The solid-state structures of two metal-pyridine-sulfate compounds, namely catena-poly[[tetra-kis-(pyridine-κN)iron(II)]-μ-sulfato-κ2O:O'], [Fe(SO4)(C5H5N)4] n , (1), and catena-poly[[tetra-kis-(pyridine-κN)cobalt(II)]-μ-sulfato-κ2O:O'-[tetra-kis-(pyridine-κN)cobalt(II)]-μ-sulfato-κ3O,O':O''-[tris-(pyridine-κN)cobalt(II)]-μ-sulfato-κ2O:O'], [Co3(SO4)3(C5H5N)11] n , (2), are reported. The iron compound (1) displays a polymeric structure, with infinite chains of FeII atoms adopting octa-hedral N4O2 coordination environments that involve four pyridine ligands and two bridging sulfate ligands. The cobalt compound (2) displays a polymeric structure, with infinite chains of CoII atoms. Two of the three Co centers have an octa-hedral N4O2 coordination environment that involves four pyridine ligands and two bridging sulfate ligands. The third Co center has an octa-hedral N3O3 coordination environment that involves three pyridine ligands, and two bridging sulfate ligands with one sulfate chelating the cobalt atom.
The solid-state structures of two metal-pyridine-sulfate compounds, namely catena-poly[[tetra-kis-(pyridine-κN)iron(II)]-μ-sulfato-κ2O:O'], [Fe(SO4)(C5H5N)4] n , (1), and catena-poly[[tetra-kis-(pyridine-κN)cobalt(II)]-μ-sulfato-κ2O:O'-[tetra-kis-(pyridine-κN)cobalt(II)]-μ-sulfato-κ3O,O':O''-[tris-(pyridine-κN)cobalt(II)]-μ-sulfato-κ2O:O'], [Co3(SO4)3(C5H5N)11] n , (2), are reported. The iron compound (1) displays a polymeric structure, with infinite chains of FeII atoms adopting octa-hedral N4O2 coordination environments that involve four pyridine ligands and two bridging sulfate ligands. The cobalt compound (2) displays a polymeric structure, with infinite chains of CoII atoms. Two of the three Co centers have an octa-hedral N4O2 coordination environment that involves four pyridine ligands and two bridging sulfate ligands. The third Co center has an octa-hedral N3O3 coordination environment that involves three pyridine ligands, and two bridging sulfate ligands with one sulfate chelating the cobalt atom.
The first reports of a pyridine–sulfato–metal complex were in the late 19th century (Reitzenstein, 1894 ▸; Reitzenstein, 1898 ▸), and this work played a significant role in the Werner–Jørgensen controversy (Howe, 1898 ▸). While most early work in coordination chemistry was based upon ammonia complexes, the demonstration of the existence of similar complexes with other organic bases such as pyridine was an important contribution to the field. Despite the long history of these complexes, and their contributing role in the development of coordination chemistry, their crystallographic characterization is limited.Against this backdrop, our lab has recently begun to study the solid-state structures of transition-metal pyridine complexes. We have recently reported the structures of nickel, copper and zinc pyridine sulfates, which showed varying coordination geometries consistent with those predicted by crystal field theory (Roy et al., 2018 ▸). Herein, we expand this series by presenting the crystal structures of the iron–pyridine–sulfate (1) and the cobalt–pyridine–sulfate (2) complexes.
Structural commentary
In the yellow crystals of (1), the asymmetric unit consists of two pyridine molecules and one half of a sulfate anion coordinated to an iron atom sitting on an inversion center (Fig. 1 ▸
a). When grown out, the iron displays an octahedral coordination environment (Fig. 1 ▸
b). There is a square-planar tetrapyridineiron unit, with FeN4 planarity enforced by the inversion. The octahedral coordination is completed by two sulfate ions that bind trans to each other. The cis N—Fe—N angles have values of 86.44 (4) and 93.56 (4)° and the cis O—Fe—N angles have values ranging from 88.12 (4) to 91.88 (4)°. The pyridine rings are rotated from the FeN4 plane by dihedral angles of 44.03 (1) and 78.20 (1)°. The 78.20 (1)° angle is constrained by two C—H⋯O interactions with the trans sulfates (Table 1 ▸).
Figure 1
The molecular structure of compound (1), including (a) the asymmetric unit and (b) the coordination environment of Fe1. Displacement ellipsoids are drawn at the 50% probability level. H atoms are drawn as spheres of arbitrary radius. C—H⋯O interactions (Table 1 ▸) are shown as dashed lines. [Symmetry codes: (i) −x, −y, −z (ii) − − x, y, −z (iii) + x, −y, z]
Table 1
Hydrogen-bond geometry (Å, °) for (1)
D—H⋯A
D—H
H⋯A
D⋯A
D—H⋯A
C6—H6⋯O2i
0.95
2.49
3.4296 (19)
169
C10—H10⋯O2ii
0.95
2.42
3.3621 (19)
171
Symmetry codes: (i) ; (ii) .
In the pink crystals of (2), the asymmetric unit consists of three cobalt atoms, eleven coordinated pyridine molecules, and three sulfate anions (Fig. 2 ▸
a). There are three crystallographically independent cobalt atoms, with Co1 (Fig. 2 ▸
b) and Co2 (Fig. 2 ▸
c) displaying octahedral N4O2 coordination environments, and Co3 showing an octahedral N3O3 coordination environment (Fig. 2 ▸
d).
Figure 2
The molecular structure of compound (2), including (a) the asymmetric unit, (b) the coordination environment of Co1, (c) the coordination environment of Co2 and (d) the coordination environment of Co3. Displacement ellipsoids are drawn at the 50% probability level. H atoms are drawn as spheres of arbitrary radius. C—H⋯O interactions (Table 2 ▸) are shown as dashed lines. [Symmetry codes: (i) − x, 1 − y, − + z]
Co1 is part of a tetrapyridinecobalt unit, with the CoN4 plane showing a maximum deviation from planarity of 0.047 Å. The octahedral coordination is completed by two sulfate anions that bind trans to each other. The cis N—Co—N angles have values ranging from 87.06 (10) to 93.21 (9)°, and the O—Co—O angle is 174.62 (9)°. The four pyridine rings are rotated from the CoN4 plane by dihedral angles of 37.51 (1), 45.21 (1), 56.40 (1) and 56.92 (1)°. Two of the rings form one C—H⋯O interaction each with the sulfateoxygen atoms (Table 2 ▸).
Table 2
Hydrogen-bond geometry (Å, °) for (2)
D—H⋯A
D—H
H⋯A
D⋯A
D—H⋯A
C1—H1⋯O1
0.95
2.56
3.421 (4)
150
C1—H1⋯O2
0.95
2.58
3.066 (4)
112
C4—H4⋯O11i
0.95
2.47
3.158 (4)
129
C6—H6⋯O3
0.95
2.48
3.263 (4)
140
C15—H15⋯O5
0.95
2.47
2.967 (4)
113
C24—H24⋯O7ii
0.95
2.59
3.322 (4)
134
C26—H26⋯O11
0.95
2.40
3.343 (4)
171
C30—H30⋯O6
0.95
2.51
3.079 (4)
119
C30—H30⋯O7
0.95
2.50
3.161 (4)
126
C31—H31⋯O6
0.95
2.59
3.107 (4)
115
C35—H35⋯O9
0.95
2.36
2.936 (4)
119
C36—H36⋯O6
0.95
2.41
3.003 (4)
121
C40—H40⋯O12
0.95
2.43
3.352 (4)
163
C46—H46⋯O11
0.95
2.30
3.225 (4)
166
C50—H50⋯O4iii
0.95
2.49
3.132 (4)
125
C51—H51⋯O10
0.95
2.46
3.019 (4)
117
Symmetry codes: (i) ; (ii) ; (iii) .
Co2 is also part of a tetrapyridinecobalt unit, with the CoN4 plane showing a maximum deviation from plarity of 0.007 Å. The octahedral coordination is completed by two sulfate anions that bind trans to each other. The cis N—Co—N angles have values ranging from 85.15 (9) to 93.19 (9)°, and the O—Co—O angle is 175.16 (9)°. The four pyridine rings are rotated from the CoN4 plane by dihedral angles of 55.37 (1), 65.88 (1), 67.08 (1) and 68.07 (1)°. Two of the rings are involved in two C—H⋯O interactions each with the sulfateoxygen atoms (Table 2 ▸).Unlike the other two metal centers, Co3 has an N3O3 coordination environment, possessing a meridional arrangement. It is part of a tripyridinecobalt unit, with a CoN3 plane showing a maximum deviation from planarity of 0.021 Å. The octahedral coordination is completed by two bridging sulfate anions (one of which chelating through the oxygen atoms O1 and O4) that form a CoO3 plane with a maximum deviation from planarity of 0.029 Å. The meridional CoN3 and CoO3 planes are rotated relative to one another by an angle of 88.93 (1)°. The cis N—Co—N angles have values of 86.76 (10) and 87.52 (9)°. The chelating sulfate exhibits an O—Co—O bite angle of 65.36 (7)° and another cis O—Co—O angle of 88.63 (8)°. The three pyridine rings are rotated from the CoN3 plane by dihedral angles of 31.855 (2), 44.111 (3) and 82.863 (4)°. The 82.863 (4)° angle is constrained by two C—H⋯O interactions with sulfateoxygen atoms (Table 2 ▸).
Supramolecular features
In compound (1), the FeII atoms are linked together into infinite chains along the [100] direction through the sulfate ligands via O—S—O bridges (Fig. 3 ▸
a). Between each successive tetrapyridineiron unit are found parallel slipped π–π interactions [inter-centroid distance: 3.651 (1) Å, inter-planar distance: 3.607 (1) Å, slippage: 0.570 (1) Å].
Figure 3
The infinite chains of (a) compound (1) along [100] and (b) compound (2) along [001]. Displacement ellipsoids are drawn at the 50% probability level. H atoms are omitted for clarity. π–π interactions are shown as dashed lines.
In compound (2), the CoII atoms linked together into infinite chains along the [001] direction through the sulfate ligands (Fig. 3 ▸
b). No π–π interactions are observed in this crystal. There are two C—H⋯O interactions between chains [C4—H4⋯O11, d(C⋯O) = 3.158 (4) Å and C24—H24⋯O7, d(C⋯O) = 3.322 (4) Å] that connect the chains in three dimensions (Table 2 ▸). The packing of both compounds is shown in Fig. 4 ▸.
Figure 4
The packing of (a) compound (1) and (b) compound (2) along the a axis. Displacement ellipsoids are drawn at the 50% probability level. In (2), H atoms are omitted for clarity in compound (1). H atoms involved in hydrogen bonding between chains are drawn as spheres of arbitrary radius, with the other H atoms omitted for clarity. C—H⋯O interactions (Table 2 ▸) are shown as dashed lines.
Database survey
Though complexes of this form have been known for more than a century, their crystallographic characterization has been limited. Prior to our report earlier this year, there were only two structures in the literature of metal–pyridine–sulfates with no other ligands or components (Cotton & Reid, 1984 ▸; Memon et al., 2006 ▸). There are a number of closely related structures that have been reported, particularly transition-metal–aqua–pyridine–sulfate complexes. Six of these are found in the literature (Ali et al., 2005 ▸; Castiñeiras & García-Santos, 2008 ▸; Cotton et al., 1994 ▸; Kožíšek et al., 1989 ▸; Shi et al., 2009 ▸; Zhang, 2004 ▸). The metrical parameters in the reported structures are consistent with those seen in the metal–pyridine–triflates (Haynes et al., 1986 ▸).In a report earlier this year, we presented the structures of the metal–pyridine–sulfates of nickel, copper and zinc. It was of note that these three structures exhibited different coordination geometries, consistent with the crystal field stabilization energies (CFSE) associated with their d-electron count: d
8 nickel is octahedral, d
9 copper is square pyramidal, and d
10 zinc is both tetrahedral and octahedral. The structures reported here both exhibit octahedral coordination environments. For d
6 iron, the observed octahedral environment gives a CFSE of 4 Dq, while the preferred geometry might be square pyramidal with a CFSE of 4.67 Dq. Similarly for d
7 cobalt, the observed octahedral environment gives a CFSE of 8 Dq, while the preferred geometry might once again be square pyramidal with a CFSE of 9.14 Dq. The difference between octahedral and square pyramidal in these two compounds is small compared to the 3.14 Dq difference for d
9 copper, where a square-pyramidal geometry is observed. With such small electronic preferences, the impact of weaker interactions (π–π and C—H⋯O) and steric effects could play significant roles in determining the observed coordination environments.
Synthesis and crystallization
Approximately 25 mg of each metal sulfate [ironsulfate heptahydrate (J. T. Baker), cobaltsulfate heptahydrate (J. T. Baker)] were dissolved in pyridine (3 mL, Fisher Chemical) in a 20 mL vial under an atmosphere of dinitrogen. In the cobalt case, 0.1 mL of water was also added. The vials were heated to 353 K for 24–48 h, after which single crystals suitable for X-ray diffraction studies were isolated.
Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3 ▸. All structure solutions were obtained by intrinsic phasing. All non-hydrogen atoms were refined anisotropically (SHELXL) by full-matrix least squares on F
2. Hydrogen atoms were placed in calculated positions and then refined with a riding model with C—H bond lengths of 0.95 Å and with isotropic displacement parameters set to 1.20 U
eq of the parent C atom.
Table 3
Experimental details
(1)
(2)
Crystal data
Chemical formula
[Fe(SO4)(C5H5N)4]
[Co3(SO4)3(C5H5N)11]
Mr
468.31
1335.07
Crystal system, space group
Monoclinic, I2/a
Orthorhombic, P212121
Temperature (K)
200
200
a, b, c (Å)
11.8259 (10), 10.0847 (9), 17.264 (2)
9.4583 (5), 18.0344 (12), 33.088 (2)
α, β, γ (°)
90, 102.569 (2), 90
90, 90, 90
V (Å3)
2009.6 (3)
5644.0 (6)
Z
4
4
Radiation type
Mo Kα
Mo Kα
μ (mm−1)
0.89
1.06
Crystal size (mm)
0.28 × 0.20 × 0.20
0.24 × 0.22 × 0.20
Data collection
Diffractometer
Bruker D8 Venture CMOS
Bruker D8 Venture CMOS
Absorption correction
Multi-scan (SADABS; Bruker, 2016 ▸)
Multi-scan (SADABS; Bruker, 2016 ▸)
Tmin, Tmax
0.397, 0.429
0.394, 0.429
No. of measured, independent and observed [I > 2σ(I)] reflections
25476, 1917, 1760
80759, 10744, 9925
Rint
0.029
0.037
(sin θ/λ)max (Å−1)
0.612
0.612
Refinement
R[F2 > 2σ(F2)], wR(F2), S
0.021, 0.057, 1.08
0.024, 0.052, 1.04
No. of reflections
1917
10744
No. of parameters
139
758
H-atom treatment
H-atom parameters constrained
H-atom parameters constrained
Δρmax, Δρmin (e Å−3)
0.30, −0.34
0.27, −0.25
Absolute structure
–
Flack x determined using 4178 quotients [(I+)−(I−)]/[(I+)+(I−)] (Parsons et al, 2013 ▸)
Absolute structure parameter
–
0.003 (3)
Computer programs: APEX3 and SAINT (Bruker 2016 ▸), SHELXS97 (Sheldrick 2008 ▸), SHELXL2014 (Sheldrick, 2015 ▸), OLEX2 (Dolomanov et al. 2009 ▸) and publCIF (Westrip 2010 ▸).
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.
Absolute structure: Flack x determined using 4178 quotients
[(I+)-(I-)]/[(I+)+(I-)]
(Parsons et al, 2013)
Primary atom site location: structure-invariant direct methods
Absolute structure parameter: 0.003 (3)
Hydrogen site location: inferred from neighbouring sites
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.
Authors: Ashfaq A Memon; Mohammad Afzaal; Mohammad A Malik; Chinh Q Nguyen; Paul O'Brien; Jim Raftery Journal: Dalton Trans Date: 2006-07-24 Impact factor: 4.390