The first structural characterization of the protonated azacyclam ligand in catena-poly[[[(perchlorato)copper(II)]-μ-3-(3-carboxypropyl)-1,5,8,12-tetraaza-3-azoniacyclotetradecane] bis(perchlorate)]

The title compound is one-dimensional coordination polymer built up of tetragonally distorted CuN4O2 octahedra formed by four N atoms of the azamacrocyclic ligand in the equatorial plane and O atoms of the protonated carboxylic acid group and the perchlorate anion in the axial positions. In the crystal, [010] polymeric chains are crosslinked by N—H⋯O hydrogen bonds to form sheets lying parallel to the (001) plane.

The asymmetric unit of the title compound, catena-poly [[[(perchlorato-O)copper(II)]--3-(3-carboxypropyl)-1,5,8,12-tetraaza-3-azoniacyclotetradecane-4 N 1 ,N 5 ,N 8 ,N 12 ] bis(perchlorate)], {[Cu(C 13 H 30 N 5 O 2 )(ClO 4 )](ClO 4 ) 2 } n , (I), consists of a macrocyclic cation, one coordinated perchlorate anion and two perchlorate ions as counter-anions. The metal ion is coordinated in a tetragonally distorted octahedral geometry by the four secondary N atoms of the macrocyclic ligand, the mutually trans O atoms of the perchlorate anion and the carbonyl O atom of the protonated carboxylic acid group of a neighbouring cation. The average equatorial Cu-N bond lengths [2.01 (6) Å ] are significantly shorter than the axial Cu-O bond lengths [2.379 (8) Å for carboxylate and average 2.62 (7) Å for disordered perchlorate]. The coordinated macrocyclic ligand in (I) adopts the most energetically favourable trans-III conformation with an equatorial orientation of the substituent at the protonated distal 3-position N atom in a six-membered chelate ring. The coordination of the carboxylic acid group of the cation to a neighbouring complex unit results in the formation of infinite chains running along the b-axis direction, which are crosslinked by N-HÁ Á ÁO hydrogen bonds between the secondary amine groups of the macrocycle and O atoms of the perchlorate counter-anions to form sheets lying parallel to the (001) plane. Additionally, the extended structure of (I) is consolidated by numerous intra-and interchain C-HÁ Á ÁO contacts.

Chemical context
Because of their exceptionally high thermodynamic stability and kinetic inertness (Melson, 1979;Yatsimirskii & Lampeka, 1985), transition-metal complexes of the macrocycles 1,4,8,11tetraazacyclotetradecane (cyclam), N 3 ,N 10 -disubstituted 1, 3,5,8,10,12-hexaazacyclotetradecane (diazacyclam) and, to a lesser extent, N 3 -substituted 1,3,5,8,12-pentaazacyclotetradecane (azacyclam) are popular building units for the assembly of metal-organic frameworks (MOFs), demonstrating many promising applications (Lampeka & Tsymbal, 2004;Suh & Moon, 2007;Suh et al., 2012;Stackhouse & Ma, 2018). Two latter types of the Cu II and Ni II complexes are readily obtainable via template-directed Mannich condensation of bis(ethylenediamine) or 3,7-diazanonane-1,9-diamine complexes, respectively, with formaldehyde and primary amines (Rosokha et al., 1993;Costisor & Linert, 2000). The use of primary amines bearing a carboxylic acid function as locking fragments in these template reactions allows for the preparation of complexes of carboxyl-functionalized diaza-cyclams, as was shown for the Ni II and Cu II complexes of diazacyclam substituted with 3-carboxypropyl groups Ou et al., 2005). Such compounds are of particular interest because they can self-polymerize due to the coordination of the donor group of the substituent to the metal ion of another molecule, thus forming coordination polymers without using additional bridging ligands, the most popular of which are carboxylates (Rao et al., 2004). Indeed, the Cu II complex of this diazacyclam ligand possesses a self-polymeric structure , whereas the Ni II complex does not form a polymer . Data on the polymeric compounds of the given type formed by the complexes of functionalized azacyclam are not available in the literature so far.
Another issue of interest is the acid-base properties of the noncoordinated distal N atom present in the macrocyclic backbones of aza-and diazacyclams. Its likely protonation was postulated first based on the solution properties of the Ni II compounds (Rosokha et al., 1993;Tsymbal et al., 1995;Hay et al., 1997) and was further confirmed by X-ray structural analysis of the diethyl-substituted Ni II diazacyclam complex (Jiang et al., 2006), while such a possibility for the Cu II complexes has not been reported yet.

Structural commentary
The Cu II ion in the complex cation in (I) is coordinated by four secondary amine N atoms of the azamacrocyclic ligand in a square-planar fashion and by O atoms from the perchlorate anion and the carboxylic acid group of a neighbouring cation in the axial positions, resulting in a tetragonally distorted octahedral geometry (Table 1 and Fig. 1). The Cu II ion is displaced by 0.075 Å from the mean plane of the N 4 donor atoms (r.m.s. deviation = 0.005 Å ) towards the O2 atom of the carboxylate group. The equatorial Cu-N bond lengths are significantly shorter than the axial Cu-O bond lengths (Table 1), which can be attributed to a large Jahn-Teller distortion.
The macrocyclic ligand in (I) adopts the most energetically favourable trans-III (R,R,S,S) conformation (Bosnich et al., 1965), with the five-membered chelate rings in gauche [average bite angle = 86.2 (18) ] and the six-membered chelate rings in chair [average bite angle = 93.6 (2) ] conformations. The methylene group of the substituent at the noncoordinated N3 atom in the six-membered chelate ring is oriented equatorially. Such an arrangement of the substituent, in contrast to an axial orientation, is relatively uncommon and only a few examples of such Cu II complexes with aza-and diazacyclam ligands have been described so far (Shin et al., 2010(Shin et al., , 2012Tsymbal et al., 2010;Husain et al., 2012;Xia et al., 2014).  The formation of the azonia N3H + group in (I) leads to clear changes in the C-N-C angles compared to the nonprotonated ones. The sum of these angles in the latter case (345-354 ) is much larger than the canonical value for an sp 3hybridized N atom (ca 327 ), thus indicating their partial sp 2 character (Tsymbal et al., 2010;Andriichuk et al., 2019), while in (I) this parameter equals 335 (2) , demonstrating an sp 2 -tosp 3 transformation of the noncoordinated N atom upon protonation.
The C-O bond lengths in the carboxylic acid group of the substituent differ considerably [1.318 (13) and 1.198 (13) Å for C13-O1 and C13-O2, respectively], thus confirming its protonated form and the lack of delocalization. Interestingly, it is coordinated to the Cu II ion via O2, the carbonyl O atom, which is analogous to the situation observed in a bis(3-carboxypropyl)-substituted diazacyclam polymeric complex .
Three disordered perchlorate anions in the title compound counterbalance the charge of the complex cations. The Cl1O 4 anion is completely disordered over two positions with site occupancies of 50% and is weakly coordinated to the metal ion (Table 1). Two remaining counter-anions are partially disordered with the retention of the positions of the central Cl atoms, with site occupancies of the major components of 80 (Cl2O 4 ) and 78% (Cl3O 4 ). Because of the low partial population, the minor components of these perchlorate anions were not considered further in the analysis of the hydrogen-bonding network.

Supramolecular features
The inter-cationic coordination of the carboxylic acid group of the substituent in the macrocycle to the metal ion results in the formation of one-dimensional polymeric chains running along the b-axis direction (Fig. 2). These chains are further reinforced by hydrogen bonding between secondary amine groups of the macrocycle acting as proton donors and O atoms of the perchlorate anions as proton acceptors [N2-H2Á Á ÁO8(Cl2) and N4-H4Á Á ÁO11(Cl3)]. Additionally, the azonia group of the macrocycle forms a bifurcated hydrogen bond with both noncoordinated perchlorate anions [N3-H3 + Á Á ÁO10(Cl2),-O12(Cl3)], so that each perchlorate anion is fixed in a chain in a ditopic manner ( Fig. 2 and Table 2). In addition, weak hydrogen bonding exists between the carboxylic acid group as the proton donor and an O atom of one of the perchlorate ions [O1-H1CÁ Á ÁO7(Cl2)(x, y À 1, z)], as well as between secondary amine groups of the macrocycle and an O atom of the carboxylic acid group as the proton acceptor [N2-H2(N4-H4)Á Á ÁO1(x, y + 1, z)]. Hydrogen bonding of the secondary amine groups of the macrocycle and the O atoms of perchlorate anions not involved in above-mentioned intrachain interactions [N1-H1Á Á ÁO7(Cl2)(x À 1 2 , Ày + 1 2 , z) and N5-H5Á Á ÁO14(Cl3)(x À 1 2 , Ày + 1 2 , z)] results in the formation of sheets lying parallel to the (001) plane (Fig. 2), with a distance between them of 6.82 Å . There are also numerous intra-and interchain C-HÁ Á ÁO contacts between methylene  Symmetry codes: (i) x; y À 1; z; (ii) x; y þ 1; z; (iii) x À 1 2 ; Ày þ 1 2 ; z; (iv) Àx þ 1 2 ; y À 1 2 ; z À 1 2 ; ( groups of the macrocycle and the O atoms of the anions (Table 2), and these latter interactions are responsible for the formation of the three-dimensional structure of (I).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All H atoms in (I) were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H = 0.99 Å , N-H = 1.00 Å and carboxylate O-H = 0.84 Å , with U iso (H) values of 1.2 or 1.5U eq of the parent atoms. The crystal of (I) chosen for data collection was found to crystallize as an inversion twin.