Crystal structures of Zn(cyclam)I2 (second monoclinic polymorph) and Zn(cyclam)I(I3)

The crystal of the first title compound contains five-coordinate [Zn(L)I]+ (L = cyclam) cations and non-coordinated iodide anions; the extended structure is consolidated by N—H⋯I and N—H⋯(I,I) hydrogen bonds. The crystals of the second title compound consist of chains of [Zn(L)I]+ units and triiodide counter-ions but without significant hydrogen-bonding interactions.


Chemical context
The 14-membered tetraazamacrocycle 1,4,8,11-tetraazacyclotetradecane (C 10 H 24 N 4 , cyclam, L) is one of the most useful and widely studied ligands because of a number of unique properties, such as exceptionally high thermodynamic stability, kinetic inertness and unusual redox properties inherent to its complexes with transition-metal ions (Melson, 1979;Yatsimirskii & Lampeka, 1985). Typically, cyclam coordinates to the metal ion by its four N atoms in a planar manner, leaving two vacant trans binding sites in the coordination sphere for additional ligands, including halide anions as an important class. To date, a number of complexes of [M(L)] 2+ cations (M = Cu II , Ni II , Zn II ) with halides X À (X = Cl, Br, I) have been reported (Ito et al., 1984;Adam et al., 1991;Porai-Koshits et al., 1994;Chen et al., 1996;Makhaev et al., 1996;Ha, 2017;Horii et al., 2020).
Typically, the compounds under consideration are prepared by the direct reaction of MX 2 salts with L. We were interested in the development of alternative methods of synthesizing zinc(II) iodide compounds by anion exchange, starting from the initially formed acetate or nitrate species. It was found in the course of this investigation that precipitation of Zn(L)I 2 from the in situ formed acetate complex by potassium iodide ISSN 2056-9890 in methanol solution occurs slowly (over several days) and results in the formation of the colorless compound I, the structure of which is different from that described previously (Porai-Koshits et al., 1994). When the metathesis reaction was carried out in aqueous solution, a small amount of the iodide/ triiodide salt (compound II) was obtained in the form of intensely colored brown crystals. The lattice parameters for this compound were reported by Heinlein & Tebbe (1985) in an alternate setting of the unit cell (see Database Survey) but no atomic coordinates were established. Here, we report the crystal structures of these two compounds, namely, iodido- (1,4,8,11-tetraazacyclotetradecane-4 N 1 N 4 N 8 N 11 )zinc(II) iodide, [ZnI(L)]I, I and iodido- (1,4,8,11-tetraazacyclotetradecane-4

Structural commentary
The molecular structure of I is shown in Fig. 1. It represents the square-pyramidal macrocyclic [Zn(L)I] + cation with one iodide anion coordinated in the axial position of the zinc(II) ion, while the second iodide anion acts as a counter-ion.
Thus, I belongs to a rather limited family of [Zn(L)] compounds in which the Zn II ion is five-coordinated. Other distinct examples are complexes with thiolate (Notni et al., 2006) and hexacyanoferrate(3-) (Colacio et al., 2001) axial ligands. In the majority of compounds, the Zn II ion is sixcoordinated. Analogously to these complexes, the macrocyclic ligand in I adopts the most energetically favorable trans-III (R,R,S,S) conformation (Bosnich et al., 1965).
The coordination polyhedron of the [Zn(L)I] + cation in I is characterized by a large deviation [0.4412 (14) Å ] of the metal ion from the mean N 4 plane of donor atoms toward the coordinated iodide ion and this results in conformational peculiarities, distinguishing it from planar tetra-or hexacoordinated species. In particular, this deviation results in non-equivalence of the six-membered chelate rings in chair conformations with syn and anti directivity of the NHhydrogen atoms with respect to the displacement of the metal ion. In the first case, the ring becomes more flattened at the Zn side, and in the second more puckered. Simultaneously, the five-membered rings in I adopt gauche-envelope conforma- View of the molecular structure of I 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 dashed lines.

Figure 2
View of the molecular structure of II showing the atom-labeling scheme with displacement ellipsoids drawn at the 30% probability level. C-bound H atoms are omitted for clarity. Symmetry codes: (i) Àx + 3 2 , Ày + 3 2 , Àz + 1 2 ; (ii) Àx + 3 2 , y À 1 2 , Àz + 1 tions (one of the carbon atoms lies almost in the N-Zn-N plane) in contrast to the symmetric gauche conformations in planar structures. As expected, the bite angles in the five-membered chelate rings in I (ca 82. The molecular structure of compound II is shown in Fig. 2. In this case the [Zn(L)] unit is centrosymmetric but the zinc(II) ion is disordered over two positions with site occupancies of 50% constrained by symmetry with a Zn1Á Á ÁZn1 i distance of 0.810 (3) Å [symmetry code: (i) Àx + 3 2 , Ày + 3 2 , Àz + 1 2 ]. Two crystallographically non-equivalent, non-coordinated centrosymmetric triiodide anions serve as counter-ions, with I2 and I4 occupying the inversion centers.
The structural characteristics of the [Zn(L)I] + unit in II are in general agreement with those described above for I, with the deviation of the zinc(II) ion from the mean N 4 plane being 0.381 (2) Å . The 'syn' and 'anti' six-membered chelate rings are characterized by even higher divergences in their bite angles as compared to I (10.5 and 6.8 , respectively, Table 1). The five-membered rings in II are also present in gaucheenvelope conformations. A notable distinction in II is the considerable difference of the Zn-N bond lengths in the 'syn' and 'anti' six-membered chelate rings [average values = 2.01 (1) and 2.20 (2) Å , respectively], while in I this difference is only 0.015 Å .

Figure 4
The structure of the hydrogen-bonded layer parallel to the ab plane in I. Hydrogen-bonding interactions are shown as dashed lines.

Figure 3
The packing in I viewed down the b-axis direction. Hydrogen-bonding interactions are shown as dashed lines.

Figure 5
The structure of the hydrogen-bonded layer parallel to the (101) plane in I. Hydrogen-bonding interactions are shown as dashed lines.
the existence of such hydrogen-bonded layers parallel to the (101) plane is not so evident, one of these sheets in Figs. 3 and 4 is highlighted in dark green.

Database survey
In the overwhelming majority of cases, these complexes form monoclinic (space group P2 1 /c or P2 1 /n) molecular crystals with the same structural motif: the complex moieties form infinite chains, in which they are joined by the pairs of N-HÁ Á ÁX hydrogen bonds between the NH group of the macrocycle and the coordinated halide ion. On the other hand, in the case of the nickel(II), two other polymorphs of the iodide salt are known. These are also chain structures; however, one of the iodide anions is not coordinated [CAFHUM (Prasad & McAuley, 1983) and JIZTUH05-08 (Horii et al., 2020)]. The peculiarity, characteristic only of zinc(II) complexes, is that quite similar to the situation observed in II, the metal ion is disordered over two positions. It should also be noted that a degree of pyramidalization of the Zn(N 4 ) chromophore progressively increases on going from Cl to I (the deviation of the Zn II ion from the mean N 4 plane is 0.237, 0.322 and 0.385 Å , respectively) and the conformations of the chelate rings and their bite angles demonstrate systematic trends consistent with this variation. The structure of the complex [Zn(L)I]I 3 is also mentioned (DEHVOB; Heinlein & Tebbe, 1985), but without atomic coordinates. The reported unit-cell parameters (space group C2/m; a = 19.189, b = 12.615, c = 10.072 Å ; = 120.65 ) represent an alternative setting of the I2/m unit cell found here for II: the matrix 0 0 1 / 0 1 0 / À1 0 1 transforms the DEHVOB cell to that of II.

Synthesis and crystallization
All chemicals and solvents used in this work were purchased from Sigma-Aldrich and were used without further purification.
To prepare I, a solution of 48 mg (0.240 mmol) of cyclam in 2 ml of MeOH was added to a solution of 50 mg (0.228 mmol) of Zn(CH 3 CO 2 ) 2 Á2H 2 O in 2 ml of MeOH and the mixture was heated at ca 333 K for 10 h. After cooling, a solution of 0.6 g of KI in 4 ml of MeOH was added and the mixture was left at room temperature. After one week, colorless prismatic crystals formed were filtered off, washed with MeOH and dried in air. Yield: 79 mg (67%). Analysis calculated for C 10 H 24 N 4 Zn 1 I 2 : C 23.12; H 4.66; N 10.78%. Found: C 22.98; H 4.72; N 10.63%. Single crystals of I in the form of colorless prisms suitable for X-ray diffraction analysis were picked from the sample resulting from the synthesis.
Crystals of II were obtained in an experiment when the precipitation of the product was attempted in aqueous solu- The packing in II viewed down the a-axis direction. C-bound H atoms are omitted for clarity.

Figure 6
The arrangement of [Zn(L)I] + cations along the b-axis direction in II. Cbound H atoms are omitted for clarity.
tion. After addition of the solution of 0.5 g of KI in 0.5 ml of H 2 O to the solution of the nitrate salt of the macrocyclic cation [obtained in situ from 50 mg (0.25 mmol) of cyclam and 75 mg (0.25 mmol) of Zn(NO 3 ) 2 Á6H 2 O] in 2 ml of H 2 O, a white precipitate formed (ca 92 mg), which was filtered off and the mother liquor was left exposed to the air. After several days, a small quantity of brown crystals of II had formed, which were picked for crystallographic investigation.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All of the H atoms in I and II were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H = 0.97 Å and N-H = 0.98 Å with U iso (H) values of 1.2U eq of the parent atoms.  Extinction correction: SHELXL2018/3 (Sheldrick 2015b), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.00134 (7) 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 I1 0.16199 ( where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 1.86 e Å −3 Δρ min = −2.20 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. Refinement. Refined as a 2-component twin.

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