Syntheses and structural characterizations of the first coordination polymers assembled from the Ni(cyclam)2+ cation and the benzene-1,3,5-tricarboxylate linker

The coordination polyhedra of the complex cations in the one-dimensional coordination polymers I and II represent tetragonally distorted NiN4O2 octahedra with the four N atoms of the azamacrocyclic cyclam ligand in the equatorial planes and two O atoms of the benzenetricarboxylate anions in the axial positions. The crystals of both compounds are composed of parallel coordination polymeric chains running along the [010] direction in I and the [110] and [1 0] directions in II. As a result of hydrogen-bonding interactions, the chains are joined together in layers oriented parallel to the (10 ) and (001) planes in I and II, respectively.


Structural commentary
The molecular structures of I and II are shown in Fig. 1. The asymmetric unit of I consists of a macrocyclic [Ni(L)] 2+ dication, a monoprotonated carboxylate Hbtc 2À dianion and eight water molecules of crystallization, while the components of II are the same dianion, two crystallographically unique centrosymmetric dications and one water molecule of crystallization. The coordination polyhedra of the metal ions in both complexes are very similar: the Ni 2+ ions are coordinated by the four secondary N atoms of the macrocycle L, which adopt the most energetically stable trans-III (R,R,S,S) conformation (Bosnich et al., 1965a;Barefield et al., 1986) in which the five-membered (N-Ni-N bite angles ' 85 ) and six-membered (N-Ni-N bite angles ' 95 ) chelate rings are in gauche and chair conformations, respectively (Table 1). The O atoms of the carboxylate ligands occupy the axial positions in the coordination spheres of the metal ions, resulting in a tetragonally elongated trans-NiN 4 O 2 coordination octahedra The extended asymmetric unit in (a) I and (b) II showing the coordination environment of the Ni atoms and the atom-labeling scheme (displacement ellipsoids are drawn at the 30% probability level). C-bound H atoms are omitted for clarity. Intramolecular hydrogen bonds are shown as dotted lines. Symmetry codes: (i) Àx + 3 2 , y À 1 2 , Àz + 3 2 ; (ii) Àx + 3 2 , y + 1 2 , Àz + 3 2 ; (iii) Àx + 1, Ày, Àz + 1; (iv) Àx, Ày + 1, Àz + 1.  (Tsymbal et al., 2021) the Ni-O bonds in I and II are reinforced by the intramolecular hydrogen bonds between the secondary NH atoms and the non-coordinated O atoms of each coordinated carboxylic group (Fig. 1, Tables 2 and 3). The C-O bond lengths in the deprotonated carboxylate groups are nearly equal, thus indicating essential electron delocalization, while protonated carboxylic groups remain non-delocalized [the lengths of the C-OH and C O bonds in I and II are 1.305 (4) and 1.200 (3) Å and 1.314 (4) and 1.205 (3) Å , respectively]. The mean planes of the carboxylate groups are slightly tilted relative to the mean plane of their attached aromatic rings (average angle equals 7.0 in I and 16.0 in II).
In both complexes, the monoprotonated carboxylate ligands display a 2 -bis-monodentate bridging function of the isophthalate type, resulting in the formation of one-dimensional coordination polymers (Figs. 2 and 3). The Ni-O coordination bonds of the Hbtc 2À bridge are characterized by the syn/syn orientation. Since the carboxylate groups are nearly coplanar with the aromatic rings, the possibility arises for appearance of different modes of ligand coordination, depending on the mutual spatial arrangement of coordinated O atoms (Tsymbal et al., 2021). In the complexes under consideration, these modes can be recognized as remote (rm) in I and intermediate (im) in II (see insets in Figs. 2 and 3).
Such peculiarities lead to several differences in the structures of the polymeric chains. In particular, the angle between the mean NiN 4 planes of the macrocyclic cations in I is 40.62 (1) , while they are nearly orthogonal in II [85.49 (1) ]. Therewith, the chains of the Ni atoms in I are non-linear [the angle NiÁ Á ÁNiÁ Á ÁNi is 169.590 (9) ], in contrast to strictly linear metal atom chains in II. The most important difference is connected with the mode of the carboxylate coordination and consists of essentially different distances between the Ni atoms in the chains formed by the rm-syn/syn coordinated ligand in I [NiÁ Á ÁNi = 11.0657 (4) Å ], as compared to the imsyn/syn coordinated one in II [8.9089 (2) Å ]. The hydrogen-bonded (dashed lines) sheet in II. C-bound H atoms and water molecule of crystallization have been omitted; the intramolecular hydrogen bonds are not shown. The mode of coordination of carboxylate ligand is shown as an inset. Symmetry code: (i) x À 1, y, z.
the Hbtc 2À dianion, which forms two O-HÁ Á ÁO hydrogen bonds acting both as the proton donor in a strong interaction with the O atom of the coordinated carboxylic ligand on neighboring chain [O5-H5Á Á ÁO4(x + 1 2 , Ày + 1 2 , z + 1 2 )] and as the proton acceptor in a weak interaction with the secondary amino group of the macrocyclic cation belonging to the same neighboring chain [N4-H4Á Á ÁO6(Àx + 2, Ày + 1, Àz + 2)] (Fig. 2). There are no hydrogen-bonding contacts between the sheets and the three-dimensional coherence of the crystal is provided by van der Waals interactions.
In the crystal of II, polymeric chains with different orientations are present, namely, running along the [110] or [110] directions. As a result of the weak hydrogen bond between the carbonyl O6 atom of the protonated carboxylic group of the acid as the acceptor and the secondary N2-H2 amino group of the macrocyclic cation of a neighboring chain as the donor (Fig. 3), they form alternating sheets oriented parallel to the (001) plane. At the same time, the hydroxyl group of the protonated carboxylate group as the donor interacts strongly with the water molecule of crystallization as acceptor, and this interaction together with two additional hydrogen bonds with participation of O1W molecule results in a three-dimensional network in II.
As estimated by PLATON (Spek, 2020), the volume of the solvent-accessible voids in I in the form of parallel onedimensional channels equals 1111 Å 3 (37.5% of the unit-cell volume) and according to SQUEEZE calculations it is filled with eight highly disordered water molecules of crystallization. The crystals of II are non-porous.

Synthesis and crystallization
All chemicals and solvents used in this work were purchased from Sigma-Aldrich and used without further purification. The complex [Ni(L)](ClO 4 ) 2 was prepared from ethanol solution as described in the literature (Bosnich et al., 1965).
The complex [Ni(L)(Hbtc)Á8H 2 O], (I), was prepared as follows. [Ni(L)](ClO 4 ) 2 (153 mg, 0.33 mmol) and H 3 btc (50 mg, 0.24 mmol) were dissolved in 10 ml of a DMF/H 2 O mixture (4:1 by volume) and the solution was heated at 358 K for 30 h. A small amount of pink needle-like crystals in the form of concretions was formed in a week. These were filtered off, washed with small amounts of methanol and diethyl ether, and dried in air. Yield: 15 mg (10% based on acid). Analysis calculated for C 19 H 44 N 4 NiO 14 : C 37.36, H 7.27, N 9.18%. Found: C 37.52, H 7.31, N 9.15%. Single crystals of I suitable for X-ray diffraction analysis were selected from the sample formed after refrigerating the mother liquor for several days.
Apparently, the complex [Ni(L)(Hbtc)ÁH 2 O], (II), is more thermodynamically stable than I and it was prepared according to similar procedure, except that initially precipitated crystals were left to remain under the mother liquor at ambient temperature. Over ca one week, the needle-like crystals of I dissolved; instead, a precipitate in the form of rhomb-shaped plates was formed and single crystals of II suitable for X-ray diffraction analysis were selected from this reaction mixture. Alternatively, larger amounts of II can be obtained using an analogous procedure but using higher concentrations of the reagents. [Ni(L)](ClO 4 ) 2 (200 mg, 0.44 mmol) and H 3 btc (65 mg, 0.31 mmol) were dissolved in 10 ml of a DMF/H 2 O mixture (4:1 by volume) and the solution was heated at 358 K for 24 h. After cooling of the reaction mixture, the product began to crystallize in several hours in the form of pink plate-like concretions. It was filtered off, washed with small amounts of methanol and diethyl ether, and dried in air. Yield: 38 mg (25% based on acid). Analysis calculated for C 19 H 30 N 4 NiO 7 : C 47.09, H 6.24, N 11.57%. Found: C 47.15, H 6.31, N 11.65%.
Caution! Perchlorate salts of metal complexes are potentially explosive and should be handled with care.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. The H atoms in I and II were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H distances of 0.93 Å   ; software used to prepare material for publication: publCIF (Westrip, 2010).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Ni1 0.69720 (4) 0.55885 (2)    where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.32 e Å −3 Δρ min = −0.43 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.