catena-Poly[[[μ-1,4-bis­(imidazol-1-ylmeth­yl)­benzene-κ²N³:N^3′]bis­[di­chloro­copper(II)]]-bis­[μ-1,4-bis­(imidazol-1-ylmeth­yl)benzene]-1:1′κ²N³:N^3′;2:2′κ²N³:N^3′]

The title compound, [Cu₂Cl₄(bix)₃]_n [bix is 1,4-bis­(imidazol-1-ylmeth­yl)benzene, C₁₄H₁₄N₄], has been synthesized by the hydro­thermal method. The copper(II) center has a five-coordinate trigonal–bipyramidal geometry. Each bix ligand binds with two Cu^II ions, forming ladder-like structures which are connected by π–π stacking inter­actions to form a two-dimensional network.

S1. Comment

In recent years, many strategies have been employed in the synthesis of polymeric architectures with nitrogen-containing heterocyclic ligands, which may play a determining role in the control of the structures (Fujita et al., 1994; Lu et al., 1999; Ho et al., 1999; Meng et al., 2004). One of the most fruitful choices consists in making good use of imidazole and its derivatives (Carlucci, Ciani & Proserpio, 2004; Liu & Li, 2003; Su et al., 2002, 2003). For example, by reactions with silver nitrate and zinc nitrate hexahydrate, the highly flexible ligand 1,4-bis(imidazole-l-ylmethyl)benzene provided low-dimensional complexes with remarkable polyrotaxane-like polymers [Ag₂(bix)₃(NO₃)₂] and [Zn(bix)₂(NO3)₂]·4.5H₂O (Hoskins et al., 1997a,b). Recently, there has been growing interest in bix complexes as a result of their intriguing frameworks (Abrahams et al., 1998, 2002; Carlucci, Ciani, Proserpio & Spadacini, 2004; Shen et al., 1999; Zhao et al., 2002). In the previous research, the syntheses of the bix compounds were all performed in solution at room temperature because the bix ligand is easily soluble in CH₃OH, CHCl₃ or acetone. In order to further investigate the influence of the bix ligands on the final frameworks, we synthesized a one-dimensional ladder-like copper(II) polymer [Cu₂(bix)₃Cl₄]_n, (I), by hydrothermal reaction of copper(II) chloride dihydrate with the bix ligand. Unlike other bix complexes, the bix ligands in compound (I) not only act as long linkers which interconnect the parallel chains but also construct the supramolecular architecture by π-π stacking interactions between the aromatic imidazole rings. As a result, this one-dimensional compound forms a two-dimensional network.

Compound (I) contains ladder-like chains, as shown in Fig. 1, in which the chloride ligands are coordinated to the copper(II) center, preventing the formation of an extended framework. The copper(II) center has a five-coordinate trigonal-bipyramidal geometry, with one N atom of a bix ligand and two chlorides anions in the basal plane, and with the other two N atoms in the trans axial positions completing the coordination sphere (Table 1). Atoms N5, Cl1 and Cl2 are coplanar, but the angles around the Cu atom are rather different, the largest being 144.34 (8)° (Table 1), far from the expected 120° of a regular trigonal bipyramid. In the axial direction, the N1—Cu1—N3 angle is close to linearity [176.17 (10)°]. There are two different types of µ₂ bridging bix ligands in the compound. The first type uses the N atoms of the apical positions to build up a linear subunit, bix–Cu–bix. Two of these subunits are then connected by the N atoms located in the equatorial plane, giving a ladder-like coordination polymer with a large grid of 13.893 ×14.170 Å (metal-to-metal distance; Fig. 2). The grid-like Cu₄(bix)₄ units can be viewed as the basic building block of the structure, in which the apices are occupied by the Cu^II ions and the sides by the bix ligands.

The basic grid is puckered and can be described as chair-like shape, although all the Cu atoms in the ladder are strictly planar. This shape is understandable, because the sp³ configuration of the –CH₂– spacer forces the bix ligand to be nonlinear, generating the nonlinear grid sides and thereby the reclining chair-shaped grids. The N—C—C angles of the bix ligands in (I) are 112.2 (2), 112.3 (2) and 113.8 (2)°, while the bridging ligands in this ladder-like structure all adopt the trans conformation, and the dihedral angles between planes N1/C1/N2/C3/C2 and C16ⁱ–C21ⁱ, N3/C12/N4/C14/C13 and C16–C21, and N5/C5/N6/C6/C7 and C9/C10/C11ⁱⁱ/C9ⁱⁱ/C10ⁱⁱ/C11 are 94.4, 99.3 and 104.7 (s.u. values available?)°, respectively. These structure data clearly depict the nonlinear configuration of the bix ligand in (I). The striking feature of the structure of (I) is that the aromatic imidazole ring of one chain parallel to a symmetry-related (symmetry code: 1 − x, 2 − y, −z) adjacent chain interacts with an offset face-to-face separation of ca 3.4 Å and a centroid–centroid distance of 3.659 (s.u.?) Å, indicating significant π–π interactions [Dance & Scudder, 1995]. The double chains are thus organized into two-dimensional molecular networks by π–π stacking interactions (Fig. 2). The grid layers are closely stacked in an offset fashion along the b direction, the cavity of each layer being blocked by the neighboring layers (Fig. 3).

S2. Experimental

Bix dihydrate was prepared as described by Hoskins et al. (1997b). Compound (I) was synthesized hydrothermally under autogenous pressure. A mixture of CuCl₂·2H₂0 (0.085 g, 0.5 mmol), bix dihydrate (0.14 g, 0.5 mmol) and water (8 ml) was sealed in a stainless steel reactor with a Teflon liner, and was heated to 393 K for two days. After slow cooling to room temperature, light-blue block-shaped crystals of (I) were obtained as a major phase by filtration; these were washed with distilled water and finally dried in air (70% yield). Analysis calcuated for (I): C 38.41, H 3.15, N 12.50%; found: C 38.13, H 3.15, N 12.65%. IR (KBr pellet): 3446 (s), 3105 (w), 1631 (m), 1520 (s), 1425 (w), 1384 (m), 1286 (w), 1243 (m), 1111 (s), 1092 (s), 1029 (w), 950 (w), 859 (w), 827 (w), 773 (w), 749 (m), 716 (w), 660 (m), 622 (w).

S3. Refinement

All H atoms were placed at calculated positions and treated as riding on their parent atoms [C—H = 0.93 and 0.97 Å, and U_iso(H) = 1.2U_eq(C)].

Computing details

Data collection: CrystalClear (Rigaku Corporation, 2000); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1997); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A section of the crystal structure of the title compound. Displacement ellipsoids are plotted at the 30% probability level. H atoms have been omitted for clarity. [Symmetry codes: (i) x − 1, y, z − 1; (ii) −x, 1 − y, 1 - z.]
	Fig. 2. The ladder-like square grid and two-dimensional molecular networks formed by π–π stacking interactions (dashed lines).
	Fig. 3. The packing of the grid layers of the title compound.

catena-Poly[[[µ-1,4-bis(imidazol-1-ylmethyl)benzene- κ²N³:N^3']bis[dichlorocopper(II)]]-bis[µ-1,4-bis(imidazol-1- ylmethyl)benzene]-1:1'κ²N³:N^3';2:2'κ²N³:N^3']

Crystal data

[Cu2Cl4(C14H14N4)3]	Z = 2
Mr = 491.89	F(000) = 504
Triclinic, P1	Dx = 1.560 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 9.752 (5) Å	Cell parameters from 2262 reflections
b = 9.894 (6) Å	θ = 3.1–27.5°
c = 11.685 (6) Å	µ = 1.32 mm^−1
α = 105.963 (5)°	T = 293 K
β = 99.760 (7)°	Block, blue
γ = 98.062 (3)°	0.25 × 0.10 × 0.10 mm
V = 1047.3 (10) Å^3

Data collection

Mercury70 (2x2 bin mode) diffractometer	4736 independent reflections
Radiation source: fine-focus sealed tube	3590 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.027
CCD–profile–fitting scans	θmax = 27.5°, θmin = 3.1°
Absorption correction: multi-scan (CrystalClear; Rigaku Corporation, 2000)	h = −12→12
Tmin = 0.766, Tmax = 0.876	k = −12→11
8202 measured reflections	l = −10→15

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)] = 0.045	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.093	H-atom parameters constrained
S = 1.06	w = 1/[σ^2(Fo^2) + (0.0299P)^2 + 0.7403P] where P = (Fo^2 + 2Fc^2)/3
4736 reflections	(Δ/σ)max < 0.001
271 parameters	Δρmax = 0.36 e Å^−3
0 restraints	Δρmin = −0.65 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
Cu1	0.53017 (4)	0.74937 (4)	0.21936 (3)	0.02686 (11)
Cl1	0.70712 (8)	0.65664 (9)	0.12999 (8)	0.0364 (2)
Cl2	0.60472 (9)	1.01460 (9)	0.34671 (7)	0.0382 (2)
N1	0.5950 (3)	0.6905 (3)	0.3653 (2)	0.0280 (6)
N2	0.6330 (2)	0.6846 (3)	0.5541 (2)	0.0266 (6)
N3	1.3258 (2)	0.9008 (3)	0.9570 (2)	0.0256 (5)
N4	1.4521 (2)	0.7998 (3)	1.0693 (2)	0.0258 (5)
H4A	1.4951	0.7807	1.1319	0.031*
N5	0.3202 (3)	0.7024 (3)	0.2351 (2)	0.0317 (6)
N6	0.1234 (3)	0.7096 (3)	0.3028 (2)	0.0292 (6)
C1	0.5910 (3)	0.7582 (3)	0.4787 (3)	0.0298 (7)
H1A	0.5627	0.8457	0.5030	0.036*
C2	0.6668 (3)	0.5627 (3)	0.4853 (3)	0.0326 (7)
H2A	0.6999	0.4911	0.5129	0.039*
C3	0.6425 (3)	0.5674 (3)	0.3694 (3)	0.0308 (7)
H3A	0.6558	0.4978	0.3026	0.037*
C4	0.6507 (3)	0.7326 (4)	0.6871 (3)	0.0327 (7)
H4B	0.6215	0.6510	0.7142	0.039*
H4C	0.5896	0.8004	0.7090	0.039*
C5	0.8023 (3)	0.8025 (3)	0.7517 (3)	0.0269 (6)
C6	0.8760 (3)	0.7502 (3)	0.8364 (3)	0.0330 (7)
H6A	0.8311	0.6726	0.8555	0.040*
C7	1.0165 (3)	0.8124 (3)	0.8933 (3)	0.0303 (7)
H7A	1.0645	0.7767	0.9507	0.036*
C8	1.0857 (3)	0.9273 (3)	0.8652 (3)	0.0255 (6)
C9	1.0099 (3)	0.9802 (3)	0.7817 (3)	0.0350 (8)
H9A	1.0545	1.0580	0.7626	0.042*
C10	0.8707 (3)	0.9205 (4)	0.7266 (3)	0.0372 (8)
H10A	0.8216	0.9592	0.6720	0.045*
C11	1.2388 (3)	0.9974 (3)	0.9223 (3)	0.0314 (7)
H11A	1.2790	1.0368	0.8651	0.038*
H11B	1.2425	1.0766	0.9942	0.038*
C12	1.3770 (3)	0.8989 (3)	1.0702 (3)	0.0278 (7)
H12A	1.3609	0.9604	1.1405	0.033*
C13	1.4495 (3)	0.7321 (3)	0.9497 (3)	0.0304 (7)
H13A	1.4937	0.6559	0.9216	0.037*
C14	1.3719 (3)	0.7943 (3)	0.8792 (3)	0.0317 (7)
H14A	1.3535	0.7697	0.7945	0.038*
C15	0.2650 (3)	0.7470 (4)	0.3317 (3)	0.0321 (7)
H15A	0.3181	0.7978	0.4097	0.039*
C16	0.2061 (3)	0.6333 (3)	0.1397 (3)	0.0332 (7)
H16A	0.2117	0.5909	0.0595	0.040*
C17	0.0842 (3)	0.6367 (4)	0.1808 (3)	0.0361 (8)
H17A	−0.0077	0.5974	0.1351	0.043*
C18	0.0309 (4)	0.7305 (4)	0.3906 (3)	0.0371 (8)
H18A	−0.0621	0.7367	0.3496	0.045*
H18B	0.0698	0.8206	0.4548	0.045*
C19	0.0155 (3)	0.6106 (3)	0.4468 (3)	0.0283 (7)
C20	−0.0417 (3)	0.4700 (4)	0.3752 (3)	0.0334 (7)
H20A	−0.0696	0.4489	0.2910	0.040*
C21	0.0573 (3)	0.6388 (4)	0.5722 (3)	0.0330 (7)
H21A	0.0963	0.7323	0.6213	0.040*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0247 (2)	0.0352 (2)	0.0239 (2)	0.00954 (16)	0.00558 (15)	0.01220 (16)
Cl1	0.0307 (4)	0.0463 (5)	0.0397 (5)	0.0169 (4)	0.0139 (4)	0.0171 (4)
Cl2	0.0518 (5)	0.0326 (4)	0.0287 (4)	0.0085 (4)	0.0078 (4)	0.0074 (3)
N1	0.0244 (13)	0.0340 (15)	0.0267 (14)	0.0091 (11)	0.0036 (11)	0.0105 (12)
N2	0.0224 (12)	0.0321 (14)	0.0227 (13)	0.0046 (11)	−0.0001 (10)	0.0077 (11)
N3	0.0253 (13)	0.0277 (14)	0.0236 (13)	0.0057 (11)	0.0024 (11)	0.0092 (11)
N4	0.0252 (13)	0.0356 (15)	0.0193 (13)	0.0079 (11)	0.0032 (10)	0.0129 (11)
N5	0.0224 (13)	0.0456 (17)	0.0304 (15)	0.0060 (12)	0.0071 (11)	0.0163 (13)
N6	0.0241 (13)	0.0383 (15)	0.0306 (15)	0.0071 (12)	0.0097 (11)	0.0167 (12)
C1	0.0275 (16)	0.0330 (18)	0.0299 (17)	0.0115 (14)	0.0038 (13)	0.0099 (14)
C2	0.0337 (17)	0.0296 (17)	0.0352 (18)	0.0096 (14)	0.0028 (14)	0.0124 (15)
C3	0.0271 (16)	0.0298 (17)	0.0333 (18)	0.0084 (14)	0.0035 (14)	0.0066 (14)
C4	0.0275 (16)	0.044 (2)	0.0282 (17)	0.0081 (15)	0.0052 (14)	0.0136 (15)
C5	0.0257 (15)	0.0319 (17)	0.0230 (16)	0.0093 (13)	0.0040 (13)	0.0075 (13)
C6	0.0352 (18)	0.0348 (18)	0.0334 (18)	0.0060 (15)	0.0086 (15)	0.0174 (15)
C7	0.0294 (16)	0.0386 (18)	0.0276 (17)	0.0093 (14)	0.0017 (13)	0.0189 (15)
C8	0.0250 (15)	0.0279 (16)	0.0224 (15)	0.0085 (13)	0.0033 (12)	0.0053 (13)
C9	0.0314 (17)	0.0321 (18)	0.042 (2)	0.0004 (14)	−0.0004 (15)	0.0199 (16)
C10	0.0339 (18)	0.041 (2)	0.040 (2)	0.0099 (15)	−0.0014 (15)	0.0240 (17)
C11	0.0289 (16)	0.0287 (17)	0.0346 (18)	0.0037 (14)	0.0008 (14)	0.0112 (14)
C12	0.0272 (16)	0.0323 (17)	0.0234 (16)	0.0084 (14)	0.0061 (13)	0.0062 (13)
C13	0.0323 (17)	0.0332 (18)	0.0276 (17)	0.0114 (14)	0.0083 (14)	0.0086 (14)
C14	0.0373 (18)	0.0335 (18)	0.0222 (16)	0.0088 (15)	0.0044 (14)	0.0057 (14)
C15	0.0277 (16)	0.0415 (19)	0.0273 (17)	0.0027 (14)	0.0053 (14)	0.0135 (15)
C16	0.0318 (17)	0.0390 (19)	0.0261 (17)	0.0009 (15)	0.0054 (14)	0.0095 (15)
C17	0.0256 (16)	0.048 (2)	0.0337 (19)	0.0017 (15)	0.0043 (14)	0.0149 (16)
C18	0.0363 (18)	0.042 (2)	0.045 (2)	0.0157 (16)	0.0209 (16)	0.0201 (17)
C19	0.0243 (15)	0.0349 (18)	0.0321 (17)	0.0118 (14)	0.0139 (13)	0.0130 (14)
C20	0.0322 (17)	0.042 (2)	0.0274 (17)	0.0105 (15)	0.0111 (14)	0.0094 (15)
C21	0.0330 (18)	0.0315 (17)	0.0327 (18)	0.0070 (14)	0.0111 (15)	0.0041 (14)

Geometric parameters (Å, º)

Cu1—N1	1.982 (3)	C5—C10	1.389 (4)
Cu1—N4^i	2.009 (3)	C6—C7	1.388 (4)
Cu1—N5	2.086 (3)	C6—H6A	0.9300
Cu1—Cl1	2.3320 (12)	C7—C8	1.386 (4)
Cu1—Cl2	2.5651 (15)	C7—H7A	0.9300
N1—C1	1.321 (4)	C8—C9	1.384 (4)
N1—C3	1.372 (4)	C8—C11	1.507 (4)
N2—C1	1.337 (4)	C9—C10	1.370 (4)
N2—C2	1.370 (4)	C9—H9A	0.9300
N2—C4	1.467 (4)	C10—H10A	0.9300
N3—C12	1.339 (4)	C11—H11A	0.9700
N3—C14	1.373 (4)	C11—H11B	0.9700
N3—C11	1.456 (4)	C12—H12A	0.9300
N4—C12	1.302 (4)	C13—C14	1.352 (4)
N4—C13	1.368 (4)	C13—H13A	0.9300
N4—Cu1^ii	2.009 (3)	C14—H14A	0.9300
N4—H4A	0.8600	C15—H15A	0.9300
N5—C15	1.326 (4)	C16—C17	1.357 (4)
N5—C16	1.376 (4)	C16—H16A	0.9300
N6—C15	1.338 (4)	C17—H17A	0.9300
N6—C17	1.368 (4)	C18—C19	1.508 (4)
N6—C18	1.469 (4)	C18—H18A	0.9700
C1—H1A	0.9300	C18—H18B	0.9700
C2—C3	1.349 (4)	C19—C21	1.389 (4)
C2—H2A	0.9300	C19—C20	1.389 (5)
C3—H3A	0.9300	C20—C21^iii	1.382 (4)
C4—C5	1.510 (4)	C20—H20A	0.9300
C4—H4B	0.9700	C21—C20^iii	1.382 (4)
C4—H4C	0.9700	C21—H21A	0.9300
C5—C6	1.382 (4)
N1—Cu1—N4^i	176.17 (10)	C8—C7—C6	120.6 (3)
N1—Cu1—N5	90.24 (10)	C8—C7—H7A	119.7
N4^i—Cu1—N5	86.39 (10)	C6—C7—H7A	119.7
N1—Cu1—Cl1	90.70 (8)	C9—C8—C7	118.2 (3)
N4^i—Cu1—Cl1	90.98 (8)	C9—C8—C11	118.9 (3)
N5—Cu1—Cl1	144.36 (8)	C7—C8—C11	122.9 (3)
N1—Cu1—Cl2	90.75 (9)	C10—C9—C8	121.5 (3)
N4^i—Cu1—Cl2	91.71 (8)	C10—C9—H9A	119.3
N5—Cu1—Cl2	101.68 (8)	C8—C9—H9A	119.3
Cl1—Cu1—Cl2	113.93 (4)	C9—C10—C5	120.5 (3)
C1—N1—C3	105.6 (3)	C9—C10—H10A	119.8
C1—N1—Cu1	126.3 (2)	C5—C10—H10A	119.8
C3—N1—Cu1	127.9 (2)	N3—C11—C8	113.9 (3)
C1—N2—C2	107.3 (3)	N3—C11—H11A	108.8
C1—N2—C4	125.8 (3)	C8—C11—H11A	108.8
C2—N2—C4	126.7 (3)	N3—C11—H11B	108.8
C12—N3—C14	106.7 (2)	C8—C11—H11B	108.8
C12—N3—C11	127.0 (3)	H11A—C11—H11B	107.7
C14—N3—C11	126.3 (3)	N4—C12—N3	111.4 (3)
C12—N4—C13	106.7 (3)	N4—C12—H12A	124.3
C12—N4—Cu1^ii	123.4 (2)	N3—C12—H12A	124.3
C13—N4—Cu1^ii	129.4 (2)	C14—C13—N4	108.7 (3)
C12—N4—H4A	126.6	C14—C13—H13A	125.7
C13—N4—H4A	126.6	N4—C13—H13A	125.7
Cu1^ii—N4—H4A	6.6	C13—C14—N3	106.6 (3)
C15—N5—C16	105.4 (3)	C13—C14—H14A	126.7
C15—N5—Cu1	128.6 (2)	N3—C14—H14A	126.7
C16—N5—Cu1	125.4 (2)	N5—C15—N6	111.3 (3)
C15—N6—C17	107.5 (2)	N5—C15—H15A	124.3
C15—N6—C18	125.0 (3)	N6—C15—H15A	124.3
C17—N6—C18	127.2 (3)	C17—C16—N5	109.5 (3)
N1—C1—N2	111.2 (3)	C17—C16—H16A	125.3
N1—C1—H1A	124.4	N5—C16—H16A	125.3
N2—C1—H1A	124.4	C16—C17—N6	106.3 (3)
C3—C2—N2	106.2 (3)	C16—C17—H17A	126.9
C3—C2—H2A	126.9	N6—C17—H17A	126.9
N2—C2—H2A	126.9	N6—C18—C19	112.3 (2)
C2—C3—N1	109.6 (3)	N6—C18—H18A	109.1
C2—C3—H3A	125.2	C19—C18—H18A	109.1
N1—C3—H3A	125.2	N6—C18—H18B	109.1
N2—C4—C5	112.2 (2)	C19—C18—H18B	109.1
N2—C4—H4B	109.2	H18A—C18—H18B	107.9
C5—C4—H4B	109.2	C21—C19—C20	118.4 (3)
N2—C4—H4C	109.2	C21—C19—C18	120.5 (3)
C5—C4—H4C	109.2	C20—C19—C18	121.1 (3)
H4B—C4—H4C	107.9	C21^iii—C20—C19	120.6 (3)
C6—C5—C10	118.6 (3)	C21^iii—C20—H20A	119.7
C6—C5—C4	120.8 (3)	C19—C20—H20A	119.7
C10—C5—C4	120.6 (3)	C20^iii—C21—C19	121.0 (3)
C5—C6—C7	120.7 (3)	C20^iii—C21—H21A	119.5
C5—C6—H6A	119.7	C19—C21—H21A	119.5
C7—C6—H6A	119.7

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