Poly[[diaqua-μ₄-pyrazine-2,3-dicarboxyl­ato-κ⁶N,O²:O^2′:O³,O^3′:O³-strontium(II)] monohydrate]

In the title compound, {[Sr(C₆H₂N₂O₄)(H₂O)₂]·H₂O}_n, the Sr^II ions are bridged by the pyrazine-2,3-dicarboxyl­ate ligands with the formation of two-dimensional polymeric layers parallel to the ac plane. Each Sr^II ion is eight-coordinated by one N and five O atoms from the four ligands and two water mol­ecules. The coordination polyhedron is derived from a penta­gonal bipyramid with an O atom at the apex on one side of the equatorial plane and two O atoms sharing the apical site on the other side. The coordinated and uncoordinated water mol­ecules are involved in O—H...O and O—H...N hydrogen bonds, which consolidate the crystal structure.

Key indicators

• Single-crystal X-ray study
• T = 120 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.025
• wR factor = 0.055
• Data-to-parameter ratio = 13.3

checkCIF/PLATON results

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Alert level C
PLAT094_ALERT_2_C Ratio of Maximum / Minimum Residual Density ....       2.06
PLAT417_ALERT_2_C Short Inter D-H..H-D       H1W1   ..  H2W2    ..       2.13 Ang.
PLAT720_ALERT_4_C Number of Unusual/Non-Standard Labels ..........          6
PLAT764_ALERT_4_C Overcomplete CIF Bond List Detected (Rep/Expd) .       1.35 Ratio

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   4 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   2 ALERT type 2 Indicator that the structure model may be wrong or deficient
   0 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

Takusagawa & Shimada (1973) first determined the structure of pyrazine-2,3-dicarboxlic acid by single-crystal X-ray analysis. Almost at the same time, the first metal-organic compound of pyrazine-2,3-dicarboxylic acid was reported (Richard et al., 1973). Among many reported compounds containing pyrazine-2,3-dicarboxylic acid, most are complexes of transition metal ions, including manganese (Zou et al., 1999), copper (Konar et al., 2004), zinc (Li et al., 2003), iron (Xu et al., 2008) and cadmium (Ma et al., 2006). Also, there are many reported compounds of pyrazine-2,3-dicarboxylic acid with main group metals such as calcium (Ptasiewicz-Bak & Leciejewicz, 1997a; Starosta & Leciejewicz, 2005), magnesium (Ptasiewicz-Bak & Leciejewicz, 1997b) and sodium (Tombul et al., 2006) complexes. For further investigation of pyrazine-2,3-dicarboxylic acid, we synthesized the title compound, (I).

The asymmetric unit of the title compound, (Fig. 1), contains molecular sheets in which Sr^II ions are bridged by the carboxylate groups of the ligand molecules. Two bridging paths are evident. In the first, an N,O-bonding moiety formed by a hetero-ring nitrogen atom and the carboxylate oxygen atom nearest to it and both oxygen atoms of the second carboxylic group are active. The second path is formed by the other oxygen atom from the carboxylic group involved in the N,O-bonding moiety and an oxygen atom from the second carboxylic group. The latter atom is bidentate. A two-dimensional molecular pattern is formed. Each Sr^II ion is also coordinated by two water oxygen atoms, making the number of coordinated atoms eight. The coordination polyhedron is a distorted pentagonal bipyramid with an oxygen atom at the apex on one side of the equatorial plane and two oxygen atoms forming the apices on the other side. There is also one non-coordinated water molecule in the asymmetric unit. The Sr—O and Sr—N bond lengths are collected in Table 1.

Intermolecular O—H···O and O—H···N hydrogen bonds (Table 2) help to consolidate the crystal packing (Fig. 2).

Related literature

For related literature, see: Takusagawa & Shimada (1973); Richard et al. (1973); Zou et al. (1999); Konar et al. (2004); Li et al. (2003); Xu et al. (2008); Ma et al. (2006); Ptasiewicz-Bak & Leciejewicz (1997a,b); Starosta & Leciejewicz (2005); Tombul et al. (2006).

S2. Experimental

A solution of pyrazine-2,3-dicarboxlic acid (0.5 g, 2.91 mmol) in methanol (40 ml) was added to a solution of Sr(NO₃)₂ (0.31 g, 1.46 mmol) in water (10 ml) and the resulting colourless solution was stirred for 10 min at room temperature. This solution was left to evaporate slowly at room temperature. After one week, colourless plate crystals of the title compound were isolated (yield 0.35 g, 78.03%).

S3. Refinement

C-bound H atoms were geometrically positioned (C-H 0.95 Å), while O-bound H atoms were found in difference Fourier maps, but placed in idealized positions with O-H of 0.85 Å. All hydrogen atoms were refined in riding model approximation with U_iso(H) = 1.2U_eq of the paren atom.

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SAINT-Plus (Bruker, 1998); data reduction: SAINT-Plus (Bruker, 1998); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. A portion of the polymeric structure of (I) with the atom-numbering scheme and displacement ellipsoids drawn at the 40% probability level [symmetry codes: (i) -x - 1/2,y - 1/2,-z + 1/2, (ii) -x - 1/2, y + 1/2,-z + 1/2, (iii) x - 1/2,-y + 1/2,z + 1/2].
	Fig. 2. A packing diagram for (I). Hydrogen bonds are shown as dashed lines.

Poly[[diaqua-µ₄-pyrazine-2,3-dicarboxylato- κ⁶N,O²:O^2':O³,O^3':O³-strontium(II)] monohydrate]

Crystal data

[Sr(C6H2N2O4)(H2O)2]·H2O	F(000) = 608
Mr = 307.76	Dx = 2.069 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 156 reflections
a = 10.4931 (7) Å	θ = 3–26°
b = 6.9839 (4) Å	µ = 5.48 mm^−1
c = 13.5208 (8) Å	T = 120 K
β = 94.267 (1)°	Plate, colorless
V = 988.10 (10) Å^3	0.28 × 0.25 × 0.10 mm
Z = 4

Data collection

Bruker SMART 1000 CCD area-detector diffractometer	1934 independent reflections
Radiation source: fine-focus sealed tube	1595 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.040
ϕ and ω scans	θmax = 26.0°, θmin = 2.4°
Absorption correction: multi-scan (SADABS; Bruker, 1998)	h = −12→12
Tmin = 0.240, Tmax = 0.568	k = −8→8
8338 measured reflections	l = −16→16

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)] = 0.024	Hydrogen site location: mixed
wR(F^2) = 0.054	H-atom parameters constrained
S = 1.01	w = 1/[σ^2(Fo^2) + (0.026P)^2] where P = (Fo^2 + 2Fc^2)/3
1934 reflections	(Δ/σ)max = 0.002
145 parameters	Δρmax = 0.92 e Å^−3
0 restraints	Δρmin = −0.45 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
Sr1	−0.44206 (2)	0.17756 (3)	0.375530 (17)	0.01058 (9)
N1	−0.4291 (2)	0.1488 (3)	0.17632 (16)	0.0137 (5)
N2	−0.3958 (2)	0.2550 (3)	−0.01781 (16)	0.0138 (5)
O1	−0.14140 (18)	0.1344 (3)	−0.07125 (13)	0.0154 (4)
O2	−0.09707 (18)	0.3655 (3)	0.03862 (13)	0.0148 (4)
O3	−0.21964 (18)	0.1162 (3)	0.30617 (13)	0.0164 (4)
O4	−0.10633 (16)	0.0171 (3)	0.18088 (13)	0.0131 (4)
C1	−0.3115 (2)	0.1518 (4)	0.14221 (19)	0.0114 (6)
C2	−0.2956 (3)	0.2059 (4)	0.04464 (19)	0.0117 (6)
C3	−0.5114 (3)	0.2480 (4)	0.0166 (2)	0.0156 (6)
H3A	−0.5841	0.2794	−0.0264	0.019*
C4	−0.5277 (3)	0.1963 (4)	0.11335 (19)	0.0150 (6)
H4A	−0.6115	0.1945	0.1356	0.018*
C5	−0.2037 (3)	0.0901 (4)	0.21630 (19)	0.0123 (6)
C6	−0.1670 (3)	0.2340 (4)	0.00239 (19)	0.0114 (6)
O1W	−0.64324 (17)	−0.0101 (3)	0.30768 (13)	0.0161 (4)
H1W1	−0.6382	−0.1106	0.2727	0.019*
H2W1	−0.7174	0.0355	0.2932	0.019*
O2W	−0.31193 (17)	0.2633 (3)	0.53262 (13)	0.0150 (4)
H1W2	−0.3220	0.3802	0.5478	0.018*
H2W2	−0.3246	0.1853	0.5791	0.018*
O3W	0.11689 (17)	0.1471 (3)	0.28299 (13)	0.0161 (4)
H1W3	0.0444	0.1203	0.2540	0.019*
H2W3	0.1011	0.1787	0.3415	0.019*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sr1	0.00953 (13)	0.01224 (14)	0.01019 (13)	0.00004 (11)	0.00220 (9)	0.00048 (11)
N1	0.0110 (12)	0.0183 (13)	0.0119 (11)	0.0000 (10)	0.0026 (9)	−0.0003 (10)
N2	0.0112 (12)	0.0163 (12)	0.0140 (11)	0.0013 (9)	0.0021 (9)	0.0000 (10)
O1	0.0168 (10)	0.0174 (10)	0.0125 (9)	−0.0015 (8)	0.0050 (8)	−0.0024 (8)
O2	0.0123 (10)	0.0160 (11)	0.0163 (10)	−0.0026 (8)	0.0029 (8)	−0.0017 (8)
O3	0.0142 (10)	0.0245 (11)	0.0106 (9)	0.0028 (8)	0.0022 (8)	−0.0006 (8)
O4	0.0084 (9)	0.0159 (10)	0.0154 (9)	0.0020 (8)	0.0033 (8)	−0.0022 (8)
C1	0.0086 (13)	0.0133 (14)	0.0124 (13)	−0.0008 (11)	0.0016 (10)	−0.0041 (11)
C2	0.0137 (14)	0.0095 (13)	0.0123 (13)	−0.0030 (11)	0.0024 (11)	−0.0016 (11)
C3	0.0119 (15)	0.0185 (14)	0.0161 (14)	0.0013 (11)	−0.0009 (11)	−0.0008 (12)
C4	0.0096 (14)	0.0195 (15)	0.0157 (14)	−0.0006 (11)	0.0005 (11)	−0.0008 (12)
C5	0.0126 (14)	0.0099 (13)	0.0144 (14)	−0.0027 (11)	0.0017 (11)	0.0027 (11)
C6	0.0115 (14)	0.0108 (13)	0.0118 (13)	0.0017 (11)	−0.0001 (11)	0.0027 (11)
O1W	0.0123 (10)	0.0176 (10)	0.0184 (10)	0.0009 (8)	0.0016 (8)	−0.0007 (8)
O2W	0.0161 (10)	0.0145 (10)	0.0142 (10)	−0.0007 (8)	0.0010 (8)	0.0013 (8)
O3W	0.0112 (10)	0.0257 (11)	0.0113 (9)	−0.0009 (8)	0.0012 (8)	−0.0013 (8)

Geometric parameters (Å, º)

Sr1—O2^i	2.4887 (18)	O2—Sr1^ii	2.4887 (18)
Sr1—O2W	2.5106 (18)	O2—Sr1^v	2.8517 (18)
Sr1—O4^ii	2.5533 (18)	O3—C5	1.252 (3)
Sr1—O1W	2.5937 (19)	O4—C5	1.267 (3)
Sr1—O3	2.6145 (18)	O4—Sr1^i	2.5533 (18)
Sr1—O1^iii	2.6155 (18)	C1—C2	1.394 (4)
Sr1—N1	2.714 (2)	C1—C5	1.517 (4)
Sr1—O2^iii	2.8517 (18)	C2—C6	1.516 (4)
Sr1—C6^iii	3.082 (3)	C3—C4	1.381 (4)
Sr1—Sr1^iv	4.4235 (5)	C3—H3A	0.9500
Sr1—H1W2	2.9292	C4—H4A	0.9500
Sr1—H2W2	2.9320	C6—Sr1^v	3.082 (3)
N1—C4	1.332 (3)	O1W—H1W1	0.8500
N1—C1	1.349 (3)	O1W—H2W1	0.8500
N2—C3	1.331 (3)	O2W—H1W2	0.8500
N2—C2	1.343 (3)	O2W—H2W2	0.8500
O1—C6	1.260 (3)	O3W—H1W3	0.8501
O1—Sr1^v	2.6155 (18)	O3W—H2W3	0.8499
O2—C6	1.252 (3)
O2^i—Sr1—O2W	75.75 (6)	O2^iii—Sr1—H1W2	70.9
O2^i—Sr1—O4^ii	157.35 (6)	C6^iii—Sr1—H1W2	76.3
O2W—Sr1—O4^ii	85.61 (6)	Sr1^iv—Sr1—H1W2	78.0
O2^i—Sr1—O1W	79.88 (6)	O2^i—Sr1—H2W2	62.3
O2W—Sr1—O1W	142.83 (6)	O2W—Sr1—H2W2	15.6
O4^ii—Sr1—O1W	122.57 (6)	O4^ii—Sr1—H2W2	100.6
O2^i—Sr1—O3	84.44 (6)	O1W—Sr1—H2W2	128.0
O2W—Sr1—O3	84.19 (6)	O3—Sr1—H2W2	90.9
O4^ii—Sr1—O3	80.93 (6)	O1^iii—Sr1—H2W2	91.2
O1W—Sr1—O3	121.00 (6)	N1—Sr1—H2W2	152.2
O2^i—Sr1—O1^iii	114.76 (6)	O2^iii—Sr1—H2W2	60.0
O2W—Sr1—O1^iii	92.48 (6)	C6^iii—Sr1—H2W2	76.1
O4^ii—Sr1—O1^iii	78.28 (6)	Sr1^iv—Sr1—H2W2	54.3
O1W—Sr1—O1^iii	72.81 (6)	H1W2—Sr1—H2W2	28.2
O3—Sr1—O1^iii	159.14 (6)	C4—N1—C1	117.7 (2)
O2^i—Sr1—N1	112.29 (6)	C4—N1—Sr1	121.46 (17)
O2W—Sr1—N1	142.46 (6)	C1—N1—Sr1	116.91 (16)
O4^ii—Sr1—N1	75.33 (6)	C3—N2—C2	117.5 (2)
O1W—Sr1—N1	73.21 (6)	C6—O1—Sr1^v	99.33 (16)
O3—Sr1—N1	61.32 (6)	C6—O2—Sr1^ii	153.65 (17)
O1^iii—Sr1—N1	114.22 (6)	C6—O2—Sr1^v	88.36 (15)
O2^i—Sr1—O2^iii	68.33 (6)	Sr1^ii—O2—Sr1^v	111.67 (6)
O2W—Sr1—O2^iii	71.13 (6)	C5—O3—Sr1	124.02 (17)
O4^ii—Sr1—O2^iii	117.81 (5)	C5—O4—Sr1^i	132.10 (16)
O1W—Sr1—O2^iii	73.99 (5)	N1—C1—C2	120.3 (2)
O3—Sr1—O2^iii	146.69 (6)	N1—C1—C5	115.2 (2)
O1^iii—Sr1—O2^iii	47.66 (5)	C2—C1—C5	124.4 (2)
N1—Sr1—O2^iii	146.41 (6)	N2—C2—C1	121.3 (2)
O2^i—Sr1—C6^iii	91.29 (7)	N2—C2—C6	114.0 (2)
O2W—Sr1—C6^iii	82.66 (6)	C1—C2—C6	124.4 (2)
O4^ii—Sr1—C6^iii	99.08 (6)	N2—C3—C4	121.4 (3)
O1W—Sr1—C6^iii	70.19 (6)	N2—C3—H3A	119.3
O3—Sr1—C6^iii	166.80 (6)	C4—C3—H3A	119.3
O1^iii—Sr1—C6^iii	23.79 (6)	N1—C4—C3	121.7 (3)
N1—Sr1—C6^iii	131.61 (7)	N1—C4—H4A	119.1
O2^iii—Sr1—C6^iii	23.97 (6)	C3—C4—H4A	119.1
O2^i—Sr1—Sr1^iv	36.81 (4)	O3—C5—O4	126.5 (2)
O2W—Sr1—Sr1^iv	69.70 (4)	O3—C5—C1	116.9 (2)
O4^ii—Sr1—Sr1^iv	145.08 (4)	O4—C5—C1	116.6 (2)
O1W—Sr1—Sr1^iv	73.93 (4)	O2—C6—O1	124.1 (2)
O3—Sr1—Sr1^iv	118.96 (4)	O2—C6—C2	117.4 (2)
O1^iii—Sr1—Sr1^iv	78.55 (4)	O1—C6—C2	118.3 (2)
N1—Sr1—Sr1^iv	138.62 (5)	O2—C6—Sr1^v	67.67 (14)
O2^iii—Sr1—Sr1^iv	31.52 (4)	O1—C6—Sr1^v	56.88 (13)
C6^iii—Sr1—Sr1^iv	54.80 (5)	C2—C6—Sr1^v	167.25 (17)
O2^i—Sr1—H1W2	90.3	Sr1—O1W—H1W1	122.1
O2W—Sr1—H1W2	15.7	Sr1—O1W—H2W1	126.8
O4^ii—Sr1—H1W2	72.9	H1W1—O1W—H2W1	105.9
O1W—Sr1—H1W2	144.7	Sr1—O2W—H1W2	111.4
O3—Sr1—H1W2	91.3	Sr1—O2W—H2W2	111.6
O1^iii—Sr1—H1W2	81.0	H1W2—O2W—H2W2	114.0
N1—Sr1—H1W2	140.8	H1W3—O3W—H2W3	104.9
O2^i—Sr1—N1—C4	121.4 (2)	C3—N2—C2—C1	−0.7 (4)
O2W—Sr1—N1—C4	−143.01 (19)	C3—N2—C2—C6	−175.0 (2)
O4^ii—Sr1—N1—C4	−81.1 (2)	N1—C1—C2—N2	−0.4 (4)
O1W—Sr1—N1—C4	50.2 (2)	C5—C1—C2—N2	178.5 (2)
O3—Sr1—N1—C4	−168.7 (2)	N1—C1—C2—C6	173.3 (2)
O1^iii—Sr1—N1—C4	−11.5 (2)	C5—C1—C2—C6	−7.8 (4)
O2^iii—Sr1—N1—C4	37.4 (3)	C2—N2—C3—C4	1.3 (4)
C6^iii—Sr1—N1—C4	8.1 (2)	C1—N1—C4—C3	−0.3 (4)
Sr1^iv—Sr1—N1—C4	89.0 (2)	Sr1—N1—C4—C3	156.5 (2)
O2^i—Sr1—N1—C1	−81.51 (18)	N2—C3—C4—N1	−0.8 (4)
O2W—Sr1—N1—C1	14.0 (2)	Sr1—O3—C5—O4	−162.37 (19)
O4^ii—Sr1—N1—C1	75.96 (18)	Sr1—O3—C5—C1	17.6 (3)
O1W—Sr1—N1—C1	−152.72 (19)	Sr1^i—O4—C5—O3	96.7 (3)
O3—Sr1—N1—C1	−11.61 (17)	Sr1^i—O4—C5—C1	−83.2 (3)
O1^iii—Sr1—N1—C1	145.59 (17)	N1—C1—C5—O3	−27.8 (3)
O2^iii—Sr1—N1—C1	−165.53 (15)	C2—C1—C5—O3	153.3 (3)
C6^iii—Sr1—N1—C1	165.13 (16)	N1—C1—C5—O4	152.2 (2)
Sr1^iv—Sr1—N1—C1	−113.97 (17)	C2—C1—C5—O4	−26.8 (4)
O2^i—Sr1—O3—C5	115.1 (2)	Sr1^ii—O2—C6—O1	148.1 (3)
O2W—Sr1—O3—C5	−168.7 (2)	Sr1^v—O2—C6—O1	7.3 (3)
O4^ii—Sr1—O3—C5	−82.2 (2)	Sr1^ii—O2—C6—C2	−26.3 (5)
O1W—Sr1—O3—C5	40.4 (2)	Sr1^v—O2—C6—C2	−167.1 (2)
O1^iii—Sr1—O3—C5	−87.1 (3)	Sr1^ii—O2—C6—Sr1^v	140.8 (4)
N1—Sr1—O3—C5	−4.08 (19)	Sr1^v—O1—C6—O2	−8.1 (3)
O2^iii—Sr1—O3—C5	149.62 (18)	Sr1^v—O1—C6—C2	166.25 (19)
C6^iii—Sr1—O3—C5	−173.4 (3)	N2—C2—C6—O2	110.2 (3)
Sr1^iv—Sr1—O3—C5	128.36 (19)	C1—C2—C6—O2	−63.9 (4)
C4—N1—C1—C2	0.9 (4)	N2—C2—C6—O1	−64.5 (3)
Sr1—N1—C1—C2	−157.03 (19)	C1—C2—C6—O1	121.4 (3)
C4—N1—C1—C5	−178.1 (2)	N2—C2—C6—Sr1^v	−0.2 (9)
Sr1—N1—C1—C5	24.0 (3)	C1—C2—C6—Sr1^v	−174.3 (7)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1W1···O3W^i	0.85	1.87	2.713 (3)	170
O1W—H2W1···O3W^vi	0.85	1.90	2.744 (3)	171
O2W—H1W2···O1^ii	0.85	1.85	2.696 (3)	174
O2W—H2W2···O1W^iv	0.85	2.01	2.857 (3)	178
O3W—H1W3···O4	0.85	1.94	2.781 (3)	170
O3W—H2W3···N2^vii	0.85	1.96	2.792 (3)	168

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