Hemi(piperazinediium) hexaaqua­aluminium(III) bis­(sulfate) tetrahydrate: a new double aluminium sulfate salt

Piperazinium aluminium sulfate decahydrate, (C₄H₁₂N₂)_0.5[Al(H₂O)₆](SO₄)₂·4H₂O, exhibits a crystal structure built from isolated [Al(H₂O)₆]³⁺, SO₄^2-, C₄H₁₂N₂²⁺ and H₂O units connected by a complex hydrogen-bond network. The title compound shows strong similarities to many double alumin­ium sulfates, such as alums and Tutton's salts. However, since its structure is not derived directly from that of these compounds, it is assumed to be a new structure type.

S1. Comment

Studies in sulfate-based chemistry have recently experienced a resurgence in interest, with the use of the SO₄²⁻ anion as a tetrahedral building block and amines as templates (Choudhury et al., 2001; Norquist et al., 2003). The new amine lanthanum sulfates obtained recently (Bataille & Louër, 2002; Xing et al., 2003) also offer a promising route to open structures. In a similar manner, by using trivalent aluminium, it would be expected that materials with open frameworks constructed only from tetrahedral building units can be prepared. Instead, the crystal structure of the new aluminium piperazinium sulfate decahydrate obtained here, viz. (C₄H₁₂N₂)_0.5Al(H₂O)₆(SO₄)₂·4H₂O, (I), consists of isolated entities linked through a complex hydrogen-bond network. The present work also deals with the similarities of the crystal structure of (I) to those of other double aluminium sulfates, such as Tutton's salts and alums, although structural features are different.

Alums [general formula A^IM^III(SO₄)₂.12H₂O] and Tutton's salts [general formula A^I₂M^II(SO₄)₂·6H₂O] are two large families of double salts that include the sulfate anion. The chemical formula of (I) can be written as [(C₄H₁₂N₂)_0.5]Al(SO₄)₂.10H₂O. Compound (I) is related to the alum family, except that A is a divalent cation with halved stoichiometry and the compound is decahydrated. Nevertheless, the space-group symmetry of (I) (P2₁/n) is comparable to that of dimethylammonium aluminium sulfate hexahydrate (P2₁/n; Galesic & Jordanovska, 1992) and Tutton's salts (P2₁/a; see e.g. Maslen et al., 1988), while alums crystallize with a cubic symmetry. The structure of (I) (Figs. 1 and 2) consists of Al³⁺ ions octahedrally coordinated by six water molecules, sulfate tetrahedra, piperazinium cations and non-bonded water molecules, linked by hydrogen bonds only. This feature has already been observed in, for example, piperazinium sulfate monohydrate (Jayaraman et al., 2002). Contrarily to other double aluminium sulfates, for which the metal atom is located at the origin of the cell, the Al atom in the crystal structure of (I) lies on a general position. Selected bond lengths are given in Table 1. The Al—OW bond lengths range from 1.862 (2) to 1.887 (2) Å [mean 1.876 (2) Å], in agreement with the value (1.876 Å) calculated from the bond-valence program VALENCE (Brown, 1996) for a sixfold oxygen-coordinated Al atom. The S—O distances fall into the range 1.461 (2)–1.481 (2) Å [mean 1.473 (2) Å], which is comparable to the value (1.474 Å) calculated from the bond-valence method. This bond length fits well with that observed in many Tutton's salts, while it is generally slightly smaller in alums (Petrusevski, 1994). No disorder of the amine group is observed, and the centre of the piperazinium group corresponds to the inversion centre of the unit cell. In the dimethylammonium salt (Galesic & Jordanovska, 1992), the amine group is disordered around the inversion centre, and in α alums, the monovalent A^I cations are disordered around the special position 4 b of space group Pa3 (Larson & Cromer, 1967), while in Tutton's salts, the A^I cations lie in general positions (Maslen et al., 1988). The presence of a diprotonated amine group and ten water molecules leads to a complex hydrogen bond network, involving 22 H atoms (Table 2).

With respect to the arguments given above, it is clear that the crystal structure of (I) has some similarities with the other double aluminium sulfate salts. Nevertheless, these similarities are not sufficent to allow us to consider (I) as belonging to the known families of double salts, such as alums and Tutton's salts. For this reason, it is likely that (I) is the first member of a new family of double aluminium sulfates. It is therefore of interest to investigate further new aluminium sulfates prepared in the presence of diprotonated amines, in order to establish whether similarities exist with (I).

S2. Experimental

Single crystals of (I) were obtained by dissolving Al₂(SO₄)₃.18H₂O (0.75 mmol) and piperazine hexahydrate (2 mmol) in H₂O (7 ml), acidified with H₂SO₄ (0.5 ml). The clear solution was allowed to stand for two months, until large crystals were obtained. The product was filtered off and washed with a small amount of distilled water, since the crystals appeared to be slightly soluble.

S3. Refinement

All 26 H atoms were located from difference Fourier syntheses and their positions were refined isotropically, with O—H, C—H and N—H distances restrained to 0.97 (2) Å and H—H distances restrained to 1.55 (3) Å. The atomic displacements parameters of the H atoms were fixed at 1.5U_eq of their bonded atoms.

Computing details

Data collection: COLLECT (Nonius, 1998); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg & Berndt, 1999); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. A projection of the structure of (I) along the a axis, showing the hydrogen-bond network between the Al(H2O)6^3+ (light grey octahedra), SO4^2− (dark grey tetrahedra), C4H12N2^2+ and H2O entities. Hydrogen bonds formed via water molecules are represented by thick dashed lines, while bonds involving N atoms are as thin lines. H atoms have been omitted for clarity.
	Fig. 2. A part of the crystal structure, showing the assymetric unit and atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen bonds are represented by dashed lines. [Symmetry code: (i) −x, −y, −z.]

Hexaaquaaluminium hemi(piperidin-1,4-diium) bis(sulfate) tetrahydrate

Crystal data

[Al(H2O)6](C4H12N2)0.5(SO4)2·4H2O	F(000) = 936
Mr = 443.32	Dx = 1.725 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 11232 reflections
a = 6.5737 (1) Å	θ = 1.0–27.5°
b = 12.0671 (2) Å	µ = 0.45 mm^−1
c = 21.5206 (5) Å	T = 293 K
β = 90.0815 (7)°	Prism, colourless
V = 1707.13 (6) Å^3	0.52 × 0.13 × 0.08 mm
Z = 4

Data collection

Nonius KappaCCD diffractometer	3911 independent reflections
Radiation source: fine-focus sealed tube	2991 reflections with I > 2σ(I)
Horizonally mounted graphite crystal monochromator	Rint = 0.070
Detector resolution: 9 pixels mm^-1	θmax = 27.5°, θmin = 1.9°
CCD scans	h = −7→8
Absorption correction: analytical (de Meulenaer & Tompa, 1965)	k = −15→15
Tmin = 0.797, Tmax = 0.967	l = −27→27
19066 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)] = 0.038	Only H-atom coordinates refined
wR(F^2) = 0.105	w = 1/[σ^2(Fo^2) + (0.047P)^2 + 0.84P] where P = (Fo^2 + 2Fc^2)/3
S = 1.07	(Δ/σ)max = 0.001
3911 reflections	Δρmax = 0.35 e Å^−3
296 parameters	Δρmin = −0.47 e Å^−3
39 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: 0.0181 (13)

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
Al	0.46346 (9)	0.06257 (5)	0.36703 (3)	0.01848 (17)
S1	−0.04464 (7)	−0.02962 (5)	0.19203 (3)	0.02159 (16)
S2	−0.03341 (7)	0.19082 (5)	0.54279 (3)	0.02035 (16)
O11	0.1573 (2)	0.00189 (17)	0.21618 (8)	0.0374 (5)
O12	−0.1636 (2)	−0.08206 (15)	0.24188 (8)	0.0321 (4)
O13	−0.1513 (3)	0.06939 (14)	0.16931 (8)	0.0310 (4)
O14	−0.0184 (2)	−0.10540 (14)	0.13885 (8)	0.0303 (4)
O21	0.0369 (2)	0.10820 (14)	0.58895 (8)	0.0296 (4)
O22	−0.2297 (2)	0.15197 (15)	0.51702 (8)	0.0311 (4)
O23	−0.0637 (3)	0.29737 (14)	0.57433 (8)	0.0332 (4)
O24	0.1169 (3)	0.20343 (15)	0.49335 (9)	0.0361 (4)
O91	0.6997 (2)	0.13038 (14)	0.39754 (8)	0.0264 (4)
H11	0.736 (4)	0.136 (2)	0.4395 (8)	0.040*
H12	0.789 (4)	0.173 (2)	0.3718 (11)	0.040*
O92	0.5822 (2)	−0.07765 (14)	0.37573 (8)	0.0254 (4)
H21	0.538 (4)	−0.135 (2)	0.3492 (12)	0.038*
H22	0.713 (3)	−0.089 (2)	0.3906 (13)	0.038*
O93	0.3435 (2)	0.20113 (13)	0.35657 (8)	0.0256 (4)
H31	0.411 (4)	0.2691 (17)	0.3573 (14)	0.038*
H32	0.207 (3)	0.210 (2)	0.3469 (14)	0.038*
O94	0.2249 (2)	−0.00430 (15)	0.33620 (8)	0.0260 (4)
H41	0.195 (4)	−0.005 (2)	0.2947 (10)	0.039*
H42	0.129 (4)	−0.041 (2)	0.3617 (11)	0.039*
O95	0.5681 (2)	0.07082 (14)	0.28555 (7)	0.0260 (4)
H51	0.541 (4)	0.1234 (19)	0.2539 (11)	0.039*
H52	0.664 (4)	0.0189 (19)	0.2694 (12)	0.039*
O96	0.3613 (2)	0.05051 (14)	0.44826 (7)	0.0236 (4)
H61	0.266 (4)	0.1013 (18)	0.4633 (13)	0.035*
H62	0.329 (4)	−0.0209 (14)	0.4600 (13)	0.035*
C1	0.2107 (4)	−0.0345 (2)	−0.00223 (13)	0.0346 (6)
H11C	0.323 (4)	−0.073 (2)	0.0168 (13)	0.052*
H12C	0.259 (4)	0.008 (2)	−0.0365 (11)	0.052*
N2	0.1358 (3)	0.04742 (19)	0.04449 (10)	0.0317 (5)
H21N	0.245 (4)	0.097 (2)	0.0569 (14)	0.048*
H22N	0.091 (4)	0.004 (2)	0.0806 (11)	0.048*
C3	0.0403 (4)	−0.1119 (2)	−0.02072 (14)	0.0342 (6)
H31C	0.081 (5)	−0.161 (2)	−0.0536 (11)	0.051*
H32C	−0.007 (5)	−0.150 (2)	0.0149 (10)	0.051*
O97	0.4655 (3)	0.23163 (15)	0.20611 (8)	0.0324 (4)
H71	0.552 (4)	0.290 (2)	0.2198 (13)	0.049*
H72	0.471 (5)	0.223 (2)	0.1627 (8)	0.049*
O98	0.4714 (3)	−0.03325 (16)	0.13190 (9)	0.0345 (4)
H81	0.378 (4)	−0.019 (3)	0.1641 (12)	0.052*
H82	0.589 (3)	0.007 (2)	0.1390 (14)	0.052*
O99	−0.0392 (2)	0.25312 (15)	0.33211 (9)	0.0309 (4)
H91	−0.034 (4)	0.3237 (18)	0.3496 (13)	0.046*
H92	−0.044 (5)	0.264 (2)	0.2879 (8)	0.046*
O910	0.0302 (3)	0.26275 (15)	0.20148 (9)	0.0359 (4)
H101	0.174 (3)	0.253 (2)	0.2008 (16)	0.054*
H102	−0.024 (4)	0.1936 (19)	0.1893 (16)	0.054*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Al	0.0163 (3)	0.0203 (4)	0.0189 (3)	−0.0004 (2)	0.0001 (2)	0.0010 (3)
S1	0.0187 (3)	0.0255 (3)	0.0206 (3)	0.0008 (2)	0.0013 (2)	0.0003 (2)
S2	0.0186 (3)	0.0213 (3)	0.0212 (3)	0.00004 (19)	0.0010 (2)	0.0000 (2)
O11	0.0210 (8)	0.0632 (13)	0.0280 (9)	−0.0058 (8)	−0.0041 (7)	−0.0015 (9)
O12	0.0297 (9)	0.0342 (10)	0.0324 (10)	0.0022 (7)	0.0091 (7)	0.0071 (8)
O13	0.0334 (9)	0.0225 (9)	0.0370 (10)	0.0039 (7)	−0.0021 (7)	0.0023 (8)
O14	0.0374 (9)	0.0284 (10)	0.0252 (9)	0.0073 (7)	0.0009 (7)	−0.0042 (7)
O21	0.0205 (7)	0.0307 (9)	0.0377 (10)	0.0020 (6)	−0.0028 (7)	0.0116 (8)
O22	0.0275 (8)	0.0378 (10)	0.0279 (9)	−0.0088 (7)	−0.0086 (7)	0.0038 (8)
O23	0.0384 (9)	0.0266 (10)	0.0346 (10)	0.0070 (7)	−0.0027 (8)	−0.0079 (8)
O24	0.0362 (10)	0.0341 (10)	0.0381 (11)	−0.0010 (7)	0.0178 (8)	0.0034 (8)
O91	0.0235 (8)	0.0344 (10)	0.0212 (8)	−0.0088 (7)	−0.0020 (6)	0.0029 (7)
O92	0.0221 (8)	0.0236 (9)	0.0305 (9)	0.0028 (6)	−0.0036 (6)	−0.0014 (7)
O93	0.0198 (8)	0.0211 (9)	0.0358 (10)	0.0006 (6)	−0.0002 (7)	0.0026 (7)
O94	0.0220 (8)	0.0336 (10)	0.0224 (9)	−0.0072 (7)	−0.0028 (6)	0.0016 (7)
O95	0.0278 (8)	0.0297 (9)	0.0205 (8)	0.0054 (7)	0.0050 (6)	0.0026 (7)
O96	0.0261 (8)	0.0227 (9)	0.0221 (8)	−0.0011 (6)	0.0041 (6)	0.0013 (7)
C1	0.0251 (12)	0.0445 (17)	0.0341 (15)	0.0022 (10)	0.0000 (10)	−0.0076 (12)
N2	0.0297 (11)	0.0381 (13)	0.0274 (11)	−0.0059 (9)	−0.0035 (8)	−0.0004 (9)
C3	0.0383 (14)	0.0297 (14)	0.0346 (15)	0.0015 (11)	−0.0056 (11)	−0.0025 (12)
O97	0.0405 (10)	0.0301 (10)	0.0265 (10)	0.0005 (7)	0.0007 (8)	0.0035 (8)
O98	0.0271 (9)	0.0375 (11)	0.0388 (11)	−0.0032 (7)	0.0001 (7)	0.0014 (8)
O99	0.0271 (8)	0.0297 (10)	0.0361 (10)	−0.0004 (7)	0.0001 (7)	0.0042 (8)
O910	0.0347 (9)	0.0249 (10)	0.0481 (12)	−0.0004 (7)	−0.0026 (8)	0.0027 (9)

Geometric parameters (Å, º)

Al—O93	1.8620 (17)	O95—H51	0.948 (17)
Al—O92	1.8726 (17)	O95—H52	0.956 (17)
Al—O91	1.8733 (16)	O96—H61	0.935 (16)
Al—O96	1.8792 (17)	O96—H62	0.924 (16)
Al—O94	1.8835 (16)	C1—N2	1.494 (3)
Al—O95	1.8872 (17)	C1—C3	1.512 (4)
S1—O13	1.4689 (17)	C1—H11C	0.964 (17)
S1—O12	1.4715 (17)	C1—H12C	0.955 (17)
S1—O11	1.4745 (16)	N2—C3^i	1.485 (3)
S1—O14	1.4753 (17)	N2—H21N	0.974 (17)
S2—O24	1.4611 (17)	N2—H22N	0.982 (17)
S2—O23	1.4677 (18)	C3—N2^i	1.485 (3)
S2—O22	1.4797 (16)	C3—H31C	0.959 (17)
S2—O21	1.4809 (17)	C3—H32C	0.946 (17)
O91—H11	0.935 (17)	O97—H71	0.946 (17)
O91—H12	0.958 (16)	O97—H72	0.941 (17)
O92—H21	0.940 (17)	O98—H81	0.944 (17)
O92—H22	0.927 (16)	O98—H82	0.929 (17)
O93—H31	0.933 (16)	O99—H91	0.931 (17)
O93—H32	0.93 (2)	O99—H92	0.961 (17)
O94—H41	0.91 (2)	O910—H101	0.950 (17)
O94—H42	0.945 (17)	O910—H102	0.945 (17)
O93—Al—O92	178.70 (9)	Al—O93—H32	122.4 (16)
O93—Al—O91	90.05 (8)	H31—O93—H32	112 (2)
O92—Al—O91	90.83 (8)	Al—O94—H41	121.5 (17)
O93—Al—O96	91.73 (8)	Al—O94—H42	123.5 (17)
O92—Al—O96	89.22 (8)	H41—O94—H42	115 (2)
O91—Al—O96	90.29 (7)	Al—O95—H51	129.5 (16)
O93—Al—O94	89.42 (8)	Al—O95—H52	123.0 (16)
O92—Al—O94	89.70 (8)	H51—O95—H52	108 (2)
O91—Al—O94	179.47 (9)	Al—O96—H61	120.8 (17)
O96—Al—O94	89.77 (7)	Al—O96—H62	114.3 (17)
O93—Al—O95	89.73 (8)	H61—O96—H62	111 (2)
O92—Al—O95	89.32 (8)	N2—C1—C3	109.9 (2)
O91—Al—O95	89.97 (8)	N2—C1—H11C	107 (2)
O96—Al—O95	178.52 (8)	C3—C1—H11C	112.3 (19)
O94—Al—O95	89.99 (8)	N2—C1—H12C	106 (2)
O13—S1—O12	109.78 (10)	C3—C1—H12C	112.1 (19)
O13—S1—O11	109.68 (11)	H11C—C1—H12C	110 (2)
O12—S1—O11	109.45 (11)	C3^i—N2—C1	111.9 (2)
O13—S1—O14	107.60 (10)	C3^i—N2—H21N	110.3 (18)
O12—S1—O14	111.22 (11)	C1—N2—H21N	110.3 (18)
O11—S1—O14	109.09 (10)	C3^i—N2—H22N	108.4 (18)
O24—S2—O23	109.76 (11)	C1—N2—H22N	106.4 (19)
O24—S2—O22	110.51 (11)	H21N—N2—H22N	109 (2)
O23—S2—O22	109.39 (10)	N2^i—C3—C1	110.1 (2)
O24—S2—O21	110.36 (10)	N2^i—C3—H31C	106.4 (19)
O23—S2—O21	108.79 (11)	C1—C3—H31C	111.6 (19)
O22—S2—O21	108.01 (10)	N2^i—C3—H32C	106.2 (19)
Al—O91—H11	125.3 (16)	C1—C3—H32C	109.2 (19)
Al—O91—H12	122.7 (16)	H31C—C3—H32C	113 (2)
H11—O91—H12	111 (2)	H71—O97—H72	112 (2)
Al—O92—H21	118.3 (17)	H81—O98—H82	109 (2)
Al—O92—H22	123.4 (17)	H91—O99—H92	106 (2)
H21—O92—H22	113 (2)	H101—O910—H102	105 (2)
Al—O93—H31	125.9 (16)

Symmetry code: (i) −x, −y, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O91—H11···O22^ii	0.94 (2)	1.70 (2)	2.625 (2)	172 (3)
O91—H12···O99^ii	0.96 (2)	1.72 (2)	2.670 (2)	174 (3)
O92—H21···O910^iii	0.94 (2)	1.71 (2)	2.648 (3)	177 (3)
O92—H22···O21^iv	0.93 (2)	1.72 (2)	2.642 (2)	175 (3)
O93—H31···O14^v	0.93 (2)	1.67 (2)	2.604 (2)	176 (3)
O93—H32···O99	0.93 (2)	1.73 (2)	2.645 (2)	169 (2)
O94—H41···O11	0.91 (2)	1.71 (2)	2.621 (2)	175 (3)
O94—H42···O21^vi	0.95 (2)	1.73 (2)	2.671 (2)	177 (3)
O95—H51···O97	0.95 (2)	1.74 (2)	2.672 (2)	170 (3)
O95—H52···O12^ii	0.96 (2)	1.77 (2)	2.720 (2)	177 (3)
O96—H61···O24	0.94 (2)	1.70 (2)	2.633 (2)	173 (3)
O96—H62···O22^vi	0.92 (2)	1.78 (2)	2.698 (2)	172 (2)
O97—H71···O12^v	0.95 (2)	1.90 (2)	2.828 (3)	165 (3)
O97—H72···O23^vii	0.94 (2)	1.93 (2)	2.864 (3)	171 (3)
O98—H81···O11	0.94 (2)	1.85 (2)	2.783 (2)	169 (3)
O98—H82···O13^ii	0.93 (2)	1.97 (2)	2.886 (2)	167 (3)
O99—H91···O98^v	0.93 (2)	1.82 (2)	2.728 (3)	165 (3)
O99—H92···O910	0.96 (2)	1.92 (2)	2.851 (3)	161 (3)
O910—H101···O97	0.95 (2)	1.94 (2)	2.887 (3)	176 (3)
O910—H102···O13	0.95 (2)	1.77 (2)	2.710 (3)	174 (3)
N2—H21N···O23^vii	0.97 (2)	1.83 (2)	2.796 (3)	173 (3)
N2—H22N···O14	0.98 (2)	1.96 (2)	2.925 (3)	167 (3)

Symmetry codes: (ii) x+1, y, z; (iii) −x+1/2, y−1/2, −z+1/2; (iv) −x+1, −y, −z+1; (v) −x+1/2, y+1/2, −z+1/2; (vi) −x, −y, −z+1; (vii) x+1/2, −y+1/2, z−1/2.