Crystal structure of orthorhombic {bis[(pyridin-2-yl)methyl](3,5,5,5-tetrachloropentyl)amine-κ3 N,N′,N′′}chloridocopper(II) perchlorate

In the crystal, weak Cu⋯Cl interactions between symmetry-related molecules create a dimerization with a chloride occupying the apical position of the square-pyramidal geometry typical of many copper(II) chloride hetero-scorpionate complexes.


Chemical context
The mechanistic and structural study of Atom Transfer Radical Addition (ATRA) reactions is a growing and promising field in organometallic chemistry. These reactions involve the formation of carbon-carbon bonds through addition of a poly-halogenated saturated hydrocarbon to alkenes (Eckenhoff & Pintauer, 2010). Also known as the Kharasch reaction, most proceed either in the presence of a free-radical precursor as the halogen transfer agent, or a transition metal complex as the halogen transfer agent (Muñ oz- Molina et al., 2011). What makes these types of reactions attractive is generation of halogen-group functionalities within the product; which can be used as starting reagents in further functionalization reactions (Kleij et al., 2000). Of interest to this project is analysis of hetero-scorpionate complexes incorporating weakly coordinating olefinic moieties in ATRA reactions. Since their discovery in the 1960s by Swiatoslaw Trofimenko (Pettinari, 2004), scorpionate ligands are considered to be some of the most useful ligand structures available in modern coordination chemistry (Trofimenko, 1999). As such, we report the synthesis and crystal structure of the title compound [Cu(C 17 H 19 N 3 Cl 4 )(Cl)][ClO 4 ] (1).

Structural commentary
The title complex, (1) (Fig. 1), adopts a distorted squareplanar geometry, as shown in the bond angles around the Cu II ion. The Cu II ion is coordinated by the binding of the two pyridine and amine nitrogen atoms and a chlorido ligand. A - ISSN 2056-9890 4 analysis of the distortions about the Cu II ion yields a value of 0.15, slightly deviant from an ideal value of zero for perfect square-planar geometry [-4 = [360 -( + )]/141; Yang et al., 2007] where and are the two greatest valence angles of the coordination center]. The Cu II ion sits 0.0922 (4) Å out of the mean basal plane formed by Cl1 and the three coordinating N atoms, giving rise to the distortion from true square-planar geometry. The Cu-Cl1 [2.2519 (8) Å ], Cu-N(amine) [2.027 (2) Å ], and Cu-N(py) [1.982 (3) and 1.987 (3) Å ] bond lengths are in the anticipated range for copper(II) complexes.

Supramolecular features
Weak [2.8535 (9) Å ] CuÁ Á ÁCl interactions between adjacent molecules creates a dimerization with two Cl atoms bridging the Cu II atoms (Fig. 2). The inter-copper distance between neighbouring cations is 3.4040 (7) Å . When considered, the weak CuÁ Á ÁCl interaction becomes the apical position of a distorted square-pyramidal geometry for the Cu II atoms. The molecular structure of (1), shown with 50% probability ellipsoids for non-H atoms and circles of arbitrary size for H atoms. Only the primary orientations of the disordered sites are shown.
HÁ Á Á Cl interactions between C11-H11AÁ Á ÁCl1 i and C12-H12B Á Á ÁCl1 i (Cl1 i is generated by the symmetry operation À x, Ày + 2, Àz; Table 1). The three-dimensional packing structure ( Fig. 3) is comprised from many weak C-H Á Á Á O interactions that occur between carbon donors on the scorpionate arm or the bis(pyridin-2-ylmethyl)amine and the oxygen atoms on varying orientations of the perchlorate counter-ion. Depending on the orientation of the chlorinated scorpionate arm, there are additional weak C-HÁ Á Á Cl interactions.

Database survey
There are 200 structures with the bis(pyridin-2-ylmethyl)amine ligand coordinating to copper with at least one bound chloride ligand (Groom & Allen 2014; CSD Version 5.36). Ignoring all the structures that have tethered pairs or tethered triplets of ligands, or have ligands whose amine group has substituents that additionally coordinate to the Cu II atom, there are 58 remaining structures. Eighteen of these remaining structures have two bridging Cl ligands with one short axial Cu-Cl bond length (average 2.25 Å ) and one long apical Cu-Cl bond length (average 2.72 Å ).

Synthesis and crystallization
The synthetic procedure is outlined in Fig. 4. Synthesis of 1butene-bis(pyridin-2-ylmethyl)amine, (B): bis(pyridin-2ylmethyl) amine (BPMA) precursor (A) was synthesized and purified following literature procedures (Carvalho et al., 2006). BPMA (8.064 g, 40.5 mmol) was dissolved in 15 mL of acetonitrile followed by the addition of triethylamine (4.098 g, 40.5 mmol) and 4-bromobutene (5.468 g 40.5 mmol). The reaction was sealed and allowed to mix for 4 days to ensure complete deprotonation and coupling occurred. Generation of the triethylamine hydrogen bromide salt Et 3 NH + ÁBr À was observed as white crystals in the brown-colored solution. The mixture was filtered and the desired product extracted from the filtrate using a hexane/water mixture. The hexane layer was separated and solvent removed to yield the ligand as a yellow-colored oil (  pitate. Solvent was removed from the flask through a vacuum line. The precipitate was washed twice by transferring 10 mL of pentane into the flask and stirring vigorously for thirty minutes. Solvent was removed and the precipitate dried under vacuum for 2 h to yield a yellow-colored solid (2.109 g, 92%). 20 mmol) was dissolved in 5 mL acetonitrile in a glass vial with a stir bar. Nitrogen gas purged CCl 4 (0.174 mL, 1.80 mmol) was added to the vial producing a bluish-greencolored mixture. The reaction vial was sealed with a plastic cap and allowed to mix for 4 h, then removed from the drybox.
Vapour diffusion crystallization at room temperature, incorporating 1 mL of the bluish-green solution with diethyl ether as the external diffusing solvent, produced blue-colored crystals suitable for X-ray analysis.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The proposed structure model includes disorder of the hetero-scorpionate arm of the bis-[(pyridin-2-yl)methyl](3,5,5,5-tetrachloropentyl)amine ligand over two sets of sites and disorder of the perchlorate anion modelled over three sites. The geometries of the disordered [C 5 H 7 Cl 4 ] arm were restrained to be the same (s.u. 0.01Å ). The perchlorate anions were also restrained to have the same geometries (s.u. 0.01 Å ). In addition, the sum of the occupancies of the three orientations for the perchlorate anions were restrained to add up to one (s.u. 0.001). All disordered sites were restrained to have similar displacement amplitudes (s.u. 0.01) for atoms overlapping by less than the sum of van der Waals radii. Displacement parameters for the perchlorate anion positions were also restrained to behave relatively The synthetic scheme.