A [Cu3(μ3-O)]–pyrazolate metallacycle with terminal nitrate ligands exhibiting point group symmetry 3

The cuprate anion in the title compound is located about a threefold rotation axis and hence forms an almost planar Cu3(μ3-O)-core, where the μ3-O atom is located 0.12 Å above the Cu3 plane.


Chemical context
Trinuclear copper complexes with a triangular arrangement of the copper(II) cations are of importance in terms of their magnetic and redox properties (Rivera-Carrillo et al., 2008). Moreover, Cu 3 ( 3 -O/OH) moieties make up the active sites of several multicopper oxidase enzymes (Solomon et al., 2014). Pyrazolate anions as ligands are of bidentate chelating nature and are able to bind to the the Cu II cations in suitable angles to form triangular complexes (Halcrow, 2009;Viciano-Chumillas et al., 2010).
Nitrato and pyrazolato ligands are commonly studied ligands in Cu II coordination chemistry. Simple Cu II nitrate complexes are aplenty in the literature and have been studied in detail with respect to their part in the nitrogen cycle. Triangular trinuclear Cu II complexes with terminal nitrate ligands, however, are scarcer (Alsalme et al., 2014). Nitrates, being good hydrogen-bonding acceptors, are able to form Cu 3 ( 3 -OH) complexes, with hydrogen bonds to the 3 -OH group and to ancilliary ligands and water molecules. ISSN 2056-9890 In this communication we describe the accidental synthesis and the structure of a trinuclear Cu-pyrazolato complex, viz.

Structural commentary
The nine-membered metallacycle Cu 3 N 6 in the cuprate anion ( Fig. 1) is strung together by a 3 -O group located at the center of the triangle (point group symmetry of the complete molecule 3.), forming an almost planar Cu 3 ( 3 -O)-core, where the 3 -O atom O1 is located 0.122 (7) Å above the Cu 3 plane. The distorted square-pyramidal geometry of the Cu II atom is completed by the two N atoms of symmetry-related transbridging pyrazolato ligands, and a terminal nitrato ligand that is bound to the metal in a chelating fashion (Table 1). The complex is slightly bent with the nitrate and pyrazolato groups occupying positions above and below the Cu 3 plane, respectively. The Cl atom of the pyrazole anion is located approximately 1.28 Å below the Cu 3 plane. The non-coordinating The molecular structure of the trinuclear pyrazolatocuprate anion in the title compound showing the atom-labeling scheme for the symmetryindependent atoms. Non-H atoms are shown as displacement ellipsoids at the 30% probability level.  Hydrogen-bond geometry (Å , ).

Figure 2
The crystal packing diagram for the title compound shown down [001].
nitrate counter-anion is located about a special position with the nitrogen atom on the threefold rotation axis. The triphenylphosphene groups in the PPN cation are staggered around the central N atom [P-N-P angle 139.5 (2) ] and show bond lengths and angles characteristic for this unit (Beckett et al., 2010).

Supramolecular features
The interstitial water O atom is also located on a threefold rotation axis which consequently results in disordered H atoms of this moiety. Although these H atoms could not be located, three OÁ Á ÁO distances to the chelating nitrate anions of 3.367 (6) Å point to weak O-HÁ Á ÁO hydrogen bonds in the structure. This nitrate O atom is additionally involved in weak non-classical hydrogen-bonding interactions with one of the C-H groups of the PPN cation ( Table 2). The latter shows also interactions [3.902 (7) Å ] with one of the pyrazolate rings, leading to an overall three-dimensional network. The packing of the molecular units is shown in Fig. 2.