Two isomorphous imidazole (Him) complexes: [MCl₂(Him)₂(H₂O)₂] (M = Co and Ni)

The structures of aqua­di­chloro­bis(1H-imidazole)­cobalt(II), [CoCl₂(Him)₂(H₂O)₂] (Him is 1H-imidazole, C₃H₄N₂), (I), and aqua­di­chloro­bis(1H-imidazole)­nickel(II), [NiCl₂(Him)₂(H₂O)₂], (II), are isomorphous and consist of monomers with inversion symmetry. The three monodentate ligands (imidazole, chlorine and aqua), together with their symmetry equivalents, define almost perfect octahedra. Hydro­gen-bonding interactions via the imidazole and aqua H atoms lead to a three-dimensional network.

S1. Comment

The study of imidazole as a complexing agent has for years been an matter of active interest, mainly because imidazole is involved in important biological processes, but also because it forms part of a number of inorganic materials with interesting structural and magnetic properties (e.g. Atria et al., 1999). While attempting to synthesize new cobalt and nickel systems of high nuclearity, we unwittingly came across two very simple though structurally unreported isomorphous monomers, viz. M(Him)₂Cl₂(H₂O)₂ (M = Co and Ni, and Him is imidazole). In spite of it simplicity the M(Cl)₂(Him)₂(H₂O)₂ group (M is a transition metal) does not seem to be very common; it has been mentioned in the literature as being detected in solution (viz. the NMR evidence of the appearance of the Ru homologue as a solvation product of the antitumoral RuCl₄Him₂; Anderson and Beauchamp, 1995) but no structural report on the neutral molecule could be found in a search of the latest release of the Cambridge Structural Database (CSD; Allen, 2002). There are, however, a few appearances of closely related ions with similar ligands, in both anionic (RuCl₄Him₂⁻²; Keppler et al., 1987; Anderson & Beauchamp, 1995; Mestroni et al., 1998; Mura et al., 2001) and cationic [Ni(Aq)₄Him₂⁺²; Polyakova et al., 2000] forms. We report here the structures of the cobalt, (I), and nickel, (II), isologs of the (presumably larger) M(Him)₂Cl₂(H₂O)₂ family.

The structures of (I) and (II) are composed of monomeric units built up around a symmetry center on which the metal atoms lie. The metal atoms are surrounded by six monodentate ligands, viz. an N-coordinated imidazole group, a chloride anion and a water molecule, and their symmetry-related counterparts. The absence of any steric hindrance due to chelation or bridging effects results in an almost perfect octahedral cation environment, with angles differing from the ideal values (90°) by less than 0.6% in (I) and 1.2% in (II), and with 180° angles being imposed by symmetry. Coordination distances are normal and similar to the average calculated for the same monodentate ligands in other Co and Ni hexacoordinated complexes. The values for N_Him and O_aq fall within 0.5% of the CSD average, while larger differences were found in the Cl bonding distances [Co—Cl = 2.5004 (4) Å in (I) and Ni—Cl = 2,4665 (5) Å in (II); CSD averages 2.37 (11) and 2.42 (8) Å, respectively].

In both (I) and (II), the imidazole groups depart from planarity by less than 0.02 Å; the internal geometries are as expected, with the N1═C3 and C1═C2 bond lengths corresponding exactly to double bond lengths. The ligands bind to the cations in a slightly angled manner, subtending to the perfectly planar basal planes dihedral angles of 8.3 (1)° (both structures) and almost bisecting the dihedral angles subtended by the lateral coordination planes [angles to N1—M—Cl1 and N1—M—O1W planes are, respectively, 49.0 (1) and 41.7 (1)° for (I), and 49.5 (1) and 41.6 (1)° for (II)].

The three potentially active H atoms (H2N, H1Wa and H1Wb) are engaged in hydrogen bonds with the Cl atom, which acts as the sole acceptor for all three interactions (Table 3). The bond involving H2N is of medium strength compared with the 19 cases in the CSD for which the H···Cl distances between a coordinated imidazole and a coordinated chlorine unit were smaller than the sum of their van der Waals radii [2.543 (17) Å in (I), 2.572 (15) Å in (II) and 2.52 (17) Å (mean for 19 cases) in the CSD]. Those involving the aqua H atoms seem to be only slightly stronger than average [2.340 (10) and 2.336 (11) Å in (I), 2.387 (11) and 2.358 (11) Å in (II), and 2.42 (18) Å (mean for 350 cases) in the CSD].

These aqua interactions link monomers along [100] and [010], thus defining two-dimensional arrays perpendicular to (001) (shortest M···M distances are 6.081 (1) Å in (I) and 6.044 (1) Å in (II)]. Fig. 2 depicts these arrays in projection (alternately drawn in heavy and light full lines, in order to distinguish between them). The aqua hydrogen bonds (heavy broken lines) are clearly visible. These two-dimensional structures, in turn, are linked via the imino hydrogen bonds (light broken lines), thus defining a complex three-dimensional network.

S2. Experimental

Crystals of (I) were obtained from an equimolar solution of CoCl₂·6H₂O (0.01 mmol, 0.2379 g) and imidazole (0.01 mmol, 0.6808 g) in methanol (35 ml), which was refluxed for 30 min. After a few days at room temperature, pink polyhedral crystals appeared. The same procedure with NiCl₂ (0.01 mmol=0.1655 g) as a starting material was used to obtain crystals of (II) in the form of dark green polyhedra. In both cases, the solvent was oxygenated for 10 min.

S3. Refinement

H atoms attached to C atoms were added at calculated positions and allowed to ride on their parent atoms; those involved in hydrogen-bonding (NH, OH) were found in a difference Fourier synthesis and refined with restrained distances [0.85 (1) Å] to the host atoms. The CCDC package (version 5.24, November 2002 and updates; Allen, 2002) was used for searches.

Computing details

For both compounds, data collection: SMART-NT (Bruker, 2001); cell refinement: SMART-NT; data reduction: SAINT-NT (Bruker, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL-NT (Sheldrick, 1994); software used to prepare material for publication: SHELXTL-NT.

Figures

	Fig. 1. : Molecular diagrams for (a) compound (I) and (b) compound (II), showing displacement ellipsoids at the 50% probability level.
	Fig. 2. : A view of the crystal packing in (I) and (II), showing the two-dimensional structures internally linked by aqua hydrogen bonds (heavy broken lines) and the imino hydrogen bonds joining the planes (light broken lines).

(I) aquadichlorobis(1H-imidazole)cobalt(II)

Crystal data

[CoCl2(C3H4N2)2(H2O)2]	Dx = 1.749 Mg m^−3
Mr = 302.03	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbca	Cell parameters from 247 reflections
a = 9.1894 (10) Å	θ = 3.0–25.1°
b = 7.9653 (9) Å	µ = 1.95 mm^−1
c = 15.6683 (17) Å	T = 293 K
V = 1146.9 (2) Å^3	Plate, pink
Z = 4	0.20 × 0.10 × 0.04 mm
F(000) = 612

Data collection

Bruker SMART Apex CCD area-detector diffractometer	1304 independent reflections
Radiation source: fine-focus sealed tube	963 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.077
ϕ and ω scans	θmax = 28.1°, θmin = 3.4°
Absorption correction: multi-scan (SADABS in SAINT-NT; Bruker, 2002)	h = −11→11
Tmin = 0.80, Tmax = 0.93	k = −6→10
6204 measured reflections	l = −15→20

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)] = 0.025	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.061	H atoms treated by a mixture of independent and constrained refinement
S = 0.94	w = 1/[σ^2(Fo^2) + (0.023P)^2] where P = (Fo^2 + 2Fc^2)/3
1304 reflections	(Δ/σ)max = 0.004
94 parameters	Δρmax = 0.28 e Å^−3
4 restraints	Δρmin = −0.26 e Å^−3

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

	x	y	z	Uiso*/Ueq
Co	0.5000	0.0000	0.5000	0.02362 (12)
Cl	0.75551 (4)	0.00107 (6)	0.55487 (2)	0.03120 (13)
N1	0.57276 (15)	0.0789 (2)	0.37967 (8)	0.0304 (3)
C1	0.5112 (2)	0.1986 (3)	0.32822 (13)	0.0381 (5)
H1	0.434 (2)	0.266 (3)	0.3473 (13)	0.055 (7)*
N2	0.67669 (19)	0.0743 (3)	0.25455 (10)	0.0481 (5)
H2N	0.734 (2)	0.040 (3)	0.2157 (11)	0.068 (8)*
C2	0.5744 (2)	0.1968 (3)	0.25088 (13)	0.0468 (6)
H2	0.560 (2)	0.259 (3)	0.2011 (13)	0.059 (7)*
C3	0.6732 (2)	0.0073 (3)	0.33297 (13)	0.0424 (5)
H3	0.728 (2)	−0.083 (3)	0.3478 (12)	0.052 (7)*
O1W	0.47372 (15)	0.25203 (18)	0.53863 (8)	0.0328 (3)
H1WA	0.5509 (16)	0.313 (3)	0.5393 (14)	0.068 (8)*
H1WB	0.4087 (16)	0.307 (2)	0.5132 (12)	0.056 (7)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Co	0.02321 (18)	0.0287 (2)	0.01894 (18)	0.00016 (15)	0.00011 (11)	0.00080 (13)
Cl	0.0254 (2)	0.0366 (3)	0.0316 (2)	−0.00182 (18)	−0.00461 (16)	0.0037 (2)
N1	0.0287 (7)	0.0395 (10)	0.0229 (7)	0.0003 (7)	0.0026 (6)	0.0015 (7)
C1	0.0369 (11)	0.0477 (14)	0.0296 (10)	0.0035 (10)	−0.0006 (8)	0.0076 (9)
N2	0.0515 (11)	0.0659 (14)	0.0269 (9)	−0.0084 (11)	0.0154 (8)	−0.0040 (9)
C2	0.0494 (13)	0.0646 (17)	0.0266 (11)	−0.0058 (12)	−0.0009 (9)	0.0117 (10)
C3	0.0413 (11)	0.0504 (15)	0.0356 (10)	0.0049 (11)	0.0090 (9)	0.0035 (10)
O1W	0.0301 (7)	0.0319 (8)	0.0363 (7)	0.0018 (6)	−0.0056 (6)	0.0000 (6)

Geometric parameters (Å, º)

Co—N1^i	2.0968 (13)	C1—H1	0.94 (2)
Co—N1	2.0968 (13)	N2—C3	1.340 (3)
Co—O1W	2.1106 (14)	N2—C2	1.356 (3)
Co—O1W^i	2.1106 (14)	N2—H2N	0.848 (10)
Co—Cl	2.5004 (4)	C2—H2	0.93 (2)
Co—Cl^i	2.5004 (4)	C3—H3	0.91 (2)
N1—C3	1.309 (2)	O1W—H1WA	0.858 (9)
N1—C1	1.371 (2)	O1W—H1WB	0.841 (9)
C1—C2	1.344 (3)
N1^i—Co—N1	180.0	C1—N1—Co	127.29 (13)
N1^i—Co—O1W	89.48 (6)	C2—C1—N1	110.2 (2)
N1—Co—O1W	90.52 (6)	C2—C1—H1	128.2 (13)
N1^i—Co—O1W^i	90.52 (6)	N1—C1—H1	121.6 (13)
N1—Co—O1W^i	89.48 (6)	C3—N2—C2	107.98 (17)
O1W—Co—O1W^i	180.0	C3—N2—H2N	122.9 (16)
N1^i—Co—Cl	89.50 (4)	C2—N2—H2N	129.1 (16)
N1—Co—Cl	90.50 (4)	C1—C2—N2	105.60 (19)
O1W—Co—Cl	90.32 (4)	C1—C2—H2	133.6 (15)
O1W^i—Co—Cl	89.68 (4)	N2—C2—H2	120.8 (14)
N1^i—Co—Cl^i	90.50 (4)	N1—C3—N2	110.9 (2)
N1—Co—Cl^i	89.50 (4)	N1—C3—H3	126.4 (12)
O1W—Co—Cl^i	89.68 (4)	N2—C3—H3	122.5 (12)
O1W^i—Co—Cl^i	90.32 (4)	Co—O1W—H1WA	116.4 (16)
Cl—Co—Cl^i	180.0	Co—O1W—H1WB	116.1 (15)
C3—N1—C1	105.38 (17)	H1WA—O1W—H1WB	107.5 (19)
C3—N1—Co	126.65 (15)

Symmetry code: (i) −x+1, −y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2N···Cl^ii	0.85 (1)	2.54 (2)	3.2461 (16)	141 (2)
O1W—H1WA···Cl^iii	0.86 (1)	2.34 (1)	3.1923 (14)	172 (2)
O1W—H1WB···Cl^iv	0.84 (1)	2.34 (1)	3.1678 (14)	170 (2)

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

(II) aquadichlorobis(1H-imidazole)nickel(II)

Crystal data

[NiCl2(C3H4N2)2(H2O)2]	Dx = 1.780 Mg m^−3
Mr = 301.80	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbca	Cell parameters from 123 reflections
a = 9.1185 (7) Å	θ = 3.0–24.7°
b = 7.9344 (6) Å	µ = 2.18 mm^−1
c = 15.5636 (12) Å	T = 293 K
V = 1126.02 (15) Å^3	Plate, pale green
Z = 4	0.20 × 0.20 × 0.02 mm
F(000) = 616

Data collection

Bruker SMART Apex CCD area-detector diffractometer	1301 independent reflections
Radiation source: fine-focus sealed tube	1018 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.043
ϕ and ω scans	θmax = 28.0°, θmin = 2.6°
Absorption correction: multi-scan (SADABS in SAINT-NT; Bruker, 2002)	h = −11→8
Tmin = 0.82, Tmax = 0.96	k = −10→10
6136 measured reflections	l = −19→18

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)] = 0.028	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.062	H atoms treated by a mixture of independent and constrained refinement
S = 1.27	w = 1/[σ^2(Fo^2) + (0.021P)^2] where P = (Fo^2 + 2Fc^2)/3
1301 reflections	(Δ/σ)max = 0.005
94 parameters	Δρmax = 0.50 e Å^−3
4 restraints	Δρmin = −0.36 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.

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

	x	y	z	Uiso*/Ueq
Ni	0.5000	0.0000	0.5000	0.02326 (12)
Cl	0.75208 (5)	0.00267 (5)	0.55406 (3)	0.03067 (13)
N1	0.57133 (16)	0.07778 (19)	0.38132 (9)	0.0293 (3)
C1	0.5106 (2)	0.1989 (3)	0.32937 (14)	0.0371 (5)
H1	0.434 (2)	0.268 (3)	0.3512 (14)	0.056 (7)*
N2	0.6774 (2)	0.0728 (2)	0.25570 (11)	0.0471 (5)
H2N	0.733 (2)	0.035 (2)	0.2167 (10)	0.040 (6)*
C2	0.5746 (3)	0.1964 (3)	0.25187 (14)	0.0456 (5)
H2	0.562 (2)	0.254 (3)	0.2045 (13)	0.051 (7)*
C3	0.6720 (3)	0.0056 (3)	0.33410 (14)	0.0406 (5)
H3	0.728 (2)	−0.084 (3)	0.3501 (13)	0.053 (7)*
O1W	0.47419 (16)	0.25030 (17)	0.53979 (9)	0.0322 (3)
H1WA	0.5536 (15)	0.306 (3)	0.5413 (15)	0.072 (8)*
H1WB	0.4105 (18)	0.303 (3)	0.5109 (13)	0.074 (9)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ni	0.0232 (2)	0.02426 (19)	0.02231 (18)	0.00010 (13)	0.00004 (12)	0.00056 (12)
Cl	0.0255 (3)	0.0321 (3)	0.0344 (2)	−0.00176 (16)	−0.00408 (19)	0.0031 (2)
N1	0.0282 (8)	0.0332 (8)	0.0266 (8)	−0.0003 (7)	0.0022 (7)	0.0010 (7)
C1	0.0366 (12)	0.0408 (12)	0.0339 (11)	0.0018 (9)	−0.0003 (9)	0.0069 (9)
N2	0.0496 (12)	0.0583 (12)	0.0334 (10)	−0.0055 (10)	0.0163 (9)	−0.0050 (9)
C2	0.0489 (14)	0.0563 (14)	0.0317 (12)	−0.0068 (12)	−0.0001 (10)	0.0113 (10)
C3	0.0409 (13)	0.0436 (13)	0.0374 (11)	0.0040 (10)	0.0080 (10)	0.0033 (10)
O1W	0.0306 (7)	0.0278 (7)	0.0381 (7)	0.0009 (6)	−0.0044 (6)	−0.0012 (6)

Geometric parameters (Å, º)

Ni—N1^i	2.0532 (14)	C1—H1	0.95 (2)
Ni—N1	2.0532 (14)	N2—C3	1.333 (3)
Ni—O1W	2.0935 (13)	N2—C2	1.358 (3)
Ni—O1W^i	2.0935 (13)	N2—H2N	0.847 (9)
Ni—Cl^i	2.4478 (5)	C2—H2	0.87 (2)
Ni—Cl	2.4478 (5)	C3—H3	0.91 (2)
N1—C3	1.308 (3)	O1W—H1WA	0.850 (9)
N1—C1	1.372 (2)	O1W—H1WB	0.847 (15)
C1—C2	1.340 (3)
N1^i—Ni—N1	180.0	C1—N1—Ni	127.77 (13)
N1^i—Ni—O1W	89.05 (6)	C2—C1—N1	110.1 (2)
N1—Ni—O1W	90.95 (6)	C2—C1—H1	130.6 (13)
N1^i—Ni—O1W^i	90.95 (6)	N1—C1—H1	119.3 (13)
N1—Ni—O1W^i	89.05 (6)	C3—N2—C2	107.70 (19)
O1W—Ni—O1W^i	180.0	C3—N2—H2N	122.3 (13)
N1^i—Ni—Cl^i	90.52 (4)	C2—N2—H2N	129.8 (13)
N1—Ni—Cl^i	89.48 (4)	C1—C2—N2	105.76 (19)
O1W—Ni—Cl^i	90.25 (4)	C1—C2—H2	134.1 (15)
O1W^i—Ni—Cl^i	89.75 (4)	N2—C2—H2	120.2 (15)
N1^i—Ni—Cl	89.48 (4)	N1—C3—N2	111.4 (2)
N1—Ni—Cl	90.52 (4)	N1—C3—H3	125.7 (13)
O1W—Ni—Cl	89.75 (4)	N2—C3—H3	122.8 (13)
O1W^i—Ni—Cl	90.25 (4)	Ni—O1W—H1WA	114.1 (17)
Cl^i—Ni—Cl	180.0	Ni—O1W—H1WB	113.0 (16)
C3—N1—C1	105.01 (17)	H1WA—O1W—H1WB	110 (2)
C3—N1—Ni	126.59 (14)

Symmetry code: (i) −x+1, −y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2N···Cl^ii	0.85 (1)	2.55 (2)	3.2591 (17)	142 (2)
O1W—H1WA···Cl^iii	0.85 (1)	2.37 (1)	3.2077 (14)	170 (2)
O1W—H1WB···Cl^iv	0.85 (2)	2.34 (1)	3.1744 (15)	168 (2)

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