catena-Poly[[[tetra­aqua­magnesium]-trans-μ-[(piperazine-1,4-diium-1,4-di­yl)bis­(methyl­ene)]di­phospho­nato] hemihydrate]

The structure of the title polymer, }[Mg(C₆H₁₄N₂O₆P₂)(H₂O)₄]·0.5H₂O}_n, is based on centrosymmetric MgO₆ octahedra, which are linked by [(piperazine-1,4-diium-1,4-di­yl)bis­(methyl­ene)]di­phospho­nate ligands, forming chains parallel to [1-1-1]. These chains are connected via hydrogen bonds primarily formed between the phospho­nate groups and water mol­ecules. The latter constitute four of the corners of the MgO₆ polyhedra and bind to the O atoms of the phospho­nate groups of neighbouring chains. The lattice water molecule is disordered around an inversion centre, exhibiting an occupancy of 0.25.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.002 Å
• Disorder in solvent or counterion
• R factor = 0.030
• wR factor = 0.080
• Data-to-parameter ratio = 19.0

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT415_ALERT_2_B Short Inter D-H..H-X       H2B    ..  H2O6    ..       2.05 Ang.

Alert level C
PLAT077_ALERT_4_C Unitcell contains non-integer number of atoms ..          ?
PLAT165_ALERT_3_C Nr. of Status R Flagged Non-Hydrogen Atoms .....          1
PLAT906_ALERT_3_C Large K value in the Analysis of Variance ......      2.616
PLAT910_ALERT_3_C Missing # of FCF Reflections Below Th(Min) .....          1
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600          2
PLAT913_ALERT_3_C Missing # of Very Strong Reflections in FCF ....          1

Alert level G
PLAT004_ALERT_5_G Info: Polymeric Structure Found with Dimension .          1
PLAT005_ALERT_5_G No _iucr_refine_instructions_details  in the CIF          ? Do !
PLAT007_ALERT_5_G Note: Number of Unrefined Donor-H Atoms ........          7
PLAT042_ALERT_1_G Calc. and Reported MoietyFormula Strings  Differ          ? Check
PLAT154_ALERT_1_G The su's on the Cell Angles are Equal ..........    0.00600 Deg.
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported   _diffrn_ambient_temperature        293 K
PLAT232_ALERT_2_G Hirshfeld Test Diff (M-X)  Mg1    --  O4      ..        5.8 su
PLAT302_ALERT_4_G Note: Anion/Solvent Disorder ...................        100 %
PLAT343_ALERT_2_G Check sp3     Angle Range in Main Residue for ..        C1
PLAT720_ALERT_4_G Number of Unusual/Non-Standard Labels ..........          7
PLAT912_ALERT_4_G Missing # of FCF Reflections Above STh/L=  0.600          5

   0 ALERT level A = Most likely a serious problem - resolve or explain
   1 ALERT level B = A potentially serious problem, consider carefully
   6 ALERT level C = Check. Ensure it is not caused by an omission or oversight
  12 ALERT level G = General information/check it is not something unexpected

   4 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
   5 ALERT type 3 Indicator that the structure quality may be low
   4 ALERT type 4 Improvement, methodology, query or suggestion
   3 ALERT type 5 Informative message, check

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S1. Comment

Due to their flexible coordination behaviour, organic linker molecules containing phosphonate groups allow the synthesis of a multitude of inorganic-organic hybrid materials (Gagnon et al., 2012). In this context, the ligand N,N'-piperazinebis(methylenephosphonic acid) (H₂O₃P—CH₂—NC₄H₈N—CH₂—PO₃H₂ = H₄L) has been the subject of intense interest, since its use has led to a number of dense metal phosphonates (Groves, Stephens et al., 2006, Groves et al., 2005a, 2005b, Choi et al., 1994, LaDuca et al., 1996, Soghomonian et al., 1995, Wang et al., 2004) as well as porous ones (Groves, Miller et al., 2006, Serre et al., 2006). The compounds [Co₂(H₂O)₂L] ^. 5.1 H₂O (denoted Co-STA-12) and [Mg₂(H₂O)₂L] ^. 3.97 H₂O (denoted CAU-2) are highly porous with micropore volumes of 0.14 cm³ g^-1 and 0.20 cm³ g^-1, respectively (Wharmby et al., 2012). Investigation of the system MgCl₂ ^. 6 H₂O / H₄L / base / H₂O led to the formation of CAU-2. We have now been able to isolate a new compound, [Mg(H₂O)₄(H₂L)] ^. 0.5 H₂O, in this system, which is obtained from slightly acidic reaction mixtures (4 ≤ pH ≤ 6.5). Optimization of the reaction conditions (concentration and reaction time) led to the formation of single crystals. The asymmetric unit of the crystal structure is depicted in Fig. 1.

[Mg(H₂O)₄(H₂L)] ^. 0.5 H₂O adopts a one-dimensional structure containing alternating inorganic and organic building units of MgO₆ polyhedra and N,N'-piperaziniumbis(methylenephosphonate) ions (Fig. 2). The Mg²⁺ ions are octahedrally coordinated by six oxygen atoms (O1, O4, O5 and their symmetry equivalents), of which four (O4 and O5) belong to water molecules while two (O1) belong to phosphonate groups of the ligand molecules. The charge of the structure is balanced by protons connected to the N atoms of the ligand making it a quaternary amine. In addition, a further water molecule is found on a partially occupied position.

Related literature

For related magnesium structures, see: Wharmby et al. (2012). For related N,N'-piperaziniumbis(methylenephosphonates), see: Choi et al. (1994); Groves et al. (2005a,b); Groves, Stephens et al. (2006); Groves, Miller et al. (2006); LaDuca et al. (1996); Serre et al. (2006); Soghomonian et al. (1995); Wang et al. (2004); Wharmby et al. (2012). As a result of their flexible coordination behaviour, organic linker molecules containing phosphonate groups allow the synthesis of a multitude of inorganic-organic hybrid materials, see: Gagnon et al. (2012).

S2. Experimental

A reaction mixture of MgCl₂ ^. 6 H₂O (13.55 mg, 50 µmol), N,N'-piperazinebis(methylenephosphonic acid) (36.55 mg, 100 nmol), potassium hydroxide (16.83 mg, 300 nmol) and 1.5 ml water was placed in a 2 ml Teflon-lined autoclave. Subsequently the reactor was heated from room temperature to 130 °C (heating rate 1 °C min^-1), the temperature was held for 52 h and then slowly lowered to room temperature over a period of 12 h. The resulting colourless crystals were collected by filtration and analysed via single-crystal XRD. Yield: 32%.

S3. Refinement

All H atoms of C—H groups were located in difference maps but were positioned with idealized geometry and were refined isotropically with U_iso(H) = 1.2 U_eq(C) using a riding model with C—H = 0.97 Å for aliphatic H atoms. The water H atoms were located in difference maps, their bond lengths were set to ideal values of 0.82 Å and they were refined using a riding model with U_iso(H) = 1.5 U_eq(O). The N—H H atom was located in a difference map but was positioned with idealized geometry and was refined isotropic with U_iso(H) = 1.2 U_eq(C) using a riding model with N—H = 0.86 Å.

Computing details

Data collection: X-AREA (Stoe & Cie, 2008); cell refinement: X-AREA (Stoe & Cie, 2008); data reduction: X-AREA (Stoe & Cie, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008) and DIAMOND Brandenburg (2011);; software used to prepare material for publication: XCIF in SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. : Asymmetric unit of the title compound with labeling and displacement ellipsoids drawn at the 50% probability level.
	Fig. 2. : Chain-formed building unit of [Mg(H2O)4(H2L)] ^. 0.5 H2O.

catena-Poly[[[tetraaquamagnesium]-trans-µ-[(piperazine-1,4-diium-1,4-diyl)bis(methylene)]diphosphonato] hemihydrate]

Crystal data

[Mg(C6H14N2O6P2)(H2O)4]·0.5H2O	Z = 1
Mr = 377.51	F(000) = 199
Triclinic, P1	Dx = 1.714 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 6.6296 (5) Å	Cell parameters from 1270 reflections
b = 6.8074 (6) Å	θ = 1.2–29.8°
c = 8.7962 (7) Å	µ = 0.40 mm^−1
α = 94.579 (6)°	T = 293 K
β = 103.326 (6)°	Needle, colorless
γ = 106.552 (6)°	0.21 × 0.12 × 0.04 mm
V = 365.75 (5) Å^3

Data collection

Stoe IPSD-2 diffractometer	1957 independent reflections
Radiation source: fine-focus sealed tube	1727 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.036
ω scan	θmax = 29.2°, θmin = 3.2°
Absorption correction: numerical (X-SHAPE and X-RED32; Stoe & Cie, 2008)	h = −9→9
Tmin = 0.886, Tmax = 0.974	k = −9→9
6973 measured reflections	l = −12→12

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.030	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.080	H-atom parameters constrained
S = 1.01	w = 1/[σ^2(Fo^2) + (0.0352P)^2 + 0.2734P] where P = (Fo^2 + 2Fc^2)/3
1957 reflections	(Δ/σ)max < 0.001
103 parameters	Δρmax = 0.43 e Å^−3
0 restraints	Δρmin = −0.43 e Å^−3

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)
Mg1	0.5000	0.5000	0.5000	0.01868 (16)
P1	0.36611 (6)	0.83891 (6)	0.71790 (4)	0.01741 (10)
O1	0.47100 (19)	0.67534 (18)	0.69031 (14)	0.0256 (2)
O2	0.22643 (18)	0.87610 (17)	0.56605 (13)	0.0228 (2)
O3	0.52336 (14)	1.04094 (13)	0.81824 (11)	0.0225 (2)
C1	0.17809 (14)	0.73201 (13)	0.83666 (11)	0.0218 (3)
H1A	0.2264	0.6279	0.8904	0.026*
H1B	0.0379	0.6240	0.8034	0.026*
N1	0.1348 (2)	0.89184 (19)	0.94153 (15)	0.0181 (2)
H1N1	0.2589	0.9558	1.0077	0.022*
C2	0.0614 (3)	1.0529 (2)	0.85892 (19)	0.0235 (3)
H2A	−0.0754	0.9870	0.7791	0.028*
H2B	0.1690	1.1225	0.8065	0.028*
C3	−0.0313 (3)	0.7900 (2)	1.02369 (19)	0.0218 (3)
H3A	0.0147	0.6857	1.0786	0.026*
H3B	−0.1695	0.7211	0.9461	0.026*
O4	0.30950 (18)	0.64149 (17)	0.34463 (13)	0.0236 (2)
H1O4	0.3778	0.7291	0.3008	0.028*
H2O4	0.2647	0.7153	0.3980	0.028*
O5	0.22487 (19)	0.26098 (18)	0.51161 (16)	0.0309 (3)
H1O5	0.2383	0.1488	0.5310	0.037*
H2O5	0.0957	0.2540	0.4922	0.037*
O6	0.5116 (13)	0.5606 (12)	1.0711 (9)	0.0620 (19)	0.25
H1O6	0.5284	0.5120	1.1538	0.093*	0.25
H2O6	0.5205	0.6822	1.0956	0.093*	0.25

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mg1	0.0172 (3)	0.0181 (3)	0.0219 (3)	0.0073 (3)	0.0059 (3)	0.0011 (3)
P1	0.01580 (17)	0.01772 (18)	0.01999 (19)	0.00653 (13)	0.00637 (13)	0.00069 (13)
O1	0.0300 (6)	0.0285 (6)	0.0246 (6)	0.0176 (5)	0.0094 (5)	0.0020 (4)
O2	0.0203 (5)	0.0246 (5)	0.0244 (5)	0.0097 (4)	0.0047 (4)	0.0025 (4)
O3	0.0200 (5)	0.0213 (5)	0.0237 (5)	0.0037 (4)	0.0053 (4)	0.0010 (4)
C1	0.0228 (7)	0.0170 (6)	0.0276 (8)	0.0055 (5)	0.0121 (6)	0.0011 (6)
N1	0.0151 (5)	0.0194 (6)	0.0206 (6)	0.0052 (4)	0.0070 (5)	0.0019 (5)
C2	0.0269 (7)	0.0258 (7)	0.0246 (7)	0.0132 (6)	0.0127 (6)	0.0077 (6)
C3	0.0216 (7)	0.0205 (7)	0.0271 (7)	0.0066 (6)	0.0129 (6)	0.0060 (6)
O4	0.0245 (5)	0.0233 (5)	0.0252 (6)	0.0101 (4)	0.0075 (4)	0.0032 (4)
O5	0.0186 (5)	0.0240 (6)	0.0501 (8)	0.0059 (4)	0.0086 (5)	0.0106 (5)
O6	0.065 (5)	0.059 (4)	0.068 (5)	0.025 (4)	0.019 (4)	0.020 (4)

Geometric parameters (Å, º)

Mg1—O1^i	2.0552 (11)	N1—H1N1	0.8600
Mg1—O1	2.0553 (11)	C2—C3^ii	1.513 (2)
Mg1—O5	2.0991 (12)	C2—H2A	0.9700
Mg1—O5^i	2.0992 (12)	C2—H2B	0.9700
Mg1—O4^i	2.1209 (11)	C3—C2^ii	1.513 (2)
Mg1—O4	2.1209 (11)	C3—H3A	0.9700
P1—O1	1.5027 (11)	C3—H3B	0.9700
P1—O2	1.5242 (12)	O4—H1O4	0.8199
P1—O3	1.5240 (10)	O4—H2O4	0.8201
P1—C1	1.8383	O5—H1O5	0.8200
C1—N1	1.5022 (15)	O5—H2O5	0.8200
C1—H1A	0.9700	O6—O6^iii	1.395 (16)
C1—H1B	0.9700	O6—H1O6	0.8201
N1—C3	1.4925 (18)	O6—H2O6	0.8200
N1—C2	1.495 (2)
O1^i—Mg1—O1	180.00 (6)	C3—N1—C2	108.49 (11)
O1^i—Mg1—O5	90.35 (5)	C3—N1—C1	110.46 (10)
O1—Mg1—O5	89.65 (5)	C2—N1—C1	114.75 (11)
O1^i—Mg1—O5^i	89.65 (5)	C3—N1—H1N1	111.5
O1—Mg1—O5^i	90.35 (5)	C2—N1—H1N1	106.5
O5—Mg1—O5^i	180.00 (7)	C1—N1—H1N1	105.1
O1^i—Mg1—O4^i	89.80 (4)	N1—C2—C3^ii	110.27 (12)
O1—Mg1—O4^i	90.20 (4)	N1—C2—H2A	109.6
O5—Mg1—O4^i	87.19 (5)	C3^ii—C2—H2A	109.6
O5^i—Mg1—O4^i	92.81 (5)	N1—C2—H2B	109.6
O1^i—Mg1—O4	90.20 (4)	C3^ii—C2—H2B	109.6
O1—Mg1—O4	89.80 (4)	H2A—C2—H2B	108.1
O5—Mg1—O4	92.81 (5)	N1—C3—C2^ii	111.06 (12)
O5^i—Mg1—O4	87.19 (5)	N1—C3—H3A	109.4
O4^i—Mg1—O4	180.0	C2^ii—C3—H3A	109.4
O1—P1—O2	113.06 (7)	N1—C3—H3B	109.4
O1—P1—O3	114.25 (6)	C2^ii—C3—H3B	109.4
O2—P1—O3	112.00 (6)	H3A—C3—H3B	108.0
O1—P1—C1	105.10 (6)	Mg1—O4—H1O4	115.4
O2—P1—C1	106.31 (6)	Mg1—O4—H2O4	108.1
O3—P1—C1	105.20 (5)	H1O4—O4—H2O4	99.6
P1—O1—Mg1	137.40 (7)	Mg1—O5—H1O5	119.2
N1—C1—P1	114.69 (7)	Mg1—O5—H2O5	130.9
N1—C1—H1A	114.7	H1O5—O5—H2O5	109.7
P1—C1—H1A	108.7	O6^iii—O6—H1O6	119.9
N1—C1—H1B	102.6	O6^iii—O6—H2O6	133.7
P1—C1—H1B	128.8	H1O6—O6—H2O6	106.3
H1A—C1—H1B	83.9

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1N1···O3^iv	0.86	1.84	2.6187 (16)	150
O4—H1O4···O3^v	0.82	1.99	2.7956 (15)	166
O4—H2O4···O2	0.82	1.88	2.6733 (17)	164
O5—H1O5···O2^vi	0.82	1.89	2.7032 (17)	172
O5—H2O5···O2^vii	0.82	1.99	2.7667 (18)	158
C1—H1B···O4^vii	0.97	2.48	3.4279 (15)	166
C2—H2B···O3	0.97	2.55	3.187 (2)	124

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