Crystal structure of [{[Ni(C10H24N4)][Ni(CN)4]}·2H2O] n , a one-dimensional coordination polymer formed from the [Ni(cyclam)]2+ cation and the [Ni(CN)4]2– anion

The title coordination polymer consists of parallel linear chains built up of macrocyclic cations possessing a slightly tetragonally distorted NiN6 octahedral coordination geometry formed by four N atoms of the azamacrocyclic ligand in the equatorial plane and two trans N atoms of the cyanide groups of the bridging tetracyanonickelate anion in the axial positions. In the crystal, two independent [1 0] polymeric chains are cross-linked by N—H⋯Ow (w = water) and Ow—H⋯Nc (c = cyanide) hydrogen bonds into a three-dimensional network.

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)]--cyanido-2 N:C-[bis(cyanido-C)nickel(II)]--cyanido-2 C:N] dihydrate], {[Ni 2 (CN) 4 (C 10 H 24 N 4 )]Á2H 2 O] n or [{[Ni(C 10 H 24 N 4 )][Ni(CN) 4 ]}Á2H 2 O] n , consists of a pair of crystallographically non-equivalent macrocyclic cations and anions. The nickel(II) ions (all with site symmetry 1) are coordinated by the four secondary N atoms of the macrocyclic ligands, which adopt the most energetically stable trans-III conformation, and the mutually trans N atoms of the tetracyanonickelate anion in a slightly tetragonally distorted NiN 6 octahedral coordination geometry. The [Ni(CN) 4 )] 2anion exhibits a bridging function, resulting in the formation of parallel polymeric chains running along the [110] direction. The water molecules of crystallization play a pivotal role in the three-dimensional supramolecular organization of the crystal. Acting as acceptors, they form N-HÁ Á ÁO w (w = water) hydrogen bonds with the secondary amino groups of the macrocycles, forming layers oriented parallel to the (001) plane. At the same time, as donors, they interact with the non-coordinated cyano groups of the anion via O w -HÁ Á ÁN c (c = cyanide) hydrogen bonds, giving two-dimensional layers oriented parallel to the (100) plane and thus generating a three-dimensional network.

Chemical context
Transition-metal complexes of tetraazamacrocyclic ligands, in particular of 1,4,8,11-tetraazacyclotetradecane (cyclam, L), have been intensively studied for decades. This is explained by their unique properties, in particular, exceptionally high thermodynamic stability, kinetic inertness and the ability to stabilize uncommon oxidation states of coordinated metals (Melson, 1979;Yatsimirskii & Lampeka, 1985). Because of their conformational rigidity during chemical transformation (preservation of two vacant or labile trans axial positions in the coordination sphere of the metal ion), these complexes are also promising secondary building units for the construction of metal-organic frameworks (MOFs) (Lampeka & Tsymbal, 2004;Suh & Moon, 2007;Suh et al., 2012;Stackhouse & Ma, 2018), which possess great potential for applications in different areas including gas storage, separation, catalysis, sensing, etc (MacGillivray & Lukehart, 2014;Kaskel, 2016).
Cyanometallate anions refer to a type of bridging ligands for the creation of MOFs of different topologies possessing promising magnetic and electronic properties (Ohkoshi et al., ISSN 2056-9890 2019). Among such linkers, the tetracyanonickelate(II) dianion has attracted less attention compared to hexa-and octacyanometallates and only one work describing the structure of the coordination polymer formed by the metal(cyclam) complex and this anion, i.e., {Cu(L)[Ni(CN) 4 ]} n , has been published to date (Č erná k et al., 2010). Interestingly, despite the diamagnetic nature of the bridging fragment, this complex displays a weak antiferromagnetic exchange coupling between the paramagnetic copper(II) centres.

Structural commentary
The molecular structure of I is shown in Fig. 1 The location of the metal ions on inversion centres enforces strict planarity of the Ni(N 4 ) and Ni(C 4 ) coordination moieties. The macrocyclic ligand in the complex cations adopts the most common and energetically favorable 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 (bite angles ca 85.5 ) and the six-membered in chair (bite angles ca 94.5 ) conformations (Table 1). The geometric parameters observed are characteristic of high-spin d 8 nickel(II) complexes with macrocyclic 14-membered tetraamine ligands (Lampeka & Tsymbal, 2004;Tsymbal et al., 2021). The axial Ni-N(CN) bond lengths are somewhat longer than the Ni-N(amine) ones, resulting in a slight tetragonal distortion of the trans-NiN 4 N 2 coordination polyhedron.
The Ni-C-N angles in the anion deviate only slightly (less than 4 ) from linearity. In I, each tetracyanonickelate unit uses two trans cyanide groups for coordination to two macrocyclic moieties in a bent fashion [Ni-N-C = 166.1 (4) ], giving rise to a linear polymeric chain, whereas the two remaining trans CN À groups are monodentate. The adjacent NiÁ Á ÁNi distance in the chain is 5.0558 (5) Å , and the shortest interchain NiÁ Á ÁNi distance is 6.6159 (5) Å . 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). C-bound H atoms are omitted for clarity. Dotted lines represent hydrogen-bonding interactions. Symmetry codes: (i) Àx + 1, Ày + 1, Àz; (ii) Àx, Ày + 2, Àz; (iii) x À 1, y + 1, z; (iv) Àx + 1, Ày, Àz + 1; (v) Àx, Ày + 1, Àz + 1.  Table 2 Hydrogen-bond geometry (Å , ).  (7)  175 crystallization play a key role in assembling them into a threedimensional supramolecular network. In particular, serving as the acceptor for N-HÁ Á ÁO hydrogen bonds arising from the secondary amino groups of different macrocyclic ligands in the crystallographically equivalent chains (O1W for Ni1/Ni3, O2W for Ni2/Ni4), the water molecules link them in two-dimensional layers oriented parallel to the (001) plane (Table 2, Fig. 2a). At the same time, acting as the donors in O-HÁ Á ÁN hydrogen-bonding interactions with the nitrogen atoms of the non-coordinating cyanide groups of the anions belonging to crystallographically non-equivalent polymeric chains, they form two-dimensional layers oriented parallel to the (100) plane (

Synthesis and crystallization
All reagents and solvents used in this work were analytical grade and were used without further purification. The macrocyclic nickel(II) complex Ni(L)(ClO 4 ) 2 was prepared according to procedures described previously (Barefield et al., 1976). Analysis calculated for C 14 H 28 N 8 Ni 2 O 2 : C,36.72;H,6.16;N,24.47%. Found: C,36.62;H,6.26;N,24.19%. Single crystals suitable for X-ray diffraction analysis were selected from the sample resulting from the synthesis. 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 View of the sheets of polymeric chains formed due to the hydrogen-bond acceptor (a) and donor (b) properties of the water molecules of crystallization. The macrocyclic ligands in the crystallographically nonequivalent nickel ions are shown in violet (Ni1/Ni3) and green (Ni2/Ni4) colors.   [[[(1,4,8,11-tetraazacyclotetradecane-κ 4 N 1 ,N 4 ,N 8 ,N 11 )

κC)nickel(II)]-µ-cyanido-κ 2 C:N] dihydrate]
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 1.31 e Å −3 Δρ min = −0.42 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