trans-Dibromidotetrakis(5-methyl-1H-pyrazole-κN 2)manganese(II)

The title compound was synthesized using Mn(CO)5Br. The manganese atom is situated on a crystallographic inversion center. The supramolecular architecture is characterized by several intermolecular C—H⋯N, N—H⋯Br and C—H⋯π interactions.


Structure description
Earth-abundant transition metals such as manganese have received much attention owing to their numerous applications in biological, industrial, and material sciences (Constable et al., 2021;Rice et al., 2017;Zhang et al., 2007;Dell, 2000).Apart from these applications, several mixed-valent multinuclear manganese cages have been assembled to understand their single molecular magnetism (SMM) behavior (Zabala-Lekuona et al., 2021).In addition, the famous Jacobson catalyst consisting of an Mn II -salen complex was developed for the enantioselective epoxidation of alkenes (Zhang et al., 1990) while Mn I carbonyls containing imidazolyl-based ligands have been used for the electrocatalytic-disproportionation of CO 2 (Myren et al., 2020).Likewise, many Mn I carbonyls containing various Nheterocyclic ligands were developed as biomimicking models for hydrogenase enzymes (Xu et al., 2016;Pan et al., 2020.) and as CO-releasing molecules (Mann, 2012;Cheng & Hu, 2021).Pyrazoles are one of the important classes of organic ligands used in many facets of coordination and organometallic chemistry (Trofimenko, 1972;Halcrow, 2009).
We aim to synthesize various CO-releasing molecules of the manganese family containing pyrazoles as primary ligands.In one such an attempt, a simple room-temperature stirring reaction involving the combination of Mn(CO) 5 Br, 5-methyl-1H-pyrazole and triethylamine base (1:2:4) was found to release all CO molecules and afforded yellow-colored crystals suitable for single-crystal X-ray diffraction analysis (SCXRD) from a dichloromethane-ethanol mixture (1:1) in quantitative yield.The SCXRD analysis reveals that it is trans-dibromo tetrakis(5-methyl-1H-pyrazole-� 2 N)manganese(II) (1).In other words, Mn I was oxidized in situ to Mn II and an octahedral heteroleptic complex containing two bromo ligands trans to each other in the axial position and four neutral 5methyl-1H-pyrazoles in the equatorial position was obtained (Fig. 1).The asymmetric unit contains half the molecule with the manganese atom located on a crystallographic inversion center.The 3-MePzH ligands of the asymmetric unit are arranged in an AABB pattern with two neighboring pyrazole pointing upwards and the other two (their counterparts by inversion) downwards.The analysis reveals that it is a distorted octahedral complex with the axial distances to the larger bromine atoms [Mn1-Br1 = 2.7274 (3) A ˚] longer than the equatorial distances [Mn1-N1 = 2.251 (2) A ˚and  Mn1-N3 = 2.261 (2) A  Earlier, many transition-metal pyrazoles were reported (Reedijk et al., 1971;Bieller et al., 2006;Cotton et al., 2002;Nelana et al., 2004;Khan et al., 2014;Al Isawi et al., 2023).In particular, Reedijk et al. (1971) MnBr 2 (C 4 H 6 N 2 ) 4 ] IUCrData (2024).9, x240237

Figure 1
The molecular structure of the title compound 1 with 50% probability displacement ellipsoids.The unlabeled atoms are related by symmetry.
AABB pattern with an r.m.s.deviation of 0.0612 A ˚.The analogous Mn II , Co II , Ni II , Cu II bromo complexes isomorphic with Reedijk's polymorph 2 were reported (Cotton et al., 2002;Nelana et al., 2004;Khan et al., 2014) and the bond parameters of 1 and 2 are both in good agreement with those reported structures.Interestingly, the Ni II bromo complex (Nelana et al., 2004) is isomorphic with compound 1.It was synthesized using (1,2-dimethoxyethane) 2 NiBr 2 as the metal source.
Compound 1 contains various intra-and intermolecular interactions in the form of N-H� � �Br and C-H� � �N interactions as well as C-H� � �� interactions (see Table 1).A perspective view of the supramolecular architecture of 1 is given in Fig. 3, which shows the presence of the various C-H� � �� interactions, leading to the formation of a herringbone-type of arrangement (Fig. 4a) along the a axis.In contrast, a pillared network along the a axis is seen in the structure of 2 (Fig. 5a).Further investigation reveals that along the b axis, the Br-Mn-Br moieties are stacked one over another in compound 1 while in 2, they are arranged in a zigzag fashion (Fig. 4b and 5b).The view along c axis is also different in both the compounds (Fig. 4c and 5c).Overall, the supramolecular architectures clearly distinguish the two polymorphic forms 1 and 2.

Synthesis and crystallization
50 mg (0.19 mmol) of Mn(CO) 5 Br [bromopentacarbonylmanganese(I)] and 30.6 mL (0.38 mmol) of 5-methyl-1Hpyrazole were dissolved in 20 ml of ethanol.After stirring for a few minutes, 105 mL (0.76 mmol) of triethylamine were added to the reaction mixture and the resultant straw-yellowcolored solution was stirred at room temperature for 20 h.Light-yellow crystals were obtained by the slow evaporation method of a 1:1 dichloromethane-ethanol solvent mixture.Crystal yield 60%. ESI-MS data: m/z 540.53290 [M -H] + .

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.

Figure 2
Figure 2 Overlay of the compounds 1 and 2 showing a slight deviation of 0.0612 A (Mercury; Macrae et al., 2020).
Figure 3Perspective view of the supramolecular pattern of compound 1 showing the presence of intermolecular C-H� � �� interactions.

Figure 4
Figure 4 Supramolecular architecture of compound 1.(a) View along the a axis showing a herringbone-type arrangement; (b) and (c) the stacking of Br-Mn-Br along the respective axes.

Figure 5
Figure 5 Supramolecular architecture of compound 2. (a) View along the a axis showing a pillared network arrangement; (b) a view along the b axis showing the zigzag pattern of Br-Mn-Br and (c) a view along the c axis.

Table 2
Experimental details.
Computer programs: CrysAlis PRO