Aqua(1,4,7,10-tetraazacyclododecane)zinc(II) bis(perchlorate)

The cationic ZnII part of aqua(1,4,7,10-tetraazacyclododecane)zinc(II) diperchlorate, [Zn(C8H20N4)H2O](ClO4)2, exhibits a slightly distorted square-pyramidal coordination environment with a water molecule in the apical position.

The cationic Zn II part of aqua(1,4,7,10-tetraazacyclododecane)zinc(II) bis(perchlorate), [Zn(C 8 H 20 N 4 )(H 2 O)](ClO 4 ) 2 , exhibits a slightly distorted square-pyramidal coordination environment with a water molecule in the apical position. In the crystal, the macrocyclic ring alternates between two conformations with equal occupancies. Two of the three perchlorate anions are situated about a twofold rotation axis, and one of them shows disorder of the O atoms with occupancies of 0.62 (7) and 0.38 (7). In the crystal, the complexes are connected by intermolecular hydrogen bonding via the perchlorate anions.

Structure description
The title complex, [Zn(C 8 H 20 N 4 )H 2 O](ClO 4 ) 2 , comprises a cationic Zn II complex and three perchlorate anions, two of which are located about a twofold rotation axis with one of them disordered [occupancy ratio for the corresponding O atoms is 0.62 (7):0.38 (7)]. The macrocyclic ring is disordered, and two alternate conformations of each N-C-C-N bridge can be observed (conformation A and B) (Fig. 1), in which four carbon atoms (C2, C4, C6, and C8) are shared. The central Zn II cation is ligated by four N atoms of 1,4,7,10tetraazacyclododecane (cyclen) in the basal plane, with a Zn II -bound H 2 O molecule occupying the apical position. Addison et al. (1984) proposed the geometry index [ = ( À )/60 ] to determine if the five-coordinate atom has a square-pyramidal or trigonalpyramidal coordination environment. The bond angles and are the largest and second-largest in the coordination sphere, respectively; an ideal square pyramid and an data reports ideal trigonal bipyramid have = 0 and 1, respectively. In conformation A, the N-Zn II -N bond angles and are 138.2 (3) and 138.7 (3) , respectively; the corresponding bond angles in conformation B are 137.4 (4) and138.7(4) . The values are 0.008 and 0.022 for conformations A and B, respectively. Therefore, the coordination geometry around the central Zn II cation can be described as slightly distorted square-pyramidal. The occupancies for the non-hydrogen atoms of cyclen except for the four carbon atoms (C2, C4, C6, and C8) were set to 0.50. Atom Zn1 is 0.755 (5) and 0.763 (3) Å above the basal plane formed by four N atoms in conformations A and B, respectively. The Zn1-O1 bond length [1.9721 (4) Å ] is within the typical range [1.94-2.03 Å ] for similar five-coordinated Zn complexes (Bazzicalupi et al., 1995;Chen et al., 1994;Kato & Ito, 1985;Koike et al., 1994;Murthy & Karlin, 1993;Schrodt et al.;1997). In addition, the mean Zn1-N bond length (2.13 Å ) in the title complex is similar to that in the crystal structure of [Zn(cyclen)EtOH](ClO 4 ) 2 (Schrodt et al., 1997).
The two perchlorate ions are involved in intermolecular hydrogen bonds with the cationic Zn II complex (Table 1). In the crystal, intermolecular hydrogen-bonding interactions connect neighboring molecules, forming a three-dimensional network (Fig. 2). As far as we know, an aqua(cyclen)-copper(II) complex has already been reported (Pé rez-Toro et al., 2015), but the aqua(cyclen)zinc(II) complex has not. The title aqua(cyclen)zinc(II) complex has been well studied as Zn II -containing enzyme models, such as alkaline phosphatase, -lactamase, and carbonic anhydrase, to elucidate the essential roles of Zn II (Kimura et al., 1995;Kitajima et al., 1993;Zhang et al., 1993;Zhang & van Eldik, 1995). We succeeded in determining its crystal structure at this time.

Synthesis and crystallization
The title complex was prepared as fine white solid according to a previously reported method (Koike et al., 1994) and then crystallized from aqueous ethanol.

Figure 2
A view of the crystal packing of the title complex. Dashed lines denote the hydrogen bonds.

Figure 1
The structures of the molecular entities within the title complex showing 50% displacement ellipsoids. [Symmetry codes: (i) Àx + 1, y, Àz + 1 2 ; (ii) Àx, y, Àz + 1 2 ].  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 1.15 e Å −3 Δρ min = −0.84 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. Refinement. All hydrogen atoms were placed on calculated positions and refined in riding mode, with U iso (H) values assigned as 1.2U eq of the parent atoms (1.5 times for water molecule O1).