Diaqua­dichloridobis(1H-imidazole)manganese(II) at 100 K

The mononuclear title complex, [MnCl₂(C₃H₄N₂)₂(H₂O)₂], is located on a crystallographic inversion center. The Mn^II ion is coordinated by two imidazole ligands [Mn-N = 2.2080 (9) Å], two Cl atoms [Mn-Cl = 2.5747 (3) Å] and two water mol­ecules [Mn-O = 2.2064 (8) Å]. These six monodentate ligands define an octa­hedron with almost ideal angles: the adjacent N-Mn-O, N-Mn-Cl and O-Mn-Cl angles are 90.56 (3), 92.04 (2) and 90.21 (2)°, respectively. Hydrogen bonds between the coordinated water mol­ecules and Cl atoms form a two-dimensional network parallel to (100) involving R₄²(8) rings. The two-dimensional networks link into a three-dimensional framework through weaker N-H...Cl inter­actions. Thermogravimetric analysis results are in accordance with the water-coordinated character of the substance and its dehydration in two successive steps.

S1. Comment

Imidazole (Im) is the structural element of many natural and/or synthetic organic compounds, including histidine and benzimidazole derivatives, exhibiting biological and pharmacological activities such as antiviral (Cheng et al., 2005), antifungal and antimycotic (Walter et al., 1978), antihistaminic and anti-allergic (Nakano et al., 2000), antimicrobial (Sheng et al., 2006), antihelminthic (Mavrova et al., 2006), antitumoral, and antimetastatic properties (Charlston, 1973; Keppler et al., 1987, 1989, 1993; Alessio et al., 1993; Mestroni et al., 1998; Mura et al., 2001; Greiner et al., 2007). The biological role of imidazole derivatives seems to be connected with the two N atoms with their different properties; the deprotonated N atom can coordinate with a metal ion, whereas the protonated N atom participates in hydrogen bonding (Santoro et al., 1969; Reimann et al., 1970; Ivarsson & Forsling, 1979; Lambert et al., 2000; Shiu et al., 2003; Masciocchi et al., 2003; Huang et al., 2004; Abuskhuna et al., 2004; Gong et al., 2005). These properties are used in different ways in proteins and enzymes that contain active sites with multiple histidine residues bound to a metal center, including carbonic anhydrase, nitrite reductase, dopamine β hydroxylase, superoxide dismutase, cytochrome c oxidase, pirin and acireductone dioxygenases (Greiner et al., 2007).

The mononuclear title compound, (I) (Fig. 1), was obtained in an attempt to synthesize new Mn^II systems with imidazole derivative ligands. Despite its simplicity, no structural report of (I) was found in a search of the Cambridge Structural Database (CSD; Version 5.30 of November 2008; Allen, 2002). However, there were a few crystal structures of manganese(II) in which the ligands were water and/or imidazole molecules, i.e. [Mn(ImH)₆]Cl₂.4H₂O (Garrett et al., 1983a) and [Mn(ImH)₄(H₂O)₂]Cl₂ (Garrett et al., 1983b). The same [MCl₂(ImH)₂(H₂O)₂] group (M is a transition metal) was also reported in the structures of nickel(II) and cobalt(II) complexes, viz. [CoCl₂(ImH)₂(H₂O)₂] and [NiCl₂(ImH)₂(H₂O)₂] (Atria et al., 2003).

The Mn^II atom in (I) is octahedrally coordinated to the monodentate ligands, i.e. two N-coordinated imidazole groups, two Cl anions and two O atoms of water molecules. The [MnCl₂(ImH)₂(H₂O)₂] octahedron is only slightly distorted, and the N1—Mn1—O1, N1—Mn1—Cl1 and O1—Mn1—Cl1 angles are 90.56 (3), 92.04 (2) and 90.21 (2)°, respectively. The equatorial plane is formed by atoms O1 and O1ⁱ of the water molecules as well as atoms N1 and N1ⁱ of the imidazole molecules [symmetry code: (i) -x + 1, -y + 1, -z], and the two axial positions are occupied by atoms Cl1 and Cl1ⁱ.

The Mn1—N1 bond distance [2.2080 (9) Å] is slightly shorter than the average value in [Mn(ImH)₆]²⁺] (2.273 Å) and those found in other Mn complexes possessing imidazole ligands (Garrett et al., 1983b; Krautscheid et al., 1993; Liu et al., 2001; Niu et al., 2004; Kooijman, 2006; Lemoine et al., 2006; Zhong et al., 2006). The contraction of the latter bond is balanced by a lengthening of the Mn1—O1 bond [2.2064 (8) Å] when compared with the average value in [Mn(H₂O)₆]²⁺] (2.177 Å; Carrell & Glusker, 1973). The Mn1—Cl1 distance [2.5747 (3) Å] is close to the value in [MnCl₂(2-MeIm)₃] (2.525 Å), in which one Cl atom is in an axial position (Phillips et al., 1976). However, this Mn1—Cl1 length is different from that of [MnCl₂(2-MeIm)₃], which has the Cl atom in equatorial position (2.392 Å; Phillips et al., 1976). The coordinated imidazole rings of the title compound are essentially planar, with r.m.s. deviations from the mean plane of 0.0026 Å. The maximum deviation from the least-square imidazole plane is observed for C2 [0.0032 (7) Å]. Atoms N1 and N3 are slightly out of the imidazole plane by -0.0015 (7) and -0.0036 (7) Å, respectively. The bond lengths in the coordinated imidazole ring are not significantly different from those in [CoCl₂(ImH)₂(H₂O)₂] and [NiCl₂(ImH)₂(H₂O)₂] (Atria et al., 2003). The shortest bond is that between N1 and C2 [1.3184 (15) Å], while the longest bond, N1—C5 [1.3850 (15) Å], is located opposite. A common feature of the imidazole derivatives is the asymmetry of the two endocyclic N—C bonds; N1—C2 [1.3184 (15) Å] shows greater double-bond character than N3—C2 [1.3440 (17) Å]. The endocyclic angles of the aromatic ring differ somewhat from one another (see Table 1). It can be observed the closing of the angle at the atom to which the Mn atom is attached and opening of two adjacent angles.

The molecules are connected in the crystal lattice through an intermolecular hydrogen bond O1—H1O···Cl1ⁱⁱ and O1—H2O···Cl1ⁱⁱⁱ interactions [symmetry code: (ii) 1 - x, -1/2 + y, 1/2 - z; (iii) x, 1.5 - y, 1/2 + z] and make eight membered rings, with a graph-set motif of R₄²(8) (Etter et al., 1990; Bernstein et al., 1995), in the bc plane leading to a 2-dimensional network (see Fig. 2 and Table 2). Each water molecule bridges two [MnCl₂(ImH)₂(H₂O)₂] molecules. In turn, each [MnCl₂(ImH)₂(H₂O)₂] molecule is hydrogen bonded to four water molecules. Moreover, a weaker intermolecular hydrogen bond N3—H3···Cl1^iv [symmetry code: (iv) x + 1, y, z] joins the molecules into a three-dimensional network. Thus, each complex molecule possesses three potentially active H atoms (H3, H1O and H2O) involved in hydrogen bonds with the Cl atom acting as the sole acceptor for all three interactions. Similarly to the [CoCl₂(ImH)₂(H₂O)₂] and [NiCl₂(ImH)₂(H₂O)₂] complexes, the H···Cl length in (I) between the coordinated imidazole group and coordinated Cl atom is slightly shorter than the sum of their van der Waals radii [2.515 (17) Å in (I), cf. 2.52 (17) Å (mean for 19 cases in the CSD; Atria et al., 2003)], whereas the H···Cl bonds involving the aqua H atoms are slightly stronger than average [2.357 (19) and 2.367 (19) Å in (I), cf. 2.42 (18) Å (mean for 350 cases in the CSD; Atria et al., 2003)]. The X-ray structure of (I) is quite similar to that of the previously reported Mn^II complex with the same ligands, [Mn(ImH)₄(H₂O)₂]Cl₂, (II) (Garrett et al., 1983b). Compound (II) crystallizes in the monoclinic C2/c space group and the Mn ion lies in an approximately octahedral coordination geometry completed by four N atoms and two coordinated water molecules. The adjacent [Mn(ImH)₄(H₂O)₂] monomers are linked parallel to the xy plane into three-dimensional metal–organic layer by hydrogen bonds between coordinated water molecules and interstitial Cl^- ions. Each Cl^- ion is also hydrogen bonded to two imidazole rings, one belonging to a complex in the same layer and the other belonging to a complex in an adjacent layer. The hydrogen-bonding interactions in (I) are shown in Fig. 2 and details are given in Table 2.

The FT–IR spectrum of [MnCl₂(ImH)₂(H₂O)₂] is in accordance with the X-ray crystallographic analysis and exhibits characteristic bands due to the functional groups of imidazole (Fig. 3). A strong and broad complex absorption between 3600 and 2000 cm^-1 originates from the stretching of the hydrogen-bonded NH and OH groups in the compound. The sharp peak centered at 3282 cm^-1 is attributed to ν_O–H of the water molecule. The narrow bands at 3151, 3133 and 3117 cm^-1, disturbing the ν_N–H band contour shape, correspond to the ν_C–H stretching modes of the imidazole ring. These frequencies are relatively close to the frequencies for pure imidazole experimentally found by INS (3145, 3125 and 3120 cm^-1; Loeffen et al., 1995). The band at 1622 cm^-1 can be attributed to the stretching of the short Cl···HO bonds (Arif et al., 2009). The vibrational bands from 1537 to 1070 cm^-1 can be assigned to the ring stretching frequency of the imidazole ligand (Naumov et al., 2001). The ν_C═N mode can be found at 1537 cm^-1. The bands remaining in the 937–729 cm^-1 region can be associated with deformations of the imidazole ring. In the far IR region, a strong band at 661 cm^-1 present in the complex is due to ν_Mn–N vibrations, and the peak at 578 cm^-1 can be assigned to the bending vibration of the hydrogen bond (Arif et al., 2009).

From the thermogravimetric analysis of (I) it results that there was a weight loss of about 86.95% in the temperature range 298–1173 K. The initial weight loss of 9.02%, occurring in two steps between 333 and 428 K, seems to be attributable to the removal of two solvent water molecules (calculated 12.09%). The next weight loss of 45.64% (calculated 45.69%) from 428 to 523 K corresponds to the removal of two imidazole molecules. Above 563 K, the release of Cl₂ occurs.

The EPR spectrum of (I) in a powdered sample at room temperature shows only one isotropic signal at g = 2.00871, corresponding to manganese(II) in a weakly distorted octahedral environment, a geometry predicted by crystal structure analysis. Such an isotropic spectrum consisting of a broad signal without the hyperfine pattern is due to intermolecular dipole–dipole interactions and enhanced spin lattice relaxation (Garg et al., 1998). When the manganese ion is magnetically diluted, the hyperfine interaction can be detected. The EPR spectrum of [MnCl₂(ImH)₂(H₂O)₂] in water solution at 298 K exhibits a six-line manganese hyperfine pattern centered at g = 2.03068. These six hyperfine lines arise from the interaction of the electron spin with the nuclear spin (⁵⁵Mn, I = 5/2) and correspond to m_I = ±5/2, ±3/2, ±1/2, resulting from allowed transitions (Δm_s = ±1, Δm_I = 0). The observed g values are close to the free electron spin value of 2.0023, suggestive of the absence of spin-orbit coupling in the ground state, ⁶A₁ (Sreekath et al., 2006) (Table 1).

Related literature

For related literature, see: Abuskhuna et al. (2004); Alessio et al. (1993); Allen (2002); Arif et al. (2009); Atria et al. (2003); Bernstein et al. (1995); Carrell & Glusker (1973); Charlston (1973); Cheng et al. (2005); Etter et al. (1990); Garg et al. (1998); Garrett et al. (1983a, 1983b); Gong et al. (2005); Greiner et al. (2007); Huang et al. (2004); Ivarsson & Forsling (1979); Keppler et al. (1987, 1989, 1993); Kooijman (2006); Krautscheid et al. (1993); Lambert et al. (2000); Lemoine et al. (2006); Liu et al. (2001); Loeffen et al. (1995); Masciocchi et al. (2003); Mavrova et al. (2006); Mestroni et al. (1998); Mura et al. (2001); Nakano et al. (2000); Naumov et al. (2001); Niu et al. (2004); Phillips et al. (1976); Reimann et al. (1970); Santoro et al. (1969); Sheng et al. (2006); Shiu et al. (2003); Sreekath et al. (2006); Walter et al. (1978); Zhong et al. (2006).

S2. Experimental

Hydrochloric acid (0.002 g, 0.05 mmol), manganese(II) chloride (0.126 g, 1 mmol) and imidazole (0.136 g, 2 mmol) were stirred in 2 ml of water until dissolved. The solution was filtered and the filtrate was left to stand undisturbed. After two days, colourless single crystals suitable for X-ray crystallographic analysis were collected and dried in air at room temperature. Elemental analysis calculated for C₆H₁₂Cl₂MnN₄O₂: C 24.18, N 18.79, H 4.06%; found: C 24.34, N 18.76, H 4.02%.

S3. Refinement

H atoms which take part in hydrogen bonding were located in a difference Fourier map and refined freely with isotropic displacement parameters, with the exception that for for atom H3 U_iso(H) was set at 1.2U_eq(N). C-bound H atoms were treated as riding on their parent C atoms [C—H = 0.95 Å and U_iso(H) = 1.2U_eq(C)].

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2008); cell refinement: CrysAlis RED (Oxford Diffraction, 2008); data reduction: CrysAlis RED (Oxford Diffraction, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and Mercury (Macrae et al., 2006); software used to prepare material for publication: publCIF (Westrip, 2009).

Figures

	Fig. 1. The asymmetric unit of (I), with the atom-numbering scheme, showing 50% probability displacement ellipsoids. H atoms are shown as small spheres of arbitrary radius. [Symmetry codes: (i) -x + 1, -y + 1, -z.]
	Fig. 2. The packing in the crystal structure of [MnCl2(ImH)2(H2O)2], viewed along the b axis of the unit cell. The dashed lines (red and blue in the electronic version of the paper) indicate the hydrogen-bonding interactions (O1···Cl1 and N3···Cl1, respectively). For the sake of clarity, all H atoms bonded to C atoms have been omitted.
	Fig. 3. IR spectrum of a sample of (I) dispersed in a KBr pellet.

Diaquadichloridobis(1H-imidazole)manganese(II)

Crystal data

[MnCl2(C3H4N2)2(H2O)2]	F(000) = 302
Mr = 298.04	Dx = 1.672 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 7619 reflections
a = 7.9364 (1) Å	θ = 3.3–34.5°
b = 9.0864 (2) Å	µ = 1.55 mm^−1
c = 8.2480 (1) Å	T = 100 K
β = 95.734 (2)°	Polyhedron, colourless
V = 591.81 (2) Å^3	0.58 × 0.39 × 0.09 mm
Z = 2

Data collection

Oxford Diffraction Xcalibur diffractometer with Sapphire3 CCD detector	1046 independent reflections
Radiation source: fine-focus sealed tube	1017 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.012
ω–scan	θmax = 25.1°, θmin = 3.4°
Absorption correction: multi-scan CrysAlis RED (Oxford Diffraction, 2008)	h = −9→9
Tmin = 0.532, Tmax = 0.867	k = −9→10
4794 measured reflections	l = −9→9

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)] = 0.014	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.038	w = 1/[σ^2(Fo^2) + (0.0233P)^2 + 0.2546P] where P = (Fo^2 + 2Fc^2)/3
S = 1.00	(Δ/σ)max = 0.001
1046 reflections	Δρmax = 0.23 e Å^−3
82 parameters	Δρmin = −0.20 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.045 (2)

Special details

Experimental. The IR spectrum of a polycrystalline sample of diaquadichlorobis(1H-imidazole)manganese(II) dispersed in KBr was measured at the room temperature using an FT–IR Nicolet Magna 560 spectrometer operating at resolution of 2 cm^-1. The IR spectrum was recorded in the range 4000–400 cm^-1 using a Ever-Glo source, a KBr beamsplitter and a DTGS detector. The thermal stability of title compound has been studied by thermogravimetric analysis (TGA) from 298 to 1173 K at a heating rate of 10 K/min in nitrogen, using Perkin-Elmer Pyris thermogravimetric analyzer. X-band Electron Paramagnetic Resonance spectra (9.7 GHz) were recorded with a Bruker EMX spectrometer in the room temperature. DPPH was used as internal field marker.

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	0.5000	0.5000	0.0000	0.00953 (11)
Cl1	0.38087 (3)	0.76376 (3)	−0.00932 (3)	0.01178 (11)
O1	0.42191 (10)	0.47073 (10)	0.24730 (10)	0.01362 (18)
H1O	0.466 (2)	0.406 (2)	0.306 (2)	0.031 (4)*
H2O	0.417 (2)	0.544 (2)	0.303 (2)	0.033 (5)*
N1	0.75240 (11)	0.57626 (10)	0.10307 (11)	0.0134 (2)
N3	1.01472 (13)	0.65532 (12)	0.11409 (14)	0.0212 (2)
H3	1.099 (2)	0.6925 (18)	0.0817 (19)	0.025*
C2	0.86214 (15)	0.65252 (13)	0.02728 (15)	0.0183 (3)
H2	0.8367	0.6993	−0.0752	0.022*
C4	1.00392 (16)	0.57514 (14)	0.25295 (16)	0.0216 (3)
H4	1.0921	0.5569	0.3372	0.026*
C5	0.84151 (15)	0.52703 (14)	0.24572 (15)	0.0168 (3)
H5	0.7959	0.4685	0.3262	0.020*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mn1	0.00786 (14)	0.00977 (15)	0.01101 (15)	−0.00040 (8)	0.00115 (9)	−0.00011 (8)
Cl1	0.01143 (15)	0.00986 (16)	0.01408 (16)	0.00018 (9)	0.00146 (10)	0.00009 (9)
O1	0.0155 (4)	0.0131 (4)	0.0123 (4)	0.0031 (3)	0.0020 (3)	0.0004 (4)
N1	0.0110 (4)	0.0118 (5)	0.0176 (5)	−0.0010 (4)	0.0025 (4)	−0.0018 (4)
N3	0.0116 (5)	0.0192 (5)	0.0340 (6)	−0.0064 (4)	0.0086 (4)	−0.0081 (5)
C2	0.0161 (6)	0.0137 (6)	0.0255 (6)	−0.0020 (4)	0.0051 (5)	−0.0004 (5)
C4	0.0122 (5)	0.0292 (7)	0.0230 (6)	−0.0003 (5)	−0.0004 (4)	−0.0093 (5)
C5	0.0136 (6)	0.0208 (6)	0.0160 (6)	0.0000 (5)	0.0009 (4)	−0.0025 (5)

Geometric parameters (Å, º)

Mn1—O1	2.2064 (8)	N1—C5	1.3850 (15)
Mn1—O1^i	2.2064 (8)	N3—C2	1.3440 (17)
Mn1—N1	2.2080 (9)	N3—C4	1.3672 (18)
Mn1—N1^i	2.2080 (9)	N3—H3	0.817 (17)
Mn1—Cl1	2.5747 (3)	C2—H2	0.9500
Mn1—Cl1^i	2.5747 (3)	C4—C5	1.3567 (17)
O1—H1O	0.816 (19)	C4—H4	0.9500
O1—H2O	0.815 (19)	C5—H5	0.9500
N1—C2	1.3184 (15)
O1—Mn1—O1^i	180	H1O—O1—H2O	106.8 (17)
O1—Mn1—N1	90.56 (3)	C2—N1—C5	105.49 (10)
O1^i—Mn1—N1	89.44 (3)	C2—N1—Mn1	126.82 (8)
O1—Mn1—N1^i	89.44 (3)	C5—N1—Mn1	126.32 (8)
O1^i—Mn1—N1^i	90.56 (3)	C2—N3—C4	107.92 (10)
N1—Mn1—N1^i	180	C2—N3—H3	123.8 (11)
O1—Mn1—Cl1	90.21 (2)	C4—N3—H3	128.0 (11)
O1^i—Mn1—Cl1	89.79 (2)	N1—C2—N3	111.10 (11)
N1—Mn1—Cl1	92.04 (2)	N1—C2—H2	124.4
N1^i—Mn1—Cl1	87.96 (2)	N3—C2—H2	124.4
O1—Mn1—Cl1^i	89.79 (2)	C5—C4—N3	105.88 (11)
O1^i—Mn1—Cl1^i	90.21 (2)	C5—C4—H4	127.1
N1—Mn1—Cl1^i	87.96 (2)	N3—C4—H4	127.1
N1^i—Mn1—Cl1^i	92.04 (2)	C4—C5—N1	109.61 (11)
Cl1—Mn1—Cl1^i	180	C4—C5—H5	125.2
Mn1—O1—H1O	119.6 (11)	N1—C5—H5	125.2
Mn1—O1—H2O	117.2 (12)
O1—Mn1—N1—C2	−160.75 (10)	C5—N1—C2—N3	−0.48 (13)
O1^i—Mn1—N1—C2	19.25 (10)	Mn1—N1—C2—N3	−167.70 (8)
Cl1—Mn1—N1—C2	−70.52 (9)	C4—N3—C2—N1	0.70 (14)
Cl1^i—Mn1—N1—C2	109.48 (9)	C2—N3—C4—C5	−0.61 (14)
O1—Mn1—N1—C5	34.59 (9)	N3—C4—C5—N1	0.33 (14)
O1^i—Mn1—N1—C5	−145.41 (9)	C2—N1—C5—C4	0.08 (13)
Cl1—Mn1—N1—C5	124.81 (9)	Mn1—N1—C5—C4	167.39 (8)
Cl1^i—Mn1—N1—C5	−55.19 (9)

Symmetry code: (i) −x+1, −y+1, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1O···Cl1^ii	0.816 (19)	2.357 (19)	3.1593 (9)	167.7 (16)
O1—H2O···Cl1^iii	0.815 (19)	2.367 (19)	3.1759 (9)	171.5 (16)
N3—H3···Cl1^iv	0.817 (17)	2.515 (17)	3.3231 (11)	170.1 (15)

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