catena-Poly[[aqua­bis(1H-benzimidazole-κN³)manganese(II)]-μ-adipato]

In the title polymeric complex, [Mn(C₆H₈O₄)(C₇H₆N₂)₂(H₂O)]_n, the Mn^II atom is surrounded by two adipate dianions, two benzimidazole mol­ecules and one coordinated water mol­ecule. The Mn atoms and coordinated water mol­ecule are located on a twofold axis, and the bridging adipate ligand is located on an inversion center. The adipate dianions bridge neighboring Mn^II atoms to form polymeric chains. Each Mn^II atom is seven-coordinate, the longest Mn—O bond length being 2.5356 (16) Å.

S1. Comment

The process of water oxidation in the photosynthetic apparatus of green plants (Bruckner et al., 1993) is generally believed to occur at a manganese cluster located in the reaction center of photosystem II (Vincent & Christou, 1989). In order to mimic the manganese cluster, a series of manganese complexes bridged by carboxylate has been synthesized in our laboratory, among which some crystal structures revealed the existence of significant electrostatic interaction between the Mn atom and the ligand (Nie et al., 2001; Hu et al., 2002; Liu & Xu, 2003). In the title Mn^II complex, (I), the seven-coordination geometry clearly suggests the electrostatic interaction between the Mn^II atom and coordinated O atoms.

The Mn^II atom in the (I) is surrounded by two adipate dianions, two benzimidazole (BZIM) molecules and one coordinated water molecule, as illustrated in Fig. 1. The Mn atom and the coordinated water molecule are located on the crystallographic twofold axis. Two benzimidazole molecules coordinate to the Mn atom in the trans mode. The Mn—N3 bond (Table 1) is longer than the Mn—N bonds of 2.183 (3) and 2.190 (3) Å found in the imidazole complex of Mn^II (Liu et al., 2003). The longer Mn—N3 bond is a result of the poor overlap of atomic orbitals between atoms Mn and N3, as verified by the larger angle [19.53 (7)°] between the Mn—N3 bond and the N1-BZIM mean plane, and the appreciable deviation [0.762 (3) Å] of the Mn atom from the BZIM mean plane. Two carboxy O2 atoms and two BZIM N3 atoms form the equatorial coordination plane. The Mn atom lies almost in the equatorial plane, with a small displacement [0.0344 (12) Å] towards atom O1. This fact implies that the coordination geometry in the complex is not square pyramidal, and some bonding interaction occurs in the direction opposite to the Mn—O1 bond, as discussed below.

Two adipate dianions symmetrically coordinate to the Mn atom in a weak chelating mode (see Fig. 1). While the Mn—O2 distance and O2—Mn—O2ⁱⁱ angle imply a normal Mn—O2 coordinate bond, the longer distance of 2.5356 (16) Å s u ggests that the Mn—O3 bond is semi-coordinate, balancing the bonding interaction between atoms Mn and O1 and resulting in the Mn atom being locating almost in the equatorial plane, as mentioned above.

Further evidence supporting the Mn—O3 bonding interaction is provided by the smaller Mn—O2—C11 bond angle. Several structures of Mn^II complexes incorporating carboxylate have been reported. Comparative geometric parameters of the carboxyl group are summarized in Table 2. Two kinds of Mn—O2—C bond angles are observed in these structures, viz. either less than 100° or larger than 120°. Corresponding to these different Mn—O2—C angles, two kinds of Mn—O3 distances are observed in those structures. The smaller Mn—O2—C angle corresponds to the shorter Mn—O3 distance (shorter than 2.6 Å), and suggests a bonding interaction between the atoms Mn and O3, i.e. the carboxy group is chelating. The larger Mn—O2—C angle corresponds to the longer Mn—O3 distance (longer than 3.3 Å) and suggests a monodentate carboxy group.

In the title Mn^II complex, both the Mn—O2—C11 bond angle and the Mn—O3 distance (Table 1) are close to those found in the chelate complexes but significantly different from those found in the monodentate coordinate complexes. These facts clearly indicate that the carboxyl group of adipate in the Mn^II complex displays the role of a chelating rather than a monodentate ligand. Thus the Mn^II atom assumes a seven-coordination geometry with a double-capped pyramidal configuration (Fig. 1).

The adipate dianion is located on an inversion centre and has an extended, nearly coplanar, carbon skeleton, the C11—C12—C13—C13ⁱ torsion angle being 173.5 (2)°. This is different from the situation found in most adipate complexes. In those reported previously, the flexible carbon skeleton of the adipate usually displays a curly conformation (Pajunen & Nasakkala, 1977; McCann et al., 1997; Suresh et al., 1997; Darensbourg et al., 1996; Tosik et al., 1995). For example, an adipato–Cu^II complex, aquabis(benzimidazole)copper(II)-µ-adipate, has been reported (Suresh & Bhadbhade, 1997). That Cu^II complex has the same chemical component (except the central ion) and the same coordination mode for adipate as the title Mn^II complex. However, the curly conformation of adipate was found in that Cu^II complex, which resulted in cell dimensions that differ from thos of the title Mn^II complex.

Adipate dianions bridge neighboring Mn^II atoms through both terminal carboxyl groups to form polymeric complex chains, as shown in Fig. 2. The neighboring polymeric chains are linked to one another via O—H···O and N—H···O hydrogen bonds (Table 3) to form a three-dimensional network.

Aromatic π–π stacking has commonly been observed in crystal structures including BZIM. Although the Cg···Cg centroid-to-centroid distance between two imidazole rings is only 3.955 (17) Å in the complex, the imidazole rings do not overlap each other and no π–π stacking occurs.

S2. Experimental

An ethanol solution (5 ml) of BZIM (0.12 g, 1 mmol) was mixed with an aqueous solution (5 ml) of Mn(CH₃COO)₂·4H₂O (0.25 g, 1 mmol). The mixture was refluxed for 30 min. An aqueous solution (5 ml) containing adipic acid (0.15 g, 1 mmol) and NaOH (0.08 g, 2 mmol) was added to the above mixture, and the solution was refluxed for a further 1 h. After the solution had been cooled to room temperature, it was filtered, and single crystals were obtained from the filtrate after two weeks.

S3. Refinement

The water H atom was located in a difference Fourier map and refined with a fixed isotropic displacement parameter of 0.05 Ų. Other H atoms were placed in calculated positions, with C—H = 0.93 (aromatic) or 0.97 Å (methylene) and N—H = 0.86 Å, and included in the final cycles of refinement in a riding model, with U_iso(H) = 1.2U_eq(carrier atom).

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT; program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and XP (Siemens, 1994); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. The structure of (I), showing 40% probability displacement ellipsoids. [Symmetry codes: (i) 1/2 − x, 3/2 − y, 1 − z; (ii) 1 − x, y, 1/2 − z.]
	Fig. 2. A stereoview of the molecular packing, showing polymeric chains. Dashed lines indicate hydrogen bonding between neighboring chains.

catena-Poly[[aquabis(1H-benzimidazole-κN³)manganese(II)]-µ-adipato]

Crystal data

[Mn(C6H8O4)(C7H6N2)2(H2O)]	F(000) = 940
Mr = 453.36	Dx = 1.480 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 5266 reflections
a = 15.159 (4) Å	θ = 2.5–24.0°
b = 16.758 (4) Å	µ = 0.69 mm^−1
c = 8.954 (2) Å	T = 295 K
β = 116.534 (4)°	Prism, colorless
V = 2035.0 (9) Å^3	0.36 × 0.28 × 0.18 mm
Z = 4

Data collection

Bruker SMART CCD diffractometer	2023 independent reflections
Radiation source: fine-focus sealed tube	1536 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.039
ω and ϕ scans	θmax = 26.1°, θmin = 1.9°
Absorption correction: empirical (SADABS; Bruker, 1999)	h = −18→17
Tmin = 0.782, Tmax = 0.881	k = −17→20
5725 measured reflections	l = −11→9

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)] = 0.038	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.086	H atoms treated by a mixture of independent and constrained refinement
S = 0.93	w = 1/[σ^2(Fo^2) + (0.0451P)^2] where P = (Fo^2 + 2Fc^2)/3
2023 reflections	(Δ/σ)max = 0.001
140 parameters	Δρmax = 0.57 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
Mn	0.5000	0.60804 (3)	0.2500	0.02231 (16)
O1	0.5000	0.48051 (14)	0.2500	0.0336 (6)
O2	0.47762 (11)	0.61073 (9)	0.48286 (18)	0.0269 (4)
O3	0.42974 (11)	0.72364 (9)	0.34538 (18)	0.0287 (4)
N1	0.79659 (13)	0.67070 (11)	0.6125 (2)	0.0266 (4)
H1	0.8332	0.6992	0.6977	0.032*
N3	0.66212 (12)	0.60945 (11)	0.4250 (2)	0.0248 (4)
C2	0.70035 (16)	0.65556 (14)	0.5580 (3)	0.0274 (5)
H2	0.6638	0.6758	0.6096	0.033*
C4	0.74632 (17)	0.54631 (14)	0.2644 (3)	0.0320 (6)
H4	0.6911	0.5199	0.1861	0.038*
C5	0.83540 (18)	0.54129 (15)	0.2609 (3)	0.0407 (6)
H5	0.8404	0.5105	0.1785	0.049*
C6	0.91957 (18)	0.58104 (16)	0.3775 (3)	0.0402 (6)
H6	0.9787	0.5762	0.3703	0.048*
C7	0.91604 (17)	0.62694 (14)	0.5021 (3)	0.0319 (6)
H7	0.9715	0.6533	0.5800	0.038*
C8	0.82603 (16)	0.63194 (13)	0.5058 (3)	0.0246 (5)
C9	0.74162 (16)	0.59263 (13)	0.3901 (3)	0.0240 (5)
C11	0.43051 (15)	0.67614 (14)	0.4541 (2)	0.0237 (5)
C12	0.37271 (16)	0.69502 (15)	0.5505 (3)	0.0317 (6)
H12A	0.4154	0.7232	0.6518	0.038*
H12B	0.3533	0.6453	0.5829	0.038*
C13	0.28131 (16)	0.74493 (14)	0.4540 (3)	0.0282 (5)
H13A	0.2419	0.7198	0.3470	0.034*
H13B	0.3010	0.7971	0.4329	0.034*
H1A	0.5058 (19)	0.4520 (16)	0.332 (3)	0.050*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mn	0.0280 (3)	0.0223 (3)	0.0169 (3)	0.000	0.0102 (2)	0.000
O1	0.0570 (16)	0.0212 (13)	0.0214 (12)	0.000	0.0165 (12)	0.000
O2	0.0330 (9)	0.0265 (9)	0.0238 (8)	0.0081 (7)	0.0150 (7)	0.0032 (7)
O3	0.0325 (9)	0.0303 (10)	0.0235 (8)	0.0007 (7)	0.0128 (7)	0.0063 (7)
N1	0.0327 (10)	0.0252 (11)	0.0188 (9)	−0.0034 (8)	0.0085 (8)	−0.0058 (8)
N3	0.0291 (10)	0.0230 (10)	0.0204 (9)	−0.0010 (8)	0.0092 (8)	−0.0011 (8)
C2	0.0318 (13)	0.0290 (13)	0.0220 (12)	0.0023 (10)	0.0127 (10)	−0.0014 (10)
C4	0.0356 (13)	0.0261 (13)	0.0274 (12)	0.0012 (11)	0.0078 (10)	−0.0080 (10)
C5	0.0448 (15)	0.0397 (16)	0.0355 (14)	0.0067 (12)	0.0162 (12)	−0.0128 (11)
C6	0.0339 (14)	0.0473 (17)	0.0416 (16)	0.0055 (12)	0.0190 (12)	−0.0044 (12)
C7	0.0319 (13)	0.0308 (14)	0.0269 (12)	−0.0028 (10)	0.0077 (10)	−0.0010 (10)
C8	0.0308 (12)	0.0194 (12)	0.0207 (11)	0.0012 (9)	0.0090 (10)	0.0013 (9)
C9	0.0285 (12)	0.0188 (12)	0.0208 (11)	0.0013 (9)	0.0074 (9)	0.0015 (8)
C11	0.0236 (11)	0.0283 (13)	0.0168 (11)	−0.0004 (10)	0.0069 (9)	−0.0012 (9)
C12	0.0370 (13)	0.0362 (14)	0.0233 (12)	0.0120 (11)	0.0149 (10)	0.0053 (10)
C13	0.0354 (13)	0.0270 (13)	0.0231 (12)	0.0061 (10)	0.0140 (10)	0.0028 (9)

Geometric parameters (Å, º)

Mn—O1	2.137 (2)	C4—H4	0.9300
Mn—O2	2.2575 (15)	C5—C6	1.404 (3)
Mn—O3	2.5356 (16)	C5—H5	0.9300
Mn—N3	2.2484 (18)	C6—C7	1.376 (3)
O1—H1A	0.85 (2)	C6—H6	0.9300
O2—C11	1.270 (3)	C7—C8	1.382 (3)
O3—C11	1.254 (2)	C7—H7	0.9300
N1—C2	1.340 (3)	C8—C9	1.400 (3)
N1—C8	1.384 (3)	C11—C12	1.512 (3)
N1—H1	0.8600	C12—C13	1.515 (3)
N3—C2	1.317 (3)	C12—H12A	0.9700
N3—C9	1.402 (3)	C12—H12B	0.9700
C2—H2	0.9300	C13—C13^i	1.518 (4)
C4—C5	1.367 (3)	C13—H13A	0.9700
C4—C9	1.395 (3)	C13—H13B	0.9700
O1—Mn—N3	90.60 (5)	C7—C6—C5	121.1 (2)
O1—Mn—O2	91.14 (4)	C7—C6—H6	119.4
O1—Mn—O3	139.82 (4)	C5—C6—H6	119.4
O2^ii—Mn—O2	177.71 (8)	C6—C7—C8	116.7 (2)
O3—Mn—O2^ii	123.70 (5)	C6—C7—H7	121.6
O3—Mn—N3	104.48 (6)	C8—C7—H7	121.6
N3^ii—Mn—N3	178.79 (9)	C7—C8—N1	132.2 (2)
N3—Mn—O2	85.67 (6)	C7—C8—C9	122.6 (2)
N3—Mn—O2^ii	94.30 (6)	N1—C8—C9	105.16 (19)
Mn—O1—H1A	124.2 (19)	C4—C9—C8	120.0 (2)
H1A—O1—H1A^ii	111 (4)	C4—C9—N3	130.6 (2)
C11—O2—Mn	97.65 (12)	C8—C9—N3	109.45 (19)
C2—N1—C8	107.14 (17)	O3—C11—O2	120.96 (19)
C2—N1—H1	126.4	O3—C11—C12	120.2 (2)
C8—N1—H1	126.4	O2—C11—C12	118.80 (19)
C2—N3—C9	104.17 (18)	C11—C12—C13	113.95 (18)
C2—N3—Mn	122.60 (15)	C11—C12—H12A	108.8
C9—N3—Mn	128.55 (13)	C13—C12—H12A	108.8
N3—C2—N1	114.1 (2)	C11—C12—H12B	108.8
N3—C2—H2	123.0	C13—C12—H12B	108.8
N1—C2—H2	123.0	H12A—C12—H12B	107.7
C5—C4—C9	117.4 (2)	C12—C13—C13^i	112.8 (2)
C5—C4—H4	121.3	C12—C13—H13A	109.0
C9—C4—H4	121.3	C13^i—C13—H13A	109.0
C4—C5—C6	122.2 (2)	C12—C13—H13B	109.0
C4—C5—H5	118.9	C13^i—C13—H13B	109.0
C6—C5—H5	118.9	H13A—C13—H13B	107.8
O1—Mn—O2—C11	−150.25 (12)	C2—N1—C8—C9	−1.2 (2)
N3^ii—Mn—O2—C11	−59.56 (13)	C5—C4—C9—C8	0.2 (3)
N3—Mn—O2—C11	119.23 (13)	C5—C4—C9—N3	179.5 (2)
O1—Mn—N3—C2	−133.60 (17)	C7—C8—C9—C4	−0.2 (3)
O2^ii—Mn—N3—C2	135.20 (17)	N1—C8—C9—C4	−179.12 (19)
O2—Mn—N3—C2	−42.50 (17)	C7—C8—C9—N3	−179.57 (19)
O1—Mn—N3—C9	74.61 (17)	N1—C8—C9—N3	1.5 (2)
O2^ii—Mn—N3—C9	−16.59 (18)	C2—N3—C9—C4	179.5 (2)
O2—Mn—N3—C9	165.71 (18)	Mn—N3—C9—C4	−24.7 (3)
C9—N3—C2—N1	0.3 (2)	C2—N3—C9—C8	−1.1 (2)
Mn—N3—C2—N1	−157.25 (14)	Mn—N3—C9—C8	154.63 (15)
C8—N1—C2—N3	0.6 (3)	Mn—O2—C11—O3	−15.2 (2)
C9—C4—C5—C6	−0.3 (4)	Mn—O2—C11—C12	163.14 (16)
C4—C5—C6—C7	0.3 (4)	O3—C11—C12—C13	29.7 (3)
C5—C6—C7—C8	−0.2 (4)	O2—C11—C12—C13	−148.7 (2)
C6—C7—C8—N1	178.8 (2)	C11—C12—C13—C13^i	173.5 (2)
C6—C7—C8—C9	0.1 (3)	C11—C12—C13—C13^iii	128.7 (2)
C2—N1—C8—C7	180.0 (2)

Symmetry codes: (i) −x+1/2, −y+3/2, −z+1; (ii) −x+1, y, −z+1/2; (iii) −x+1/2, −y+1/2, −z+2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1A···O2^iv	0.85 (3)	1.88 (3)	2.729 (2)	178 (3)
N1—H1···O3^v	0.86	1.96	2.792 (2)	163

Symmetry codes: (iv) −x+1, −y+1, −z+1; (v) x+1/2, −y+3/2, z+1/2.