Crystal structure and spectroscopic properties of chlorido{hydridotris[3-,5-dimethylpyrazol-1-yl-κN3]borato}(3-,5-dimethylpyrazol-1-yl-κN)copper(II), C20H30BClCuN8

C20H30BClCuN8, monoclinic, P21/c (no. 14), a = 17.1345(7) Å, b = 7.8207(2) Å, c = 19.0213(8) Å, β = 108.268(1)°, V = 2420.46(16) Å, Z = 4, Rgt(F) = 0.0322, wRref(F ) = 0.0876, T = 184 K.


Experimental details
The C-and B-bound H atoms were geometrically placed (C-H = 0.95-0.98 Å & B-H = 1.00 Å) and refined as riding with U iso (H) = 1.2-1.5 U eq (C) and 1.2 U eq (B). The N-bound H atom was refined with N-H = 0.88 ± 0.01 Å, and with U iso (H) = 1.2 U eq (N).

Comment
Boron-substituted poly(1-pyrazolyl)borates occupy a prominent position in current coordination chemistry [6]. Among this class of ligand, the methyl substituted hydridotris(3,5dimethyl-pyrazolyl-1-yl]borato-κN 3 anion is very common. It has been designated as "Tp*" [7][8][9][10] and also named "homoscorpionates-first generation" [7,10]. The Tp* ligand is relatively sterically unhindered so it can readily form coordinatively saturated six-coordinate, bis-chelate complexes, formulated as [M(Tp*) 2 ]. For copper(II), the structure of [Cu(Tp*) 2 ] has been reported [11]. To avoid the formation of this bis-chelate complex, the synthetic methodology needs to be carefully modified: the solution containing the Tp* ligand needs to be added slowly to a solution containing a small amount of excess metal salt [12]. This work reports the crystal structure and some properties of a five-coordinate copper(II) complex with the first generation Tp* ligand, also containing a coordinated 3,5-dimethylpyrazol-1-yl molecule, i.e.

}], (I).
It is well-known that four-coordinate copper(II) geometries are not so common in coordination chemistry [13]. In particular, the tetrahedral geometry is very unstable for

Atom
x  less sterically hindered ligands such as Tp*. Indeed, the slow reaction of a copper(II) salt, such as CuCl 2 , with Tp* yielded a mixture of four-(red) and five-coordinate (green) complexes. To ensure the formation of a five-coordinate complex, one equivalent of pyrazole was also added to the reaction mixture. In the IR spectrum of (I), the ν (C=N) signals were split, with absorptions at 1567 and 1542 cm −1 , reflecting the presence of two kinds of pyrazole ligands.
The IR also provides evidence for hydrogen bonding by the pzH-N-H residue with a very sharp absorption noted at 3211 cm −1 . The ground state of (I) is d x2−y2 , as confirmed by ESR [14]. This ground state is also supported by UV-Vis spectroscopy. In the molecular packing, the only directional contact is a long pyrazolyl-C-H···π(pyrazolyl) [C33-H33···Cg(N21, N22, C22-C24) i : H33···Cg(N21, N22, C22-C24) i = 2.98 Å with angle at H33 = 129°for symmetry operation (i): x, 1 + y, z] contact. The result is the formation of a linear, supramolecular chain parallel to the b-axis. To investigate the molecular packing further, with the aid of Crystal Explorer 17 [18] and following literature methods [19], the Hirshfeld surface along with the full and delineated twodimensional fingerprint plots were calculated. Consistent with the lack of evident directional interactions in the crystal of (I), the major contribution to the surface comes from H···H contacts, at 73.9%. After this are H···C/C···H [