Crystal structure of trans-(1,8-dibutyl-1,3,6,8,10,13-hexaazacyclotetradecane-κ4 N 3,N 6,N 10,N 13)bis(perchlorato-κO)copper(II) from synchrotron data

The CuII ion in the title compound shows a slightly distorted octahedral coordination geometry with four N atoms of the azamacrocyclic ligand and two perchlorate anions. In the crystal, molecules are linked by N–H⋯O and C–H⋯O hydrogen bonds, forming a three-dimensional network.


Chemical context
Coordination compounds with macrocyclic ligands have attracted considerable attention in chemistry, biological chemistry and materials science (Lehn, 1995). In particular, macrocyclic Cu II complexes with vacant sites in the axial positions are good building blocks for assembling multidimensional frameworks (Ko et al., 2002), with potential applications as metal extractants, radiotherapeutic materials and as medical imaging agents (Sowen et al., 2013). For example, Cu II complexes with tetra-azamacrocyclic ligands have been studied with various auxiliary anionic ligands such as ferricyanide and hexacyanidochromate and their biological redox-sensing and magnetic properties (Xiang et al., 2009) have been investigated. Moreover, the perchlorate ion is a versatile anion which can easily bridge two transition metal complexes, allowing the assembly of multi-dimensional compounds (Kwak et al., 2001).

Structural commentary
In the title compound, the coordination environment around the Cu II ion, which lies on an inversion center, is tetragonally distorted octahedral. The copper(II) ion binds to the four secondary N atoms of the azamacrocyclic ligand in a squareplanar fashion in the equatorial plane, with two O atoms from the perchlorate anions in axial positions as shown in Fig. 1. The bonds to the two axially located perchlorate anions are significantly longer than those to the donor N atoms in the equatorial plane. This can be attributed either to a rather large Jahn-Teller distortion of the Cu II ion and/or to a considerable ring contraction of the azamacrocyclic ligand (Halcrow, 2013). The six-membered chelate rings adopt chair conformations and the five-membered chelate rings assume gauche conformations (Min & Suh, 2001). Intramolecular N-HÁ Á ÁO hydrogen bonds between the secondary amine groups of the azamacrocyclic ligand and an O atom of each perchlorate ion contribute to the molecular conformation ( Fig. 1 and Table 1).

Supramolecular features
Each complex molecule forms three N-HÁ Á ÁO and two C-HÁ Á ÁO hydrogen bonds (Steed & Atwood, 2009), as shown in Table 1, Fig. 2. Sheets of complex molecules form in the ab plane, Fig. 3, and additional C6-H6BÁ Á ÁO3 contacts link these sheets into a three-dimensional network.

Database survey
A search of the Cambridge Structural Database (Version 5.35, May 2014 with three updates; Groom & Allen 2014) indicated that 51 azamacrocyclic Cu II complexes with pendant alkyl groups had been reported previously. These complexes have been studied as good building blocks for supramolecular chemistry and contain a variety of pendant alkyl groups (Cho et al., 2003). Their magnetic properties and guest-exchange effects with cyanido groups and carboxylic acid groups as ligands have also been investigated (Ko et al., 2002;Zhou et al., 2014). No corresponding azamacrocyclic Cu II complex with View of the molecular structure of the title compound, showing the atom labelling scheme, with displacement ellipsoids drawn at the 50% probability level. H atoms bonded to C atoms have been omitted for clarity. Intramolecular N-HÁ Á ÁO hydrogen bonds are shown as black dashed lines. [Symmetry code: (i) Àx + 1, Ày + 1, Àz + 1.]

Figure 3
Sheets of complex molecules in the ab plane. Hydrogen-bonding interactions are shown as dashed lines.
pendant butyl groups has been reported and the title compound was newly synthesized for this research.

Synthesis and crystallization
The title compound was prepared as follows. Ethylenediamine (3.4 mL, 0.05 mol), paraformaldehyde (3.0 g, 0.10 mol), and butylamine (3.7 g, 0.05 mol) were slowly added to a stirred solution of CuCl 2 Á2H 2 O (4.26 g, 0.025 mol) in MeOH (50 mL Safety note: Although we have experienced no problems with the compound reported in this study, perchlorate salts of metal complexes are often explosive and should be handled with great caution.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H distances of 0.98-0.99 Å and an N-H distance of 1.0 Å with U iso (H) values of 1.2 or 1.5 U eq of the parent atoms.   -(1,8-dibutyl-1,3,6,8,10,13-hexaazacyclotetradecaneκ 4 N 3 ,N 6 ,N 10 ,N 13 )