Crystal structure and Hirshfeld surface analysis of trans-2,5-di­methyl­piperazine-1,4-diium tetra­chlorido­cobaltate(II)

In the title mol­ecular salt, (C₆H₁₆N₂)[CoCl₄], the complete dication is generated by crystallographic inversion symmetry and the piperazine ring adopts a chair conformation with the pendant methyl groups in equatorial orientations. The complete dianion is generated by crystallographic twofold symmetry. In the crystal, the (C₆H₁₆N₂)²⁺ and [CoCl₄]²⁻ ions are linked by N—H⋯Cl and C—H⋯Cl hydrogen bonds, thereby forming a two-dimensional supra­molecular network.

Abstract

In the title mol­ecular salt, (C₆H₁₆N₂)[CoCl₄], the complete dication is generated by crystallographic inversion symmetry and the piperazine ring adopts a chair conformation with the pendant methyl groups in equatorial orientations. The complete dianion is generated by crystallographic twofold symmetry. In the crystal, the (C₆H₁₆N₂)²⁺ and [CoCl₄]²⁻ ions are linked by N—H⋯Cl and C—H⋯Cl hydrogen bonds, thereby forming a two-dimensional supra­molecular network. The Hirshfeld surface analysis and fingerprint plots reveal that the largest contributions to the crystal stability come from H⋯Cl/Cl⋯H (68.4%) and H⋯H (27.4%) contacts.

Chemical context  

Tetra­chloro­cobalt/copper (II) salts with organic cations, such as (C₆H₁₀N₃)₂[CoCl₄] (Titi et al. 2020 ▸), [(CH₃)₂NH₂]₂[CoCl₄] (Pietraszko et al. 2006 ▸) and (C₇H₇N₂S)₂[CuCl₄] (Vishwakarma et al. 2017 ▸) have received attention due to their potential applications in the electronic, magnetic, optical and anti­microbial fields. In these materials, the negative charge on the inorganic complex ion is balanced by the organic groups, which usually act as structure-directing agents by the formation of N—H⋯Cl hydrogen bonds and significantly affect the structure and dimensionality of the supra­molecular network.

As an extension of these studies, we now describe the synthesis, structure and Hirshfeld surface analysis of the title mol­ecular salt, (I).

Structural commentary  

The asymmetric unit of (I) comprises half of a trans-2,5-di­methyl­piperazine-1,4-dium cation and a half tetra­chlorido­cobaltate anion (Fig. 1 ▸). The cation and anion are completed by crystallographic inversion and twofold symmetry, respectively. In the organic species, the N—C and C—C bond lengths vary from 1.490 (2) to 1.513 (2) Å and the angles C—C—C, N—C—C and C—N—C range from 109.15 (14) to 113.54 (15)°. These data are in agreement with those reported in other salts of the trans-2,5-di­methyl­piperazine-1,4-diium cation (Gatfaoui et al., 2014 ▸; Ben Mleh et al., 2016 ▸). The Co²⁺ ion in (I) has a tetra­hedral geometry, with Cl—Co—Cl angles ranging from 103.32 (2) to 116.57 (3)°. The average length of the Co—Cl bonds, 2.27 Å, is close to that observed in similar complexes (Tahenti et al., 2020 ▸; Zhang et al., 2005 ▸; Zeller et al., 2005 ▸).

Figure 1.

The mol­ecular structure of (I) with displacement ellipsoids set to 50% probability and hydrogen bonds shown as dashed lines. Symmetry codes: (i) −x + 1, y, −z + ; (ii) −x + 2, −y + 1, −z + 1.

Supra­molecular features  

In the crystal of (I), adjacent anions are inter­connected by the cations via N—H⋯Cl hydrogen bonds and C—H⋯Cl inter­actions (Table 1 ▸) to form a layer built up from the organic and inorganic species, lying parallel to (101) (Fig. 2 ▸). The hydrogen bonds engage the chloride ions of the [CoCl₄]^2– tetra­hedron, producing four types of graph-set motifs on the basis of Etter’s notation (Etter et al., 1990 ▸; Bernstein et al., 1995 ▸). The isolated mol­ecules can be described by the elementary graph-set descriptors E^a_d (n) (Daszkiewicz, 2012 ▸). The graph-set descriptor of the pattern can be easily obtained by the summation of elementary E^a_d (n) graph-sets of isolated ions and mol­ecules. In the case of (I), the elementary graph-sets can be collected (Fig. 3 ▸) as follows:

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯Cl1i	0.89	2.30	3.1777 (2)	171
N1—H1B⋯Cl1	0.89	2.65	3.2594 (2)	126
N1—H1B⋯Cl2	0.89	2.49	3.2631 (2)	145
C1—H1C⋯Cl2ii	0.97	2.82	3.7065 (2)	153

Symmetry codes: (i) -x+2, y, -z+{\script{3\over 2}}; (ii) -x+1, -y+1, -z+1.

Figure 2.

(a) Crystal packing in the structure of (I) along the crystallographic a axis. (b) View of a supra­molecular layer along the b-axis direction.

Figure 3.

Hydrogen-bonding inter­actions between cations and anions showing the ring patterns of weak inter­actions formed by N—H⋯Cl/C—H⋯Cl links.

E ⁰ ₁ (1) + E ² ₀ (3) = (4)

2E ⁰ ₂ (3) + 2E ¹ ₀ (1) = (8)

E ⁰ ₂ (3) + E ² ₀ (5) = (8)

2E ¹ ₀ (1) + 2E ⁰ ₂ (4) = (10).

Hirshfeld surface analysis  

To further understand the different inter­actions and contacts in the crystal of (I), its Hirshfeld surface (HS) (McKinnon et al., 2004 ▸) was calculated. The d _norm surface (Fig. 4 ▸) and the associated two-dimensional fingerprint plots (see supporting information) were calculated using CrystalExplorer 3.1 (Wolff et al., 2013 ▸; Spackman & Jayatilaka, 2009 ▸). This figure shows the areas mapped in the range from −0.480 to 1.048 of the asymmetric ion-pair surrounded by neighboring ions where we can see some of the closest inter­molecular contacts. The large dark-red spots on the HS indicate close contact inter­actions, which are primarily responsible for significant hydrogen-bond contacts. The fingerprint plots indicate that the most important inter­actions are H⋯Cl/Cl⋯H, which cover a HS range of 68.4% and appear as two shape-symmetric spikes in the two-dimensional fingerprint maps (where d _i ∼d _e ∼1.4 Å). It should be also noted that the the van der Waals radii of the hydrogen and chlorine atoms are 1.20 and 1.75 Å, respectively. The H⋯H contacts represent the second most abundant inter­actions with 27.4% of the total Hirshfeld surface, including a short H⋯H contact near 2.4 Å (where d _i ∼d _e ∼1.2 Å), represented by a cluster of points accumulated on the diagonal of the graph. Other contacts including Cl⋯Cl and Co⋯H/H⋯Co have negligible contributions (respectively 2.7% and 1.5%). It can be concluded that the Cl⋯H/H⋯Cl inter­actions dominate in the title compound.

Figure 4.

Hirshfeld surface of (I) mapped over d _norm and the two-dimensional fingerprint plot for all inter­actions.

Synthesis and crystallization  

A 1:1 mixture of trans-2,5-di­methyl­piperazine and cobalt(II) chloride hexa­hydrate was dissolved in a solution of concentrated hydro­chloric acid and the resulting solution was magnetically stirred for 1 h. After two weeks of evaporation, dark-blue prismatic crystals of (I) had formed, which were recovered by filtration and dried in air.

Refinement  

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. The N-bound and C-bound hydrogen atoms were positioned geometrically and treated as riding atoms: N—H = 0.86 Å, C—H = 0.96 Å with U _iso(H) = 1.2U _eq(N,C).

Table 2. Experimental details.

Crystal data
Chemical formula	C6H16N2 2+·Cl4Co2−
M r	316.94
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	293
a, b, c (Å)	7.6431 (3), 11.9347 (6), 14.0058 (7)
β (°)	95.519 (4)
V (Å3)	1271.66 (10)
Z	4
Radiation type	Mo Kα
μ (mm−1)	2.15
Crystal size (mm)	0.15 × 0.10 × 0.08
Data collection
Diffractometer	Agilent SuperNova, Single source at offset, Eos
Absorption correction	Multi-scan (CrysAlis PRO; Agilent 2014 ▸)
T min, T max	0.816, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	4627, 1546, 1370
R int	0.029
(sin θ/λ)max (Å−1)	0.685
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.028, 0.074, 1.08
No. of reflections	1546
No. of parameters	60
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	0.27, −0.59

Computer programs: CrysAlis PRO (Agilent, 2014 ▸), SIR92 (Altomare et al., 1994 ▸), SHELXL2017/1 (Sheldrick, 2015 ▸), DIAMOND (Brandenburg, 2006 ▸) and ORTEP-III (Burnett & Johnson, 1996 ▸).

Supplementary Material

CCDC reference: 1831453

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

supplementary crystallographic information

Crystal data

C6H16N22+·Cl4Co2−	F(000) = 644
Mr = 316.94	Dx = 1.655 Mg m−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 7.6431 (3) Å	Cell parameters from 2258 reflections
b = 11.9347 (6) Å	θ = 4.1–29.0°
c = 14.0058 (7) Å	µ = 2.15 mm−1
β = 95.519 (4)°	T = 293 K
V = 1271.66 (10) Å3	Prism, blue
Z = 4	0.15 × 0.10 × 0.08 mm

Data collection

Agilent SuperNova, Single source at offset, Eos diffractometer	1370 reflections with I > 2σ(I)
Detector resolution: 16.0233 pixels mm-1	Rint = 0.029
ω scans	θmax = 29.1°, θmin = 3.4°
Absorption correction: multi-scan (CrysAlisPro; Agilent 2014)	h = −10→9
Tmin = 0.816, Tmax = 1.000	k = −15→15
4627 measured reflections	l = −18→13
1546 independent reflections

Refinement

Refinement on F2	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.028	H-atom parameters constrained
wR(F2) = 0.074	w = 1/[σ2(Fo2) + (0.0365P)2 + 0.515P] where P = (Fo2 + 2Fc2)/3
S = 1.08	(Δ/σ)max = 0.027
1546 reflections	Δρmax = 0.27 e Å−3
60 parameters	Δρmin = −0.59 e Å−3

Special details

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.

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

	x	y	z	Uiso*/Ueq
Co1	0.500000	0.52995 (3)	0.750000	0.02694 (13)
Cl1	0.74705 (6)	0.42227 (4)	0.77647 (3)	0.03237 (14)
Cl2	0.54849 (7)	0.62944 (5)	0.61790 (4)	0.04332 (16)
N1	0.9250 (2)	0.51194 (13)	0.58839 (11)	0.0276 (3)
H1A	1.015221	0.493869	0.630538	0.033*
H1B	0.833857	0.527625	0.621121	0.033*
C1	0.8798 (2)	0.41357 (16)	0.52524 (14)	0.0290 (4)
H1C	0.774246	0.429831	0.483440	0.035*
H1D	0.856092	0.349324	0.564406	0.035*
C2	1.0282 (2)	0.38575 (15)	0.46508 (13)	0.0272 (4)
H2	1.130901	0.361989	0.507561	0.033*
C3	0.9775 (3)	0.29268 (17)	0.39440 (16)	0.0404 (5)
H3A	0.947344	0.226813	0.428597	0.061*
H3B	0.878228	0.315843	0.351734	0.061*
H3C	1.074621	0.276353	0.358031	0.061*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Co1	0.02007 (18)	0.0374 (2)	0.0236 (2)	0.000	0.00304 (14)	0.000
Cl1	0.0239 (2)	0.0401 (3)	0.0327 (3)	0.00345 (18)	0.00040 (18)	0.00462 (18)
Cl2	0.0334 (3)	0.0564 (3)	0.0408 (3)	0.0047 (2)	0.0073 (2)	0.0198 (2)
N1	0.0252 (7)	0.0368 (8)	0.0217 (8)	−0.0012 (6)	0.0072 (6)	0.0004 (6)
C1	0.0262 (9)	0.0337 (10)	0.0279 (10)	−0.0075 (7)	0.0065 (7)	−0.0013 (7)
C2	0.0253 (8)	0.0307 (9)	0.0255 (9)	0.0012 (7)	0.0023 (7)	0.0026 (7)
C3	0.0450 (11)	0.0375 (11)	0.0394 (12)	−0.0026 (9)	0.0074 (10)	−0.0076 (9)

Geometric parameters (Å, º)

Co1—Cl2i	2.2588 (5)	C1—C2	1.513 (2)
Co1—Cl2	2.2588 (5)	C1—H1C	0.9700
Co1—Cl1	2.2846 (5)	C1—H1D	0.9700
Co1—Cl1i	2.2847 (5)	C2—C3	1.513 (3)
N1—C1	1.490 (2)	C2—H2	0.9800
N1—C2ii	1.494 (2)	C3—H3A	0.9600
N1—H1A	0.8900	C3—H3B	0.9600
N1—H1B	0.8900	C3—H3C	0.9600
Cl2i—Co1—Cl2	116.57 (3)	N1—C1—H1D	109.4
Cl2i—Co1—Cl1	111.157 (19)	C2—C1—H1D	109.4
Cl2—Co1—Cl1	103.324 (18)	H1C—C1—H1D	108.0
Cl2i—Co1—Cl1i	103.325 (18)	N1ii—C2—C1	109.15 (14)
Cl2—Co1—Cl1i	111.155 (19)	N1ii—C2—C3	109.31 (16)
Cl1—Co1—Cl1i	111.54 (3)	C1—C2—C3	111.50 (16)
C1—N1—C2ii	113.54 (15)	N1ii—C2—H2	108.9
C1—N1—H1A	108.9	C1—C2—H2	108.9
C2ii—N1—H1A	108.9	C3—C2—H2	108.9
C1—N1—H1B	108.9	C2—C3—H3A	109.5
C2ii—N1—H1B	108.9	C2—C3—H3B	109.5
H1A—N1—H1B	107.7	H3A—C3—H3B	109.5
N1—C1—C2	111.10 (14)	C2—C3—H3C	109.5
N1—C1—H1C	109.4	H3A—C3—H3C	109.5
C2—C1—H1C	109.4	H3B—C3—H3C	109.5
C2ii—N1—C1—C2	56.5 (2)	N1—C1—C2—C3	−174.91 (16)
N1—C1—C2—N1ii	−54.0 (2)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···Cl1iii	0.89	2.30	3.1777 (2)	171
N1—H1B···Cl1	0.89	2.65	3.2594 (2)	126
N1—H1B···Cl2	0.89	2.49	3.2631 (2)	145
C1—H1C···Cl2iv	0.97	2.82	3.7065 (2)	153

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