Bis(1,3,4-trimethyl­pyridinium) tetra­chloridocuprate(II) and bis­(1,3,4-trimethyl­pyridinium) tetra­bromido­cuprate(II): an examination of the A₂CuX₄ Fdd2 structure type

The title bis­(1,3,4-trimethyl­pyridinium) tetra­halidocuprate(II) structures, (C₈H₁₂N)₂[CuCl₄], (I), and (C₈H₁₂N)₂[CuBr₄], (II), respectively, consist of flattened [CuX₄]^2- tetra­hedral complex anions and planar 1,3,4-trimethyl­pyridinium cations. Chloride compound (I) is a rare example of an A₂CuCl₄ structure with an elongated unit cell in the polar space group Fdd2. The [CuCl₄]^2- anions have twofold rotational symmetry and are arranged in distorted hexa­gonal close-packed (hcp) layers, which are inter­leaved with layers of cations, each in a four-layer repeat sequence, to generate the elongated axis. The organic cations stack along [101] or [10] in alternating layers. The methyl groups meta on the cation ring and the larger of the trans Cl-Cu-Cl angles both face the same direction along the polar axis and are the most prominent features determining the polarity of the structure. Bromide compound (II) crystallizes in a centrosymmetric structure with a similar layer structure but with only a two-layer repeat sequence. Here, symmetry-inequivalent cations are segregated into alternating layers with cations, forming hcp layers of inversion-related cation pairs in one layer and parallel stacks of cations in the other. The change in space group when the larger Br^- ion is present suggests that the 1,3,4-trimethyl­pyridinium ion has a minimal size to allow the Fdd2 A₂CuX₄ structure type.

S1. Comment

The structural chemistry of halidocuprate compounds with an A₂CuX₄ stoichiometry is rich, ranging from layer perovskite structures, in which the copper(II) ion possesses an elongated octahedral geometry (Long et al., 1997), to thermochromic compounds with isolated square-planar CuCl₄^2- anions in the low-temperature phase, which transform into flattened tetrahedral anions at higher temperature (Riley et al., 1998). Isolated CuX₄^2- anions with a compressed or flattened tetrahedral geometry are well known and by themselves merit little comment. However, A₂CuX₄ compounds with isolated CuX₄^2- ions are, in many cases, found to crystallize in complicated extended structures. A₂CuCl₄ compounds with high-symmetry cations, such as (CH₃)₄N⁺ (Gesi, 1982) and (CH₃)₄P⁺ (Pressprich et al., 1989; Nishijima & Mashiyama, 2000), exhibit commensurately and incommensurately modulated superstructures. Larger high-symmetry cations, such as (CH₃)₄As⁺ and (CH₃)₄Sb^+, yield compounds that crystallize in high-symmetry tetragonal or cubic space groups with, in some cases, commensurate modulations (Pressprich et al., 1991, 2002). The low-symmetry (C₂H₅)₂NH₂⁺ cation produces an elongated unit cell with three unique CuCl₄^2- anions in which the degree of flattening varies dramatically at low temperature (Willett & Twamley, 2007), while undergoing a thermochromic phase transition at higher temperature to a smaller unit cell with two unique CuCl₄^2- anions (Bloomquist et al., 1988).

A rare A₂CuX₄ structure type with an elongated cell in space group Fdd2 was first reported by Pauling (1966) for [(C₆H₅)₃CH₃As]₂CuX₄ (X = Cl or Br). Although no structure was determined, this structure type is unique from the cubic P2₁3 structures found for other first-row transition metals. Later, the [(C₆H₅)₃CH₃P]₂CuCl₄ structure was determined (El Essawi, 1997), with unit-cell constants differing only slightly from those for the arsonium analogue. Here, the corresponding tetrachloridomangate and tetrachloridocobaltate salts were also found to crystallize in cubic unit cells with cell-axis lengths close to those found in their arsonium analogues. More recently, the {Cu[H₃C₅N(CH₂NⁱPr₂)₂]Cl}₂CuCl₄ structure has been reported (Vedernikov et al., 2002) with the longest elongated unit-cell axis in this class, 56.083 (2) Å compared with values of 32.27 (2) and 32.791 Å, respectively, for the two previously mentioned chloride structures.

Compound (I) crystallizes at room temperature in space group Fdd2 with an elongated unit-cell axis of 35.3359 (7) Å, and it is the newest addition to this structure type. The structures of the organic cation and complex anion are illustrated in Fig. 1. The bond lengths and angles for the organic cation agree with expected values (Reference for standard values?). Bond lengths and angles for the complex anion are presented in Table 1. The CuCl₄^2- anion in (I) possesses twofold rotation symmetry about c. The trans-Cl—Cu—Cl angles of 129.41 (5)° for Cl1—Cu1—Cl1ⁱ and 134.79 (4)° for Cl2—Cu1—Cl2ⁱ [symmetry code: (i) 1/2 - x, 1/2 - y, z] are typical for isolated CuCl₄^2- anions in the absence of strong hydrogen bonding from the organic cation. The shortest H···Cl contacts in this structure are long (ca 2.77–2.78 Å) with unfavourable C—H···Cl angles (ca 145°), thus supporting the notion that strong hydrogen bonding is absent. The twofold rotation axis bisects the two large trans-Cl—Cu—Cl angles, with the smaller trans angle facing the positive c-axis direction and the larger facing the negative c-axis direction.

The organic cations and complex anions in (I) are separated into interleaved layers that stack parallel to [010], with a four-layer repeat sequence for each. Within the anionic layer, the complexes pack in a distorted hcp arrangement, with an a- to c-axis length ratio of 1.517, less than the ideal value of 1.732. All the anions within the layer are translationally equivalent with the Cl1—Cu1—Cl2 plane, almost parallel to (101), and the Clⁱ—Cu1—Cl2ⁱ plane, almost parallel to (101). Neighbouring layers are related by a diamond glide-plane operation perpendicular to [100], such that successive diamond glide-plane operations generate the four-layer repeat sequence that yields the long b axis of the unit cell. The large trans-Cl—Cu—Cl angles define planes that are almost at 45° to the a- and b-axes [the Cl1—Cu1—Cl1ⁱ plane forms an angle of 50.22 (2)°, and the Cl2—Cu1—Cl2ⁱ plane forms an angle of 40.19 (2)°, both with respect to the b axis]. The diamond glide-plane operation switches the orientation of these two planes in neighbouring anion layers.

Within the cation layer, the long axis of the cation, from the N atom to the opposite C atom in the ring, is almost parallel [7.42 (7)°] to [010] and hence almost perpendicular to the layer plane. This places the methyl group, in the meta-position in the ring, within the layer. The methyl groups in the meta-positions for all the cations all face in the negative c-axis direction, another consequence of the polar space-group symmetry. The C3—C31 bond forms an angle of 26.54 (15)° with respect to c, and angles of 73.05 (15) and 70.20 (16)° with respect to axes a and b. The direction of the C3—C31 bond differs from cation to cation, but the component of the bond relative to c is the same for all. The methyl group attached to the N atom on the cation ring penetrates into the anionic layer. Since the N atom is formally the seat of positive charge on the cation, this would place the N atom close to the formally negative Cl^- ions of the complex. The shortest N···Cl contact distance is 3.777 (2) Å to Cl1.

The cation layer consists of parallel stacks of aromatic rings along [101] or, in alternating layers, along [101] with complex anions nesting in voids between cation stacks. Neighbouring cations in a stack are related by a d-glide operation perpendicular to b, with a distance of 3.9652 (1) Å between cation planes. The cations are staggered in the stack so that the C atom in the para-position in the ring sits approximately above the centres of the two neighbouring rings. Neighbouring stacks in the layer can be related by lattice translations. A packing diagram viewed parallel to [101], showing the layered structure and looking down the stacks of organic cations in two of the layers, is presented in Fig. 2.

Cation stacking along [101 and [101] also occurs in the [(C₆H₅)₃CH₃P]₂CuCl₄ structure, where two different phenyl rings of the cation form facing pairs with phenyl rings on two neighbouring cations. The bulky ⁱPr groups in {Cu[H₃C₅N(CH₂NⁱPr₂)₂]Cl}₂CuCl₄ prevent phenyl ring stacking, but similar stacks can be discerned in which the ⁱPr groups of neighbouring cations abut. The [(C₆H₅)₃CH₃P]₂CuCl₄ and {Cu[H₃C₅N(CH₂NⁱPr₂)₂]Cl}₂CuCl₄ structures both have the four-layer repeat sequence and twofold rotational symmetry of the CuCl₄^2- ion, as in (I). However, the twofold axis in these cases bisects smaller Cl—Cu—Cl angles so that the compression axis of the flattened tetrahedron is not perpendicular to the elongated axis of the unit cell. In this manner the larger aspect of the flattened CuCl₄^2- ion is placed more within the anion layer, so as to accomodate better the spacing enforced by the bulkier cations. The compression axis is most closely aligned with the elongated axis in the [(C₆H₅)₃CH₃P]₂CuCl₄ structure, while the CuCl₄^2- ion has the largest Cl—Cu—Cl angle in the {Cu[H₃C₅N(CH₂NⁱPr₂)₂]Cl}₂CuCl₄ structure. This variation in orientation and structure of the CuCl₄^2- ion suggests that cation stacking determines a structure type in which the stereochemical flexibility of the CuCl₄^2- ion allows it to occupy voids that a regular tetrahedral complex could not.

The structure of the corresponding bromide compound, (II), offers an interesting contrast, since it does not crystallize in space group Fdd2. Instead it is found to crystallize in the monoclinic space group P2₁/c with the longest unit-cell axis, a, about half as long as the elongated axis in the choride salt. The structures of the organic cation and complex anion in (II) are presented in Fig. 3. Bond lengths and angles of the organic cation agree with expected values (Reference for standard values?). Bond lengths and angles for the complex ion are presented in Table 2. The extended structure in (II) has interleaved layers of CuBr₄^2- anions and of organic cations that stack along a, each in a two-layer repeat sequence. Within the anion layer, the complexes pack in an hcp arrangement, although with a b/c axis-length ratio of 1.775, which is less distorted from the ideal value (1.732) than in (I). Within the layer, two neighbouring complexes are related by c-axis translations and the other four by c-glide-plane operations. The two large trans-Br—Cu—Br angles are very similar [130.66 (3)° for Br2—Cu1—Br3 and 129.58 (3)° for Br1—Cu1—Br4].

The most striking feature of this structure is the segregated packing of symmetrically inequivalent organic cations into layers with very different arrangements. Cation 1 (containing atom N11) packs in a layer along the bc faces of the unit cell, while cation 2 (containing atom N21) packs in a parallel layer midway in the unit cell.

The molecular axis of cation 1 (as defined by the N11—C14 line) is almost perpendicular to the layer plane, forming a small angle of 9.24 (11)° relative to the normal to the layer plane. Cation 1 forms inversion-related pairs in which the parallel cation planes are separated by a distance of 3.56 (2) Å. The cation pairs form an hcp layer where two neighbouring pairs are related by a c-axis translation, while the other four neighbours are related by a c-glide operation. Since the normal to the cation plane forms an angle of 36.43 (7)° with respect to b, the orientation of the planes of the neighbours related by the c-glide is switched. The inversion-related cations in each pair are shifted along their molecular axes relative to one another so that the N atom of each extends into opposite anionic layers. Complex anions from neighbouring layers nest in the voids formed by neighbouring cation pairs.

Cation 2 packs to give a corrugated layer made up of uneven stacks of cations parallel to c. This stacking bears some resemblence to the cation stacking in (I), but with substantial differences. Within a given stack, the molecular axes of the cations all point in the same direction along a, rather than alternating directions as seen in (I). The molecular axes, however, are not parallel to a but tilted at an angle of 13.57 (12)° [and at an angle of 79.89 (11)° with respect to b]. Neighbouring cations within the stack are related by a c-glide operation which switches the orientation of the cation plane relative to b, so neighbouring cations are not coplanar, and it also switches the orientation of the molecular axis relative to a. This results in an unevenness in the stacking and in the staggering of the molecular axes within the stack, so as to increase the distance between the formal seats of positive charge on neighbouring cations. The distance between neighbouring cations [4.1886 (1) Å, as measured by one-half the c-axis length] is larger than that found in (I). Expansion of the unit cell to accomodate the larger bromide complex allows for this looser stacking of the cations. Neighbouring stacks in the layer are related by inversion and are offset from one another along a so that the N atoms of the stack penetrate into the nearest anion layer, thus giving rise to the layer corrugation. Complex anions nest in grooves between stacks. A packing diagram of the structure viewed down c (and down the stacks of cation 2) is presented in Fig. 4.

The 1,3,4-trimethylpyridinium cation is the smallest of the four cations for which the Fdd2 A₂CuX₄ structure type has been found. The fact that the bromide structure, (II), is not isomorphous with the chloride structure, (I) - unlike the situation for the methyltriphenylarsonium salts - with a significantly different packing of the organic cations, indicates that this ion has a minimal size required to form this structure type. However, the other (1-methyllutidinium)₂CuCl₄ structures studied so far do not exhibit this structure type (Bond, 2009). Thus, while cation size may be an important consideration in forming this structure type, cation structure must also play an important role.

S2. Experimental

Both compounds were prepared by slow evaporation of approximately 6 M HCl or HBr solutions of 1,3,4-trimethylpyridinium halide and copper(II) chloride dihydrate or copper(II) bromide, respectively, in a 2:1 stoichimetry. 1,3,4-Trimethylpyridinium halide was prepared by the reaction of 3,4-lutidine with an excess of iodomethane. The mixture was then stirred with an excess of silver halide to convert the iodide to the chloride or bromide salt. The resulting silver halide solid was removed by filtration. Suitable crystals of (I) and (II) were obtained by slow evaporation of the filtrates, giving yellow prism-like crystals of (I) and dark-purple prism-like crystals of (II).

S3. Refinement

For both compounds, the H atoms were included in calculated positions and treated as riding atoms, with C—H = 0.93–0.96 Å and with U_iso(H) = kU_eq(C), where k = 1.2 for aromatic H atoms and 1.5 for methyl H atoms. In compound (II), the C11 and C41 methyl groups were refined with twofold disorder (occupancies 0.5 and 0.5).

Computing details

For both compounds, data collection: COLLECT (Nonius, 2000); cell refinement: HKL SCALEPACK (Otwinowski & Minor 1997); data reduction: HKL DENZO and SCALEPACK (Otwinowski & Minor 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. The organic cation and complex anion of the chloride structure, (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. [Symmetry code: (i) 1/2 - x, 1/2 - y, z].
	Fig. 2. A packing diagram for (I), viewed parallel to the [101] lattice line. The view is down stacks of organic cations in alternate layers that nest between lines of complex anions.
	Fig. 3. The organic cation and complex anion of the bromide structure, (II), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. [Symmetry code: (i) 1/2 - x, 1/2 - y, z].
	Fig. 4. A packing diagram for (II), viewed parallel to the c axis. The stacks of cation 2 are visible in the middle layer, while the hcp pairs of cation 1 are found in the top and bottom layers of the illustration.

(I) bis(1,3,4-trimethylpyridinium) tetrachloridocuprate(II)

Crystal data

(C8H12N)2[CuCl4]	Dx = 1.462 Mg m^−3
Mr = 449.71	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Fdd2	Cell parameters from 15098 reflections
a = 13.2423 (2) Å	θ = 1.0–31.0°
b = 35.3359 (7) Å	µ = 1.59 mm^−1
c = 8.7298 (1) Å	T = 298 K
V = 4084.92 (11) Å^3	Prism, yellow
Z = 8	0.30 × 0.20 × 0.10 mm
F(000) = 1848

Data collection

Nonius KappaCCD area-detector diffractometer	3101 independent reflections
Radiation source: Enraf Nonius FR590	2457 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.080
Detector resolution: 9 pixels mm^-1	θmax = 31.0°, θmin = 3.3°
CCD rotation images, thick slices scans	h = −19→18
Absorption correction: gaussian (grid of 8 x 8 x 8 sampling points; Software?)	k = −50→50
Tmin = 0.661, Tmax = 0.874	l = −12→11
24053 measured reflections

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.034	w = 1/[σ^2(Fo^2) + (0.0491P)^2 + 0.4115P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.087	(Δ/σ)max < 0.001
S = 1.03	Δρmax = 0.37 e Å^−3
3101 reflections	Δρmin = −0.43 e Å^−3
107 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
1 restraint	Extinction coefficient: 0.00241 (19)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack (1983), with 1374 Friedel pairs
Secondary atom site location: difference Fourier map	Absolute structure parameter: −0.015 (12)

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	Occ. (<1)
Cu1	0.25	0.25	0.29137 (4)	0.03924 (12)
Cl1	0.34789 (5)	0.20593 (2)	0.40105 (9)	0.0688 (2)
Cl2	0.13061 (5)	0.212203 (19)	0.19266 (8)	0.0625 (2)
N1	0.10248 (14)	0.18327 (5)	0.7289 (2)	0.0452 (4)
C11	0.0961 (2)	0.22470 (7)	0.7506 (4)	0.0695 (8)
H11A	0.0755	0.2301	0.8537	0.104*	0.5
H11B	0.0476	0.235	0.6803	0.104*	0.5
H11C	0.161	0.2359	0.7318	0.104*	0.5
H11D	0.1139	0.2372	0.6568	0.104*	0.5
H11E	0.1418	0.2323	0.8302	0.104*	0.5
H11F	0.0284	0.2315	0.7788	0.104*	0.5
C2	0.13007 (17)	0.16853 (7)	0.5938 (3)	0.0451 (5)
H2	0.144	0.1848	0.5127	0.054*
C3	0.13847 (16)	0.13020 (7)	0.5715 (3)	0.0446 (5)
C31	0.1713 (2)	0.11588 (9)	0.4184 (4)	0.0704 (7)
H31A	0.1796	0.1368	0.3494	0.106*
H31B	0.1211	0.0989	0.3786	0.106*
H31C	0.2344	0.1027	0.4287	0.106*
C4	0.11654 (16)	0.10603 (6)	0.6942 (3)	0.0482 (5)
C41	0.1237 (2)	0.06404 (8)	0.6744 (5)	0.0739 (9)
H41A	0.1439	0.0584	0.5713	0.111*	0.5
H41B	0.059	0.0528	0.6945	0.111*	0.5
H41C	0.1727	0.054	0.7446	0.111*	0.5
H41D	0.1065	0.0518	0.769	0.111*	0.5
H41E	0.1914	0.0573	0.6458	0.111*	0.5
H41F	0.0777	0.0561	0.5956	0.111*	0.5
C5	0.0896 (2)	0.12205 (8)	0.8312 (3)	0.0557 (6)
H5	0.0759	0.1065	0.9145	0.067*
C6	0.0822 (2)	0.16039 (8)	0.8483 (3)	0.0558 (6)
H6	0.0633	0.1706	0.9422	0.067*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.04469 (19)	0.03268 (17)	0.04034 (19)	−0.00218 (15)	0	0
Cl1	0.0600 (4)	0.0582 (4)	0.0881 (6)	0.0038 (3)	−0.0121 (4)	0.0282 (4)
Cl2	0.0629 (4)	0.0542 (4)	0.0705 (5)	−0.0108 (3)	−0.0146 (3)	−0.0141 (3)
N1	0.0491 (10)	0.0344 (9)	0.0522 (11)	−0.0004 (7)	0.0095 (8)	−0.0022 (7)
C11	0.0807 (18)	0.0344 (11)	0.093 (2)	0.0038 (11)	0.0161 (16)	−0.0067 (13)
C2	0.0482 (11)	0.0442 (12)	0.0428 (11)	−0.0016 (9)	0.0089 (9)	0.0024 (9)
C3	0.0426 (11)	0.0478 (12)	0.0435 (13)	−0.0009 (9)	0.0056 (8)	−0.0060 (9)
C31	0.088 (2)	0.0711 (18)	0.0522 (17)	0.0011 (15)	0.0091 (14)	−0.0143 (14)
C4	0.0432 (11)	0.0385 (11)	0.0629 (14)	−0.0001 (9)	0.0075 (10)	−0.0058 (11)
C41	0.0815 (18)	0.0387 (13)	0.102 (3)	−0.0015 (12)	0.0224 (18)	−0.0074 (15)
C5	0.0715 (16)	0.0464 (13)	0.0491 (15)	0.0037 (11)	0.0161 (11)	0.0092 (10)
C6	0.0686 (15)	0.0536 (14)	0.0452 (13)	0.0022 (12)	0.0149 (11)	−0.0057 (11)

Geometric parameters (Å, º)

Cu1—Cl1	2.2410 (7)	C31—H31A	0.96
Cu1—Cl2	2.2419 (6)	C31—H31B	0.96
N1—C2	1.340 (3)	C31—H31C	0.96
N1—C6	1.346 (3)	C4—C5	1.371 (4)
N1—C11	1.479 (3)	C4—C41	1.497 (4)
C11—H11A	0.96	C41—H41A	0.96
C11—H11B	0.96	C41—H41B	0.96
C11—H11C	0.96	C41—H41C	0.96
C11—H11D	0.96	C41—H41D	0.96
C11—H11E	0.96	C41—H41E	0.96
C11—H11F	0.96	C41—H41F	0.96
C2—C3	1.373 (3)	C5—C6	1.367 (4)
C2—H2	0.93	C5—H5	0.93
C3—C4	1.401 (3)	C6—H6	0.93
C3—C31	1.494 (3)
Cl1^i—Cu1—Cl1	129.41 (5)	C3—C31—H31B	109.5
Cl1—Cu1—Cl2^i	99.80 (3)	H31A—C31—H31B	109.5
Cl1—Cu1—Cl2	99.10 (3)	C3—C31—H31C	109.5
Cl2^i—Cu1—Cl2	134.79 (4)	H31A—C31—H31C	109.5
C2—N1—C6	120.2 (2)	H31B—C31—H31C	109.5
C2—N1—C11	120.9 (2)	C5—C4—C3	118.0 (2)
C6—N1—C11	118.9 (2)	C5—C4—C41	121.8 (3)
N1—C11—H11A	109.5	C3—C4—C41	120.2 (3)
N1—C11—H11B	109.5	C4—C41—H41A	109.5
H11A—C11—H11B	109.5	C4—C41—H41B	109.5
N1—C11—H11C	109.5	H41A—C41—H41B	109.5
H11A—C11—H11C	109.5	C4—C41—H41C	109.5
H11B—C11—H11C	109.5	H41A—C41—H41C	109.5
N1—C11—H11D	109.5	H41B—C41—H41C	109.5
N1—C11—H11E	109.5	C4—C41—H41D	109.5
H11D—C11—H11E	109.5	C4—C41—H41E	109.5
N1—C11—H11F	109.5	H41D—C41—H41E	109.5
H11D—C11—H11F	109.5	C4—C41—H41F	109.5
H11E—C11—H11F	109.5	H41D—C41—H41F	109.5
N1—C2—C3	122.1 (2)	H41E—C41—H41F	109.5
N1—C2—H2	119	C6—C5—C4	121.6 (2)
C3—C2—H2	119	C6—C5—H5	119.2
C2—C3—C4	118.4 (2)	C4—C5—H5	119.2
C2—C3—C31	119.0 (2)	N1—C6—C5	119.8 (2)
C4—C3—C31	122.6 (2)	N1—C6—H6	120.1
C3—C31—H31A	109.5	C5—C6—H6	120.1

Symmetry code: (i) −x+1/2, −y+1/2, z.

(II) bis(1,3,4-trimethylpyridinium) tetrabromidocuprate(II)

Crystal data

(C8H12N)2[CuBr4]	F(000) = 1212
Mr = 627.55	Dx = 1.884 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 17.8882 (4) Å	Cell parameters from 17042 reflections
b = 14.8736 (3) Å	θ = 1.0–27.5°
c = 8.3772 (1) Å	µ = 8.21 mm^−1
β = 96.854 (1)°	T = 298 K
V = 2212.93 (7) Å^3	Prism, dark purple
Z = 4	0.21 × 0.17 × 0.09 mm

Data collection

Nonius KappaCCD area-detector diffractometer	5071 independent reflections
Radiation source: Enraf Nonius FR590	3469 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.083
Detector resolution: 9 pixels mm^-1	θmax = 27.5°, θmin = 3.7°
CCD rotation images, thick slices scans	h = −23→23
Absorption correction: gaussian (grid of 8 x 8 x 8 sampling points; Software?)	k = −19→19
Tmin = 0.242, Tmax = 0.534	l = −10→10
37761 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)] = 0.039	H-atom parameters constrained
wR(F^2) = 0.090	w = 1/[σ^2(Fo^2) + (0.0399P)^2 + 0.655P] where P = (Fo^2 + 2Fc^2)/3
S = 1.04	(Δ/σ)max = 0.001
5071 reflections	Δρmax = 0.46 e Å^−3
215 parameters	Δρmin = −0.46 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0033 (2)

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
Cu1	0.25000 (3)	0.99261 (3)	0.14313 (5)	0.04220 (13)
Br1	0.31668 (3)	0.98811 (3)	0.40717 (5)	0.05812 (14)
Br2	0.15837 (3)	0.87738 (3)	0.16072 (6)	0.06027 (15)
Br3	0.35288 (3)	1.00011 (4)	−0.00919 (6)	0.06865 (16)
Br4	0.17302 (3)	1.10939 (3)	0.01372 (5)	0.05383 (14)
N11	0.10866 (18)	0.8925 (2)	0.6638 (4)	0.0453 (8)
C11A	0.1910 (3)	0.8908 (4)	0.7140 (6)	0.0687 (13)
H11A	0.2172	0.9002	0.6219	0.103*
H11B	0.205	0.8336	0.7615	0.103*
H11C	0.2041	0.9376	0.7912	0.103*
C12	0.0794 (2)	0.8460 (2)	0.5333 (4)	0.0421 (9)
H12	0.1117	0.8141	0.4749	0.05*
C13	0.0043 (2)	0.8443 (2)	0.4840 (4)	0.0394 (8)
C13A	−0.0230 (3)	0.7900 (3)	0.3373 (5)	0.0627 (12)
H13A	0.0195	0.7688	0.2879	0.094*
H13B	−0.0541	0.8269	0.2624	0.094*
H13C	−0.0517	0.7396	0.3677	0.094*
C14	−0.0441 (2)	0.8917 (2)	0.5719 (4)	0.0407 (8)
C14A	−0.1277 (3)	0.8900 (3)	0.5253 (6)	0.0647 (12)
H14A	−0.1385	0.8993	0.4115	0.097*
H14B	−0.1507	0.9368	0.5813	0.097*
H14C	−0.1473	0.8328	0.5532	0.097*
C15	−0.0122 (2)	0.9396 (3)	0.7053 (5)	0.0472 (10)
H15	−0.0431	0.9728	0.7651	0.057*
C16	0.0628 (3)	0.9389 (3)	0.7496 (5)	0.0516 (10)
H16	0.083	0.9707	0.8402	0.062*
N21	0.38648 (19)	0.2118 (2)	0.7192 (4)	0.0479 (8)
C21A	0.3047 (3)	0.1953 (3)	0.6927 (7)	0.0703 (14)
H21A	0.2794	0.2488	0.6512	0.105*
H21B	0.2871	0.1792	0.7927	0.105*
H21C	0.2944	0.1472	0.6169	0.105*
C22	0.4129 (2)	0.2958 (3)	0.7470 (5)	0.0512 (10)
H22	0.3788	0.3428	0.7488	0.061*
C23	0.4879 (2)	0.3143 (3)	0.7728 (5)	0.0471 (9)
C23A	0.5129 (3)	0.4104 (3)	0.8007 (7)	0.0749 (15)
H23A	0.5346	0.432	0.7085	0.112*
H23B	0.5498	0.4135	0.8938	0.112*
H23C	0.4703	0.4469	0.8177	0.112*
C24	0.5389 (2)	0.2443 (3)	0.7703 (5)	0.0504 (10)
C24A	0.6224 (3)	0.2608 (4)	0.7945 (8)	0.0802 (16)
H24A	0.6364	0.2968	0.7077	0.12*
H24B	0.6485	0.2044	0.7969	0.12*
H24C	0.6356	0.2918	0.8944	0.12*
C25	0.5100 (3)	0.1587 (3)	0.7404 (6)	0.0615 (12)
H25	0.5429	0.1105	0.7366	0.074*
C26	0.4351 (3)	0.1441 (3)	0.7167 (6)	0.0583 (12)
H26	0.417	0.0859	0.6983	0.07*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0376 (3)	0.0468 (3)	0.0423 (3)	−0.0010 (2)	0.00483 (19)	0.0025 (2)
Br1	0.0488 (3)	0.0797 (3)	0.0444 (2)	0.0033 (2)	−0.00064 (18)	0.0036 (2)
Br2	0.0639 (3)	0.0548 (3)	0.0635 (3)	−0.0175 (2)	0.0133 (2)	0.0027 (2)
Br3	0.0483 (3)	0.1033 (4)	0.0573 (3)	0.0036 (3)	0.0185 (2)	0.0070 (3)
Br4	0.0534 (3)	0.0454 (2)	0.0607 (3)	0.00455 (19)	−0.0011 (2)	0.00366 (19)
N11	0.0385 (19)	0.0535 (19)	0.0435 (18)	−0.0031 (15)	0.0036 (14)	0.0033 (15)
C11A	0.042 (3)	0.096 (4)	0.067 (3)	−0.012 (3)	0.003 (2)	0.000 (3)
C12	0.048 (2)	0.042 (2)	0.038 (2)	0.0015 (17)	0.0135 (17)	−0.0008 (16)
C13	0.046 (2)	0.0351 (19)	0.0371 (19)	−0.0035 (16)	0.0043 (16)	0.0000 (15)
C13A	0.068 (3)	0.066 (3)	0.054 (3)	−0.007 (2)	0.004 (2)	−0.015 (2)
C14	0.041 (2)	0.0371 (19)	0.045 (2)	−0.0020 (16)	0.0068 (16)	0.0058 (16)
C14A	0.048 (3)	0.074 (3)	0.072 (3)	0.004 (2)	0.008 (2)	0.002 (3)
C15	0.054 (3)	0.041 (2)	0.049 (2)	−0.0022 (18)	0.016 (2)	−0.0058 (18)
C16	0.065 (3)	0.049 (2)	0.041 (2)	−0.015 (2)	0.009 (2)	−0.0078 (18)
N21	0.044 (2)	0.0393 (17)	0.060 (2)	−0.0030 (15)	0.0059 (16)	0.0016 (15)
C21A	0.044 (3)	0.058 (3)	0.108 (4)	−0.006 (2)	0.004 (3)	0.005 (3)
C22	0.051 (3)	0.0323 (19)	0.071 (3)	0.0050 (18)	0.011 (2)	0.0008 (18)
C23	0.045 (2)	0.038 (2)	0.058 (2)	−0.0031 (18)	0.0086 (19)	−0.0014 (18)
C23A	0.056 (3)	0.044 (3)	0.126 (5)	−0.005 (2)	0.015 (3)	−0.009 (3)
C24	0.044 (2)	0.048 (2)	0.060 (3)	0.0012 (18)	0.0061 (19)	−0.0032 (19)
C24A	0.051 (3)	0.068 (3)	0.120 (5)	0.002 (3)	0.004 (3)	−0.010 (3)
C25	0.049 (3)	0.038 (2)	0.096 (4)	0.009 (2)	0.005 (2)	−0.008 (2)
C26	0.058 (3)	0.0299 (19)	0.087 (3)	0.0014 (19)	0.008 (2)	−0.004 (2)

Geometric parameters (Å, º)

Cu1—Br1	2.3854 (6)	C15—H15	0.93
Cu1—Br2	2.3881 (6)	C16—H16	0.93
Cu1—Br3	2.3639 (6)	N21—C26	1.332 (5)
Cu1—Br4	2.3943 (6)	N21—C22	1.345 (5)
N11—C16	1.344 (5)	N21—C21A	1.473 (5)
N11—C12	1.346 (5)	C21A—H21A	0.96
N11—C11A	1.484 (5)	C21A—H21B	0.96
C11A—H11A	0.96	C21A—H21C	0.96
C11A—H11B	0.96	C22—C23	1.361 (6)
C11A—H11C	0.96	C22—H22	0.93
C12—C13	1.358 (5)	C23—C24	1.386 (6)
C12—H12	0.93	C23—C23A	1.507 (6)
C13—C14	1.392 (5)	C23A—H23A	0.96
C13—C13A	1.503 (5)	C23A—H23B	0.96
C13A—H13A	0.96	C23A—H23C	0.96
C13A—H13B	0.96	C24—C25	1.385 (6)
C13A—H13C	0.96	C24—C24A	1.503 (6)
C14—C15	1.390 (5)	C24A—H24A	0.96
C14—C14A	1.500 (6)	C24A—H24B	0.96
C14A—H14A	0.96	C24A—H24C	0.96
C14A—H14B	0.96	C25—C26	1.349 (6)
C14A—H14C	0.96	C25—H25	0.93
C15—C16	1.350 (6)	C26—H26	0.93
Br1—Cu1—Br3	99.58 (2)	N11—C16—C15	120.5 (4)
Br1—Cu1—Br2	101.16 (2)	N11—C16—H16	119.8
Br1—Cu1—Br4	129.58 (3)	C15—C16—H16	119.8
Br2—Cu1—Br3	130.66 (3)	C26—N21—C22	119.2 (4)
Br2—Cu1—Br4	100.76 (2)	C26—N21—C21A	120.6 (3)
Br3—Cu1—Br4	99.45 (2)	C22—N21—C21A	120.2 (3)
C16—N11—C12	119.7 (4)	N21—C21A—H21A	109.5
C16—N11—C11A	120.4 (4)	N21—C21A—H21B	109.5
C12—N11—C11A	119.9 (4)	H21A—C21A—H21B	109.5
N11—C11A—H11A	109.5	N21—C21A—H21C	109.5
N11—C11A—H11B	109.5	H21A—C21A—H21C	109.5
H11A—C11A—H11B	109.5	H21B—C21A—H21C	109.5
N11—C11A—H11C	109.5	N21—C22—C23	122.4 (4)
H11A—C11A—H11C	109.5	N21—C22—H22	118.8
H11B—C11A—H11C	109.5	C23—C22—H22	118.8
N11—C12—C13	122.1 (3)	C22—C23—C24	118.8 (4)
N11—C12—H12	119	C22—C23—C23A	119.0 (4)
C13—C12—H12	119	C24—C23—C23A	122.1 (4)
C12—C13—C14	119.0 (3)	C23—C23A—H23A	109.5
C12—C13—C13A	118.1 (4)	C23—C23A—H23B	109.5
C14—C13—C13A	122.9 (4)	H23A—C23A—H23B	109.5
C13—C13A—H13A	109.5	C23—C23A—H23C	109.5
C13—C13A—H13B	109.5	H23A—C23A—H23C	109.5
H13A—C13A—H13B	109.5	H23B—C23A—H23C	109.5
C13—C13A—H13C	109.5	C25—C24—C23	117.5 (4)
H13A—C13A—H13C	109.5	C25—C24—C24A	121.2 (4)
H13B—C13A—H13C	109.5	C23—C24—C24A	121.3 (4)
C15—C14—C13	117.6 (4)	C24—C24A—H24A	109.5
C15—C14—C14A	121.2 (4)	C24—C24A—H24B	109.5
C13—C14—C14A	121.1 (4)	H24A—C24A—H24B	109.5
C14—C14A—H14A	109.5	C24—C24A—H24C	109.5
C14—C14A—H14B	109.5	H24A—C24A—H24C	109.5
H14A—C14A—H14B	109.5	H24B—C24A—H24C	109.5
C14—C14A—H14C	109.5	C26—C25—C24	121.1 (4)
H14A—C14A—H14C	109.5	C26—C25—H25	119.4
H14B—C14A—H14C	109.5	C24—C25—H25	119.4
C16—C15—C14	121.1 (4)	N21—C26—C25	121.0 (4)
C16—C15—H15	119.5	N21—C26—H26	119.5
C14—C15—H15	119.5	C25—C26—H26	119.5