Crystal structure of bis{μ-2-[bis(2-hydroxyethyl)amino]ethanolato}bis(μ-3,5-dimethylpyrazolato)tricopper(II) dibromide sesquihydrate

In the title bicyclic trinuclear pyrazolate aminoalcohol complex, the central Cu atom lies on a center of symmetry and has a distorted tetrahedral coordination geometry while the peripheral Cu atom is in a trigonal–bipyramidal coordination environment.

In the title bicyclic trinuclear pyrazolate aminoalcohol complex, [Cu 3 (C 5 H 7 N 2 ) 2 -(C 6 H 14 NO 3 ) 2 ]Br 2 Á1.5H 2 O, the central Cu atom lies on a center of symmetry and is involved in the formation of two five-membered rings. It has a coordination number of 4, is in a distorted tetrahedral environment and is connected by the bridging oxygen atoms of the deprotonated OH groups of different aminoalcohol groups, and by the N atoms of deprotonated dimethylpyrazole ligands. The peripheral Cu atom is in a trigonal-bipyramidal coordination environment formed by the nitrogen atom of the deprotonated bridging dimethylpyrazole unit, the bridging oxygen atom of the deprotonated OH group, two oxygen atoms of the protonated hydroxy groups and the nitrogen atom of triethanolamine. One of the C atoms and the Br À anion were found to be disordered over two positions with occupancy factors of 0.808 (9):0.192 (9) and 0.922 (3):0.078 (3), respectively.

Chemical context
Coordination compounds of paramagnetic transition-metal complexes with polydentate and polynuclear ligands are of great interest because of their versatile magnetic properties, in particular, magnetic superexchange mediated by ligand-bridging functions (Pavlishchuk et al., 2010(Pavlishchuk et al., , 2011Strotmeyer et al., 2003;Gumienna-Kontecka et al., 2007) or spin-crossover behavior (Suleimanov et al., 2015;Gural'skiy et al., 2012). Amino alcohols can be used for the synthesis of similar complexes since they are versatile and effective polydentate ligands in coordination chemistry (Vynohradov et al., 2020). It is well known that polynuclear complexes of 3d metals with amino alcohols (acting both as neutral and acidic ligands) can indicate non-trivial magnetic properties and biological activity. Mono-, di-, and trinuclear complexes of copper(II) with triethanolamine are widely studied because of their interesting magnetic properties (Escovar et al., 2005). The magnetic properties of copper(II) complexes with triethanolamine range from ferromagnetic to antiferromagnetic, with minor changes in the structure of the complex affecting the nature of the exchange interactions that control the ultimate magnetization (Boulsourani et al., 2011). In addition, copper(II) complexes with triethanolamine can bind to DNA (Sama et al., 2019) and show catecholase activity (Sama et al., 2017). Amino ISSN 2056-9890 alcohol complexes of copper(II) and zinc show catalytic activity in the reactions of conversion of alkanes or cycloalkanes to carboxylic acids, which can help to increase the yield of products (Ansari et al., 2016). Triethanolamine is a polyfunctional O,N-ligand that can bind metal ions in its neutral or deprotonated form leading to an alcoholate. Finally, atoms of the same or different metals can be linked by bridging oxygen atoms to form mono-and heterometallic polynuclear complexes (Dias et al., 2015;Kirillov et al., 2007). As part of our continuing interest in multifunctional transitionmetal complexes with polydentate and polynuclear ligands, we report herein the synthesis and crystal structure of a new trinuclear copper(II) mixed-ligand complex with triethanolamine and 3,5-dimethylpyrazole.

Structural commentary
The crystal structure of the title compound ( Fig. 1) comprises trinuclear Cu 3 (dmpz-H) 2 (H 2 TEA) 2 2+ cationic units linked via two bridging bromine anions. The central Cu2 atom lies on a center of symmetry and is involved in the formation of two five-membered rings. Each ring is formed by two copper atoms connected by the bridging oxygen atom of the monodeprotonated triethanolamine and the bridging deprotonated dimethylpyrazole. The five-membered bimetallic rings are not planar. The nitrogen atoms of the dimethylpyrazole bridging ligand are practically in the same plane as the metal atoms, while the bridging oxygen atom is out of the plane by 0.450 (3) Å . The copper(II) atoms have different coordination environments. The peripheral Cu1 atom is in a trigonalbipyramidal coordination environment formed by two N2 nitrogen atoms of the deprotonated bridging dimethylpyrazole ligands, the bridging oxygen atom of the deprotonated OH group, two oxygen atoms of the protonated hydroxy groups and the triethanolamine nitrogen atom. The central Cu2 atom (coordination number 4) is in a distorted (flattened) tetrahedral environment and is surrounded by the bridging oxygen atoms of the deprotonated OH groups of different amino alcohol molecules, and by N3 and N3 i symmetry code: (i) 3 2 À x, y, 1 À z] atoms of different deprotonated molecules of dimethylpyrazole. The interatomic distances between the N3, O1 and N3 i , O1 i atoms are 2.726 (4) Å . The distances between the atoms O1, O1 i and N3, N3 i are similar at 2.915 (4) and 2.970 (5) Å , respectively. The intermetallic separations are Cu1Á Á ÁCu2 = 3.2829 (5) and Cu1Á Á ÁCu1 i = 6.4784 (10) Å .
The triethanolamine ligand is coordinated in a tetradentate manner by all donor atoms. As a result of such a coordination of triethanolamine from both sides of the complex molecule, three similar five-membered cyclic Cu-O-C-C-N fragments are formed. Bridging oxygen atoms arise from the coordination of the amino alcohol to a metal atom with the deprotonation of only one OH group. The coordinated triethanolamine is monodeprotonated, and the other two hydroxy groups are protonated and bonded by hydrogen bonds to the adjacent molecules via bridging bromine anions. The distances between Cu1 and the oxygen atoms of the deprotonated [Cu1-O1 = 1.930 (2) Å ] and protonated [Cu1-O2 = 2.308 (2), Cu1-O3 = 2.060 (3) Å ] OH groups are different.

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level [Symmetry code: (i) 3 2 À x, y, 1 À z].

Synthesis and crystallization
Cu 3 (dmpz-H) 2 (H 2 TEA) 2 Br 2 (dmpz-H = deprotonated 3,5dimethyl-1H-pyrazole and H 2 TEA = monodeprotonated triethanolamine) was synthesized at room temperature by the addition of a copper powder (2.34 mmol, 0.15 g) and copper(II) bromide (2.34 mmol, 0.525 g) mixture to an acetonitrile solution of 3,5-dimethyl-1H-pyrazole (4.68 mmol, 0.45 g). Triethanolamine (2.34 mmol, 0.31 ml) was added immediately. The reaction mixture was stirred without heating for one h with free air access until dissolution of the copper powder, and a green precipitate of the product was obtained. The precipitate was filtered off, dissolved in methanol, and filtered off from the undissolved copper residues. Green crystals suitable for X-ray analysis were obtained by slow evaporation of the solvent. The yield was 50%. The obtained dark-green crystals were studied by elemental analysis (calculated C 31.56%, H 5.05% and N 10.04%, found C 30.83%, H 5.73%, N 10.38%). The reaction scheme is shown in Fig. 3.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Hydrogen atoms were included in geometrically calculated positions (O-H = 0.83-0.88 Å , C-H = 0.96-0.97 Å ) with U iso = 1.2U eq C) or U iso = 1.5U eq (O,Cmethyl). Atom C6 and the Br À anion were found to be disordered over two resolvable positions with occupancy factors of 0.808 (9):0.192 (9) and 0.922 (3):0.078 (3), respectively. Their positional parameters were refined using available tools (see the CIF in the supporting information).

Figure 3
Reaction scheme to obtain the title compound.  CrysAlis PRO (Rigaku OD, 2019); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.61 e Å −3 Δρ min = −0.52 e Å −3 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.