Crystal structures of the complexes containing macrocyclic cations [M(cyclam)]2+ (M = Ni, Zn) and tetraiodidocadmate(2–) anion

The isostructural compounds I and II are composed of planar macrocyclic cations [M(cyclam)]2+ and the tetrahedral anion [CdI4]2−, which plays a purely charge-compensation function in the NiII complex I and is axially coordinated via the iodide atom in the ZnII complex II. In both complexes, as a result of N–H⋯I hydrogen bonding, the alternating cations and anions form chains running along the b-axis direction that are arranged into di-periodic sheets oriented parallel to the (101) and ( 01) planes.

The asymmetric units of the isostructural compounds (1,4,8,11-tetraazacyclotetradecane-� 4 N)nickel(II) tetraiodidocadmate(II), [Ni(C 10 H 24 N 4 )][CdI 4 ] (I), and triiodido-1� 3 I-�-iodido- (1,4,8,11-tetraazacyclotetradecane-2� 4 N)cadmium(II)zinc(II), [CdZnI 4 (C 10 H 24 N 4 )] (II) (C 10 H 24 N 4 = 1,4,8,11-tetraazacyclotetradecane, cyclam, L), consist of the centrosymmetric macrocyclic cation [M(L)] 2+ [M = Ni II or Zn II ] with the metal ion lying on a twofold screw axis, and the tetraiodocadmate anion [CdI 4 ] 2À located on the mirror plane.In I, the anion acts as an uncoordinated counter-ion while in II it is bound to the Zn II atom via one of the iodide atoms, thus forming an electroneutral heterobimetallic complex [Zn(L)(CdI 4 )].The Ni II and Zn II ions are coordinated in a square-planar manner by the four secondary N atoms of the macrocyclic ligand L, which adopts the most energetically stable trans-III conformation.The [CdI 4 ] 2À anions in I and II are structurally very similar and represent slightly deformed tetrahedrons with average Cd-I bond lengths and I-Cd-I angles of ca 2.79 A ånd 109.6 � , respectively.The supramolecular organization of the complexes under consideration in the crystals is very similar and is determined by the hydrogen-bonding interactions between the secondary amino groups of the ligand L in the [M(L)] 2+ cations and iodide atoms of the [CdI 4 ] 2À anion.In particular, the alternating cations and anions form chains running along the baxis direction that are arranged into di-periodic sheets oriented parallel to the (101) and (101) planes.Because both kinds of sheets are built from the same cations and anions, this feature provides the three-dimensional coherence of the crystals of I and II.cations formed by the tetraazamacrocyclic ligand cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane, C 10 H 24 N 4 , L), which is the most suitable for binding of 3d transition-metal ions (Yatsimirskii & Lampeka, 1985) were never exploited in this respect, though the fruitfulness of such an approach was shown formerly during the preparation of iodoplumbate hybrids containing the [Ni(TMC)] 2+ cation (TMC = 1,4,8,11tetramethyl-1,4,8,11-tetraazacyclotetradecane) (Zhang et al., 2019).
The present work describes the preparation and structural characterization of two representatives of iodocadmate hybrids formed under the structure-directing influence of the Ni II and Zn II cyclam complexes, namely (1,4,8,11-

Structural commentary
The asymmetric units of the isostructural compounds I and II involve the centrosymmetric macrocyclic cation [M(L)] 2+ [M = Ni II and Zn II , respectively] with the metal ions lying on a twofold screw axis and the tetraiodocadmate anion [CdI 4 ] 2À .The latter acts as an uncoordinated counter-ion in I but is coordinated to the Zn II in II, thus forming an electroneutral heterobimetallic complex [Zn(L)(CdI 4 )] in which the I1 atom plays a � 2 -bridging function (Fig. 1).The Cd1, I2 and I3 atoms of the tetraiodocadmate anions in I and II are located on the mirror plane.The [CdI 4 ] 2À moieties as a whole represent slightly deformed tetrahedrons with Cd-I bond lengths and I-Cd-I angles varying in the narrow ranges not exceeding 0.08 A ˚and 8.2 � , respectively (Table 1).
The Ni II ion in I is coordinated by the four secondary N atoms of the macrocycle L (Fig. 1a) and the centrosymmetry of the cation ensures the strict planarity of the Ni(N 4 ) coordination environment.The Ni-N bond lengths of ca 1.94 A ˚(Table 1) are typical of four-coordinated low-spin square-planar d 8 Ni II complexes with macrocyclic 14-membered tetraamine ligands and are much shorter than those (ca 2.05 A ˚) observed in the high-spin six-coordinated tetragonalbipyramidal macrocyclic species (Yatsimirskii & Lampeka, 1985).The macrocyclic ligand L in the complex cations of I adopts the most common and energetically favorable trans-III (R,R,S,S) conformation (Bosnich et al., 1965a;Barefield et al., 1986).Its five-and six-membered chelate rings are present in gauche and chair conformations with the bite angles of ca 87 and 93 � , respectively (Table 1).
The bifurcating hydrogen-bonding interaction between the I1 atom of the anion and the secondary amino groups of the macrocyclic ligand of the cation as well as the N1-H1� � �I2 contact (Fig. 1a, for parameters of the hydrogen bonds see Table 2) in I arrange the [CdI 4 ] 2À fragment in such a way that its I1 atom is located just above the Ni(N 4 ) plane in a potential axial position of the coordination sphere of the Ni II ion (the deviation of the mean angles N-Ni1-I1 from 90 � do not exceed 4 � ).However, the very long distance between the metal ion and this iodide [3.3618 (3) A ˚] allows a coordinative interaction between them to be excluded.This is in agreement with the Ni-N bond lengths typical of the square-planar Ni II species (see Database survey).

I II
The molecular structure of II is shown in Fig. 1b.Similarly to the Ni II atom in I, the Zn II ion in the macrocyclic cation is coordinated by the four secondary N atoms of the macrocycle L but is displaced by 0.336 (1) A ˚from the N 4 plane towards the apically coordinated I1 atom.Because the [Zn(L)] unit is centrosymmetric, the metal ion was found to be disordered around a center of inversion and thus was refined with half occupancy.
The weak coordination of the iodide atom in the axial position of the macrocyclic cation (Zn1-I1 bond length ca 2.9 A ˚, Table 1) is reinforced by the hydrogen-bonding interaction N1-H1� � �I2 (Table 3) and results in the deformed square-pyramidal coordination environment of the Zn II ion.Though the Zn-I-Cd angle [119.79 (4) � ] and the mean Ni� � �I-Cd angle [120.13 (2) � ] are practically identical, the displacement of the Zn II ion from the mean N4 plane of the macrocycle and a shorter distance between Zn II and the apical iodide than for Ni II leads to the reduction of the M II � � �Cd II distance in II as compared to I [5.332 (1) and 4.945 (1) A ˚, respectively].
Similar deformed square-pyramidal coordination polyhedra (in some cases with disordering of the metal ion) have also been observed in several other five-coordinate complexes containing the [Zn(L)X] moiety (X = axial ligand) but were never found in complexes involving the [Ni(L)] fragment (see Database survey).The reasons for such differences have been considered in detail during analysis of the structure of the fivecoordinate macrocyclic Zn II complex with X = tetrathioantimonato axial ligand and were explained mainly by preferable ligand field stabilization energy for the d 8 Ni II electronic configuration as compared that for d 10 Zn II (Na ¨ther et al.,  2022).
In general, the structure of the coordination polyhedron of the Zn II ion in II has much in common with that discussed recently in detail for the [Zn(L)I]I 3 complex (Gavrish et al., 2021).In both compounds, the macrocyclic ligand L adopts the energetically favorable trans-III R,R,S,S) conformation (Bosnich et al., 1965a;Barefield et al., 1986), though with some peculiarities connected with the displacement of the Zn II ion from the mean N 4 plane of the macrocycle donor atoms toward the coordinated iodide ion [0.336 (1) A ˚in II and 0.381 A ˚in triiodide complex].In particular, the fivemembered rings in II adopt gauche-envelope conformations with very similar bite angles [average value ca 83.5 � (Table 1)].The six-membered chelate rings in II are present in a chair conformation and differ from each other more significantly, both from the point of view of the Zn-N bond lengths and bite angles.So, the chelate ring in which the hydrogen atoms of the secondary amino groups have the same orientation as the displacement of the metal ion is characterized by smaller values of the Zn-N coordination bond lengths (average value 2.041 A ˚) and bite angle (ca 90 � ) as compared to the ring with the opposite orientation of the hydrogen atoms (average value 2.163 A ˚and ca 97 � , respectively; Table 1).Similarly to [Zn(L) I]I 3 , a flattening of the former six-membered chelate ring at the Zn side is observed.
It should also be mentioned that the Zn-I1 distance to the symmetry-related I1(À x + 1, À y + 1, À z + 1) atom on the other side of the N 4 plane is 3.579 (1) A ˚and this value seems to be too long for it to be considered as a coordination bond.This means that each component of the disordered Zn II ion is truly five-coordinate.Therefore, the connectivity within the crystal is not uniquely defined and, in principle, the [CdI 4 ] 2À anions can interact either with one or two [Zn(L)] 2+ cations (Fig. 2).

Supramolecular features
The N1-H� � �I2 interactions in both I and II together with either N1-H/N2-H� � �I1 hydrogen-bonding in I or Zn-I1 coordination in II determine close similarity in the mutual spatial arrangements of the cation and anion in both compounds (Fig. 1).As expected, the supramolecular organization of the complexes under consideration is also very similar and is determined by the hydrogen-bonding interactions between the secondary amino groups of the ligand L in

Figure 2
View of the two possible coordination modes of the [CdI 4 ] 2À anion in II.

Figure 3
Nearest surrounding of the macrocyclic cation (a) and the anion (b) in I formed by N-H� � �I hydrogen bonding (black dashed lines).Symmetry codes: (i) the [M(L)] 2+ cations as the proton donors and I2 and I3 atoms of the [CdI 4 ] 2À anions as the proton acceptors (Tables 2 and  3).Therefore, only complex I will be used for further illustration.
As a result of the hydrogen bonds N1-H� � �I2 and N2-H� � �I3, each macrocyclic cation [M(L)] 2+ in I and II is surrounded by four [CdI 4 ] 2À anions (Fig. 3a).In turn, each of these iodide atoms forms two bonds with different macrocyclic cations, thus resulting in binding of four cations by a single anion (Fig. 3b).
In the crystal, the alternating cations and anions form chains running along the b-axis direction that are arranged in twodimensional sheets oriented parallel to the ( 101) and ( 101) planes (Fig. 4).Since these sheets are built from the same cations and anions, this feature provides the three-dimensional coherence of crystals I and II.

Database survey
A search of the Cambridge Structural Database (CSD, version 5.44; Groom et al., 2016) indicated that more than 20 compounds containing low-spin square-planar [Ni(L)] 2+ cation have been characterized crystallographically.For all of them, relatively short Ni-N bond lengths in the equatorial planes typically not exceeding 1.97 A ˚and the absence of potential donor atoms in the axial positions of the Ni II ion at distances shorter than 3.2 A ˚are inherent.Among them, several complexes containing a non-coordinated iodide anion as the counter-ion have also been described [CAFHUM (Prasad & McAuley, 1983) In eight of the more than forty compounds containing the [Zn(L)] 2+ cation that are present in the CSD, the Zn II ion is five-coordinated in a square-pyramidal manner with different axial ligands including hexacyanoferrate(III) (NEPYUC; Colacio et al., 2001), thiolate (ICUFES and ICUFIW; Notni et al., 2006), thioantimonate [GALPUI (Danker et al., 2021) and KECVIB (Na ¨ther et al., 2022)] as well as iodide [HEGNOW (Porai-Koshits et al., 1994); JALBIL and JALBOR (Gavrish et al., 2021)].In all these five-coordinate complexes, the Zn II atom is displaced from the mean N 4 plane of the donor atoms of the macrocycle toward the axial ligand.Additionally, in some compounds (GALPUI, KECVIB and JALBOR), similar to II, some kind of disorder of the metal ion is also present.The Zn-I axial bond lengths of 2.66-2.77A ˚observed in the iodide complexes are shorter than that found in II [2.8957 (11) A ˚].
A search of the CSD gives more than 90 hits related to the structural characterization of compounds containing the [CdI 4 ] 2À anion.Like I, the majority of them are ionic species in which the charge of the anion is compensated by organic (ca 60 hits) or metalocomplex (ca 30 hits) cations.Besides, similarly to II, in three compounds that include the complex cations formed by Cd II [ITAFAL (Satapathi et al., 2011) and MATKUO (Seitz et al., 2005)] or Cu II (NEZXAS; Yu et al., 2007), the tetraiodocadmate anion displays the � 2 -bridging function with the M-I coordination bonds shorter than 3.0 A (ca 2.83, 2.97 and 2.76 A ˚, respectively).In general, regardless the nature of the cation and whether the [CdI 4 ] 2À moiety is coordinated to the M II ion, it demonstrates a slightly distorted tetrahedral shape similar to that observed in I and II.

Synthesis and crystallization
All chemicals and solvents used in this work were purchased from Sigma-Aldrich and were used without further purification.The complex [Ni(L)](ClO 4 ) 2 was prepared from ethanol solutions as described in the literature (Bosnich et al., 1965b).The complex [Zn(L)](ClO 4 ) 2 was prepared analogously by mixing of equimolar amounts of L and zinc perchlorate hexahydrate in ethanol.
Alternatively, complex I can be obtained using the chloride salt of Cd II .To 50 ml of an aqueous solution of CdCl 2 (20 mg, 0.11 mmol) were added 0.4 ml of 57% aqueous HI and this mixture was added dropwise to a solution of [Ni(L)](ClO 4 ) 2 (50 mg, 0.11 mmol) in 40 ml of an EtOH/H 2 O mixture (3:1 by volume).Brown crystals formed in 5 days, were filtered off, washed with ethanol and dried in air.Yield: 35 mg (36%).Analysis calculated for C 10 H 24 CdI 4 N 4 Ni: C 13.66, H 2.75, N 6.37%.Found: C 13.78, H 2.60, N 6.42%.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. 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 methylene H atoms of 0.97 A ˚(in I) or 0.99 A ˚(in II) and N-H distance of 0.91 A ẘith U iso (H) values of 1.2 U eq of the parent atoms.(Rigaku OD, 2022), SHELXT (Sheldrick, 2015a), SHELXL2018/3 (Sheldrick, 2015b), Mercury (Macrae et al., 2020) and publCIF (Westrip, 2010).

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.

Figure 1
Figure 1View of the molecular structures of I and II showing the atom-labeling scheme, with displacement ellipsoids drawn at the 30% probability level.C-bound H atoms are omitted for clarity.Hydrogen-bonding interactions are shown as dotted lines.Symmetry codes: (i) À x + 1, À y + 1, À z + 1; (ii) x, À y + 3 2 , z.

Figure 4
Figure 4 Fragment of the two-dimensional sheet in I parallel to the (101) plane as viewed along the c axis.Iodide atoms involved in the formation of sheets parallel to the (101) plane are shown in red.Hydrogen-bonding interactions are shown as dotted lines.

Table 4
Experimental details.
Computer programs: CrysAlis PRO atomic coordinates and isotropic or equivalent isotropic displacement parameters(Å 2 )