Redetermination of the crystal structure of bis(tri-2-pyridylamine)iron(II) bis(perchlorate), and a new refinement of the isotypic nickel(II) analogue: treatment of the perchlorate anion disorder

The crystal structure of bis(tri-2-pyridylamine)iron(II) bis(perchlorate) has been redetermined, and that of the isotypic bis(tri-2-pyridylamine)nickel(II) bis(perchlorate) complex has been rerefined. In each case, the perchlorate anion is disordered over four sets of atomic sites, and the ions are linked by C—H⋯O hydrogen bonds to form a supramolecular three-dimensional framework.


Chemical context
The crystal structure of bis(tri-2-pyridylamine)iron(II) bis-(perchlorate) was reported a number of years ago (Kucharski et al., 1978a), as was that of the isotypic Co II analogue (Kucharski et al., 1978b). In each of these structures, the metal centre lies at a centre of inversion, with a single perchlorate anion occupying a general position: the metal-N distances are consistent with a low-spin configuration in the Fe II complex, but a high-spin configuration in the Co II complex (Kucharski et al., 1978a,b). In each structure the unique perchlorate anion was modelled using a single set of atomic sites, but the anisotropic displacement parameters give a clear indication of unmodelled disorder in this species.
As a part of our continuing study of the structural and magnetic properties of iron complexes containing poly-pyridyl ligands (Setifi et al., 2013a(Setifi et al., ,b, 2014(Setifi et al., , 2016(Setifi et al., , 2017, we have now re-investigated the structure of compound (I), using a new data set. However, we have used the P2 1 /n setting of space group No. 14 rather than P2 1 /a, as used in the original report, as this setting has a smaller value of , 98.716 (7) , than the P2 1 /a setting where is 121.38 (3) (Kucharski et al., 1978a). The sample used here was prepared under solvothermal conditions in a 4:1 water/ethanol mixture, in the presence of potassium 1,1,3,3-tetracyano-2-ethoxypropenide. ISSN 2056-9890 The Ni II analogue (III) is isotypic with compounds (I) and (II), although in this case the refinement was conducted (Wang et al., 2011) in space group P2 1 /n rather than in the alternative P2 1 /a setting used for (I) and (II) (Kucharski et al., 1978a,b). In their refinement of the Ni complex, the perchlorate anion was modelled using two sets of atomic sites, having occupancies 0.528 (19) and 0.472 (19). However, the reported Cl-O distances range from 1.2136 (4) to 1.5356 (6) Å while the reported O-Cl-O angles lie in the range 96.48 (3)-118.284 (12) ; both of these ranges seem to be too wide to be correct, and accordingly we have undertaken a new refinement of this structure using the original data set (Wang et al., 2011). 2. Structural commentary, and treatment of the perchlorate anion disorder As noted above, the metal atom in compound (I) lies on a centre of inversion, selected here as that at (0.5, 0.5, 0.5), and the organic ligand is tridentate with the ligating atoms N11, N21 and N31 (Fig. 1) adopting a facial configuration: the Fe-N distances are 1.983 (2), 1.970 (3) and 1.982 (3) Å , respectively, fully consistent with low-spin Fe II (Orpen et al., 1989). However, when the refinement used only a single set of atomic sites for the perchlorate anion, this resulted in very large, prolate displacement ellipsoids for the O atoms, indicative of positional disorder. Accordingly, this anion was modelled using, in succession, two, three or four sets of atomic sites and only for the last could the anisotropic displacement parameters be regarded as satisfactory: the final refined values of the occupancies are 0.415 (3), 0.267 (3), 0.256 (3) and 0.061 (3) (Fig. 1).
For the isotypic Ni II complex (III) (Fig. 2), the same set of multi-component disorder models as employed for (I) were investigated, but only the four-component model gave satisfactory displacement parameters: the refined occupancies of the perchlorate components are 0.424 (3), 0.280 (3), 0.244 (3) and 0.052 (3), very similar to those for (I). The resulting range of Cl-O distances in (III) is 1.401 (5)-1.438 (5) Å and that of the O-Cl-O angles is 107.1 (4)-112.5 (5) , both more satisfactory that those obtained in the original two-component model (Wang et al., 2011).

Figure 2
The ionic components of compound (III), with atom labelling and displacement ellipsoids drawn at the 30% probability level. For clarity, the H atoms and the symmetry-equivalent anion have been omitted, and unmarked atoms and atoms marked 'a' are at the symmetry position (Àx + 1, Ày + 1, Àz + 1).

Figure 1
The ionic components of compound (I), with atom labelling and displacement ellipsoids drawn at the 30% probability level. For clarity, the H atoms and the symmetry-equivalent anion have been omitted, and unmarked atoms and atoms marked 'a' are at the symmetry position (Àx + 1, Ày + 1, Àz + 1).

Supramolecular features
There are neither C-HÁ Á ÁN nor C-HÁ Á Á(pyridyl) hydrogen bonds in the crystal structure of compound (I); nor are there anystacking interactions. The supramolecular assembly is dependent on C-HÁ Á ÁO hydrogen bonds (Table 1): although the anion disorder introduces complexity, the close similarity between the patterns of the interactions involving the different disorder components means that, only those of the dominant component, based on atom Cl1, need be considered, as entirely similar aggregation arises from the other components also. There are just three C-HÁ Á ÁO hydrogen bonds involving the major component, one of which lies within the selected asymmetric unit: in combination, these three hydrogen bonds link the ions into a three-dimensional supramolecular framework whose formation is readily analysed in terms of two sub-structures (Ferguson et al., 1998a,b;Gregson et al., 2000). In the simpler sub-structure, the two hydrogen bonds involving atoms C23 and C26 as the donors and atoms O12 and O13 as the acceptors link the ions into a ribbon running parallel to the [001] direction and in which R 4 4 (22) rings centred at (0.5, 0.5, n) link the metal complexes centred at (0.5, 0.5, 0.5 + n), where n represents an integer in each case (Fig. 3). In the second substructure, the two hydrogen bonds having atom O13 as the acceptor, link the ions into a sheet lying parallel to (101); see Fig. 4. The combination of the [001] chain and the (101) sheet is sufficient to generate a three-dimensional supramolecular framework. For compound (III), the pattern of the hydrogen bonds (Table 2) is very similar to that in (I), as is the supramolecular assembly. It is interesting to note that no C-HÁ Á ÁO hydrogen bonds were mentioned in the original report on (I) (Kucharski et al., 1978a), possibly because only a decade or so earlier, the very idea of such interactions had been authoritatively dismissed (Donohue, 1968): perhaps more surprising is the absence of any mention of these interactions in the original report on compound (III) (Wang et al., 2011 Table 2 Hydrogen-bond geometry (Å , ) for (III). Symmetry codes: (i) Àx; Ày þ 1; Àz þ 1; (ii) Àx þ 1 2 ; y þ 1 2 ; Àz þ 1 2 ; (iii) x; y; z þ 1; (iv) x À 1 2 ; Ày þ 1 2 ; z þ 1 2 .

Database survey
As noted above, the cobalt analogue (II) of compounds (I) and (III) is isotypic with them (Kucharski et al., 1978b).
The corresponding copper complex (IV) has the same composition as compounds (I)-(III) and, like them, crystal-lizes in space group P2 1 /n with Z 0 = 0.5 (Boys et al., 1992) but its constitution is different: the organic ligand is only bidentate, giving a square planar CuN 4 array with Cu-N distances of 1.992 (3) and 2.006 (3) Å ; the usual (4 + 2) coordination of Cu II is completed by two weakly-coordinated perchlorato ligands with a Cu-O distance of 2.593 (8) Å . By contrast, in the corresponding bis(trifluoromethanesulfonate) salt the anion plays no role in the metal coordination, where the bidentate amine ligands form a distorted tetrahedral geometry (Pé rez et al., 2009).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All H atoms were located in difference-Fourier maps. They were then treated as riding atoms in geometrically idealized positions with C-H = 0.93 Å and U iso (H) = 1.2U eq (C). For the minor disorder components of the perchlorate anion in each compound the bonded distances and the 1,2 non-bonded distances were restrained to be the same as the corresponding distances in the dominant component, subject to s.u.s of 0.005 Å and 0.01 , respectively: in addition, the anisotropic displacement parameters for corresponding atom sites were constrained to be the same. Subject to these conditions, the refined values of the anion occupancies were 0.415 (3) )/mean(F c 2 )], 11.399 for the group of 368 very weak reflections having F c /F c (max) in the range 0.000 < F c /F c (max) < 0.007, and 3.057 for the group of 312 very weak reflections having F c /F c (max) in the range 0.008 < F c /F c (max) < 0.0014; the corresponding value for (III) was 23.606 for 417 reflections having F c /F c (max) in the range 0.000 < F c /F c (max) < 0.007.  Computer programs: X-AREA and X-RED32 (Stoe & Cie, 2002), SMART and SAINT (Bruker, 2007), SHELXS (Sheldrick, 2008), SHELXL2014 (Sheldrick, 2015) and PLATON (Spek, 2009 PLATON (Spek, 2009); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015) and PLATON (Spek, 2009). 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.

Bis(tri-2-pyridylamine)nickel(II) bis(perchlorate) (III)
Crystal data [Ni(C 15  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. (