Crystal structure of 1,4-bis-(3-ammonio-prop-yl)piperazine-1,4-diium bis-[dichromate(VI)].

The asymmetric unit of the organic-inorganic title salt, (C10H28N4)[Cr2O7]2, comprises one half of an 1,4-bis-(3-ammonio-prop-yl)piperazinediium cation (the other half being generated by the application of inversion symmetry) and a dichromate anion. The piperazine ring of the cation adopts a chair conformation, and the two CrO4 tetra-hedra of the anion are in an almost eclipsed conformation. In the crystal, the cations and anions form a layered arrangement parallel to (001). N-H⋯O hydrogen bonds between the cations and anions and additional C-H⋯O inter-actions lead to the formation of a three-dimensional network structure.

Chemical context

Chromium is usually found in trivalent and hexa­valent oxidation states in soil, ground water and seawater (Cespón-Romero et al., 1996 ▸). Trivalent chromium is an essential element in mammals for maintaining efficient glucose, lipid and protein metabolism. On the other hand, hexa­valent chromium is toxic and recognized as a carcinogen to humans and wildlife. Hence the dichromate ion is environmentally important due to its high toxicity (Yusof & Malek, 2009 ▸) and its use in many industrial processes (Goyal et al., 2003 ▸). Recently, the reactions between hexa­ureachromium(III) and inorganic oxoanions (such as Cr2O7 2− or CrO4 2−) in aqueous solution have been investigated (Moon et al., 2015 ▸). Numerous piperazine derivatives have shown a wide spectrum of biological activities, viz. anti­bacterial (Foroumadi et al., 2007 ▸), anti­fungal (Upadhayaya et al., 2004 ▸), anti­cancer (Chen et al., 2006 ▸), anti­parasitic (Cunico et al., 2009 ▸), anti­histamine (Smits et al., 2008 ▸) or anti­depressive activities (Becker et al., 2006 ▸). Anti­diabetic, anti-inflammatory, anti­tubercular, anti­malarial, anti­convulsant, anti­pyretic, anti­tumor, anthelmintic and analgesic activities (Gan et al., 2009a ▸,b ▸; Willems & Ilzerman, 2010 ▸) have also been found to be caused by this versatile moiety. In view of these important properties, we have undertaken the synthesis and X-ray diffraction study of the title compound.

Structural commentary

The mol­ecular entities of the title compound, consisting of a centrosymmetric 1,4-bis­(3-ammonio­prop­yl)piperazinediium cation and a dichromate anion, are shown in Fig. 1 ▸. In the cation, the central piperazine ring (N1/C1/C2/N1i/C1i/C2i; for symmetry operators, see Fig. 1 ▸) is substituted at the two N atoms by two ammonio­propyl moieties. The piperazine ring adopts a chair conformation, as is evident from the puckering parameters: Q = 0.599 (2) Å, τ = 180.0° and φ = 0°. Atoms N1 and N1i are on opposite sides of the C1/C1i/C2/C2i plane and are both displaced from it by 0.2446 (19) Å. The chair conformation of the cation in the title structure is very similar to those of the same cation in the crystal structures of the 2-hy­droxy­benzoate (Cukrowski et al., 2012 ▸), the nitrate (Junk & Smith, 2005 ▸) and the tetra­hydrogenpenta­borate (Jiang et al., 2009 ▸) salts, despite the differences in the size and shape of the anions in the various structures. The tetra­hedral CrO4 groups in the anion of the title structure are fused together by a common O atom (O8) and are in an almost eclipsed conformation (Brandon & Brown, 1968 ▸). The Cr—O bond lengths follow the characteristic distribution for dichromate anions, with two longer bridging Cr—O bonds of 1.7676 (16) and 1.7746 (15) Å and six shorter terminal Cr—O bonds [range 1.5909 (19)–1.6185 (15) Å]. The Cr1—O8—Cr2 bridging angle in the complex anion is 127.48 (10)°. The tetra­hedral O—Cr—O bond angles [range 106.52 (8) to 112.85 (12)°] indicate slight angular distortions.

Figure 1

The entities of the organic–inorganic title salt. Displacement ellipsoids are drawn at the 30% probability level. [Symmetry code: (i) −x + 2, −y, −z + 1.]

Supra­molecular features

The organic cations and inorganic anions are each arranged in rows parallel to [100] and alternate with each other along [010], forming a layered arrangement parallel to (001). N—H⋯O hydrogen bonds (Table 1 ▸) between the cations, involving both primary and tertiary ammonium groups, and the anions lead to a three-dimensional network structure (Figs. 2 ▸ and 3 ▸). Additional C—H⋯O inter­actions consolidate this arrangement.

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C1—H1A⋯O3i	0.97	2.28	3.176 (3)	152
C1—H1A⋯O4ii	0.97	2.61	3.248 (3)	123
C1—H1B⋯O6	0.97	2.53	3.353 (3)	143
C2—H2A⋯O2iii	0.97	2.49	3.298 (3)	141
C2—H2A⋯O4iii	0.97	2.59	3.061 (3)	110
C2—H2B⋯O7iv	0.97	2.59	3.232 (2)	124
C3—H3B⋯O3i	0.97	2.58	3.383 (3)	140
C4—H4A⋯O5v	0.97	2.38	3.208 (3)	143
C4—H4B⋯O7iii	0.97	2.64	3.309 (2)	127
N2—H6A⋯O2vi	0.89	2.18	3.040 (2)	161
N2—H6B⋯O7iii	0.89	2.05	2.854 (2)	149
N2—H6C⋯O2v	0.89	2.22	2.865 (2)	129
N2—H6C⋯O5iii	0.89	2.64	3.239 (3)	125
N1—H1⋯O4iii	0.98	2.43	3.113 (2)	126
N1—H1⋯O7	0.98	1.95	2.763 (2)	139

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) ; (vi) .

Figure 2

The packing of the mol­ecular entities in the crystal structure of the title salt.

Figure 3

A part of the crystal structure of the title salt in a view along [100] showing N—H⋯O hydrogen-bonding inter­actions as dashed lines. C—H⋯O inter­actions are omitted for clarity.

Synthesis and crystallization

Potassium dichromate and 1,4-bis­(3-amino­prop­yl)piperazine (PDBP) were mixed in a molar ratio of 2:1 in water. Potassium dichromate was first dissolved in Millipore water of 18.2 MΩ·cm resistivity. Then the amount of PDBP was slowly added to the solution together with a few drops of concentrated hydro­chloric acid and the mixture stirred for 18 h. The solution was then filtered twice with Wattmann filter paper and poured into petri dishes to evaporate at room temperature for several days. Recrystallization from water improved the quality of the material and increased the size of the crystals (maximum crystal size 5×3×2 mm3 after 35 d). A specimen was cleaved for the present structure determination.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. All hydrogen atoms were placed geometrically and refined using a riding model: N—H = 0.89 Å for the primary ammonium group with U iso(H) = 1.5U eq(N); N—H = 0.98 Å for the tertiary ammonium group with U iso(H) = 1.2U eq(N); C—H = 0.97 Å with U iso(H) = 1.2U eq(C).

Table 2

Experimental details

Crystal data
Chemical formula	(C10H28N4)[Cr2O7]2
M r	636.36
Crystal system, space group	Triclinic, P
Temperature (K)	293
a, b, c (Å)	8.5361 (3), 8.6272 (3), 8.8576 (3)
α, β, γ (°)	77.761 (1), 72.307 (1), 60.985 (1)
V (Å3)	541.81 (3)
Z	1
Radiation type	Mo Kα
μ (mm−1)	2.03
Crystal size (mm)	0.35 × 0.30 × 0.25
Data collection
Diffractometer	Bruker Kappa APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2004 ▸)
T min, T max	0.528, 0.649
No. of measured, independent and observed [I > 2σ(I)] reflections	10263, 1913, 1835
R int	0.020
(sin θ/λ)max (Å−1)	0.595
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.023, 0.068, 1.06
No. of reflections	1913
No. of parameters	145
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	0.44, −0.45

Computer programs: APEX2 and SAINT (Bruker, 2004 ▸), SHELXT (Sheldrick, 2015a ▸), SHELXL2014/7 (Sheldrick, 2015b ▸), ORTEP-3 for Windows and WinGX (Farrugia, 2012 ▸) and PLATON (Spek, 2009 ▸).

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S2056989016005284/wm5281sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989016005284/wm5281Isup2.hkl

CCDC reference: 1471068

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

(C10H28N4)[Cr2O7]2	Z = 1
Mr = 636.36	F(000) = 324
Triclinic, P1	Dx = 1.950 Mg m−3
a = 8.5361 (3) Å	Mo Kα radiation, λ = 0.71073 Å
b = 8.6272 (3) Å	Cell parameters from 9982 reflections
c = 8.8576 (3) Å	θ = 2.4–39.1°
α = 77.761 (1)°	µ = 2.03 mm−1
β = 72.307 (1)°	T = 293 K
γ = 60.985 (1)°	Needle, brown
V = 541.81 (3) Å3	0.35 × 0.30 × 0.25 mm

Bruker Kappa APEXII CCD diffractometer	1913 independent reflections
Radiation source: fine-focus sealed tube	1835 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.020
ω and φ scan	θmax = 25.0°, θmin = 2.4°
Absorption correction: multi-scan (SADABS; Bruker, 2004)	h = −10→10
Tmin = 0.528, Tmax = 0.649	k = −10→10
10263 measured reflections	l = −10→10

Refinement on F2	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.023	H-atom parameters constrained
wR(F2) = 0.068	w = 1/[σ2(Fo2) + (0.0379P)2 + 0.4739P] where P = (Fo2 + 2Fc2)/3
S = 1.06	(Δ/σ)max < 0.001
1913 reflections	Δρmax = 0.44 e Å−3
145 parameters	Δρmin = −0.45 e Å−3

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.

	x	y	z	Uiso*/Ueq
C1	0.9278 (3)	0.1703 (3)	0.4169 (2)	0.0217 (4)
H1A	0.9548	0.2371	0.4721	0.026*
H1B	0.8679	0.2498	0.3344	0.026*
C2	0.8955 (3)	−0.0195 (3)	0.6574 (2)	0.0209 (4)
H2A	0.8158	−0.0661	0.7319	0.025*
H2B	0.9217	0.0454	0.7154	0.025*
C3	0.6197 (3)	0.2538 (3)	0.5974 (3)	0.0247 (4)
H3A	0.5710	0.3344	0.5101	0.030*
H3B	0.6391	0.3191	0.6608	0.030*
C4	0.4805 (3)	0.1911 (3)	0.6986 (2)	0.0218 (4)
H4A	0.5194	0.1252	0.7946	0.026*
H4B	0.4723	0.1127	0.6407	0.026*
C5	0.2943 (3)	0.3494 (3)	0.7415 (3)	0.0259 (4)
H5A	0.3046	0.4315	0.7931	0.031*
H5B	0.2522	0.4109	0.6457	0.031*
N2	0.1592 (2)	0.2910 (2)	0.8492 (2)	0.0261 (4)
H6A	0.0501	0.3852	0.8736	0.039*
H6B	0.1488	0.2168	0.8012	0.039*
H6C	0.1973	0.2358	0.9376	0.039*
N1	0.8006 (2)	0.1028 (2)	0.53184 (19)	0.0183 (3)
H1	0.7772	0.0338	0.4742	0.022*
O2	0.1839 (2)	0.3536 (2)	0.14426 (19)	0.0359 (4)
O3	0.1272 (2)	0.5696 (2)	0.3451 (2)	0.0402 (4)
O4	0.2800 (2)	0.2224 (2)	0.41686 (19)	0.0359 (4)
O5	0.6705 (3)	0.1105 (3)	−0.0133 (2)	0.0612 (6)
O6	0.8440 (3)	0.2646 (3)	0.0538 (3)	0.0564 (6)
O7	0.7517 (2)	0.0359 (2)	0.26223 (19)	0.0325 (4)
O8	0.4835 (2)	0.3730 (2)	0.1987 (2)	0.0370 (4)
Cr1	0.26337 (4)	0.37840 (4)	0.27693 (4)	0.02227 (12)
Cr2	0.69282 (5)	0.19141 (5)	0.11987 (4)	0.02748 (13)

	U11	U22	U33	U12	U13	U23
C1	0.0192 (10)	0.0226 (9)	0.0222 (10)	−0.0120 (8)	−0.0008 (8)	0.0007 (8)
C2	0.0202 (10)	0.0260 (10)	0.0166 (9)	−0.0124 (8)	−0.0013 (7)	−0.0014 (8)
C3	0.0179 (10)	0.0213 (10)	0.0303 (11)	−0.0073 (8)	0.0011 (8)	−0.0071 (8)
C4	0.0157 (9)	0.0230 (10)	0.0246 (10)	−0.0080 (8)	−0.0029 (8)	−0.0026 (8)
C5	0.0200 (10)	0.0246 (10)	0.0281 (11)	−0.0088 (8)	0.0008 (8)	−0.0051 (8)
N2	0.0163 (8)	0.0313 (9)	0.0275 (9)	−0.0091 (7)	−0.0014 (7)	−0.0056 (7)
N1	0.0155 (8)	0.0201 (8)	0.0190 (8)	−0.0087 (7)	−0.0006 (6)	−0.0042 (6)
O2	0.0460 (10)	0.0430 (9)	0.0291 (8)	−0.0252 (8)	−0.0145 (7)	−0.0021 (7)
O3	0.0322 (9)	0.0346 (9)	0.0514 (10)	−0.0121 (7)	−0.0011 (8)	−0.0190 (8)
O4	0.0387 (9)	0.0418 (9)	0.0313 (8)	−0.0217 (8)	−0.0124 (7)	0.0042 (7)
O5	0.0591 (13)	0.0843 (15)	0.0348 (10)	−0.0178 (12)	−0.0145 (9)	−0.0260 (10)
O6	0.0323 (10)	0.0645 (13)	0.0619 (13)	−0.0286 (9)	0.0011 (9)	0.0150 (10)
O7	0.0384 (9)	0.0356 (9)	0.0321 (8)	−0.0221 (7)	−0.0120 (7)	−0.0006 (7)
O8	0.0250 (8)	0.0364 (9)	0.0484 (10)	−0.0163 (7)	0.0005 (7)	−0.0085 (7)
Cr1	0.02026 (19)	0.0254 (2)	0.02321 (19)	−0.01134 (15)	−0.00346 (13)	−0.00582 (13)
Cr2	0.02130 (19)	0.0382 (2)	0.0210 (2)	−0.01414 (16)	−0.00041 (14)	−0.00334 (15)

C1—N1	1.498 (2)	C5—N2	1.478 (3)
C1—C2i	1.502 (3)	C5—H5A	0.9700
C1—H1A	0.9700	C5—H5B	0.9700
C1—H1B	0.9700	N2—H6A	0.8900
C2—N1	1.493 (2)	N2—H6B	0.8900
C2—C1i	1.502 (3)	N2—H6C	0.8900
C2—H2A	0.9700	N1—H1	0.9800
C2—H2B	0.9700	O2—Cr1	1.6185 (15)
C3—N1	1.498 (2)	O3—Cr1	1.6035 (16)
C3—C4	1.509 (3)	O4—Cr1	1.6070 (16)
C3—H3A	0.9700	O5—Cr2	1.5909 (19)
C3—H3B	0.9700	O6—Cr2	1.6068 (18)
C4—C5	1.511 (3)	O7—Cr2	1.6299 (16)
C4—H4A	0.9700	O8—Cr2	1.7676 (16)
C4—H4B	0.9700	O8—Cr1	1.7746 (15)
N1—C1—C2i	111.02 (16)	C4—C5—H5B	109.6
N1—C1—H1A	109.4	H5A—C5—H5B	108.1
C2i—C1—H1A	109.4	C5—N2—H6A	109.5
N1—C1—H1B	109.4	C5—N2—H6B	109.5
C2i—C1—H1B	109.4	H6A—N2—H6B	109.5
H1A—C1—H1B	108.0	C5—N2—H6C	109.5
N1—C2—C1i	110.02 (15)	H6A—N2—H6C	109.5
N1—C2—H2A	109.7	H6B—N2—H6C	109.5
C1i—C2—H2A	109.7	C2—N1—C3	113.18 (15)
N1—C2—H2B	109.7	C2—N1—C1	108.55 (15)
C1i—C2—H2B	109.7	C3—N1—C1	110.86 (15)
H2A—C2—H2B	108.2	C2—N1—H1	108.0
N1—C3—C4	112.22 (16)	C3—N1—H1	108.0
N1—C3—H3A	109.2	C1—N1—H1	108.0
C4—C3—H3A	109.2	Cr2—O8—Cr1	127.48 (10)
N1—C3—H3B	109.2	O3—Cr1—O4	110.80 (9)
C4—C3—H3B	109.2	O3—Cr1—O2	108.95 (9)
H3A—C3—H3B	107.9	O4—Cr1—O2	109.39 (8)
C3—C4—C5	109.66 (16)	O3—Cr1—O8	106.52 (8)
C3—C4—H4A	109.7	O4—Cr1—O8	108.31 (8)
C5—C4—H4A	109.7	O2—Cr1—O8	112.85 (9)
C3—C4—H4B	109.7	O5—Cr2—O6	112.85 (12)
C5—C4—H4B	109.7	O5—Cr2—O7	107.91 (11)
H4A—C4—H4B	108.2	O6—Cr2—O7	109.68 (9)
N2—C5—C4	110.30 (16)	O5—Cr2—O8	111.08 (10)
N2—C5—H5A	109.6	O6—Cr2—O8	106.39 (10)
C4—C5—H5A	109.6	O7—Cr2—O8	108.89 (8)
N2—C5—H5B	109.6
N1—C3—C4—C5	−171.94 (16)	C2i—C1—N1—C3	−176.16 (16)
C3—C4—C5—N2	−176.35 (16)	Cr2—O8—Cr1—O3	175.26 (12)
C1i—C2—N1—C3	178.15 (15)	Cr2—O8—Cr1—O4	56.03 (15)
C1i—C2—N1—C1	−58.3 (2)	Cr2—O8—Cr1—O2	−65.22 (15)
C4—C3—N1—C2	−64.5 (2)	Cr1—O8—Cr2—O5	52.36 (17)
C4—C3—N1—C1	173.31 (16)	Cr1—O8—Cr2—O6	175.53 (13)
C2i—C1—N1—C2	58.9 (2)	Cr1—O8—Cr2—O7	−66.33 (14)

D—H···A	D—H	H···A	D···A	D—H···A
C1—H1A···O3ii	0.97	2.28	3.176 (3)	152
C1—H1A···O4iii	0.97	2.61	3.248 (3)	123
C1—H1B···O6	0.97	2.53	3.353 (3)	143
C2—H2A···O2iv	0.97	2.49	3.298 (3)	141
C2—H2A···O4iv	0.97	2.59	3.061 (3)	110
C2—H2B···O7i	0.97	2.59	3.232 (2)	124
C3—H3B···O3ii	0.97	2.58	3.383 (3)	140
C4—H4A···O5v	0.97	2.38	3.208 (3)	143
C4—H4B···O7iv	0.97	2.64	3.309 (2)	127
N2—H6A···O2vi	0.89	2.18	3.040 (2)	161
N2—H6B···O7iv	0.89	2.05	2.854 (2)	149
N2—H6C···O2v	0.89	2.22	2.865 (2)	129
N2—H6C···O5iv	0.89	2.64	3.239 (3)	125
N1—H1···O4iv	0.98	2.43	3.113 (2)	126
N1—H1···O7	0.98	1.95	2.763 (2)	139