trans-Diaquabis(1H-imidazole-4,5-di­carboxyl­ate-κ²N³,O⁴)­manganese(II)

In the title compound, [Mn(C₅H₃N₂O₄)₂(H₂O)₂], the Mn^II atom lies on an inversion centre, is trans-coordinated by two N,O-bidentate 1H-imidazole-4,5-di­carboxyl­ate monoanionic ligands [Mn—O = 2.202 (3) Å and Mn—N = 2.201 (4) Å] and two water mol­ecules [Mn—O = 2.197 (4) Å], and exhibits a distorted octahedral geometry, with adjacent cis angles of 76.45 (13), 86.09 (13) and 89.20 (13)°. The complete solid-state structure can be described as a three-dimensional supramol­ecular framework, stabilized by extensive hydrogen-bonding interactions involving the coordinated water mol­ecules, the carboxy O atoms and the protonated imidazole N atoms of the imidazole-4,5-di­carboxyl­ate ligands.

S1. Comment

It is well established that manganese is one of the trace elements in biosystems, and it plays an important role in the active sites of various redox-based enzymes (Weighardt, 1989). In addition to the well known oxygen-evolving complex, which is generally believed to contain a tetranuclear manganese cluster catalyzing the oxidation of water to yield O₂ during photosynthesis (Debus, 1992), there are three known enzymes containing a mononuclear manganese site, viz. superoxide dismutase, peroxidase and dioxygenase, which participate in the redox changes of biological systems (Law et al., 1999). In order to better understand the exact nature and mechanism of action of these active sites, N,O-containing ligands are often employed to prepare model compounds for them, based on the knowledge that the coordination sphere of the Mn centers in these enzymes are predominated by N,O-donors from available amino acid residues (Pecoraro & Butler, 1986). In the course of our studies of manganese biochemistry, we have investigated manganese complexation by imidazole-4,5-dicarboxylic acid (H₃ida), considering that it possesses the biologically important imidazole ring, which is known as a functional group of histidine, and potentially versatile bonding modes with the metal ion. We report here the single-crystal structure of a new compound, (I), in which the H₂ida monoanion coordinates to the Mn atom acting as one bidentate ligand. The coordination mode of the ligand exhibited in (I) is unique and has not been reported previously in other manganese–imidazole-4,5-dicarboxylate complexes.

As shown in Fig. 1, (I) is a discrete neutral monomeric molecule, in which the Mn atom resides on a crystallographic inversion centre and the asymmetric unit contains one-half of the formula [Mn(H₂ida)₂(H₂O)₂]. The octahedral sphere on the manganese(II) centre is highly distorted because of the N,O-chelation of the rigid H₂ida ligand (Table 1), with the cis angles [76.45 (13)–103.55 (13)°] deviating sifgnificantly from the ideal value of 90°.

The Mn atom, atoms O1 and N2, and the inversion-related pair are strictly coplanar as a result of the Mn atom lying on the inversion centre. The two O atoms from the symmetry-related water molecules complete the octahedral coordination The Mn—O distance (Table 1) is comparable with those in the Mn^(II)–water complexes (Schlueter & Geiser, 2003; Okabe & Koizumi, 1997; Hao et al., 2000; Ma et al., 2002).

The H₂ida ligand adopts a bidentate coordination mode to the Mn atom through one imidazolyl N atom and one O atom from one deprotonated carboxy group; the other carboxy group is protonated, as indicated by the significant difference between the O3—C5 [1.321 (6) Å] and O4—C5 [1.204 (6) Å] bond lengths. This type of binding mode is different from those found in the previously reported Mn complexes [Mn(salen)(H₂ida)(H₂O)] (Huang et al., 2001) and [Mn₂(salpn)₂(ida)]⁺ (Caudle et al., 1997). The N—Mn—O angle is 76.45 (13)°, and the Mn—N and Mn—O (H₂ida) bond lengths [2.201 (4) and 2.202 (3) Å, respectively] are comparable to those reported in Mn complexes with the formula [Mn(L)₂(H₂O)₂] (L is N-heteroaromatic acid) similar to the title compound, e.g. L = pyridine-2,5-dicarboxylate (Goher & Mak, 1994), and L = pyridine-2-carboxylate (Okabe & Koizumi, 1998). All non-H atoms in the H₂ida ligand are nearly coplanar [the mean deviation is 0.090 (9) Å)], with the maximun of deviation of 0.196 (3) Å for atom O1 being the result of the hydrogen-bonding interaction involving atoms O1 and O5.

As listed in Table 2, N1—H1···O3ⁱⁱⁱ hydrogen bonds link the molecules, thus generating a two-dimensional hydrogen-bonded network sheet (Fig. 2). These sheets are further linked via pairs of hydrogen bonds involving the coordinated water O5 atoms and two carboxy O atoms (O1 and O2) of symmetry-related monomers. Each of the monomers in one sheet further connects four monomers belonging to the two symmetry-related sheets above and below, thus generating centrosymmetric pentamers (Fig. 3), giving rise to an overall three-dimensional hydrogen-bonded network.

S2. Experimental

To a refluxing suspension of MnCl₂·4H₂O (0.40 g, 2 mmol) and H₃ida (0.31 g, 2 mmol) in of water (50 ml), NaOH (0.1M) was added slowly, dropwise via a dropping funnel, under continuous stirring until the mixture became clear. The mixture was refluxed and stirred for 8 h. The resulting hot solution was filtered, and the filtrate was left undisturbed for 4 h at room temperature, resulting in the deposition of pale-yellow crystals of (I).

S3. Refinement

Water H atoms and the H atom of the carboxy group were located from difference maps and refined with a DFIX restraint of 0.85 (2) Å applied to the three O—H distances. H atoms bonded to atoms of the aromatic ring were placed in calculated positions and treated as riding atoms.

Computing details

Data collection: SMART (Siemens,1996); cell refinement: SAINT (Siemens,1994); data reduction: XPREP in SHELXTL (Siemens,1994); program(s) used to solve structure: SHELXTL; program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A view of the molecule of (I), showing the labelling scheme and displacement ellipsoids at the 30% probability level.
	Fig. 2. The crystal packing of (I), showing (a) part of the two-dimensional hydrogen-bondin network [atoms marked with an ampersand (&) symbol are at the symmetry position (x − 1/2, 1/2 − y, 1/2 + z)] and (b) the hydrogen-bonding three-dimensional stacked-layer network.
	Fig. 3. The centrosymmetric pentamers produced by the coordinated water molecules of (I). Atoms labeled with an asterisk (*) or a hash (#) are at the symmetry positions (-x + 2,-y,-z) and (x,y,z + 1), respectively.

trans-Diaquabis(imidazole-4,5-dicarboxylate-κ²N³,O)manganese(II)

Crystal data

[Mn(C5H3N2O4)2(H2O)2]	F(000) = 406
Mr = 401.16	Dx = 1.875 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 1282 reflections
a = 5.0550 (3) Å	θ = 1.8–25.0°
b = 22.9305 (7) Å	µ = 1.00 mm^−1
c = 6.5918 (4) Å	T = 293 K
β = 111.596 (2)°	Needle, pale yellow
V = 710.44 (6) Å^3	0.49 × 0.15 × 0.14 mm
Z = 2

Data collection

Siemans SMART CCD area-detector diffractometer	1216 independent reflections
Radiation source: fine-focus sealed tube	852 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.049
ϕ and ω scans	θmax = 25.0°, θmin = 1.8°
Absorption correction: empirical (using intensity measurements) (SADABS, Sheldrick, 1996)	h = −6→5
Tmin = 0.836, Tmax = 0.870	k = −14→27
2152 measured reflections	l = −7→7

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)] = 0.060	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.156	H atoms treated by a mixture of independent and constrained refinement
S = 1.01	w = 1/[σ^2(Fo^2) + (0.08P)^2] where P = (Fo^2 + 2Fc^2)/3
1216 reflections	(Δ/σ)max < 0.001
126 parameters	Δρmax = 0.74 e Å^−3
3 restraints	Δρmin = −1.13 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
Mn	0.5000	0.0000	0.0000	0.0293 (4)
O1	0.6557 (7)	0.02485 (14)	−0.2590 (6)	0.0298 (8)
O2	0.6865 (7)	0.09792 (15)	−0.4728 (6)	0.0353 (9)
O3	0.5569 (9)	0.20426 (17)	−0.5240 (7)	0.0437 (10)
H3	0.631 (15)	0.1705 (16)	−0.509 (12)	0.08 (3)*
O4	0.3520 (8)	0.26847 (15)	−0.3793 (7)	0.0468 (11)
O5	0.8819 (8)	0.03964 (17)	0.2418 (6)	0.0381 (10)
H5A	0.852 (12)	0.056 (2)	0.345 (7)	0.050*
H5B	1.036 (6)	0.0197 (18)	0.295 (8)	0.026 (14)*
N1	0.2267 (8)	0.18239 (16)	−0.1269 (6)	0.0279 (10)
H1	0.1562	0.2155	−0.1114	0.034*
N2	0.3435 (8)	0.08980 (16)	−0.0822 (6)	0.0254 (9)
C1	0.2162 (10)	0.1338 (2)	−0.0218 (8)	0.0280 (12)
H1A	0.1310	0.1307	0.0811	0.034*
C2	0.4396 (10)	0.1136 (2)	−0.2356 (8)	0.0278 (11)
C3	0.3677 (10)	0.1713 (2)	−0.2638 (8)	0.0287 (12)
C4	0.6036 (9)	0.0761 (2)	−0.3318 (7)	0.0244 (11)
C5	0.4226 (11)	0.2189 (2)	−0.3934 (9)	0.0349 (13)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mn	0.0369 (7)	0.0240 (6)	0.0322 (7)	0.0031 (5)	0.0187 (5)	0.0045 (5)
O1	0.036 (2)	0.0267 (18)	0.033 (2)	0.0073 (16)	0.0203 (16)	0.0013 (16)
O2	0.047 (2)	0.0328 (19)	0.037 (2)	0.0016 (17)	0.0290 (18)	0.0005 (17)
O3	0.062 (3)	0.032 (2)	0.051 (3)	0.004 (2)	0.038 (2)	0.0099 (19)
O4	0.062 (3)	0.026 (2)	0.062 (3)	0.009 (2)	0.034 (2)	0.013 (2)
O5	0.035 (2)	0.042 (2)	0.039 (2)	0.0136 (19)	0.0163 (18)	−0.0050 (19)
N1	0.035 (3)	0.023 (2)	0.031 (2)	0.0059 (19)	0.018 (2)	0.0017 (19)
N2	0.030 (2)	0.023 (2)	0.026 (2)	0.0049 (18)	0.0149 (19)	0.0061 (18)
C1	0.033 (3)	0.032 (3)	0.024 (3)	0.002 (2)	0.016 (2)	0.000 (2)
C2	0.027 (3)	0.032 (3)	0.029 (3)	−0.004 (2)	0.016 (2)	−0.003 (2)
C3	0.034 (3)	0.025 (3)	0.032 (3)	0.000 (2)	0.017 (2)	−0.003 (2)
C4	0.025 (3)	0.029 (3)	0.020 (2)	0.001 (2)	0.009 (2)	−0.002 (2)
C5	0.038 (3)	0.037 (3)	0.035 (3)	−0.003 (3)	0.019 (3)	0.005 (2)

Geometric parameters (Å, º)

Mn—O5^i	2.197 (4)	O5—H5A	0.84 (5)
Mn—O5	2.197 (4)	O5—H5B	0.86 (4)
Mn—N2	2.201 (4)	N1—C1	1.324 (6)
Mn—N2^i	2.201 (4)	N1—C3	1.364 (6)
Mn—O1^i	2.202 (3)	N1—H1	0.8600
Mn—O1	2.202 (3)	N2—C1	1.333 (6)
O1—C4	1.261 (6)	N2—C2	1.385 (6)
O2—C4	1.255 (5)	C1—H1A	0.9300
O2—O3	2.515 (5)	C2—C3	1.366 (7)
O3—C5	1.321 (6)	C2—C4	1.489 (6)
O3—H3	0.85 (5)	C3—C5	1.475 (7)
O4—C5	1.204 (6)
O5^i—Mn—O5	180	C3—N1—O3^iv	126.5 (3)
O5^i—Mn—N2	93.91 (14)	C1—N1—O4^iv	83.2 (3)
O5—Mn—N2	86.09 (14)	C3—N1—O4^iv	167.4 (3)
N2—Mn—N2^i	180	C1—N1—H1	125.6
O5—Mn—O1^i	90.80 (13)	C3—N1—H1	125.6
N2—Mn—O1^i	103.55 (13)	C1—N2—C2	104.9 (4)
O5—Mn—O1	89.20 (13)	C1—N2—Mn	143.4 (3)
N2—Mn—O1	76.45 (13)	C2—N2—Mn	111.0 (3)
N2^i—Mn—O1	103.55 (13)	N1—C1—N2	111.3 (4)
O1^i—Mn—O1	180	N1—C1—H1A	124.3
C4—O1—Mn	116.9 (3)	N2—C1—H1A	124.3
C4—O2—O3	110.1 (3)	C3—C2—N2	109.5 (4)
C5—O3—O2	109.3 (3)	C3—C2—C4	131.5 (4)
C5—O3—H3	118 (5)	N2—C2—C4	118.9 (4)
Mn—O5—O1^ii	108.43 (15)	N1—C3—C2	105.5 (4)
Mn—O5—O2^iii	104.74 (15)	N1—C3—C5	120.1 (4)
O1^ii—O5—O2^iii	138.27 (17)	C2—C3—C5	134.3 (4)
Mn—O5—H5A	114 (4)	O2—C4—O1	125.0 (4)
O1^ii—O5—H5A	128 (4)	O2—C4—C2	118.4 (4)
Mn—O5—H5B	120 (3)	O1—C4—C2	116.6 (4)
H5A—O5—H5B	108 (5)	O4—C5—O3	121.9 (5)
C1—N1—C3	108.7 (4)	O4—C5—C3	121.9 (5)
C1—N1—O3^iv	124.1 (3)	O3—C5—C3	116.1 (5)
O5^i—Mn—O1—C4	96.4 (3)	Mn—N2—C2—C3	−172.9 (3)
O5—Mn—O1—C4	−83.6 (3)	C1—N2—C2—C4	177.7 (4)
N2—Mn—O1—C4	2.5 (3)	Mn—N2—C2—C4	4.9 (5)
N2^i—Mn—O1—C4	−177.5 (3)	C1—N1—C3—C2	0.2 (5)
C4—O2—O3—C5	−0.2 (5)	O3^iv—N1—C3—C2	170.9 (3)
N2—Mn—O5—O1^ii	−143.68 (17)	O4^iv—N1—C3—C2	−160.3 (13)
N2^i—Mn—O5—O1^ii	36.32 (17)	C1—N1—C3—C5	−176.9 (4)
O1^i—Mn—O5—O1^ii	112.79 (18)	O3^iv—N1—C3—C5	−6.2 (7)
O1—Mn—O5—O1^ii	−67.21 (18)	O4^iv—N1—C3—C5	22.5 (18)
N2—Mn—O5—O2^iii	62.02 (17)	N2—C2—C3—N1	−0.1 (5)
N2^i—Mn—O5—O2^iii	−117.98 (17)	C4—C2—C3—N1	−177.5 (5)
O1^i—Mn—O5—O2^iii	−41.51 (16)	N2—C2—C3—C5	176.4 (5)
O1—Mn—O5—O2^iii	138.49 (16)	C4—C2—C3—C5	−1.0 (10)
O5^i—Mn—N2—C1	98.0 (5)	O3—O2—C4—O1	−174.5 (4)
O5—Mn—N2—C1	−82.0 (5)	O3—O2—C4—C2	3.3 (5)
O1^i—Mn—N2—C1	7.9 (6)	Mn—O1—C4—O2	177.1 (4)
O1—Mn—N2—C1	−172.1 (6)	Mn—O1—C4—C2	−0.7 (5)
O5^i—Mn—N2—C2	−93.7 (3)	C3—C2—C4—O2	−3.7 (8)
O5—Mn—N2—C2	86.3 (3)	N2—C2—C4—O2	179.1 (4)
O1^i—Mn—N2—C2	176.2 (3)	C3—C2—C4—O1	174.2 (5)
O1—Mn—N2—C2	−3.8 (3)	N2—C2—C4—O1	−3.0 (7)
C3—N1—C1—N2	−0.3 (6)	O2—O3—C5—O4	175.9 (5)
O3^iv—N1—C1—N2	−171.2 (3)	O2—O3—C5—C3	−3.3 (6)
O4^iv—N1—C1—N2	175.5 (4)	N1—C3—C5—O4	1.7 (8)
C2—N2—C1—N1	0.2 (5)	C2—C3—C5—O4	−174.5 (6)
Mn—N2—C1—N1	168.9 (4)	N1—C3—C5—O3	−179.1 (5)
C1—N2—C2—C3	0.0 (5)	C2—C3—C5—O3	4.7 (9)

Symmetry codes: (i) −x+1, −y, −z; (ii) −x+2, −y, −z; (iii) x, y, z+1; (iv) 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
O5—H5B···O1^ii	0.86 (4)	1.95 (4)	2.733 (5)	151 (5)
O5—H5A···O2^iii	0.84 (5)	1.94 (5)	2.770 (5)	165 (5)
N1—H1···O3^iv	0.86	2.05	2.895 (5)	169
N1—H1···O4^iv	0.86	2.56	3.130 (5)	124
O3—H3···O2	0.85 (5)	1.69 (3)	2.515 (5)	163 (8)

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