Crystal structure of the one-dimensional coordination polymer formed by the macrocyclic [Ni(cyclam)]2+ cation and the dianion of diphenylsilanediylbis(4-benzoic acid)

The title coordination polymer consists of parallel zigzag-like chains of [Ni(cyclam)]2+ cations bridged by the dianions of the acid in the axial positions of the trans-NiN4O2 coordination polyhedron. Polymeric chains propagating along the [101] direction are assembled into a three-dimensional network by O—H⋯O hydrogen bonds.

The asymmetric unit of the title compound, catena-poly [[[(1,4,8,11-tetraazacyclotetradecane-4 N 1 ,N 4 ,N 8 ,N 11 )nickel(II)]--4,4 0 -(diphenylsilanediyl)dibenzoato-2 O:O 0 ] sesquihydrate], {[Ni(C 26 H 18 O 4 Si)(C 10 H 24 N 4 )]Á1.5H 2 O} n , consists of the halves of the centrosymmetric macrocyclic cation and the C 2 -symmetric dicarboxylate dianion and of the water molecule of crystallization. The Ni 2+ ion is coordinated by the four secondary N atoms of the macrocyclic ligand characterized by the most energetically favourable trans-III conformation and two mutually trans O atoms of the carboxylate, forming a slightly tetragonally elongated trans-N 4 O 2 octahedron. The crystals are composed of parallel polymeric chains of the macrocyclic cations linked by the anions of the acid running along the [101] direction. Each polymeric chain is bonded to four neighbouring ones via water molecules providing O-HÁ Á ÁO hydrogen bonds to the non-coordinated carboxyl O atoms to form a three-dimensional supramolecular network.

Chemical context
Aromatic carboxylates are the most popular ligands employed as linkers joining metal-containing fragments (secondary building units, SBUs) in the construction of coordination polymers (Rao et al., 2004). This class of hybrid organicinorganic materials possesses great potential for applications in gas storage, separation, catalysis, etc. (MacGillivray & Lukehart, 2014;Kaskel, 2016). At the same time, carboxylate linkers containing a silicon core are still rare objects of investigation, although it is assumed that the presence of these heteroatoms may affect the topology and properties of the resulting coordination polymers, which are known to be rather sensitive to tiny structural variations in the constituting parts. Besides these structural aspects, carboxylate ligands containing heteroatoms are of current interest as precursors for the preparation of structured heteroatom-doped carbonaceous materials possessing excellent electron conductivity, high porosity and diverse applications, including electrocatalysis and energy storage and conversion (Yang et al., 2019;Zhong et al., 2019).
Diphenylsilanediylbis(4-benzoic acid), a dicarboxylate possessing a characteristic bent shape, has been already utilized for the synthesis of coordination polymers with tetranuclear Zn II (Liu et al., 2009) and dinuclear Zn II and Mn II (Turcan-Trofin et al., 2018) SBUs, as well as a copper(II) complex with 1,10-phenanthroline as co-ligand (Cazacu et al., 2014). However, no attempt has been made thus far to combine this linker with macrocyclic complexes, which provide pre-formed SBUs of another type (two vacant trans axial positions in the coordination sphere of the metal ion) with an additional benefit of extremely high thermodynamic stability and kinetic inertness (Melson, 1979;Yatsimirskii & Lampeka, 1985). At the same time, such SBUs have been used successfully for the assembly of a number of coordination polymers (Lampeka & Tsymbal, 2004;Suh & Moon, 2007;Suh et al., 2012;Stackhouse & Ma, 2018), including those with some other Si-containing carboxylates (Gavrish et al., 2020a;Gavrish et al., 2020b).

Structural commentary
The molecular structure of the title compound I is shown in Fig. 1. It represents a one-dimensional coordination polymer built of the centrosymmetric macrocyclic [Ni(L)] 2+ cations coordinated in axial positions by the oxygen atoms of the carboxyl groups of the acid.
The macrocyclic ligand in the complex cation adopts the most abundant energetically favourable trans-III (R,R,S,S) conformation (Bosnich et al., 1965) with almost equal Ni-N bond lengths (Table 1). The five-membered chelate rings are present in gauche and the six-membered in chair conformations. The geometric parameters observed are characteristic of high-spin nickel(II) complexes with 14-membered tetraamine ligands (Lampeka & Tsymbal, 2004). The axial Ni-O bond lengths are somewhat longer than the Ni-N ones resulting in a slight tetragonal distortion of the trans-N 4 O 2 nickel(II) coordination polyhedron. The location of the metal ion on the inversion centre enforces strict planarity of the equatorial Ni(N 4 ) fragment.
The dianion of the acid in complex I possesses intrinsic twofold axial symmetry, with the Si atom lying on the rotation axis. An analogous C 2 -symmetric conformation was found [Cambridge Structural Database (CSD, Version 5.40, last update February 2019;Groom et al., 2016)] for the molecules/ anions of the acid in the structures XOZVIT (Cazacu et al., 2014) and ZIGXEV (Turcan-Trofin et al., 2018). In two cases [XOZWAM (Cazacu et al., 2014) and ZIGXIZ (Turcan-Trofin et al., 2018)], the carboxylate is present in an asymmetric conformation. At the same time, the coordination polymer XOQXIL (Liu et al., 2009) includes dianions of the acid in both C 2 -symmetric and asymmetric conformations. All these data are summarized in Fig. 2, which clearly illustrates the capability of rotation of aromatic rings in the tetraphenylsilane moiety around the Si-C aryl bonds by a wide range of angles. Another feature worth noting is that the symmetric and asymmetric species in fact refer to essentially different types with minor structural variations within each group, with the exception of anion XOQXIL-1.
The carboxyl groups in I are coordinated in a monodentate fashion via the O1 atom. The non-coordinated O2 atom is involved as proton acceptor in strong hydrogen bonding with the NH group of the macrocycle (Fig. 1, Table 2), a situation that is frequently observed in carboxylate complexes of cyclam-like ligands. Almost identical C-O bond lengths [C6-O1 = 1.254 (4) and C6-O2 = 1.260 (4) Å ] support the model of essential electronic delocalization in the carboxylate group. The carboxyl group is tilted with respect to the plane of benzene ring by 23.6 (2) . In general, this angle is prone to large variations, e.g. for the structures presented in Fig. 2 (2) Symmetry code: (i) Àx + 1 2 , Ày + 1 2 , Àz.

Figure 1
The extended asymmetric unit in I showing the coordination environment of the Ni atoms and the atom-labelling scheme (displacement ellipsoids are drawn at the 40% probability level). The atoms obtained by symmetry transformations are shown with 50% transparency. C-bound H atoms are omitted for clarity. Dashed lines represent hydrogen-bonding interactions. [Symmetry codes: (i) Àx + 1 2 , Ày + 1 2 , Àz; (ii) Àx + 1, y, Àz + 1 2 ].

Supramolecular features
The crystals of I are composed of polymeric chains of [Ni(L)] 2+ cations bridged by the carboxylate ligands, which propagate along the [101] direction. These chains have a distinctive zigzag shape with a chain link length (SiÁ Á ÁSi distance) of 17.854 (3) Å and an almost ideal tetrahedral angle (SiÁ Á ÁSiÁ Á ÁSi) of 109.09 (2) (Fig. 3). The nickel(II) cations in a chain are arranged in line with an NiÁ Á ÁNi separation of 14.543 (2) Å .
In the crystal, each such chain is linked to four neighbouring ones due to formation of water-mediated hydrogen bonds between the non-coordinated O2 atoms of the carboxyl group: O2Á Á ÁHO1W-HÁ Á ÁO2 (Table 2). In turn, each O2 atom is involved in hydrogen bonding with two H 2 O molecules [symmetry codes: x, y, z; Àx + 1 2 , y À 1 2 , Àz + 1 2 ], which in conjunction with the N1-HÁ Á ÁO2 hydrogen bond makes it a triple proton acceptor, while the water molecule serves as a proton donor only. Thus, the water molecules of crystallization play a key role in assembling the one-dimensional polymeric chains into a three-dimensional supramolecular network (Fig. 4).

Figure 3
The structure of the polymeric chain in I. C-bound H atoms are omitted for clarity.

Figure 4
The packing in I viewed down the [101] direction with polymeric chains cross-linked by O2Á Á ÁH-O1W-HÁ Á ÁO2 hydrogen bonds (dotted lines) to form a three-dimensional supramolecular network. C-bound H atoms are omitted for clarity. Single crystals of I in the form of light-yellow prisms suitable for X-ray diffraction analysis were obtained analogously using ca 10 times lower concentration of reagents.
Safety note: 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 3. All H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H distances of 0.93 (ring H atoms) or 0.97 Å (open-chain H atoms), an N-H distance of 0.98 Å and an aqua O-H distance of 0.85 Å with U iso (H) values of 1.2 or 1.5U eq times that of the parent atoms. Since the water molecule of crystallization at full occupancy exhibited unrea-sonably high displacement ellipsoids, its occupancy parameter was reduced to 75%.

µ-4,4′-(diphenylsilanediyl)dibenzoato-κ 2 O:O′] sesquihydrate]
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.51 e Å −3 Δρ min = −0.51 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (