Bis(μ-pyridine-2,6-carboxyl­ato-O,N,O′:O)­bis­[tri­aqua­manganese(II)]–pyridine-2,6-di­carboxylic acid (1/2)

In the structure of the title compound, [Mn₂(C₇H₃NO₄)₂(H₂O)₆]·2C₇H₅NO₄, a centrosymmetric dinuclear complex, hexaa­aqua­bis­(pyri­dine-2,6-di­carboxyl­ato)­dimanganese(II) and free pyri­dine-2,6-di­carboxyl­ic acid are present in a 1:2 ratio. In the complex, each Mn²⁺ ion is coordinated by three O atoms and one N atom from the pyridine-2,6-di­carboxyl­ate ligands and by three water O atoms, resulting in a distorted pentagonal bipyramidal coordination. Within the centrosymmetric dinuclear complex, two Mn²⁺ ions are bridged by two carboxyl­ate O atoms. The crystal structure is stabilized by hydrogen bonds involving all the H atoms of the water ligands.

S1. Comment

Pyridine-2,6-dicarboxylic acid (dipicolinic acid), (I), is present in large amounts in bacterial spores (Powell, 1953; Church & Halvorson, 1959). This compound is the main component of bacterial spores, in which it forms a metal complex with divalent metal ions, especially with the calcium ion. The Mn²⁺ ion appeared to substitute for the Ca²⁺ ion to some degree in conferring heat resistance (Chung et al., 1971). It also has biological activity, such as inhibition of the zinc enzyme, bovine carbonic anhydrase (Pocker & Fong, 1980) or E. coli dihydrodipicolinate reductase (Scapin et al., 1997), or selective activation of the metalloenzyme calmodulin-activated protein phosphatase calcineurin (Martin, 1997). The selective activation of calcineurin by pyridine-2,6-dicarboxylic acid is reduced by the Mn²⁺ ion, which may be explained by the formation of a manganese–pyridine-2,6-dicarboxylic acid complex (Martin, 1997). We have analyzed the title complex, (II), in order to confirm the coordination mode of a manganese–pyridine-2,6-dicarboxylic acid complex.

Crystals of (II) were obtained as a 1:2 mixture of the dinuclear metal complex and free pyridine-2,6-dicarboxylic acid (see Fig. 1 and Table 1). The dinuclear complex sits on a crystallographic inversion center. Each Mn²⁺ ion is coordinated by two O atoms and one N atom from one pyridine-2,6-dicarboxylic acid ligand, one carboxylate O atom of the second pyridine-2,6-dicarboxylic acid ligand and by three water O atoms. In each dinuclear complex, the carboxylate group and the N atom form a five-membered chelate ring with the Mn²⁺ ion (N1/C1/C6/O2/Mn1 and N1/C5/C7/O4/Mn1), and two Mn²⁺ ions are bridged by two bifurcated coordination bonds of two carboxylate O atoms [O2 and O2ⁱ; symmetry code: (i) −x, −y, 1 − z]. Each Mn²⁺ ion has seven coordinate bonds forming a distorted pentagonal bipyramid, in which the N1, O2, O2ⁱ, O9 and O4 atoms form the distorted pentagonal plane. The pentagonal bipyramidal coordination of the d³sp³ hybrid orbital of Mn²⁺ ion seems to be rare, since it usually forms an octahedral d²sp³ hybrid orbital consisting of six coordination bonds. The planar conformation of the free pyridine-2,6-dicarboxylic acid molecules cocrystallized with the chelate complex in (II) resembles the crystal structure of pyridine-2,6-dicarboxylic acid itself (Takusagawa et al., 1973).

Up until now, many crystal structures of chelate compounds of pyridine-2,6-dicarboxylic acid with various metal ions have been determined: Ca²⁺ (Strahs & Dickerson, 1968), Ag²⁺ (Drew et al., 1969, 1970), Ti²⁺ (Schwarzenbach, 1970), Sr²⁺ (Palmer et al., 1972), Ni²⁺ (Quaglieri et al., 1972), Fe²⁺ (Lainé, Gourdon & Launay, 1995; Lainé, Gourdon, Launay & Tuchagues, 1995), and Cu²⁺ and Zn²⁺ (Okabe & Oya, 2000). In most of these crystal structures, the pyridine-2,6-dicarboxylic acid ligand is coordinated to a mononuclear metal ion and acts as a terdentate ligand, in which the central metal ion is bonded to two N and four O atoms of two ligand molecules. But the Ti⁵⁺ (Schwarzenbach, 1970), Fe²⁺ (Lainé, Gourdon, Launay & Tuchagues, 1995) and Ca²⁺ complexes (Strahs & Dickerson, 1968) are dinuclear, and the Sr²⁺ complex is polynuclear. Among these, the structure of the Fe²⁺ complex is isomorphous with the Mn²⁺ complex. Not only do these structures have the same geometry, but they also have the same space group and similar cell constants. Each metal has three bonds to one ligand molecule, one to the second ligand molecule and three to water molecules. Substitution of the Mn²⁺ ion for Ca²⁺ in bacterial spores in conferring heat resistance (Chung et al., 1971) may be caused by the similarities of the coordination polyhedron of the dinuclear octacoordinated Ca²⁺ and the dinuclear heptacoordinated Mn²⁺ complexes.

In the crystal structure of (II), the complex molecules and free ligand molecules are connected by all available hydrogen bonds through the hydrated water molecules (Table 2). There are π-stacking interactions between the pyridine rings both in the metal complexes and in the free ligand along the a axis

S2. Experimental

The colorless pillar-shaped crystal used for analysis was obtained by slow evapolation from a 50% ethanol–water solution of pyridine-2,6-dicarboxylic acid and manganese chloride tetrahydrate in a 10:1 molar ratio at room temperature.

S3. Refinement

The H atoms were located from difference Fourier maps.

Computing details

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1992a); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: TEXSAN PROCESS (Molecular Structure Corporation, 1992b); program(s) used to solve structure: SAPI91 (Fan, 1991) and DIRDIF (Beurskens et al., 1994); program(s) used to refine structure: TEXSAN LS; molecular graphics: ORTEPII (Johnson, 1976).

Figures

Fig. 1. ORTEPII (Johnson, 1976) drawing of (II) with the atomic numbering scheme. Another free ligand molecule located centrosymmetrically has been omitted. Ellipsoids for non-H atoms correspond to 50% probability.

Bis(µ-pyridine-2,6-carboxylato-N,O,O':O)bis[triaquamanganese(II)]– pyridine-2,6-dicarboxylic acid (1/2)

Crystal data

[Mn2(C7H3NO4)2(H2O)6]·2C7H5NO4	Dx = 1.811 Mg m^−3
Mr = 882.42	Mo Kα radiation, λ = 0.71069 Å
Monoclinic, P21/c	Cell parameters from 25 reflections
a = 9.166 (3) Å	θ = 14.6–15.0°
b = 14.603 (3) Å	µ = 0.89 mm^−1
c = 12.192 (3) Å	T = 296 K
β = 97.43 (2)°	Pillar, colorless
V = 1618.2 (7) Å^3	0.60 × 0.30 × 0.10 mm
Z = 2

Data collection

Rigaku AFC-5R diffractometer	Rint = 0.023
ω–2θ scans	θmax = 27.5°
Absorption correction: ψ scan (North et al., 1968)	h = 0→11
Tmin = 0.816, Tmax = 0.915	k = 0→18
4093 measured reflections	l = −15→15
3711 independent reflections	3 standard reflections every 150 reflections
2524 reflections with F^2 > 2.0σ(F^2)	intensity decay: 0.4%

Refinement

Refinement on F^2	H-atom parameters not refined
R[F^2 > 2σ(F^2)] = 0.037	w = 1/[σ^2(Fo^2) + {0.06000[Max(Fo^2,0) + 2Fc^2]/3}^2]
wR(F^2) = 0.122	(Δ/σ)max = 0.003
S = 1.10	Δρmax = 0.58 e Å^−3
3711 reflections	Δρmin = −0.67 e Å^−3
253 parameters

Special details

Refinement. Refinement using reflections with F² > −10.0 σ(F²). The weighted

R-factor (wR) and goodness of fit (S) are based on F². R-factor (gt) are

based on F. The threshold expression of F² > 2.0 σ(F²) is used only

for calculating R-factor (gt).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Mn1	0.08193 (5)	0.08403 (3)	0.40568 (3)	0.0232 (1)
O1	−0.2031 (2)	0.1409 (1)	0.6562 (2)	0.0328 (5)
O2	−0.0740 (2)	0.0672 (1)	0.5390 (1)	0.0242 (5)
O3	0.1370 (2)	0.3563 (1)	0.2437 (2)	0.0302 (5)
O4	0.1482 (2)	0.2075 (1)	0.2831 (2)	0.0319 (5)
O5	0.6277 (3)	0.3966 (2)	−0.2210 (2)	0.0465 (7)
O6	0.5763 (2)	0.4257 (1)	−0.0496 (2)	0.0377 (6)
O7	0.2985 (3)	0.0729 (1)	0.0930 (2)	0.0462 (7)
O8	0.3021 (3)	0.2214 (1)	0.1282 (2)	0.0427 (7)
O9	0.2510 (2)	0.0325 (1)	0.3119 (2)	0.0350 (6)
O10	−0.0898 (2)	0.0402 (1)	0.2742 (2)	0.0306 (5)
O11	0.2742 (2)	0.0962 (1)	0.5468 (2)	0.0287 (5)
N1	−0.0162 (2)	0.2227 (1)	0.4421 (2)	0.0203 (5)
N2	0.4542 (2)	0.2589 (1)	−0.0362 (2)	0.0236 (5)
C1	−0.0992 (3)	0.2279 (2)	0.5242 (2)	0.0215 (6)
C2	−0.1576 (3)	0.3090 (2)	0.5566 (2)	0.0288 (7)
C3	−0.1304 (4)	0.3887 (2)	0.5014 (2)	0.0335 (8)
C4	−0.0452 (3)	0.3842 (2)	0.4156 (2)	0.0287 (7)
C5	0.0104 (3)	0.3000 (2)	0.3885 (2)	0.0226 (6)
C6	−0.1282 (3)	0.1381 (2)	0.5787 (2)	0.0222 (6)
C7	0.1055 (3)	0.2888 (2)	0.2973 (2)	0.0238 (6)
C8	0.5279 (3)	0.2767 (2)	−0.1221 (2)	0.0265 (7)
C9	0.5600 (3)	0.2108 (2)	−0.1972 (2)	0.0343 (8)
C10	0.5170 (4)	0.1215 (2)	−0.1827 (3)	0.0378 (8)
C11	0.4437 (3)	0.1011 (2)	−0.0938 (2)	0.0324 (7)
C12	0.4140 (3)	0.1721 (2)	−0.0232 (2)	0.0247 (6)
C13	0.5806 (3)	0.3731 (2)	−0.1362 (2)	0.0319 (7)
C14	0.3316 (3)	0.1509 (2)	0.0724 (2)	0.0267 (7)
H1	−0.2157	0.3104	0.6158	0.0340
H2	−0.1701	0.4452	0.5216	0.0397
H3	−0.0252	0.4379	0.3761	0.0345
H4	0.6096	0.2271	−0.2582	0.0412
H5	0.5375	0.0748	−0.2329	0.0455
H6	0.4139	0.0400	−0.0807	0.0385
H7	0.6120	0.4797	−0.0697	0.0439
H8	0.2302	0.2048	0.1774	0.0439
H9	0.2632	0.0516	0.2498	0.0439
H10	0.2596	−0.0288	0.3228	0.0439
H11	−0.0965	−0.0190	0.2787	0.0439
H12	−0.1867	0.0565	0.2816	0.0439
H13	0.3319	0.1379	0.5269	0.0439
H14	0.2356	0.1181	0.6015	0.0439

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mn1	0.0303 (2)	0.0196 (2)	0.0219 (2)	0.0019 (2)	0.0116 (2)	0.0002 (2)
O1	0.047 (1)	0.0245 (10)	0.033 (1)	0.0054 (8)	0.0274 (9)	0.0031 (8)
O2	0.034 (1)	0.0189 (9)	0.0225 (9)	0.0033 (7)	0.0159 (8)	0.0014 (7)
O3	0.040 (1)	0.0235 (10)	0.031 (1)	0.0017 (8)	0.0174 (9)	0.0078 (8)
O4	0.046 (1)	0.0227 (9)	0.032 (1)	0.0028 (8)	0.0232 (9)	0.0033 (8)
O5	0.055 (1)	0.049 (1)	0.040 (1)	−0.016 (1)	0.021 (1)	0.009 (1)
O6	0.046 (1)	0.031 (1)	0.039 (1)	−0.0069 (9)	0.0152 (10)	0.0005 (9)
O7	0.078 (2)	0.027 (1)	0.040 (1)	−0.010 (1)	0.031 (1)	−0.0009 (9)
O8	0.071 (2)	0.024 (1)	0.042 (1)	−0.0006 (10)	0.040 (1)	0.0015 (9)
O9	0.050 (1)	0.027 (1)	0.033 (1)	0.0073 (9)	0.0241 (10)	0.0086 (8)
O10	0.037 (1)	0.026 (1)	0.0295 (10)	0.0005 (8)	0.0084 (8)	−0.0005 (8)
O11	0.037 (1)	0.0248 (10)	0.0274 (10)	−0.0040 (8)	0.0147 (8)	−0.0030 (7)
N1	0.026 (1)	0.021 (1)	0.0162 (10)	0.0015 (8)	0.0082 (8)	0.0024 (8)
N2	0.024 (1)	0.025 (1)	0.023 (1)	0.0002 (9)	0.0090 (9)	0.0026 (8)
C1	0.027 (1)	0.018 (1)	0.020 (1)	0.0009 (10)	0.0073 (10)	0.0009 (9)
C2	0.041 (2)	0.024 (1)	0.025 (1)	0.005 (1)	0.015 (1)	0.000 (1)
C3	0.051 (2)	0.019 (1)	0.033 (1)	0.009 (1)	0.017 (1)	−0.001 (1)
C4	0.042 (2)	0.019 (1)	0.027 (1)	0.003 (1)	0.014 (1)	0.005 (1)
C5	0.030 (1)	0.020 (1)	0.019 (1)	0.0006 (10)	0.0084 (10)	0.0005 (9)
C6	0.029 (1)	0.021 (1)	0.019 (1)	0.0010 (10)	0.0095 (10)	0.0003 (9)
C7	0.026 (1)	0.025 (1)	0.020 (1)	−0.0002 (10)	0.005 (1)	0.0020 (10)
C8	0.024 (1)	0.032 (1)	0.025 (1)	0.000 (1)	0.010 (1)	0.003 (1)
C9	0.037 (2)	0.038 (2)	0.030 (1)	0.005 (1)	0.018 (1)	0.002 (1)
C10	0.048 (2)	0.035 (2)	0.034 (2)	0.007 (1)	0.018 (1)	−0.007 (1)
C11	0.040 (2)	0.025 (1)	0.034 (1)	0.002 (1)	0.011 (1)	−0.002 (1)
C12	0.026 (1)	0.026 (1)	0.023 (1)	0.002 (1)	0.007 (1)	0.0014 (10)
C13	0.028 (1)	0.035 (2)	0.035 (1)	−0.002 (1)	0.009 (1)	0.008 (1)
C14	0.033 (1)	0.027 (1)	0.020 (1)	0.000 (1)	0.007 (1)	0.002 (1)

Geometric parameters (Å, º)

Mn1—O2	2.312 (2)	N1—C5	1.342 (3)
Mn1—O2^i	2.313 (2)	N2—C8	1.343 (3)
Mn1—O4	2.467 (2)	N2—C12	1.334 (3)
Mn1—O9	2.176 (2)	C1—C2	1.379 (4)
Mn1—O10	2.192 (2)	C1—C6	1.509 (3)
Mn1—O11	2.305 (2)	C2—C3	1.382 (4)
Mn1—N1	2.283 (2)	C3—C4	1.386 (4)
O1—C6	1.238 (3)	C4—C5	1.388 (4)
O2—C6	1.271 (3)	C5—C7	1.507 (4)
O3—C7	1.238 (3)	C8—C9	1.387 (4)
O4—C7	1.269 (3)	C8—C13	1.505 (4)
O5—C13	1.220 (4)	C9—C10	1.379 (4)
O6—C13	1.311 (4)	C10—C11	1.380 (4)
O7—C14	1.215 (3)	C11—C12	1.397 (4)
O8—C14	1.281 (3)	C12—C14	1.500 (4)
N1—C1	1.336 (3)
O2—Mn1—O2^i	69.39 (7)	C2—C3—C4	118.9 (2)
O2—Mn1—O4	136.61 (6)	C3—C4—C5	118.8 (2)
O2—Mn1—O9	151.61 (7)	N1—C5—C4	122.3 (2)
O2—Mn1—O10	91.87 (7)	N1—C5—C7	115.2 (2)
O2—Mn1—O11	88.06 (7)	C4—C5—C7	122.5 (2)
O2—Mn1—N1	70.29 (7)	O1—C6—O2	126.9 (2)
O4—Mn1—O9	71.71 (7)	O1—C6—C1	117.0 (2)
O4—Mn1—O10	88.83 (7)	O2—C6—C1	116.1 (2)
O4—Mn1—O11	99.85 (7)	O3—C7—O4	125.2 (2)
O4—Mn1—N1	66.67 (7)	O3—C7—C5	119.9 (2)
O9—Mn1—O10	90.41 (8)	O4—C7—C5	114.9 (2)
O9—Mn1—O11	83.76 (8)	N2—C8—C9	123.4 (3)
O9—Mn1—N1	137.26 (7)	N2—C8—C13	118.2 (2)
O10—Mn1—O11	167.40 (7)	C9—C8—C13	118.4 (2)
O10—Mn1—N1	97.91 (7)	C8—C9—C10	118.9 (3)
O11—Mn1—N1	93.93 (7)	C9—C10—C11	118.8 (3)
Mn1—O2—C6	119.2 (2)	C10—C11—C12	118.5 (3)
Mn1^i—O2—C6	129.7 (2)	N2—C12—C11	123.5 (2)
Mn1—O4—C7	119.7 (2)	N2—C12—C14	117.6 (2)
Mn1—N1—C1	118.2 (2)	C11—C12—C14	118.9 (2)
Mn1—N1—C5	123.4 (2)	O5—C13—O6	124.7 (3)
C1—N1—C5	118.3 (2)	O5—C13—C8	121.0 (3)
C8—N2—C12	116.9 (2)	O6—C13—C8	114.3 (2)
N1—C1—C2	122.9 (2)	O7—C14—O8	124.6 (3)
N1—C1—C6	115.5 (2)	O7—C14—C12	121.3 (2)
C2—C1—C6	121.6 (2)	O8—C14—C12	114.1 (2)
C1—C2—C3	118.8 (2)
Mn1—O2—C6—O1	−173.7 (2)	O9—Mn1—O2—C6	161.0 (2)
Mn1—O2—C6—C1	7.1 (3)	O9—Mn1—O4—C7	−167.3 (2)
Mn1—O4—C7—O3	177.1 (2)	O9—Mn1—N1—C1	−165.8 (2)
Mn1—O4—C7—C5	−2.4 (3)	O9—Mn1—N1—C5	11.2 (3)
Mn1—N1—C1—C2	176.7 (2)	O10—Mn1—O2—C6	−104.7 (2)
Mn1—N1—C1—C6	−4.5 (3)	O10—Mn1—O4—C7	101.9 (2)
Mn1—N1—C5—C4	−177.0 (2)	O10—Mn1—N1—C1	94.9 (2)
Mn1—N1—C5—C7	2.7 (3)	O10—Mn1—N1—C5	−88.0 (2)
O2—Mn1—O2^i—C6^i	171.9 (3)	O11—Mn1—O2—C6	87.9 (2)
O2—Mn1—O4—C7	10.4 (3)	O11—Mn1—O4—C7	−87.3 (2)
O2—Mn1—N1—C1	5.8 (2)	O11—Mn1—N1—C1	−80.8 (2)
O2—Mn1—N1—C5	−177.2 (2)	O11—Mn1—N1—C5	96.3 (2)
O4—Mn1—O2—C6	−14.4 (2)	N1—Mn1—O2—C6	−7.0 (2)
O4—Mn1—N1—C1	−179.8 (2)	N1—Mn1—O4—C7	2.7 (2)
O4—Mn1—N1—C5	−2.8 (2)

Symmetry code: (i) −x, −y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O6—H7···O11^ii	0.90	2.0	2.841 (2)	156
O8—H8···O4	0.98	1.57	2.507 (3)	158
O9—H10···O1^i	0.91	1.75	2.608 (2)	158
O9—H9···O7	0.83	2.00	2.821 (3)	169
O10—H11···O3^iii	0.87	1.87	2.724 (2)	167
O10—H12···O5^iv	0.94	1.83	2.756 (3)	170
O11—H13···O8^v	0.86	2.43	2.842 (3)	110
O11—H14···O3^v	0.86	2.09	2.934 (3)	168

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