Tetra­aqua­bis(5-carb­oxy-2-nitro­benzo­ato-κO)manganese(II) dihydrate: a metal–water chain complex containing cyclic water tetra­mers

In the title complex, [Mn(C₈H₄NO₆)₂(H₂O)₄]·2H₂O, cyclic water tetra­mers forming one-dimensional metal–water chains have been observed. The water clusters are trapped by the co-­operative association of coordination inter­actions and hydrogen bonds. The Mn^II ion resides on a center of symmetry and is in an octa­hedral coordination environment comprising two O atoms from two 5-carboxy-2-nitrobenzoate ligands and four O atoms from water mol­ecules.

S1. Comment

Water clusters are bridges between a single water molecule and liquid water or ice. Recent years have witnessed intense studies of small water clusters (Mascal et al., 2006) from the theoretical (Xantheas 1994, 1995; Kim et al., 1994, 1999) and experimental aspects (Buck & Huisken, 2000; Barbour et al., 1998; Raghuraman et al., 2003; Janiak & Scharamann, 2002). Among them, the cyclic water tetramer is of great interest since it is a simple two-structure model for liquid water (Benson & Siebert, 1992; Ludwig, 2001). Their configurations have been predicted by ab initio electronic structure calculations (Gregory & Clary, 1996; Udalde et al., 2000; Radhakrishnan & Herndon, 1991), and some of them have been characterized by far-IR vibration–rotation tunneling spectroscopy (Cruzan et al., 1996) or found in different crystal hosts (Mascal et al., 2006; Xu et al., 2000; Supriya & Das, 2003; Long et al., 2004; Zuhayra et al., 2006). We report here the title metal–water chain complex [Mn(NO₂—HBDC)₂·4H₂O]·2H₂O [NO₂—H₂BDC is 4-nitro-1,3-benzenedicarboxylic acid], (I), which contains the cyclic water tetramer.

The asymmetric unit of complex (I) consists of one Mn atom, two NO₂—H₂BDC ligands, four coordinated water molecules and two solvent water molecules (Fig. 1). The Mn^II ion is located on a symmetry center and is coordinated by two O atoms of two monodentate carboxylate groups from two NO₂—HBDC ligands [Mn—O1 = 2.1493 (17) Å; symmetry code: (i) -x, -y + 2, -z + 1] and two O atoms from two water molecules [Mn—O7 = 2.1815 (19) Å] forming the equatorial plane, and two O atoms from the other two water molecules [Mn—O8 = 2.2060 (18) Å] at the axial positions. The coordination geometry around the Mn^II ion can be described as a slightly distorted octahedron. The distortion arises from the axis O8—Mn1—O8ⁱ, which is not actually perpendicular to the coordination plane (O1/O7/O1ⁱ/O7ⁱ/Mn1). In fact, the angle O1—Mn1—O8 is 89.26 (6)°. In the NO₂—H₂BDC ligand, the dihedral angles between the benzene ring (C2–C7; plane I) and the planes formed by carboxylate groups atoms are 68.8 (3) and 27.9 (2) ° for the O1/C1/O2 plane and the O3/C8/O4 plane, respectively; that between plane I and the O5/N1/O6 plane is 26.1 (2)°.

There are O—H···O hydrogen bonds between the coordination water molecules and carboxylate O atoms [O8···O4ⁱⁱⁱ = 2.725 (2) Å; see Table 2 fro symmetry codes], which bridge molecules, forming an infinite one-dimensional chain along the c axis. The NO₂—H₂BDC ligands are parallel to each other in the chain; the distance between the benzene rings of the NO₂—HBDC ligands is 3.588 (2) Å. These chains are further interconnected by solvent water molecules via hydrogen bonds [O9···O2^v = 2.665 (3) Å, O3···O9ⁱⁱ = 2.608 (2) Å and O7···O9 = 2.829 (2) Å], giving rise to a two-dimensional structure in the bc plane, as shown in Fig. 2.

Interestingly, a cyclic water tetramer is observed in the solid state (Fig. 3). The solvent water molecule in the cluster is in a tetrahedral environment with two water–water hydrogen bonds and two water–carboxylate hydrogen bonds. Meanwhile, the coordinated water molecule involves two water–water hydrogen bonds and one water–metal coordination bond. Within the cluster, the four water molecules are completely coplanar without regard to connectivity of the H atoms. Though the distance of O9···O7 (3.155 Å) is longer than the sum of van der Waals radii (3.04 Å), we think there still exist weak hydrogen-bonding interactions as found in a lots of compounds reported (Liu & Xu, 2005; Oscar et al., 2006). The average O···O distance is 2.99 Å. This distance is significantly longer than the 2.78 Å e stimated in the water tetramer of (D₂O)₄ in the gas phase (Cruzan et al., 1996), and longer than in other tetrameric clusters reported previously (2.768–2.94 Å; Supriya & Das, 2003; Long et al., 2004; Zuhayra et al., 2006; Tao et al., 2004; Ye et al., 2005). However, it is shorter than that observed in 1,4,7,10-tetraazacyclododecane·3H₂O (3.004 Å; Pal et al., 2003). Two of the water molecules in the cyclic tetramers of (I) bind to the Mn^II ions, resulting in an infinite metal–water chain along the a axis. To the best of our knowledge, such cyclic water clusters containing metal–water chains are not common (Turner et al., 2004; Ghosh & Bharadwaj, 2003; Ye et al., 2004; Liu & Xu, 2005; Li et al., 2006). Another remarkable feature is that the two-dimensional structure is assembled into a three-dimensional network (Fig. 4) by the water tetramers through metal–water chains, indicating that the cyclic water tetramer plays a crucial role in the formation of the three-dimensional network.

Related literature

For related literature, see: Barbour et al. (1998); Benson & Siebert (1992); Buck & Huisken (2000); Cruzan et al. (1996); Ghosh & Bharadwaj (2003); Gregory & Clary (1996); Janiak & Scharamann (2002); Kim et al. (1994, 1999); Li et al. (2006); Liu & Xu (2005); Long et al. (2004); Ludwig (2001); Mascal et al. (2006); Oscar et al. (2006); Pal et al. (2003); Radhakrishnan & Herndon (1991); Raghuraman et al. (2003); Supriya & Das (2003); Tao et al. (2004); Turner et al. (2004); Udalde et al. (2000); Xantheas (1994, 1995); Xu et al. (2000); Ye et al. (2004, 2005); Zuhayra et al. (2006).

S2. Experimental

A solution of MnSO₄ (0.0151 g, 0.10 mmol) in water (5 ml) was added dropwise with constant stirring to an aqueous solution (5 ml) of 4-nitro-1,3-benzenedicarboxylic acid (0.0211 g, 0.1 mmol). The resulting mixture was then transferred into a Teflon-lined stainless steel vessel, which was sealed and heated to 403 K for 72 h, then cooled to room temperature. The reaction mixture was then filtered and single crystals were obtained from the filtrate at room temperature after a few days.

S3. Refinement

H atoms attached to C atoms were placed at calculated positions (C—H = 0.93 Å) and allowed to ride on their parent atoms [U_iso(H) = 1.2U_eq(C)]. H atoms attached to O atoms were located in a difference map and refined as riding in their as-found positions (O—H = 0.82–0.86 Å), with U_iso(H) = 1.2U_eq(O). Please check changes to text.

Computing details

Data collection: SMART (Bruker, 1997); cell refinement: SAINT (Bruker, 1997); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1998); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The molecular structure of (I), showing 30% probability displacement ellipsoids and the atom-mumbering scheme. [Symmetry code: (A) - x, 2 - y, 1 - z.]
	Fig. 2. A view of the two-dimensional hydrogen-bonded net projected on to the bc plane in (I). Dashed lines indicate hydrogen bonds. [Symmetry codes: (A) x, y, -1 + z; (B) x, y, z; (AA) - x, 2 - y, - z; (AD) 1 - x, 1 - y, - z.]
	Fig. 3. A view of the cyclic water tetramer and its coordination environment in (I). Dashed lines indicate hydrogen bonds. [Symmetry codes: (A) Please provide. (B) 1 - x, 2 - y, 1 - z; (AB) 1 + x, y, z; (AC) 1 - x, 1 - y, 1 - z; (AD) x, 1 + y, z; (AE) 1 - x, 2 - y, - z; (AF) x, y, 1 + z.]
	Fig. 4. The crystal packing of (I) viewed down the c axis. Dashed lines indicate hydrogen bonds.

Tetraaquabis(3-carboxy-4-nitrobenzoato-κO)manganese(II) dihydrate

Crystal data

[Mn(C8H4NO6)2(H2O)4]·2H2O	Z = 1
Mr = 583.28	F(000) = 299
Triclinic, P1	Dx = 1.738 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 7.355 (4) Å	Cell parameters from 1957 reflections
b = 7.965 (4) Å	θ = 3.1–26.5°
c = 11.056 (6) Å	µ = 0.69 mm^−1
α = 73.827 (8)°	T = 273 K
β = 83.588 (7)°	Block, colourless
γ = 63.647 (7)°	0.24 × 0.22 × 0.20 mm
V = 557.4 (5) Å^3

Data collection

Bruker SMART CCD area-detector diffractometer	1957 independent reflections
Radiation source: fine-focus sealed tube	1741 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.019
ϕ and ω scans	θmax = 25.0°, θmin = 1.9°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −8→8
Tmin = 0.852, Tmax = 0.875	k = −9→5
2863 measured reflections	l = −13→13

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)] = 0.030	H-atom parameters constrained
wR(F^2) = 0.084	w = 1/[σ^2(Fo^2) + (0.0461P)^2 + 0.1749P] where P = (Fo^2 + 2Fc^2)/3
S = 1.04	(Δ/σ)max < 0.001
1957 reflections	Δρmax = 0.25 e Å^−3
171 parameters	Δρmin = −0.28 e Å^−3
9 restraints	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.331 (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
Mn1	0.0000	1.0000	0.5000	0.02650 (19)
O1	−0.0201 (2)	0.9464 (2)	0.32299 (13)	0.0343 (4)
O2	0.1911 (3)	0.6336 (2)	0.37183 (15)	0.0513 (5)
O3	0.4305 (2)	0.7371 (2)	−0.11896 (14)	0.0375 (4)
H3	0.4998	0.7314	−0.1825	0.056*
O4	0.2952 (2)	0.5942 (2)	−0.20296 (13)	0.0343 (4)
O5	−0.5054 (2)	0.8809 (3)	0.20446 (17)	0.0510 (5)
O6	−0.2785 (3)	0.7428 (3)	0.35109 (14)	0.0502 (5)
O7	0.3273 (2)	0.9039 (2)	0.48277 (15)	0.0439 (4)
H7A	0.4060	0.8576	0.5470	0.053*
H7B	0.3794	0.8559	0.4202	0.053*
O8	−0.0371 (2)	1.2945 (2)	0.39871 (13)	0.0350 (4)
H8A	−0.1195	1.3394	0.3367	0.042*
H8B	−0.0833	1.3470	0.4600	0.042*
N1	−0.3294 (3)	0.8061 (2)	0.24005 (17)	0.0328 (4)
C1	0.0658 (3)	0.7828 (3)	0.30173 (18)	0.0294 (5)
C2	0.0175 (3)	0.7680 (3)	0.17634 (17)	0.0248 (4)
C3	0.1659 (3)	0.7385 (3)	0.08529 (17)	0.0254 (4)
H3A	0.2917	0.7289	0.1020	0.031*
C4	0.1289 (3)	0.7232 (3)	−0.03059 (17)	0.0250 (4)
C5	−0.0604 (3)	0.7434 (3)	−0.05823 (18)	0.0300 (4)
H5	−0.0849	0.7342	−0.1363	0.036*
C6	−0.2121 (3)	0.7772 (3)	0.02976 (19)	0.0298 (4)
H6	−0.3404	0.7939	0.0114	0.036*
C7	−0.1693 (3)	0.7855 (3)	0.14552 (18)	0.0257 (4)
C8	0.2910 (3)	0.6791 (3)	−0.12654 (17)	0.0259 (4)
O9	0.6331 (2)	0.7165 (2)	0.67225 (14)	0.0397 (4)
H9A	0.7013	0.7825	0.6446	0.048*
H9B	0.6933	0.5980	0.6696	0.048*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mn1	0.0317 (3)	0.0320 (3)	0.0209 (3)	−0.0169 (2)	0.00441 (16)	−0.01065 (18)
O1	0.0447 (8)	0.0327 (8)	0.0250 (7)	−0.0121 (7)	0.0004 (6)	−0.0149 (6)
O2	0.0537 (10)	0.0456 (10)	0.0319 (8)	0.0074 (8)	−0.0144 (7)	−0.0195 (7)
O3	0.0350 (8)	0.0558 (10)	0.0353 (8)	−0.0267 (8)	0.0131 (6)	−0.0249 (8)
O4	0.0395 (8)	0.0416 (8)	0.0282 (7)	−0.0186 (7)	0.0067 (6)	−0.0190 (7)
O5	0.0281 (8)	0.0674 (12)	0.0553 (11)	−0.0179 (8)	0.0105 (7)	−0.0209 (9)
O6	0.0492 (10)	0.0665 (12)	0.0290 (9)	−0.0231 (9)	0.0139 (7)	−0.0120 (8)
O7	0.0305 (8)	0.0613 (10)	0.0410 (9)	−0.0157 (8)	0.0100 (7)	−0.0256 (8)
O8	0.0445 (8)	0.0344 (8)	0.0275 (7)	−0.0172 (7)	−0.0017 (6)	−0.0087 (6)
N1	0.0314 (9)	0.0330 (9)	0.0354 (10)	−0.0147 (8)	0.0114 (7)	−0.0138 (8)
C1	0.0292 (10)	0.0358 (11)	0.0218 (10)	−0.0107 (9)	0.0045 (8)	−0.0127 (9)
C2	0.0279 (9)	0.0220 (9)	0.0217 (9)	−0.0073 (8)	0.0008 (7)	−0.0073 (7)
C3	0.0239 (9)	0.0290 (10)	0.0254 (10)	−0.0112 (8)	0.0002 (7)	−0.0105 (8)
C4	0.0275 (10)	0.0248 (9)	0.0232 (9)	−0.0111 (8)	0.0019 (8)	−0.0081 (8)
C5	0.0334 (10)	0.0377 (11)	0.0224 (10)	−0.0159 (9)	−0.0009 (8)	−0.0115 (8)
C6	0.0270 (10)	0.0363 (11)	0.0303 (10)	−0.0159 (9)	0.0011 (8)	−0.0111 (9)
C7	0.0262 (9)	0.0242 (9)	0.0262 (10)	−0.0106 (8)	0.0052 (8)	−0.0081 (8)
C8	0.0294 (10)	0.0267 (10)	0.0203 (9)	−0.0104 (8)	−0.0001 (8)	−0.0067 (8)
O9	0.0395 (8)	0.0407 (8)	0.0439 (9)	−0.0213 (7)	0.0170 (7)	−0.0178 (7)

Geometric parameters (Å, º)

Mn1—O1^i	2.1493 (17)	O8—H8B	0.8542
Mn1—O1	2.1494 (17)	N1—C7	1.468 (3)
Mn1—O7	2.1815 (19)	C1—C2	1.517 (3)
Mn1—O7^i	2.1815 (19)	C2—C3	1.385 (3)
Mn1—O8^i	2.2062 (17)	C2—C7	1.390 (3)
Mn1—O8	2.2062 (17)	C3—C4	1.387 (3)
O1—C1	1.249 (3)	C3—H3A	0.9300
O2—C1	1.240 (2)	C4—C5	1.387 (3)
O3—C8	1.317 (2)	C4—C8	1.491 (3)
O3—H3	0.8200	C5—C6	1.379 (3)
O4—C8	1.211 (2)	C5—H5	0.9300
O5—N1	1.218 (2)	C6—C7	1.377 (3)
O6—N1	1.221 (2)	C6—H6	0.9300
O7—H7A	0.8558	O9—H9A	0.8558
O7—H7B	0.8543	O9—H9B	0.8536
O8—H8A	0.8543
O1^i—Mn1—O1	180.0	O2—C1—O1	125.96 (18)
O1^i—Mn1—O7	88.22 (6)	O2—C1—C2	117.33 (17)
O1—Mn1—O7	91.77 (6)	O1—C1—C2	116.67 (17)
O1^i—Mn1—O7^i	91.78 (6)	C3—C2—C7	117.29 (17)
O1—Mn1—O7^i	88.22 (6)	C3—C2—C1	118.74 (17)
O7—Mn1—O7^i	180.00 (3)	C7—C2—C1	123.96 (17)
O1^i—Mn1—O8^i	89.26 (6)	C2—C3—C4	120.77 (17)
O1—Mn1—O8^i	90.74 (6)	C2—C3—H3A	119.6
O7—Mn1—O8^i	92.13 (6)	C4—C3—H3A	119.6
O7^i—Mn1—O8^i	87.87 (6)	C3—C4—C5	120.18 (18)
O1^i—Mn1—O8	90.74 (6)	C3—C4—C8	121.44 (17)
O1—Mn1—O8	89.26 (6)	C5—C4—C8	118.36 (17)
O7—Mn1—O8	87.87 (6)	C6—C5—C4	120.16 (18)
O7^i—Mn1—O8	92.13 (6)	C6—C5—H5	119.9
O8^i—Mn1—O8	180.0	C4—C5—H5	119.9
C1—O1—Mn1	123.79 (13)	C7—C6—C5	118.46 (18)
C8—O3—H3	109.5	C7—C6—H6	120.8
Mn1—O7—H7A	122.3	C5—C6—H6	120.8
Mn1—O7—H7B	114.8	C6—C7—C2	123.09 (18)
H7A—O7—H7B	114.9	C6—C7—N1	116.83 (17)
Mn1—O8—H8A	109.7	C2—C7—N1	120.03 (17)
Mn1—O8—H8B	97.5	O4—C8—O3	123.24 (18)
H8A—O8—H8B	114.9	O4—C8—C4	122.68 (17)
O5—N1—O6	123.17 (18)	O3—C8—C4	114.07 (16)
O5—N1—C7	118.78 (18)	H9A—O9—H9B	115.3
O6—N1—C7	118.02 (17)
O7—Mn1—O1—C1	62.49 (17)	C4—C5—C6—C7	−1.5 (3)
O7^i—Mn1—O1—C1	−117.51 (17)	C5—C6—C7—C2	2.2 (3)
O8^i—Mn1—O1—C1	−29.67 (16)	C5—C6—C7—N1	−175.23 (18)
O8—Mn1—O1—C1	150.33 (16)	C3—C2—C7—C6	−0.8 (3)
Mn1—O1—C1—O2	−8.7 (3)	C1—C2—C7—C6	178.08 (18)
Mn1—O1—C1—C2	173.81 (12)	C3—C2—C7—N1	176.59 (16)
O2—C1—C2—C3	−68.7 (3)	C1—C2—C7—N1	−4.5 (3)
O1—C1—C2—C3	109.1 (2)	O5—N1—C7—C6	−25.5 (3)
O2—C1—C2—C7	112.4 (2)	O6—N1—C7—C6	152.8 (2)
O1—C1—C2—C7	−69.8 (3)	O5—N1—C7—C2	156.97 (19)
C7—C2—C3—C4	−1.4 (3)	O6—N1—C7—C2	−24.7 (3)
C1—C2—C3—C4	179.70 (17)	C3—C4—C8—O4	150.97 (19)
C2—C3—C4—C5	2.1 (3)	C5—C4—C8—O4	−27.2 (3)
C2—C3—C4—C8	−176.09 (17)	C3—C4—C8—O3	−27.7 (3)
C3—C4—C5—C6	−0.6 (3)	C5—C4—C8—O3	154.09 (18)
C8—C4—C5—C6	177.62 (17)

Symmetry code: (i) −x, −y+2, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3···O9^ii	0.82	1.79	2.608 (2)	175
O7—H7A···O9	0.86	1.99	2.829 (2)	168
O8—H8A···O4^iii	0.85	1.88	2.726 (2)	173
O8—H8B···O2^i	0.85	1.96	2.764 (2)	157
O9—H9A···O7^iv	0.86	2.43	3.155 (3)	143
O9—H9A···O8^iv	0.86	2.29	2.956 (3)	134
O9—H9B···O2^v	0.85	1.82	2.665 (3)	168

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