Bis(2,6-dimethyl­pyridinium) tetra­bromido­cobaltate(II)

In the crystal structure of the title compound, (C₇H₁₀N)₂[CoBr₄], the [CoBr₄]²⁻ anion is connected to two cations through N—H...Br and H₂C—H...Br hydrogen bonds to form two-dimensional cation–anion–cation layers normal to the crystallographic b axis. Inter­actions of the π–π type are absent between cations in the stacks [centroid–centroid separation = 5.01 (5) Å]. Significant inter­molecular Br–aryl inter­actions are present in the structure, especially an unusually short Br–ring centroid inter­action of 3.78 (1) Å. The coordination geometry of the anion is approximately tetrahedral and a twofold rotation axis passes through the Co atom.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.016 Å
• R factor = 0.055
• wR factor = 0.117
• Data-to-parameter ratio = 19.9

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT341_ALERT_3_B Low Bond Precision on C-C Bonds (x 1000) Ang ...         16

Alert level C
PLAT026_ALERT_3_C Ratio Observed / Unique Reflections too Low ....         46 Perc.
PLAT066_ALERT_1_C Predicted and Reported Transmissions Identical .          ?
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         C2
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         C6
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for        Co1
PLAT380_ALERT_4_C Check Incorrectly? Oriented X(sp2)-Methyl Moiety         C7
PLAT380_ALERT_4_C Check Incorrectly? Oriented X(sp2)-Methyl Moiety         C8
PLAT480_ALERT_4_C Long H...A H-Bond Reported H7A    ..  BR2     ..       2.97 Ang.
PLAT764_ALERT_4_C Overcomplete CIF Bond List Detected (Rep/Expd) .       1.20 Ratio
PLAT790_ALERT_4_C Centre of Gravity not Within Unit Cell: Resd.  #          1
              C7 H10 N
PLAT790_ALERT_4_C Centre of Gravity not Within Unit Cell: Resd.  #          2
              Br4 Co

Alert level G
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported _diffrn_ambient_temperature .        293 K

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

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

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S1. Comment

Noncovalent interactions play an important role in organizing structural units in both natural and artificial systems (Desiraju, 1997). They exercise important effects on the organization and properties of many materials in areas such as biology (Hunter 1994; Desiraju & Steiner 1999), crystal engineering (see for example: Allen et al.,1997; Dolling et al., 2001) and material science (Panunto et al., 1987; Robinson et al., 2000). The interactions governing the crystal organization are expected to affect the packing and then the specific properties of solids. In connection with ongoing studies (Ali & Al-Far, 2008; Al-Far & Ali, 2008; Ali & Al-Far, 2007; Al-Far & Ali, 2007a,b) of the structural aspects of halo-metal anion salts, we herein report the crystal structure of the title compound (I) along with its crystal supramolecularity.

The asymmetric unit in (I), contains half an anion and one cation (Fig. 1). The geometry of CoBr₄^2- anions is nearly tetrahedral (T_d) about Co metal (Table 1). Co—Br distances are similar, but Co—Br that are engaged in Co—Br···H—N,C hydrogen bonding, Co—Br2 and Co—Br2 [1 - x, y, 1/2 - z], are slightly longer than the others (Table 1). The bond distances and angles fall in the range of those reported previously for compounds containing Co—Br anions (Ali & Al-Far 2008; Al-Far & Ali 2008; Zhang et al., 2005). In the cation, the bond lengths and angles are within normal range (Allen et al., 1987).

The packing of the structure (Fig. 2) can be regarded as alternating stacks of anions and stacks of cations. The anion stacks are parallel to the cation stacks, with Co···Co distance of 9.0691 (10) Å (b axis), with no significant inter- and intra-stack halogen···halogen interactions (shortest Br···Br interactions being 4.4236 (20) Å). The anions and cations are interacting significantly through extensive N—H···Br and C—H···Br hydrogen bonding involving Br^- anions and N—H and CH₃ groups (Table 2; Fig. 3). These interactions link anions and cations into two-dimensional cation···anion···cation layers approximately normal to the crystallographic b axis (Fig. 3).

There is no π···π stacking of cations, the inter-stack centroid separations X1A···X1A [1 - x, y, 1/2 - z] and X1A···X1A [3/2 - x, 1/2 + y, z] being 5.01 (5) Å. This correlates well with the significant intermolecular Br···aryl interactions present in the structure. These are represented by the unusually short Br2···X1A [1 - x, -y, 1 - z] contact (3.78 (1) Å) and Br1···X1A [1 - x, y, 1/2 - z] (4.17 (3) Å) interaction.

Related literature

For general background, see: Al-Far & Ali (2007a,b); Ali & Al-Far (2007); Allen et al. (1997); Desiraju & Steiner (1999); Dolling et al. (2001); Hunter (1994); Panunto et al. (1987); Robinson et al. (2000). For related literature, see: Al-Far & Ali (2008); Ali & Al-Far (2008); Allen et al. (1987); Desiraju (1997); Zhang et al. (2005). N.B. the cystal description in the CIF is currently `Shunk'; should this be changed to `chunk' or `block'?

S2. Experimental

Boiling CoCl₂(1.0 mmol), dissolved in absolute ethanol (10 ml) was added to a stirred absolute ethanol solution (10 ml) of 2,6-lutidine (1 mmol) and 48% HBr (3 ml). The mixture was then treated with liquid Br₂ (2 ml). After refluxing for ca 1 h, the mixture was filtered off and allowed to evaporate undisturbed at room temperature. The salt crystallized out over 1 d as blue crystals.

S3. Refinement

H atoms bound to carbon and nitrogen were placed at idealized positions [C—H = 0.93 and 0.96 Å and N—H = 0.86 Å] and allowed to ride on their parent atoms with U_iso fixed at 1.2 or 1.5 U_eq(C,N).

Computing details

Data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS (Siemens, 1996); data reduction: SHELXTL (Sheldrick, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. A view of the asymmetric unit of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry operation: (A) -x + 1, y, -z + 1/2].
	Fig. 2. A packing diagram of (I), shows alternating stacks of anions and cations. Hydrogen atoms have been omitted for clarity.
	Fig. 3. Anion···cation intermolecular interactions. C,N—H···Br—Co intermolecular interactions are shown as dashed lines. Hydrogen atoms not involved in hydrogen bonding omitted for clarity. [Symmetry operation: (i) -x + 1, y, -z + 1/2]

Bis(2,6-dimethylpyridinium) tetrabromidocobaltate(II)

Crystal data

(C7H10N)2[CoBr4]	F(000) = 1140
Mr = 594.89	Dx = 1.842 Mg m^−3
Orthorhombic, Pbcn	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2n 2ab	Cell parameters from 36 reflections
a = 17.234 (2) Å	θ = 2.4–16.8°
b = 9.0691 (10) Å	µ = 8.24 mm^−1
c = 13.729 (2) Å	T = 293 K
V = 2145.7 (5) Å^3	Chunk, blue
Z = 4	0.40 × 0.30 × 0.20 mm

Data collection

Bruker P4 diffractometer	1930 independent reflections
Radiation source: fine-focus sealed tube	885 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.072
Detector resolution: 3 pixels mm^-1	θmax = 25.2°, θmin = 2.4°
ω Scans scans	h = −1→20
Absorption correction: ψ scan (North et al., 1968)	k = −1→10
Tmin = 0.064, Tmax = 0.192	l = −16→1
2534 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)] = 0.055	H-atom parameters constrained
wR(F^2) = 0.117	w = 1/[σ^2(Fo^2) + (0.0321P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.97	(Δ/σ)max < 0.001
1930 reflections	Δρmax = 0.55 e Å^−3
97 parameters	Δρmin = −0.40 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: 0.0060 (4)

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
Br1	0.39353 (5)	−0.42729 (12)	0.18719 (7)	0.0680 (4)
Co1	0.5000	−0.2856 (2)	0.2500	0.0500 (6)
Br2	0.45145 (6)	−0.13081 (14)	0.37845 (7)	0.0845 (5)
N1	0.6230 (4)	−0.1559 (9)	0.4945 (5)	0.056 (2)
H1	0.5806	−0.1498	0.4618	0.067*
C2	0.6211 (6)	−0.2366 (13)	0.5769 (8)	0.071 (3)
C3	0.6900 (8)	−0.2499 (13)	0.6250 (9)	0.097 (4)
H3	0.6928	−0.3052	0.6819	0.116*
C4	0.7556 (7)	−0.1811 (15)	0.5891 (10)	0.099 (4)
H4	0.8025	−0.1918	0.6218	0.119*
C5	0.7527 (6)	−0.0991 (13)	0.5078 (8)	0.085 (4)
H5	0.7973	−0.0526	0.4852	0.102*
C6	0.6850 (6)	−0.0840 (11)	0.4588 (6)	0.061 (3)
C7	0.5478 (6)	−0.3092 (14)	0.6029 (8)	0.116 (5)
H7A	0.5083	−0.2813	0.5572	0.174*
H7B	0.5325	−0.2795	0.6672	0.174*
H7C	0.5546	−0.4142	0.6012	0.174*
C8	0.6727 (5)	0.0072 (13)	0.3689 (7)	0.106 (4)
H8A	0.6197	−0.0011	0.3483	0.159*
H8B	0.7063	−0.0274	0.3180	0.159*
H8C	0.6843	0.1086	0.3829	0.159*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0521 (6)	0.0757 (8)	0.0762 (7)	−0.0135 (6)	−0.0140 (6)	0.0045 (6)
Co1	0.0379 (9)	0.0594 (14)	0.0527 (10)	0.000	−0.0008 (9)	0.000
Br2	0.0537 (6)	0.1130 (11)	0.0867 (8)	0.0146 (7)	−0.0040 (6)	−0.0405 (7)
N1	0.036 (4)	0.069 (6)	0.063 (5)	−0.006 (4)	0.001 (4)	−0.005 (5)
C2	0.056 (7)	0.081 (8)	0.075 (7)	−0.007 (6)	−0.003 (6)	0.018 (7)
C3	0.106 (10)	0.080 (10)	0.103 (9)	0.013 (8)	−0.024 (9)	0.009 (8)
C4	0.065 (8)	0.116 (12)	0.117 (11)	0.032 (9)	−0.045 (8)	−0.020 (9)
C5	0.055 (7)	0.113 (11)	0.087 (8)	0.006 (7)	−0.012 (7)	−0.007 (8)
C6	0.050 (6)	0.068 (7)	0.065 (7)	−0.014 (6)	0.005 (5)	−0.017 (6)
C7	0.104 (10)	0.124 (12)	0.120 (9)	−0.034 (9)	0.006 (8)	0.055 (9)
C8	0.085 (8)	0.150 (13)	0.082 (8)	−0.045 (9)	0.002 (7)	0.040 (9)

Geometric parameters (Å, º)

Br1—Co1	2.4002 (13)	C4—C5	1.341 (15)
Co1—Br1^i	2.4002 (13)	C4—H4	0.9300
Co1—Br2	2.4044 (15)	C5—C6	1.354 (12)
Co1—Br2^i	2.4044 (15)	C5—H5	0.9300
N1—C2	1.348 (11)	C6—C8	1.501 (12)
N1—C6	1.345 (10)	C7—H7A	0.9600
N1—H1	0.8600	C7—H7B	0.9600
C2—C3	1.363 (13)	C7—H7C	0.9600
C2—C7	1.468 (12)	C8—H8A	0.9600
C3—C4	1.383 (15)	C8—H8B	0.9600
C3—H3	0.9300	C8—H8C	0.9600
Br1—Co1—Br1^i	115.28 (9)	C4—C5—C6	120.1 (12)
Br1—Co1—Br2	108.06 (3)	C4—C5—H5	119.9
Br1^i—Co1—Br2	108.37 (4)	C6—C5—H5	119.9
Br1—Co1—Br2^i	108.37 (4)	N1—C6—C5	117.0 (10)
Br1^i—Co1—Br2^i	108.06 (3)	N1—C6—C8	117.1 (9)
Br2—Co1—Br2^i	108.54 (9)	C5—C6—C8	125.9 (10)
C2—N1—C6	126.0 (8)	C2—C7—H7A	109.5
C2—N1—H1	117.0	C2—C7—H7B	109.5
C6—N1—H1	117.0	H7A—C7—H7B	109.5
N1—C2—C3	115.7 (10)	C2—C7—H7C	109.5
N1—C2—C7	117.9 (9)	H7A—C7—H7C	109.5
C3—C2—C7	126.3 (11)	H7B—C7—H7C	109.5
C2—C3—C4	120.0 (11)	C6—C8—H8A	109.5
C2—C3—H3	120.0	C6—C8—H8B	109.5
C4—C3—H3	120.0	H8A—C8—H8B	109.5
C5—C4—C3	121.1 (11)	C6—C8—H8C	109.5
C5—C4—H4	119.5	H8A—C8—H8C	109.5
C3—C4—H4	119.5	H8B—C8—H8C	109.5
C6—N1—C2—C3	−2.9 (16)	C3—C4—C5—C6	−1 (2)
C6—N1—C2—C7	−178.9 (10)	C2—N1—C6—C5	3.0 (15)
N1—C2—C3—C4	0.8 (18)	C2—N1—C6—C8	−176.3 (9)
C7—C2—C3—C4	176.5 (12)	C4—C5—C6—N1	−1.0 (16)
C2—C3—C4—C5	1 (2)	C4—C5—C6—C8	178.2 (11)

Symmetry code: (i) −x+1, y, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···Br2	0.86	2.51	3.366 (7)	176
C7—H7A···Br2	0.96	2.97	3.856 (10)	153