Crystal structures of two nickel(II) macrocyclic salts: (5,7,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)nickel(II) bis(perchlorate) monohydrate and (5,7,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)nickel(II) dibromide trihydrate

The crystal structure of the perchlorate salt of a cis-hexamethyl-substituted Ni-14 macrocycle contains two diastereomeric macrocyclic cations in the asymmetric unit, one with two NH protons on each side of the cation, and the other with all four NH protons on the same side. The latter diastereomer is also found in the crystal structure of a bromide trihydrate salt of the same Ni-14 macrocycle.


Chemical context
Reports of the formation of cyclic Schiff base-amine complexes of Ni by condensation of acetone with tris(ethylenediamine)nickel(II) salts and their reduction to 14membered macrocyclic tetraamine complexes (Curtis, 1960(Curtis, , 1964 led to extensive research on these and similar complexes in the 1960s and 1970s in the hope of using such metaltemplate reactions in chemical synthesis and of understanding the role of macrocyclic ligands in metalloproteins such as hemoglobin. Their chemical inertness enables chemical reactions of the ligand without losing stereochemistry of the N atoms (Busch, 1978) and allows characterization of numerous possible isomers (Warner & Busch, 1969). Crystal structures of isomers of the macrocyclic nickel complexes continue to appear (e.g. Shi et al., 2010;Curtis et al., 2016). The major product of the condensation referred to above is a 5,5,7,12,12,4,8,11, ion, where the dimethyl-substituted C atoms are trans to each other, and most chemical and structural studies have been concerned with these compounds and The perchlorate anions and water molecule in the asymmetric unit of double salt I, showing their relationship with the cations, and hydrogen bonds formed. The disordered ClO 4 À (2) anion does not appear to form any hydrogen bonds. Displacement ellipsoids are drawn at the 50% probability level.

Figure 1
The [Nime 6 cyclam] 2+ cations in the asymmetric unit of the double salt I. Displacement ellipsoids are drawn at the 50% probability level. The cation centered on Ni1 is structure Ia in the text, and the other cation is Ib.

Figure 3
Projection down the a axis for the double salt, I, showing the hydrogenbonded network extending along the c-axis direction. Ions and the water molecule in the asymmetric unit are in bold.

Figure 4
The [Nime 6 cyclam] 2+ cation in the macrocycle bromide salt II. Displacement ellipsoids are at the 50% probability level. are in the chair form, and all singly substituted methyl groups are in the equatorial position. In the reference molecule for Ia there are two NH atoms above and two below the N 4 plane, designated as uudd, in an RRSS configuration, whereas cations Ib and II are diastereomers of Ia, with all four NH atoms lying on the same side of the molecule, uuuu, and the N atoms in an RSRS configuration. Cation Ia is roughly planar in overall shape, whereas the N-H geometry in Ib and II makes the cations in these structures more bowl shaped. The configurational differences at N appear to affect the Ni-N bond lengths slightly: the mean Ni-N distance in Ia is 1.952 (2) Å while that for Ib and II is 1.928 (2) Å .
The conformations of the five-membered chelate rings in the reference cations shown in the scheme are on the left and on the right for Ia, and on the right and on the left for Ib and II. (Mirror-related cations are present in both crystals.) The twists of these five-membered rings necessarily differentiate between the top and bottom six-membered chelate rings in Ib and II, whereas this is not the case in Ia. In diastereomers Ib and II, the top plane (N4, C5, C7, N8) is bent at a less steep angle to the NiN 4 coordination plane than the bottom plane (N11, C12, C14, N1) (add 20 to atom numbers for structure Ib) and the outer C atoms C6 and C13 are at widely different distances from the NiN 4 plane. Thus in Ib and II, the angles between the NiN 4 plane and the N 2 C 2 plane of the top chelate ring are 29.6 (1) and 31.7 (3) , respectively, while corresponding angles for the bottom rings are 52.7 (2) and 57.1 (2) . The top outer carbon C6 is 0.317 (6) Å from the N 4 plane in Ib and 0.407 (10) Å in II, while the corresponding distances for the bottom outer atom C13 are respectively 1.176 (5) and 1.314 (11) Å . The Ni coordination geometry reflects this difference between the top and bottom of the molecule, with the top N4-Ni-N8 angle opened out to 94.58 (12) in Ib and 94.79 (19) in II, compared with bottom angles N1-  , respectively. The five-membered chelate ring angles at the Ni atom,average 88.48 (16) in these two structures.
Molecule Ia is less-buckled, with angles between the N 4 plane and central planes of the chelate chairs more nearly equal, at 27.6 (2) for the top chair and 31.9 (2) for the bottom, and outer C atom distances from the N 4 plane of 0.250 (6) Å for C6 at the top, and À0.389 (6) for C13 at the bottom. The Ni coordination plane is more nearly symmetrical, with six-membered chelate angles N4-Ni1-N8 of 93.49 (14) (top) and N1-Ni1-N11 of 92.88 (13) (bottom), and five-membered chelate angles averaging 86.87 (13) , somewhat smaller than for Ib and II.
In both of the Ib and II cations, hydrogen bonding of an anion or of a solvent molecule brings an O atom close to the axial direction of the Ni atom on the same side of the cation as the four NH bonds, though at distances too long to be regarded as due to Ni-O bonding. In Ib, perchlorate atom O31 is at 2.799 (3) Å from atom Ni2, while in II, water molecule O1 is at 2.863 (10) Å from the Ni atom.

Supramolecular features
Details of hydrogen bonding are given in Tables 1 and 2. The N-H bonds in all three cations form hydrogen bonds; to water or perchlorate O atoms in I, and to water O atoms or Br À ions in II.
In the double salt I, hydrogen bonding between the cations, the four perchlorate ions ClO 4 À (1)-ClO 4 À (4) and the water molecule form a one-dimensional network extending along the c-axis direction, as shown in Fig. 3. Three of the four O atoms in the relatively ordered ClO 4 À (1) anion link the two reference molecules together by N-HÁ Á ÁO hydrogen bonds. Neither of the alternative orientations for ClO 4 À (2) form any N-HÁ Á ÁO or O-HÁ Á ÁO H bonds. These disordered ions lie in a hydrophobic cavity in the crystal structure, and may be held in position by C-HÁ Á ÁO bonds. The relatively ordered ion ClO 4 À (3) is tethered by only one hydrogen bond, while each orientation for disordered ClO 4 À (4) is hydrogen bonded to the water molecule and to either one or two N-H groups of the cations. The water molecule is well stabilized in its position by three separate hydrogen bonds.

Database survey
A search in the Cambridge Structural Database (CSD, Version of 2017; Groom et al., 2016) for cis-[Nime 6 cyclam] 2+ structures produced only one hit (TICCOX; Wang et al., 1996). This structure has a configuration with all NH atoms on the same side of the molecule, or uuuu, with a configuration the same as that of the structures Ib and II in the present work. The sole other cis-cyclam structure of any kind has Cu as the chelated metal ion (HMTZCP; Ochiai et al., 1978), with a configuration the same as that of structure Ia.
Of 38 3D trans-[Nime 6 cyclam] 2+ structures found in the CSD, 26 have the NH configuration uudd of cation Ia in the present work, five have a udud configuration, and five have the NH configuration uuuu (or equivalently dddd), but with or conformations for the five-membered chelate rings, different from the conformations of Ib and II in the present work. In these 36 structures, there need be no difference between the geometries of the six-membered chelate rings, and indeed, minus a few exceptions, both N-Ni-N sixmembered ring chelate angles are identical, with a mean of 93.2 (4) . The last two trans structures [LIFYEG (Ou et al., 2013), NIBTET (Curtis et al., 1973)] have cations with the same conformation as in Ib and II, and with the same differentiation in six-membered ring N-Ni-N chelate angles as in the present work. Projection down the c axis for the macrocycle bromide salt II. The asymmetric unit is in bold. Bromide ions are green, and water molecules red.

Figure 6
Details of the proposed hydrogen-bond network for the macrocycle bromide salt II. Displacement ellipsoids are at the 50% probability level, with anions and solvent in the asymmetric unit drawn in bold. Bromide ions are green, and water O atoms red. Putative hydrogen bonds involving water molecules for which protons were not found are in cyan while other hydrogen bonds are black. Water O atoms and Br1 at the top of the figure are related to the corresponding atoms at the bottom via the translation vector (0, 1 2 , À 1 2 ).
A search for structures where Ni 2+ is coordinated solely by the unsubstituted cyclam ligand gave 20 hits. Of these, one had the RRRR configuration, or udud, with alternate NH atoms pointing upwards and downwards, while 19 had the RRSS configuration, or uudd, as in the present Ia structure, the more stable isomer according to Bosnich et al. (1965). None of these unsubstituted Ni-cyclam structures had the RSRS configuration, or uuuu, with all NH atoms on the same side of the molecule, as in the present Ib and II structures. Presumably this particular configuration is stabilized by the methyl substituent groups.

Synthesis and crystallization
The double salt I was prepared in Daryle H. Busch's laboratories by methods described in Curtis (1967). The bromide salt II was prepared by a solution of I in methanol/KBr/HBr, precipitation with ether, and recrystallization from hot aqueous HBr.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3.
Data for I were collected at The Ohio State University many years ago. As was the custom then, reflection data were stored as F values, so that those reflections for which F 2 values were negative were stored with values of zero. During the preparation of this manuscript, we found that the original absorption correction had been carried out with an incorrect value for the absorption coefficient, . While correcting this problem, we converted the reflection data into the F 2 values used in the final refinements. Thermal parameters for the perchlorate O atoms in I are all large, indicating probable positional disorder, common for these anions. After extensive modeling attempts, ClO 4 À ions 1 and 3 were refined with an ordered model, while ClO 4 À ions 2 and 4 were refined in two alternative orientations, with 50% occupancy each and a common Cl atom in ClO 4 À (2), and occupancies of 65.0 (8)% and 35.0 (8)% and separate sites for the disordered Cl atoms in ClO 4 À (4). Initially, tight restraints on the ClO 4 geometry were imposed, but these were relaxed during the final refinements. However, it proved useful to impose restraints on the thermal parameters for the O atoms with the Shelx RIGU command, and a DFIX command was used to prevent the too close approach of two O atoms from different perchlorate groups.  Table 3 Experimental details.

I I I
Crystal data Chemical formula [Ni(C 16  Crystal data for compound II, the bromide salt, were originally obtained with the same Picker four-circle diffractometer as used for compound I. (Three octants merged to give 1916 observations; Gaussian absorption correction applied; R 1 = 0.026 for 1780 observed > 2, R 2 = 0.078, NV = 241, GOOF = 0.876, Á = À0.42 to +0.60 e Å À3 .) We recollected data on the same crystal much later with the KappaCCD system at Fordham University to expand the data set and because some of the previous processing details had been lost. Refinements with the two sets of data gave very similar results, with no bond length or interior bond angle differing by more than 2.0 and average difference 0.7. Twinning by reflection about the (001) plane, perpendicular to the polar twofold axis in Fdd2, was indicated by the Flack parameter of 0.57 (2) as well as by the low value of 0.030 found for R merg if the observed I(hkl) and I(hkl) intensities were merged, compared with 0.070 if the calculated intensities for an untwinned crystal were merged.
As noted in the section on Supramolecular features, the water molecules refined to positions rather close to one another. It was necessary to introduce anti-bumping restraints in the SHELXL refinements to avoid unreasonably short OÁ Á ÁO contacts. Difference maps at the end of the leastsquares refinements were dominated by features associated with the Br À ions, and were uninformative regarding the positions of H atoms, even when calculated with only lowangle data. Thus, none of the H atoms on the water molecules were located. Potential positions for some water H atoms could be derived from the presumed hydrogen-bonding pattern, but refinements including these atoms were inconclusive. We tried refining the SHELXL BASF factor to see if this improved the difference maps, obtaining BASF = 0.58 (2), with negligible changes in the difference map or R factors. Hence our final refinements assume equal contributions from each twin component. The close proximity of O3 to the crystallographic twofold axis suggests disorder of at least the H atoms on O3, and the large U eq value for O3 suggests probable disorder of the O3 atoms themselves. It was possible to generate two closely positioned sites for O3, but extensive efforts to refine a suitable disordered model for O3 did not improve the R factors, nor give more reasonable U eq values for the disordered O3 atoms, while difference maps from these refinements did not give any useful information either on water H atoms. In light of these factors, we have not reported a model with a disordered O3 atom.
In both compounds, H atoms on the cation were constrained to idealized positions, with C-H distances of 0.97 Å for the methylene groups, 0.98 Å for the methine CH groups, and 0.96 Å for the methyl groups, while the U eq factors for these H atoms were set at 1.2 times the U iso of the bonded atoms for methylene and methine groups, and 1.5 times for the methyl groups. All NH atoms were refined, with U eq values set at 1.2 times the U iso for their bonded N atom in I and 1.0 times U iso for II.

11-tetraazacyclotetradecane)nickel(II) bis(perchlorate) hemihydrate (I)
Crystal data [Ni(C 16  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.30 e Å −3 Δρ min = −0.30 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.