Crystal structure of the co-crystal fac-tri-aqua-tris(thio-cyanato-κN)iron(III)-2,3-di-methyl-pyrazine (1/3).

In the crystal of the title compound, [Fe(NCS)3(H2O)3]·3C6H8N2, the Fe(III) cation is located on a threefold rotation axis and is coordinated by three N atoms of the thiocyanate anions and three water mol-ecules in a fac arrangement, forming a slightly distorted N3O3 octa-hedron. Stabilization within the crystal structure is provided by O-H⋯N hydrogen bonds; the H atoms from coordinating water mol-ecules act as donors to the N atoms of guest 2,3-di-methyl-pyrazine mol-ecules, leading to a three-dimensional supra-molecular framework.

Chemical context

In the large family of coordination compounds, materials showing a tunable character of their physical properties (e.g., electrical, magnetic, optical etc) are of special inter­est. Attempts to design compounds with such tunability have revealed the possibility to target the property of inter­est through the rational choice of ligands in transition metal complexes. For instance, variation of the aromatic n class="Chemical">N-donor ligand can lead to possible spin-state modulation of transition metals. In certain cases, these complexes can even possess spin crossover behaviour (transition between low and high spin states of a metal). The phenomenon of spin transition, which is one of the most known examples of mol­ecular bis­tability, can be provoked by some external stimuli (temperature, pressure, light, magnetic field, absorption of some compounds) and is followed by a change of the optical, magnetic and electric properties (Gütlich & Goodwin, 2004 ▸).

One of the simplest bridging N-n class="Species">donor ligands in the design of coordination polymers is pyrazine. This ligand is known for the formation of not only low-dimensional chains and sheets but also of some more complicated architectures, such as [Ag(pz)](CB11H12) [CB11H12 − is the monocarba-closo-dodeca­borate(−) anion], which exhibits a three-dimensional structure made up of checkerboard sheets of silver cations and anions connected by pillars of bridging pyrazine ligands (Cunha-Silva et al., 2006 ▸). In addition, pyrazine is able to construct Hofmann clathrates – spin crossover compounds with general formula [FeII M II (pz)(CN)4]∞ where M = Ni, Pd or Pt (Niel et al., 2001 ▸). A combination of pyrazine ligands with thiocyanates instead of tetracyanidometalates leads to the two-dimensional coordin­ation polymer [Fe(pz)2(NCS)2]∞ with an anti­ferromagnetic exchange between the metal cations (Real et al., 1991 ▸). In this context, we attempted to synthesize an FeII thio­cyanate complex with 2,3-di­methyl­pyrazine; however, the exposure of the starting material [Fe(OTs)2]·6H2O (OTs = p-toluene­sulfonate) to the oxygen in the air led to the oxidation of FeII and to the formation of the title compound.

Structural commentary

In the crystal structure of the title compound, the FeIII cation is located on a threefold n class="Disease">rotation axis and is in an octa­hedral coordination environment formed by three N atoms of the thio­cyanate anions and three O atoms of water mol­ecules arranged in a fac configuration (Fig. 1 ▸). The distance between the FeIII ion and the N atoms [2.025 (4) Å] is longer than that between the FeIII ion and the O atoms [2.034 (3) Å] and therefore the FeN3O3 octa­hedron is slightly distorted. These structural features are typical for related compounds (Shylin et al., 2013 ▸, 2015 ▸). The thio­cyanate ligands are bound through nitro­gen atoms and are quasi-linear [N1—C1—S1 = 179.5 (4)°], while the Fe–NCS linkages are bent [C1—N1—Fe1 = 157.0 (4)°]. Previously reported complexes with an N-bound NCS group possess similar structural features (Petrusenko et al., 1997 ▸).

Figure 1

The mol­ecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level. [Symmetry codes: (i) −y + 1, x − y + 1, z; (ii) −x + y, −x + 1, z.]

Supra­molecular features

In the title compound, the crystal packing is stabilized by O—H⋯N n class="Chemical">hydrogen bonds (Table 1 ▸): the H atoms from coordin­ating water mol­ecules act as donors to the N atoms of guest 2,3-di­methyl­pyrazine mol­ecules. The compound contains three guest mol­ecules of pyrazine per FeIII cation. In the crystal lattice, each mol­ecule of the complex is attached to six mol­ecules of pyrazine, while each pyrazine is connected with two water mol­ecules of the host complexes, leading to the formation of a three-dimensional network (Fig. 2 ▸).

Table 1

Hydrogen-bond geometry (, )

DHA	DH	HA	D A	DHA
O1H1AN2	0.80(3)	1.95(3)	2.745(4)	172(8)

Figure 2

Crystal structure of the title compound, showing hydrogen bonds as dashed lines. H atoms not involved in hydrogen bonding have been omitted for clarity. Colour key: bronze Fe, yellow S, blue N, grey C and red O.

Synthesis and crystallization

Crystals of the title compound were obtained by the slow-diffusion method between three layers, the first layer being a solution of [Fe(n class="Chemical">OTs)2]·6H2O (0.096 g, 0.2 mmol) and NH4SCN (0.046 g, 0.6 mmol) in water (10 ml), the second being a water/methanol mixture (1/1, 10 ml) and the third a solution of 2,3-di­methyl­pyrazine (0.065 g, 0.6 mmol) in methanol (3 ml). After two weeks, red plates grew in the second layer; they were collected, washed with water and dried in air, yield 0.028 g (23%).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. All hydrogen atoms connected to C and O atoms were placed in their expected calculated positions and refined as riding with C—H = 0.98 (CH3), 0.95 (Carom), O—H = 0.80 (3) Å, and with U iso(H) = 1.2U iso(C) with the exception of methyl n class="Chemical">hydrogen atoms, which were refined with U iso(H) = 1.5U eq(C).

Table 2

Experimental details

Crystal data
Chemical formula	[Fe(NCS)3(H2O)3]3C6H8N2
M r	608.57
Crystal system, space group	Trigonal, R3c
Temperature (K)	133
a, c ()	16.9383(12), 17.6259(13)
V (3)	4379.5(7)
Z	6
Radiation type	Mo K
(mm1)	0.77
Crystal size (mm)	0.16 0.12 0.1
Data collection
Diffractometer	Stoe IPDS II
Absorption correction	Numerical (X-RED; Stoe Cie, 2002 ▸)
T min, T max	0.908, 0.939
No. of measured, independent and observed [I > 2(I)] reflections	5784, 1903, 1716
R int	0.058
(sin /)max (1)	0.633
Refinement
R[F 2 > 2(F 2)], wR(F 2), S	0.038, 0.070, 1.07
No. of reflections	1903
No. of parameters	120
No. of restraints	3
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
max, min (e 3)	0.27, 0.28
Absolute structure	Flack x determined using 685 quotients [(I +)(I )]/[(I +)+(I )] (Parsons et al., 2013 ▸)
Absolute structure parameter	0.03(3)

Computer programs: X-AREA and X-RED (Stoe Cie, 2002 ▸), SHELXS97 (Sheldrick, 2008 ▸), SHELXL2014 (Sheldrick, 2015 ▸), OLEX2 (Dolomanov et al., 2009 ▸) and publCIF (Westrip, 2010 ▸).

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S2056989015004831/xu5840sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989015004831/xu5840Isup2.hkl

CCDC reference: 1053032

Additional supporting information: crystallographic information; 3D view; checkCIF report

[Fe(NCS)3(H2O)3]·3C6H8N2	F(000) = 1902
Mr = 608.57	Dx = 1.384 Mg m−3
Trigonal, R3c	Mo Kα radiation, λ = 0.71073 Å
a = 16.9383 (12) Å	µ = 0.77 mm−1
c = 17.6259 (13) Å	T = 133 K
V = 4379.5 (7) Å3	Block, red
Z = 6	0.16 × 0.12 × 0.1 mm

Stoe IPDS II diffractometer	1716 reflections with I > 2σ(I)
φ scans and ω scans with κ offset	Rint = 0.058
Absorption correction: numerical (X-RED; Stoe & Cie, 2002)	θmax = 26.8°, θmin = 2.4°
Tmin = 0.908, Tmax = 0.939	h = −18→21
5784 measured reflections	k = −21→15
1903 independent reflections	l = −18→22

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.038	H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.070	w = 1/[σ2(Fo2) + (0.0297P)2] where P = (Fo2 + 2Fc2)/3
S = 1.07	(Δ/σ)max < 0.001
1903 reflections	Δρmax = 0.27 e Å−3
120 parameters	Δρmin = −0.28 e Å−3
3 restraints	Absolute structure: Flack x determined using 685 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.03 (3)

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

	x	y	z	Uiso*/Ueq
Fe1	0.3333	0.6667	0.99891 (7)	0.0201 (2)
S1	0.29300 (8)	0.86373 (8)	1.16318 (7)	0.0300 (3)
N1	0.2860 (3)	0.7347 (3)	1.0611 (2)	0.0297 (9)
O1	0.2256 (2)	0.62277 (19)	0.92686 (19)	0.0221 (6)
C1	0.2893 (3)	0.7891 (3)	1.1041 (3)	0.0238 (9)
N2	0.0562 (2)	0.5854 (2)	0.9750 (2)	0.0250 (8)
N3	−0.1220 (2)	0.5016 (2)	1.0276 (2)	0.0254 (8)
C2	0.0336 (3)	0.5471 (3)	1.0439 (3)	0.0299 (10)
H2	0.0796	0.5481	1.0753	0.036*
C3	−0.0543 (3)	0.5064 (3)	1.0704 (3)	0.0288 (10)
H3	−0.0674	0.4812	1.1201	0.035*
C4	−0.1008 (3)	0.5385 (3)	0.9586 (2)	0.0235 (9)
C5	−0.0099 (3)	0.5815 (3)	0.9318 (3)	0.0229 (9)
C6	−0.1766 (3)	0.5322 (3)	0.9107 (3)	0.0322 (10)
H6A	−0.2345	0.4977	0.9379	0.048*
H6B	−0.1795	0.5010	0.8630	0.048*
H6C	−0.1655	0.5936	0.8996	0.048*
C7	0.0144 (3)	0.6246 (3)	0.8553 (3)	0.0304 (10)
H7A	0.0795	0.6484	0.8459	0.046*
H7B	0.0012	0.6747	0.8531	0.046*
H7C	−0.0214	0.5791	0.8166	0.046*
H1A	0.179 (3)	0.617 (5)	0.943 (4)	0.080*
H1B	0.206 (5)	0.572 (3)	0.912 (4)	0.080*

	U11	U22	U33	U12	U13	U23
Fe1	0.0197 (3)	0.0197 (3)	0.0209 (5)	0.00986 (13)	0.000	0.000
S1	0.0320 (6)	0.0293 (5)	0.0316 (6)	0.0175 (5)	0.0009 (5)	−0.0061 (5)
N1	0.030 (2)	0.031 (2)	0.029 (2)	0.0157 (18)	0.0031 (17)	−0.0024 (18)
O1	0.0180 (14)	0.0201 (14)	0.0283 (17)	0.0096 (13)	−0.0011 (13)	−0.0021 (13)
C1	0.022 (2)	0.030 (2)	0.022 (2)	0.0141 (18)	0.0019 (17)	0.0053 (18)
N2	0.0234 (18)	0.0234 (17)	0.028 (2)	0.0119 (15)	−0.0004 (16)	−0.0026 (15)
N3	0.0236 (17)	0.0233 (17)	0.029 (2)	0.0113 (15)	0.0027 (15)	0.0001 (15)
C2	0.027 (2)	0.037 (2)	0.030 (3)	0.019 (2)	−0.0040 (19)	−0.001 (2)
C3	0.032 (2)	0.029 (2)	0.028 (3)	0.018 (2)	0.0022 (19)	0.0030 (19)
C4	0.021 (2)	0.023 (2)	0.027 (2)	0.0113 (16)	0.0008 (18)	−0.0022 (18)
C5	0.023 (2)	0.0203 (19)	0.027 (2)	0.0121 (17)	0.0023 (17)	−0.0028 (17)
C6	0.027 (2)	0.036 (3)	0.035 (3)	0.017 (2)	−0.002 (2)	−0.002 (2)
C7	0.026 (2)	0.037 (2)	0.028 (3)	0.016 (2)	0.0020 (19)	0.0020 (19)

Fe1—N1	2.025 (4)	N3—C4	1.333 (6)
Fe1—N1i	2.025 (4)	C2—H2	0.9500
Fe1—N1ii	2.025 (4)	C2—C3	1.372 (6)
Fe1—O1	2.034 (3)	C3—H3	0.9500
Fe1—O1i	2.034 (3)	C4—C5	1.415 (6)
Fe1—O1ii	2.034 (3)	C4—C6	1.495 (6)
S1—C1	1.615 (5)	C5—C7	1.491 (6)
N1—C1	1.172 (6)	C6—H6A	0.9800
O1—H1A	0.80 (3)	C6—H6B	0.9800
O1—H1B	0.80 (3)	C6—H6C	0.9800
N2—C2	1.339 (6)	C7—H7A	0.9800
N2—C5	1.329 (5)	C7—H7B	0.9800
N3—C3	1.340 (6)	C7—H7C	0.9800
N1—Fe1—N1i	93.42 (17)	N2—C2—C3	121.9 (4)
N1—Fe1—N1ii	93.42 (17)	C3—C2—H2	119.0
N1i—Fe1—N1ii	93.42 (16)	N3—C3—C2	121.2 (5)
N1—Fe1—O1ii	90.67 (14)	N3—C3—H3	119.4
N1ii—Fe1—O1ii	90.47 (14)	C2—C3—H3	119.4
N1ii—Fe1—O1i	90.67 (14)	N3—C4—C5	120.9 (4)
N1i—Fe1—O1ii	174.17 (17)	N3—C4—C6	117.6 (4)
N1—Fe1—O1	90.47 (14)	C5—C4—C6	121.5 (4)
N1i—Fe1—O1i	90.47 (14)	N2—C5—C4	120.5 (4)
N1ii—Fe1—O1	174.17 (17)	N2—C5—C7	118.3 (4)
N1i—Fe1—O1	90.67 (14)	C4—C5—C7	121.2 (4)
N1—Fe1—O1i	174.17 (17)	C4—C6—H6A	109.5
O1—Fe1—O1ii	85.15 (14)	C4—C6—H6B	109.5
O1ii—Fe1—O1i	85.15 (14)	C4—C6—H6C	109.5
O1—Fe1—O1i	85.15 (14)	H6A—C6—H6B	109.5
C1—N1—Fe1	157.0 (4)	H6A—C6—H6C	109.5
Fe1—O1—H1A	118 (6)	H6B—C6—H6C	109.5
Fe1—O1—H1B	115 (6)	C5—C7—H7A	109.5
H1A—O1—H1B	98 (7)	C5—C7—H7B	109.5
N1—C1—S1	179.5 (4)	C5—C7—H7C	109.5
C5—N2—C2	117.7 (4)	H7A—C7—H7B	109.5
C4—N3—C3	117.7 (4)	H7A—C7—H7C	109.5
N2—C2—H2	119.0	H7B—C7—H7C	109.5
N2—C2—C3—N3	1.5 (7)	C3—N3—C4—C6	179.4 (4)
N3—C4—C5—N2	0.4 (6)	C4—N3—C3—C2	−0.7 (7)
N3—C4—C5—C7	−178.7 (4)	C5—N2—C2—C3	−1.2 (6)
C2—N2—C5—C4	0.3 (6)	C6—C4—C5—N2	−179.2 (4)
C2—N2—C5—C7	179.5 (4)	C6—C4—C5—C7	1.7 (6)
C3—N3—C4—C5	−0.2 (6)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1A···N2	0.80 (3)	1.95 (3)	2.745 (4)	172 (8)