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Volume 68 
Part 5 
Pages m121-m126  
May 2012  

Received 12 March 2012
Accepted 4 April 2012
Online 19 April 2012

Four NiII complexes with the new cyclam-methylimidazole ligand 1-[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane

aINQUIMAE, Departamento de Química Inorgánica, Analítica y Química Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina, and bGerencia de Investigación y Aplicaciones, Centro Atómico Constituyentes, Comisión Nacional de Energía Atómica, Buenos Aires, Argentina
Correspondence e-mail: slep@qi.fcen.uba.ar, baggio@cnea.gov.ar

Although it has not proved possible to crystallize the newly prepared cyclam-methylimidazole ligand 1-[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane (LIm1), the trans and cis isomers of an NiII complex, namely trans-aqua{1-[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane}nickel(II) bis(perchlorate) monohydrate, [Ni(C15H30N6)(H2O)](ClO4)2·H2O, (1), and cis-aqua{1-[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane}nickel(II) bis(perchlorate), [Ni(C15H30N6)(H2O)](ClO4)2, (2), have been prepared and structurally characterized. At different stages of the crystallization and thermal treatment from which (1) and (2) were obtained, a further two compounds were isolated in crystalline form and their structures also analysed, namely trans-{1-[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane}(perchlorato)nickel(II) perchlorate, [Ni(ClO4)(C15H30N6)]ClO4, (3), and cis-{1,8-bis[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane}nickel(II) bis(perchlorate) 0.24-hydrate, [Ni(C20H36N6)](ClO4)2·0.24H2O, (4); the 1,8-bis[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane ligand is a minor side product, probably formed in trace amounts in the synthesis of LIm1. The configurations of the cyclam macrocycles in the complexes have been analysed and the structures are compared with analogues from the literature.

Comment

Macrocyclic polyamines such as cyclam and cyclen, bearing potentially coordinating pendant arms, are useful in applications such as diagnostic medicine, waste-water treatment and others, due to the stability conferred on their metallic complexes by the additional donor groups in the pendant arms (Curtis, 2003[Curtis, N. F. N. (2003). Macrocyclic Ligands, in Comprehensive Coordination Chemistry II, Vol. 1, edited by J. A. McCleverty & T. J. Meyer. Oxford: Elsevier Science Limited.]). This stability is especially important in processes where the release of free metals is particularly undesirable, as in, for instance, the majority of medical treatments. A paradigmatic example can be found in the administration of the gadolinium cation as a contrast agent for magnetic resonance imaging (MRI), a process where the stability of the tetraacetate cyclen (DOTA) complex of the GdIII cation, viz. Gd(DOTA)H2O, has made the complex, and some of its derivatives, a `must' for the safe and successful use of the technique (Schwietert & McCue, 1999[Schwietert, C. W. & McCue, J. P. (1999). Coord. Chem. Rev. 184, 67-89.]; Yam & Lo, 1999[Yam, V. W. W. & Lo, K. K. W. (1999). Coord. Chem. Rev. 184, 157-240.]; Caravan et al., 1999[Caravan, P., Ellison, J. J., McMurry, T. J. & Lauffer, R. B. (1999). Chem. Rev. 99, 2293-2352.]).

Complexes of substituted macrocyclic polyamines are also interesting from a purely structural point of view, in particular due to the many different ring conformations attainable, as well as the diversity in binding modes provided by the functionalized side arms (Bosnich et al., 1965[Flack, H. D. (1983). Acta Cryst. A39, 876-881.]; De Candia et al., 2007[De Candia, A. G., Marcolongo, J. P. & Slep, L. D. (2007). Polyhedron, 26, 4719-4730.]).

There are a large number of reported ligands of this type, with a wide range of pendant side groups, and, consistent with the above-mentioned stability, the majority of their complexes are clathrates [Cambridge Structural Database (CSD), Version 5.32; Allen, 2002[Allen, F. H. (2002). Acta Cryst. B58, 380-388.]].

[Scheme 1]

Exploring further the substantial body of chemistry already based on the cyclam macrocycle, we have prepared a new cyclam-methylimidazole ligand, 1-[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane (LIm1). Crystallizing the free ligand has proved impossible so far. However, we succeeded in obtaining the trans and cis isomers of an NiII complex, viz. trans-[Ni(LIm1)(H2O)](ClO4)2·H2O, (1)[link], and cis-[Ni(LIm1)(H2O)](ClO4)2, (2)[link], reported herein. At different stages of the crystallization and thermal treatment processes (see Experimental for details), another two compounds were obtained in crystalline form and their structures are also reported here, viz. trans-[Ni(ClO4)(LIm1)]ClO4, (3)[link], and cis-[Ni(LIm2)](ClO4)2, (4)[link] (where LIm2 is 1,8-bis[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane, a minor side product probably formed in trace amounts during the synthesis of LIm1).

The structures of (1)[link]-(4)[link] (Figs. 1[link]-4[link][link][link]) all have a central NiII cation chelated by a cyclam ring (four N atoms), the common fifth ligand being the imidazole N atom. They differ in the sixth ligand completing the octahedral coordination of atom Ni1, this being water in (1)[link] and (2)[link], a perchlorate anion in (3)[link] and a second imidazole N atom in (4)[link]. All four structures present perchlorate groups as either isolated counter-ions or a coordinated ligand, and invariably this fragment is disordered, as a result of which the quality of the refinement is in most cases diminished.

Chelation of the NiII cation by the four cyclic N atoms of the cyclam unit is achieved in two different fashions in these compounds, which can be described by the relative orientations of the Ni1/N1-N3 and Ni1/N1/N4/N3 mean planes. The dihedral angles are 3.9 (2) and 7.7 (2)° in (1)[link] and (3)[link], respectively, describing a fairly planar arrangement of the cyclam macrocycle, and angles of 79.6 (2) and 81.5 (2)° in (2)[link] and (4)[link], respectively, describing a `butterfly-like' conformation. This is closely associated with the way the two extra ligands bind the cation, viz. trans in (1)[link] and (3)[link], and cis in (2)[link] and (4)[link]. The similarities and differences in the coordination parameters are related to these differences in ligand conformation, as well as to the character of the sixth ligand, as reflected in the comparison of the geometric data given in Table 1[link]. The bond angles are split into two groups, those in the first and third column of Table 1[link] (the `trans' moieties), and those in the second and fourth columns (`cis'), with the differences within each group being smaller than those between groups. The Ni-N bond distances fall between 2.046 (3) and 2.144 (3) Å, in the range expected for high-spin NiII-N bonds.

[Scheme 2]

As described by Bonisch et al. (1965[Bonisch, B., Poon, C. V. & Tobe, M. L. (1965). Inorg. Chem. 4, 1102-1108.]), the designation `trans' does not fully characterize these complexes since the cyclic ligand has a number of possible distinct configurations. Bonisch and co-workers analysed the principles which apply to any cyclic tetradentate ligand whose donor atoms are tetrahedral when coordinated, and concluded that, in the case of cyclam, each N atom when coordinated is an asymmetric centre. Five distinct non-enantiomeric combinations can be produced. Thus, they proposed a simple description of the five different possible configurations of a cyclam macrocycle upon chelation (named I to V in their paper) by stating the directions, either up (u) or down (d), which the N substituents adopt (in our case, either H atoms or the methylimidazole arm). According to this classification, in (1)[link] and (3)[link] the group adopts a trans type III configuration (see Scheme 2[link]), while in (2)[link] and (4)[link] the cis form is preferred, described by Bonisch and co-workers as V.

Similar NiII complexes with closely related monosusbtituted cyclam derivatives have been reported in the literature. El Ghachtouli et al. (2006[El Ghachtouli, S., Cadiou, C., Dechamps-Olivier, I., Chuburu, F., Aplincourt, M., Patinec, V., Le Baccon, M., Handel, H. & Roisnel, T. (2006). New J. Chem. 30, 392-398.]) described two structures, (II) and (III) therein, having 2-methylpyridine as a pendant arm and CH3CN and H2O, respectively, occupying the sixth coordination sites, and which present coordination analogous to that of (1)[link] and (2)[link]. But while their compound (III) shares with our (2)[link] the same cis-V cyclam configuration (Bonisch classification), compound (II) of El Ghachtouli and co-workers adopts a trans-I configuration (all up, see Scheme 2[link]). A search of the CSD shows that the configuration found in (1)[link] occurs slightly more frequently than that displayed by (II), appearing with a 60:40 relative frequency.

The disordered perchlorate groups, in addition to providing charge balance, act as acceptors in generally weak hydrogen bonds having the cyclam N-H and water O-H groups as donors (Tables 2[link]-5[link][link][link]). The result is an arrangement with the Ni-cyclam units isolated from each other in space but interconnected by a dense network of these perchlorate-mediated interactions.

The redox behaviour of the configurational isomers (1)[link] and (2)[link] was investigated in aqueous solution by means of cyclic voltammetry experiments. The oxidation of the trans isomer, (1)[link], is quasi-reversible and occurs at E1/2 = 0.77 V. In contrast, and analogous with what is observed in the closely related derivatives reported by El Ghachtouli et al. (2006[El Ghachtouli, S., Cadiou, C., Dechamps-Olivier, I., Chuburu, F., Aplincourt, M., Patinec, V., Le Baccon, M., Handel, H. & Roisnel, T. (2006). New J. Chem. 30, 392-398.]), the oxidation of the cis isomer, (2)[link], is irreversible (Eox = 1.03 V) and after several scans leads to the exclusive formation of (1)[link].

[Figure 1]
Figure 1
The molecular structure of (1)[link], with displacement ellipsoids drawn at the 35% probability level. The major components of the disordered perchlorate anions are shown with broken lines. The minor component(s) and H atoms have been omitted for clarity.
[Figure 2]
Figure 2
The molecular structure of (2)[link], with displacement ellipsoids drawn at the 35% probability level. The major components of the disordered perchlorate anions are shown with broken lines. The minor component(s) and H atoms have been omitted for clarity.
[Figure 3]
Figure 3
The molecular structure of (3)[link], with displacement ellipsoids drawn at the 35% probability level. The major components of the disordered perchlorate anions are shown with broken lines. The minor component(s) and H atoms have been omitted for clarity.
[Figure 4]
Figure 4
The molecular structure of (4)[link], with displacement ellipsoids drawn at the 35% probability level. The major components of the disordered perchlorate anions are shown with broken lines. The minor component(s) and H atoms have been omitted for clarity.

Experimental

The compounds 2-(chloromethyl)imidazole hydrochloride and 1,4,8,11-tetraazacyclotetradecane (cyclam) were prepared according to previously published procedures (Jones, 1949[Jones, R. G. (1949). J. Am. Chem. Soc. 71, 383-386.]; Barefield, 1975[Barefield, E. K. (1975). Inorg. Synth. 16, 220-225.]). All other reagents employed were obtained commercially and used as supplied.

For the synthesis of 1-[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane (LIm1), cyclam (2.50 g, 12.5 mmol) was partially dissolved in hot (388 K) dimethylformamide (DMF, 60 ml) and the suspension stirred vigorously. 2-(Chloromethyl)imidazole hydrochloride (0.7 g) dissolved in DMF (32 ml) was added dropwise over a period of 4 h. The reaction mixture was heated at 388-393 K for an extra hour and then allowed to cool to 277 K. The unreacted cyclam separated as white needles, which were removed by filtration. The solution was concentrated to 15 ml at room temperature under reduced pressure and treated with water (10 ml) and KOH (4 M), raising the pH to 11.5. This solution was extracted with CHCl3 (10 × 50 ml). The organic extracts were evaporated to dryness, leaving a colourless oily residue.

Purification of this residue was achieved by chromatography on a column (diameter 4 cm and length 15 cm) packed with silica gel 40 (35-70 mesh) in a CH2Cl2-MeOH (9:1 v/v) mixture. The column was first eluted with the same solvent mixture to remove some nonmacrocyclic contaminants, then with CH2Cl2-MeOH-NH3 (5:5:1 v/v/v) to remove polysubstituted cyclam species and finally with CH2Cl2-MeOH-NH3 (2:2:1 v/v/v) to elute the monosubstituted derivative. Removal of the solvent in vacuo yielded 0.90 g (66%) of the oily product, LIm1.

For the synthesis of [Ni(LIm1)(H2O)](ClO4)2, LIm1 (150.4 mg, 0.51 mmol) dissolved in water (3 ml) was added dropwise and with constant stirring to a solution of Ni(ClO4)2·6H2O (189.7 mg, 0.52 mmol) in water (3 ml). The resulting pink solution was heated at 343 K for 80 min and then concentrated in a rotary evaporator to yield a microcrystalline pink-violet solid, which was collected by filtration, washed with chilled water and dried in vacuo (yield 220 mg, 0.39 mmol, 75%). Elemental analysis, found: C 31.6, N 14.7, H 5.6%; calculated for [Ni(LIm1)(H2O)](ClO4)2 (C15H32Cl2N6NiO9): C 31.6, N 14.7, H 5.7%.

This material was redissolved in water and the solution was allowed to evaporate slowly, yielding three consecutive crops of crystals, all of them suitable for single-crystal X-ray diffraction (XRD) studies. The first crop was a pink crystalline material which, upon XRD analysis, proved to be the cis-[Ni(LIm1)(H2O)](ClO4)2 isomer, (2)[link]. A second crop consisted of a very small number of pale-pink crystals which were found to be cis-[Ni(LIm2)](ClO4)2, (4)[link], where LIm2 is a minor side product, probably formed in trace amounts during the synthesis of LIm1. Further evaporation of the mother liquors finally gave another pink crystalline solid which was identified by X-ray diffraction as the trans-[Ni(LIm1)(H2O)](ClO4)2 isomer, (1)[link].

The thermal cis-trans conversion between (2)[link] and (1)[link] (see Comment) was followed spectrophotometrically. For that purpose, compound (2)[link] ([lambda]/nm-1 [[epsilon]/M-1 cm-1] = 344 [13], 544 [10], 788 (sh) [6], 833 (sh) [7], 942 [9]) was dissolved in water and the solution heated at 363 K for several hours, following the course of the process by changes in the electronic spectrum. The experiments show a cis [rightwards arrow] trans [(2)[link] [rightwards arrow] (1)[link]] conversion, as indicated by the appearance of new UV-vis features which are compatible with those found for isomer (1)[link] ([lambda]/nm-1 [[epsilon]/M-1 cm-1] = 335 [13], 515 [9], 721 [3], 803 [2], 961 [5]). This thermal isomerization process was also followed by cyclic voltammetry measurements and suggests that trans-[Ni(LIm1)(H2O)](ClO4)2 is the thermodynamically stable isomer. Solutions kept at 363 K for longer periods of time (4-5 days) followed by slow evaporation of the solvent yielded single crystals of a major product identified by X-ray diffraction as trans-[Ni(ClO4)(LIm1)]ClO4, (3)[link].

Compound (1)[link]

Crystal data
  • [Ni(C15H30N6)(H2O)](ClO4)2·H2O

  • Mr = 588.09

  • Monoclinic, P 21 /c

  • a = 14.596 (3) Å

  • b = 10.995 (2) Å

  • c = 16.192 (3) Å

  • [beta] = 107.96 (3)°

  • V = 2471.9 (9) Å3

  • Z = 4

  • Mo K[alpha] radiation

  • [mu] = 1.06 mm-1

  • T = 294 K

  • 0.18 × 0.16 × 0.12 mm

Data collection
  • Oxford Gemini S Ultra CCD area-detector diffractometer

  • Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2009[Oxford Diffraction (2009). CrysAlis PRO. Oxford Diffraction Ltd, Yarnton, Oxfordshire, England.]) Tmin = 0.98, Tmax = 0.99

  • 8284 measured reflections

  • 4852 independent reflections

  • 2770 reflections with I > 2[sigma](I)

  • Rint = 0.077

Refinement
  • R[F2 > 2[sigma](F2)] = 0.057

  • wR(F2) = 0.136

  • S = 1.23

  • 4852 reflections

  • 362 parameters

  • 452 restraints

  • H-atom parameters constrained

  • [Delta][rho]max = 0.51 e Å-3

  • [Delta][rho]min = -0.91 e Å-3

Table 1
Selected geometric parameters (Å, °) for (1)[link], (2)[link], (3)[link] and (4)[link]

Atom X is O1W for (1)[link] and (2)[link], O11 for (3)[link] and N6 for (4)[link].

Bond or angle (1)[link] (2)[link] (3)[link] (4)[link]
Ni1-N1 2.120 (5) 2.144 (6) 2.124 (3) 2.144 (3)
Ni1-N2 2.071 (5) 2.085 (6) 2.059 (3) 2.098 (3)
Ni1-N3 2.068 (5) 2.094 (6) 2.068 (3) 2.144 (3)
Ni1-N4 2.073 (5) 2.088 (6) 2.046 (3) 2.099 (3)
Ni1-N5 2.083 (5) 2.051 (6) 2.077 (3) 2.068 (3)
Ni1-X 2.268 (4) 2.222 (6) 2.359 (3) 2.073 (3)
         
N1-Ni1-N2 85.7 (2) 92.7 (2) 85.85 (11) 83.84 (12)
N1-Ni1-N3 178.4 (2) 173.9 (2) 176.57 (12) 174.60 (12)
N1-Ni1-N4 95.0 (2) 84.6 (2) 95.69 (12) 92.39 (12)
N1-Ni1-N5 81.2 (2) 81.9 (2) 82.30 (11) 102.34 (11)
N1-Ni1-X 90.92 (18) 92.6 (2) 86.83 (10) 81.60 (11)
N2-Ni1-N3 94.4 (2) 83.5 (2) 92.83 (12) 92.52 (12)
N2-Ni1-N4 175.0 (2) 97.6 (2) 169.98 (12) 96.10 (13)
N2-Ni1-N5 92.4 (2) 169.5 (3) 95.16 (11) 171.31 (12)
N2-Ni1-X 84.89 (18) 85.9 (2) 84.06 (11) 88.20 (12)
N3-Ni1-N4 84.8 (2) 91.2 (2) 85.07 (13) 84.01 (13)
N3-Ni1-N5 100.3 (2) 102.6 (2) 100.98 (11) 81.72 (12)
N3-Ni1-X 87.54 (18) 91.8 (2) 89.89 (11) 102.32 (13)
N4-Ni1-N5 92.5 (2) 90.9 (3) 94.86 (11) 89.80 (12)
N4-Ni1-X 90.17 (19) 175.6 (2) 86.15 (12) 172.22 (13)
N5-Ni1-X 171.89 (19) 85.3 (2) 169.13 (10) 86.69 (11)

Table 2
Hydrogen-bond geometry (Å, °) for (1)[link]

D-H...A D-H H...A D...A D-H...A
N2-H2...O32Ai 0.91 2.37 3.198 (13) 151
N3-H3...O12 0.91 2.17 3.053 (8) 162
O1W-H1WA...O2W 0.85 1.99 2.790 (7) 156
O1W-H1WB...O22B 0.85 2.19 3.041 (15) 176
O1W-H1WB...O22A 0.85 2.38 3.163 (15) 153
O2W-H2WA...O11ii 0.85 2.18 3.034 (11) 179
O2W-H2WB...O21B 0.85 2.26 3.107 (19) 175
O2W-H2WB...O21A 0.85 2.01 2.855 (18) 174
Symmetry codes: (i) -x+1, -y+1, -z+1; (ii) [-x, y-{\script{1\over 2}}, -z+{\script{1\over 2}}].

Compound (2)[link]

Crystal data
  • [Ni(C15H30N6)(H2O)](ClO4)2

  • Mr = 570.08

  • Orthorhombic, P 21 21 21

  • a = 9.428 (5) Å

  • b = 16.047 (5) Å

  • c = 16.060 (5) Å

  • V = 2429.7 (17) Å3

  • Z = 4

  • Mo K[alpha] radiation

  • [mu] = 1.08 mm-1

  • T = 294 K

  • 0.32 × 0.30 × 0.20 mm

Data collection
  • Oxford Gemini S Ultra CCD area-detector diffractometer

  • Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2009[Oxford Diffraction (2009). CrysAlis PRO. Oxford Diffraction Ltd, Yarnton, Oxfordshire, England.]) Tmin = 0.98, Tmax = 0.99

  • 8056 measured reflections

  • 4312 independent reflections

  • 3342 reflections with I > 2[sigma](I)

  • Rint = 0.049

Refinement
  • R[F2 > 2[sigma](F2)] = 0.059

  • wR(F2) = 0.153

  • S = 1.07

  • 4312 reflections

  • 362 parameters

  • 720 restraints

  • H atoms treated by a mixture of independent and constrained refinement

  • [Delta][rho]max = 0.58 e Å-3

  • [Delta][rho]min = -0.37 e Å-3

  • Absolute structure: Flack (1983[Flack, H. D. (1983). Acta Cryst. A39, 876-881.]), 1601 Friedel pairs

  • Flack parameter: 0.14 (3)

Table 3
Hydrogen-bond geometry (Å, °) for (2)[link]

D-H...A D-H H...A D...A D-H...A
N3-H3...O11 0.91 2.32 3.140 (9) 150
N4-H4...O42A 0.91 2.16 3.068 (15) 173
N4-H4...O42B 0.91 2.24 3.12 (2) 161
O1W-H1WA...O12i 0.85 (1) 2.29 (3) 3.098 (10) 161 (7)
O1W-H1WB...O31B 0.85 (1) 2.04 (4) 2.86 (2) 163 (9)
O1W-H1WB...O31A 0.85 (1) 2.06 (7) 2.740 (13) 137 (8)
Symmetry code: (i) [-x+1, y+{\script{1\over 2}}, -z+{\script{3\over 2}}].

Compound (3)[link]

Crystal data
  • [Ni(ClO4)(C15H30N6)]ClO4

  • Mr = 552.06

  • Monoclinic, P 21 /c

  • a = 16.665 (5) Å

  • b = 9.696 (5) Å

  • c = 13.936 (5) Å

  • [beta] = 92.849 (5)°

  • V = 2249.0 (16) Å3

  • Z = 4

  • Mo K[alpha] radiation

  • [mu] = 1.16 mm-1

  • T = 294 K

  • 0.12 × 0.12 × 0.10 mm

Data collection
  • Oxford Gemini S Ultra CCD area-detector diffractometer

  • Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2009[Oxford Diffraction (2009). CrysAlis PRO. Oxford Diffraction Ltd, Yarnton, Oxfordshire, England.]) Tmin = 0.98, Tmax = 0.99

  • 23451 measured reflections

  • 4403 independent reflections

  • 2878 reflections with I > 2[sigma](I)

  • Rint = 0.051

Refinement
  • R[F2 > 2[sigma](F2)] = 0.037

  • wR(F2) = 0.092

  • S = 0.90

  • 4403 reflections

  • 356 parameters

  • 732 restraints

  • H-atom parameters constrained

  • [Delta][rho]max = 0.92 e Å-3

  • [Delta][rho]min = -0.26 e Å-3

Table 4
Hydrogen-bond geometry (Å, °) for (3)[link]

D-H...A D-H H...A D...A D-H...A
N3-H3...O21B 0.91 2.29 3.140 (13) 155
N4-H4...O12B 0.91 2.15 3.035 (14) 165
N4-H4...O12A 0.91 2.15 2.997 (15) 154

Compound (4)[link]

Crystal data
  • [Ni(C20H36N6)](ClO4)2·0.24H2O

  • Mr = 650.50

  • Orthorhombic, P b c a

  • a = 13.7285 (12) Å

  • b = 19.2330 (18) Å

  • c = 21.171 (2) Å

  • V = 5589.9 (9) Å3

  • Z = 8

  • Mo K[alpha] radiation

  • [mu] = 0.95 mm-1

  • T = 294 K

  • 0.22 × 0.16 × 0.16 mm

Data collection
  • Oxford Gemini S Ultra CCD area-detector diffractometer

  • Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2009[Oxford Diffraction (2009). CrysAlis PRO. Oxford Diffraction Ltd, Yarnton, Oxfordshire, England.]) Tmin = 0.98, Tmax = 0.99

  • 40257 measured reflections

  • 5489 independent reflections

  • 3936 reflections with I > 2[sigma](I)

  • Rint = 0.053

Refinement
  • R[F2 > 2[sigma](F2)] = 0.064

  • wR(F2) = 0.151

  • S = 1.08

  • 5489 reflections

  • 479 parameters

  • 934 restraints

  • H-atom parameters constrained

  • [Delta][rho]max = 0.49 e Å-3

  • [Delta][rho]min = -0.27 e Å-3

Table 5
Hydrogen-bond geometry (Å, °) for (4)[link]

D-H...A D-H H...A D...A D-H...A
N2-H2C...O12 0.91 2.27 3.123 (8) 156

All H atoms attached to C and N atoms were placed at calculated positions, with aromatic C-H = 0.95 Å, methylene C-H = 0.97 Å, methyl C-H = 0.96 Å and N-H = 0.91 Å, the N-H group having been identified previously in difference Fourier maps. The O-H groups showed varying behaviours and were accordingly treated differently in the refinements of (1)[link]-(4)[link]. In (1)[link] and (2)[link] they were found in difference maps, and while those in (2)[link] could be refined successfully with restraints [O-H = 0.85 (1) Å and H...H = 1.35 (3) Å], those in (1)[link] would not refine properly. They were thus kept at their original positions as found in the difference map, corrected to an idealized O-H distance of 0.85 Å. Structure (3)[link] does not include any solvent or ligand water molecules. In (4)[link], the O-H atoms could not be located in the difference map and were accordingly not included in the model. In all cases, H atoms were assigned Uiso(H) = 1.2Ueq(host) [or 1.5Ueq(host) for methyl].

All the perchlorate anions showed some kind of disorder, which was treated through the use of split models, in most cases in the form of a rotation around a nondisordered Cl-O bond. Similarity restraints were used for Cl-O and O...O distances, as well as for displacement parameters. For the first three structures, a simple twofold splitting was enough, with occupancies of 0.53 (3):0.47 (3) for (1), 0.62 (3):0.38 (3) and 0.61 (3):0.39 (3) for (2), and 0.48 (2):0.52 (2) for (3). In the case of (4), a threefold splitting was required, with occupancies of 0.405 (18):0.405 (18):0.190 (18). All four structures were refined in a homogeneous way, with similarity restraints applied to perchlorate geometries (s.u. values: Cl-O = 0.010 Å and O...O = 0.015 Å). Continuity in anisotropic displacement parameters for neighbouring atoms (except metallic centres) were also applied (SHELXL instructions DELU 0.01 and SIMU 0.02). An isolated peak in structure (4) was satisfactorily refined as a partially occupied solvent water molecule [occupancy factor 0.248 (15)].

Although (2)[link] is metrically tetragonal, the Rint values indicate unequivocally that the diffraction pattern has orthorhombic symmetry [Rint(tetragonal 4/m) 0.31; Rint(tetragonal 4/mmm) 0.41; Rint(orthorhombic mmm): 0.06]. In addition, in this same structure, the Flack (1983[Flack, H. D. (1983). Acta Cryst. A39, 876-881.]) parameter refined to 0.14 (3), thus suggesting the presence of a significant fraction of an inversion twin, even if far removed from being a racemate. The noncentrosymmetric character is clearly in line with |E| statistics [mean values for |E*E - 1|: 0.740 (experimental), 0.968 (centrosymmetric) and 0.736 (noncentrosymmetric)].

For all compounds, data collection: CrysAlis PRO (Oxford Diffraction, 2009[Oxford Diffraction (2009). CrysAlis PRO. Oxford Diffraction Ltd, Yarnton, Oxfordshire, England.]); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2009[Spek, A. L. (2009). Acta Cryst. D65, 148-155.]).


Supplementary data for this paper are available from the IUCr electronic archives (Reference: FA3274 ). Services for accessing these data are described at the back of the journal.


Acknowledgements

The authors acknowledge ANPCyT (project No. PME 2006-01113) for the purchase of the Oxford Gemini CCD diffractometer, and the Spanish Research Council (CSIC) for the provision of a free-of-charge licence to the Cambridge Structural Database (Allen, 2002[Allen, F. H. (2002). Acta Cryst. B58, 380-388.]).

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Acta Cryst (2012). C68, m121-m126   [ doi:10.1107/S0108270112014904 ]