyrazole is known to be a good linker to bind metal ions and play a key role in the design of new functional coordination polymers.It can serve as a monodentate ligand or upon deprotonation as a bridging ligand, effectively linking metal ions into polynuclear or polymeric moieties (Parshad et al., 2024).We have discovered that 3-aminopyrazole (3-apz) can form coordination polymers without the need to deprotonate the pyrazole moiety, due to the participation of the amino group in the coordination of the metal ion.Having an interest in polymeric complexes formed by bridging ligands (Pin ˜eiro-Lo ´pez et al., 2018, 2021;Seredyuk et al., 2007), we report here on the coordination polymer of the apz ligand with a Cd 2+ cation and Br À anions as co-ligands.

Structural commentary
The asymmetric unit comprises half of the monomeric neutral unit [Cd(3-apz) 2 Br 2 ], which is composed of a Cd 2+ cation, two 3-apz bridging ligands and two Br À anions, balancing the charge (Fig. 1).The tautomerism of the ligand molecule, which can interconvert between 3-and 5-aminopyrazole in solution, is blocked, and only the first form is observed in the structure.
The coordination geometry around the central ion can be described as an elongated octahedron with the Br atoms being in axial positions  A ˚] and the amino nitrogen atom of the 3-apz ligand [Cd-N1 = 2.358 (9) A ˚, Cd-N3 = 2.446 (9) A ˚] in the equatorial plane.The average trigonal distortion parameters � = � 1 12 (|90 -' i |), where ' i is the angle N/Br-Cd-N 0 /Br 0 (Drew et al., 1995), and � = � 1 24 (|60 -� i |), where � i is the angle generated by superposition of two opposite faces of an octahedron (Chang et al., 1990) are 34.6 and 112.4 � , respectively.The values reveal a deviation of the coordination environment from an ideal octahedron (where � = � = 0).The calculated continuous shape measure (CShM) value relative to the ideal O h symmetry is 0.578 (Kershaw Cook et al., 2015).The volume of the [CdN 4 Br 2 ] coordination polyhedron is equal to 20.952A ˚3.The 3-apz ligand is close to planarity with a maximum deviation of 0.19 (1) A ˚from the plane of the pyrazole ring for the amino N3 atom.

Supramolecular features
The [Cd(3-apz) 2 Br 2 ] units are linked by alternating amino/ pyrazole nitrogen atoms of the 3-apz ligand to give an infinite one-dimensional linear chain propagating along the a-axis direction (Figs. 1 and 2).The Cd� � �Cd distance separated by 5aminopyrazole within the chain is 5.051 (1) A ˚.The N2 atom and one hydrogen of the NH 2 groups of pyrazole are involved in interactions within the coordination chain, forming intrachain hydrogen bonds with the Br atom (Table 1).The second hydrogen atom of the NH 2 group forms a hydrogen bond with the Br atom of a neighboring chain.This interaction expands  the chains to a two-dimensional supramolecular network (Fig. 2).The planes stack along the c axis with no interactions below the van der Waals radii.

Hirshfeld surface and two-dimensional fingerprint plots
Hirshfeld surface analysis was performed and the associated two-dimensional fingerprint plots were generated using CrystalExplorer (Spackman et al., 2021), with a standard resolution of the three-dimensional d norm surfaces plotted over a fixed colour scale of À 0.4941 (red) to 1.0389 (blue) a.u.(Fig. 3a).Since the title compound is a coordination polymer, this analysis also includes the bonding information at the edge of the asymmetric unit.The overall two-dimensional fingerprint plot is depicted in Fig. 3b

Database survey
A search of the Cambridge Structural Database (CSD version 5.43, update of November 2022; Groom et al., 2016) reveals one hit with the 3-apz bridging ligand in a binuclear Cu 2+ complex TIXDAH with oxalyl anions as coligands (S ´witlicka-Olszewska et al., 2014).In the complex, the same coordination mode of the ligand is observed, but with a shorter intermetallic separation (4.583A ˚) than in the title compound, which is due to the different chemical nature and square-pyramidal coordination geometry of the central ion.

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

Figure 1
Figure 1Crystal structure of the title compound with labelling and displacement ellipsoids drawn at the 50% probability level.The strong intra-and interchain N-H� � �Br hydrogen bonds are shown as dashed red and orange lines, respectively.Symmetry code: (i) 1 À x, À y, 1 À z.
decomposed into specific interactions.The central spike with the tip at (d i , d e ) = (1.30,1.41) directly represents the Cd-Br bond length with the relative contribution of 2.5%, while two other closely lying spikes with tips at (d i , d e ) = (1.10,1.30)/(1.30/1.10)correspond to the shorter Cd-N bond length with the contribution of 12.3%.The rest of the contacts belong to weak hydrogen bonds.At 37.5%, the largest contribution to the overall crystal packing is from Br� � �H/H� � �Br interactions, which form characteristic wings of the plot with tips at (d i , d e ) = (0.90, 1.60)/(1.60/0.90).Other interactions, H� � �H (22.2%),H� � �C/ C� � �H (9.3%) and H� � �N/N� � �H (10.6%), are mainly distributed in the middle part of the plot.

Figure 3 (
Figure 3 (a) A projection of d norm mapped on the Hirshfeld surface onto a fragment of the polymeric chain in the asymmetric unit, visualizing intra-and intermolecular interactions.Red/blue and white areas represent regions where contacts are shorter/longer than the sum and close to the sum of the van der Waals radii, respectively; (b) decomposition of the twodimensional fingerprint plot into specific interactions.

Table 2
Experimental details.