Dimethyl­pyrazinium tetra­bromidoferrate(II): Br...ar­yl...Br and Br...Br inter­molecular inter­actions

In the title compound, (C₆H₁₀N₂)[FeBr₄], the asymmetric unit contains one half-cation and one half-anion, where the Fe atom has a distorted tetra­hedral environment. The Fe atom and two Br atoms lie on a mirror plane; the cation is centrosymmetric. In the crystal structure, the cations and anions are packed into alternate stacking with no significant inter­molecular Br...Br and/or aryl...aryl inter­actions within each stack. The anion...anion stacks inter­act via Br...Br inter­actions [Br...Br = 3.8773 (15) Å] to form one-dimensional arrays. The Br...aryl inter­actions are arranged in a ...Br...ar­yl...Br...ar­yl... infinite motif [Br...centroid distance of 3.928 (1) Å]. All of them link the anions and cations into two-dimensional layers.

Key indicators

• Single-crystal X-ray study
• T = 294 K
• Mean [sigma](C-C) = 0.014 Å
• R factor = 0.043
• wR factor = 0.113
• Data-to-parameter ratio = 18.4

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT230_ALERT_2_B Hirshfeld Test Diff for    N4     -   C3      ..      11.16 su
PLAT413_ALERT_2_B Short Inter XH3 .. XHn     H1B    ..  H1B     ..       2.09 Ang.

Alert level C
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         C3
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for        Fe1
PLAT341_ALERT_3_C Low Bond Precision on C-C Bonds (x 1000) Ang ...         15
PLAT420_ALERT_2_C D-H Without Acceptor       N4     -   H4A    ...          ?
PLAT764_ALERT_4_C Overcomplete CIF Bond List Detected (Rep/Expd) .       1.29 Ratio

Alert level G
PLAT794_ALERT_5_G Check Predicted Bond Valency for Fe1         (2)       2.84

   0 ALERT level A = In general: serious problem
   2 ALERT level B = Potentially serious problem
   5 ALERT level C = Check and explain
   1 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   5 ALERT type 2 Indicator that the structure model may be wrong or deficient
   1 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   1 ALERT type 5 Informative message, check

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S1. Comment

The research in the field of inorganic-organic hybrids is of great interest due to their magnetic, electronic and optoelectric properties (Cui et al., 2000; Lacroix et al., 1994; Chakravarthy & Guloy, 1997). The packing interactions that govern the crystal organization is expected to affect the packing and then the specific properties of such solids. For example, pyrazine (pyz) and similar ligands have been used through their two nitrogen atoms as neutral linkers to generate and stabilize many open 1-, 2- and 3-D coordination polymers and forming supramolecular coordination assemblies (Hao & Liu, 2007; Huang & Wang, 2007). We herein report the crystal structure of the title complex, (I), wherein, the protonated dimethylpyrazinium ligand [pyzH₂]²⁺ is not involved in coordination, but in extensive infinite aryl···Br···aryl···Br intermolecular interactions, affording a 2-D network structure by the aid of Br···Br interactions.

The asymmetric unit of the title compound, (I), contains one half [pyzH₂]²⁺ cation and [FeBr₃]^1- unit of the anion, where the Fe atom has a distorted tetrahedral environment (Fig. 1, Table 1). The Fe—Br bonds and Br—Fe—Br angles are in the range of 2.3182 (17)–2.3348 (11) Å [mean value is 2.3305 (14) Å] and 108.72 (4)–110.63 (7) °, respectively, in which they are in accordance with the corresponding values (Benito-Garagorri et al., 2006; Kruszynski & Wyrzykowski, 2006). The bond lengths and angles in the brominated cation are also in accordance with the corresponding ones (Hao & Liu, 2007; Churakov et al., 2006; Yang et al., 2004).

The molecules of discrete anions, packed into stacks, are separated by stacks of cations. The anion stacks along the c axis are parallel to the cation stacks with Fe···Fe distance of 6.8583 (14) Å, with no significant interactions between anions and cations within a stack. Inter anion-stacks are linked only through one Br···Br interaction parallel to b axis [Br3···Br3A = 3.8773 (15) Å (symmetry code A: 2 - x, 1 - y, 1 - z)]. The anions and cations are not involved in any of Br···H interactions, but only through Br···aryl interactions, that are represented in the ···Br···aryl···Br···aryl··· infinite motif (Al-Far & Ali, 2007), in which the bromide ions of the anion lie between the two cationic species with centroid···Br···centroid (symmetry code: 2 - x, 1/2 + y, 1 - z) repeat distance of 3.928 (1) Å. Beside these interactions along with inter anion-stacks, the Br···Br interactions also link the anions and cations together into 2-D layers approximately normal to the a axis (Fig 2).

Related literature

For general background, see: Cui et al. (2000); Lacroix et al. (1994); Chakravarthy & Guloy (1997); Huang & Wang (2007); Al-Far & Ali (2007). For related literature, see: Garagorri-Benito et al. (2006); Kruszynski & Wyrzykowski (2006); Hao & Liu (2007); Churakov et al. (2006); Yang et al. (2004).

S2. Experimental

For the preparation of (I), FeCl₂ (127 mg, 1 mmol) dissolved in absolute ethanol (10 ml) and liquid Br₂ (20%, 1 ml), was added dropwise to a stirred hot ethanolic solution of dimethylpyrazine (77%, 1 ml) dissolved in ethanol (10 ml) and HBr (60%, 2 ml). After heating for 3 h, the mixture was filtered off and allowed to stand undisturbed at room temperature. The salt crystallized out over 3 d as black blocks. Crystals were filtered off, washed with ethanol then diethylether, and dried under vacuum (yield; 300 mg, 61.8%).

S3. Refinement

H atoms were positioned geometrically, with N—H = 0.86 Å (for NH) and C—H = 0.93 and 0.96 Å for aromatic and methyl H, respectively, and constrained to ride on their parent atoms, with U_iso(H) = xU_eq(C,N), where x = 1.5 for methyl H, and x = 1.2 for all other H atoms.

Computing details

Data collection: CrystalClear (Rigaku, 2000); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1999); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The molecular structure of the title molecule, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level (symmetry code A: x, 3/2 - y, z).
	Fig. 2. A packing diagram for (I). The Br···Br and Br···aryl interactions are shown as dashed lines.

Dimethylpyrazinium tetrabromidoferrate(II)

Crystal data

(C6H10N2)[FeBr4]	F(000) = 452
Mr = 485.61	Dx = 2.461 Mg m^−3
Monoclinic, P21/m	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yb	Cell parameters from 1974 reflections
a = 6.6591 (13) Å	θ = 3.0–27.9°
b = 14.352 (3) Å	µ = 13.31 mm^−1
c = 6.8583 (14) Å	T = 294 K
β = 90.92 (3)°	Block, black
V = 655.4 (2) Å^3	0.20 × 0.15 × 0.10 mm
Z = 2

Data collection

Rigaku Mercury CCD diffractometer	1213 independent reflections
Radiation source: fine-focus sealed tube	856 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.084
Detector resolution: 14.6306 pixels mm^-1	θmax = 25.2°, θmin = 3.0°
dtintegrate.ref scans	h = −6→7
Absorption correction: numerical (Shape Tracing Software; REFERENCE?)	k = −15→17
Tmin = 0.103, Tmax = 0.262	l = −8→8
5269 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.044	H-atom parameters constrained
wR(F^2) = 0.113	w = 1/[σ^2(Fo^2) + (0.0601P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.97	(Δ/σ)max = 0.043
1213 reflections	Δρmax = 0.66 e Å^−3
66 parameters	Δρmin = −0.92 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.032 (3)

Special details

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.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Fe1	0.81018 (19)	0.7500	0.77976 (18)	0.0431 (4)
Br2	0.92375 (18)	0.7500	1.10355 (15)	0.0725 (4)
Br1	0.46205 (15)	0.7500	0.76938 (16)	0.0627 (4)
Br3	0.92512 (11)	0.61623 (5)	0.62320 (11)	0.0649 (4)
C3	0.3172 (15)	0.5452 (7)	1.0157 (16)	0.084 (3)
H3A	0.1937	0.5752	1.0225	0.100*
N4	0.3605 (14)	0.4879 (7)	0.8654 (18)	0.123 (4)
H4A	0.2698	0.4790	0.7766	0.148*
C2	0.4576 (15)	0.5570 (7)	1.1530 (15)	0.085 (3)
C1	0.4033 (16)	0.6165 (7)	1.3151 (13)	0.095 (3)
H1A	0.2912	0.5898	1.3814	0.143*
H1B	0.3673	0.6772	1.2669	0.143*
H1C	0.5154	0.6219	1.4042	0.143*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Fe1	0.0450 (8)	0.0465 (8)	0.0377 (7)	0.000	−0.0013 (6)	0.000
Br2	0.0831 (9)	0.0942 (10)	0.0398 (6)	0.000	−0.0103 (6)	0.000
Br1	0.0458 (6)	0.0744 (8)	0.0681 (8)	0.000	0.0037 (5)	0.000
Br3	0.0702 (6)	0.0626 (6)	0.0617 (6)	0.0158 (4)	−0.0042 (4)	−0.0125 (4)
C3	0.077 (7)	0.080 (6)	0.092 (7)	−0.006 (5)	−0.027 (6)	0.015 (6)
N4	0.082 (6)	0.125 (8)	0.160 (10)	−0.036 (6)	−0.062 (6)	0.057 (7)
C2	0.083 (7)	0.081 (7)	0.090 (7)	−0.028 (5)	−0.026 (6)	0.037 (5)
C1	0.110 (8)	0.096 (8)	0.080 (7)	−0.024 (6)	−0.010 (6)	−0.011 (6)

Geometric parameters (Å, º)

Fe1—Br1	2.3182 (17)	N4—C2^ii	1.380 (13)
Fe1—Br2	2.3343 (17)	N4—H4A	0.8600
Fe1—Br3^i	2.3348 (11)	C2—N4^ii	1.380 (13)
Fe1—Br3	2.3348 (11)	C2—C1	1.452 (13)
C3—C2	1.328 (12)	C1—H1A	0.9600
C3—N4	1.353 (13)	C1—H1B	0.9600
C3—H3A	0.9300	C1—H1C	0.9600
Br1—Fe1—Br2	109.74 (7)	C2^ii—N4—H4A	118.3
Br1—Fe1—Br3^i	108.72 (4)	C3—C2—N4^ii	119.0 (10)
Br2—Fe1—Br3^i	109.51 (4)	C3—C2—C1	115.9 (11)
Br1—Fe1—Br3	108.72 (4)	N4^ii—C2—C1	125.1 (10)
Br2—Fe1—Br3	109.51 (4)	C2—C1—H1A	109.5
Br3^i—Fe1—Br3	110.63 (7)	C2—C1—H1B	109.5
C2—C3—N4	117.5 (10)	H1A—C1—H1B	109.5
C2—C3—H3A	121.2	C2—C1—H1C	109.5
N4—C3—H3A	121.2	H1A—C1—H1C	109.5
C3—N4—C2^ii	123.5 (9)	H1B—C1—H1C	109.5
C3—N4—H4A	118.3
C2—C3—N4—C2^ii	−1.0 (16)	N4—C3—C2—C1	−178.0 (9)
N4—C3—C2—N4^ii	1.0 (16)

Symmetry codes: (i) x, −y+3/2, z; (ii) −x+1, −y+1, −z+2.