Poly[di-μ₃-chloro-μ₂-trans-1,2-di-4-pyridylethyl­ene-dicopper(I)]: a two-dimensional organic–inorganic hybrid constructed from linear CuCl clusters and bridging ligands

The structure of the title compound, [Cu₂Cl₂(C₁₂H₁₀N₂)]_n, contains infinite CuCl staircase-like chains, which lie about inversion centres. The trans-1,2-di-4-pyrid­ylethyl­ene mol­ecules also lie about inversion centres and connect the CuCl chains through Cu—N coordination bonds into a two-dimensional organic–inorganic hybrid network. The planar sheets are stacked along the c axis and associated through weak C—H...Cl inter­actions. The results show a reliable structural motif with controllable separation of the CuCl chains by variation of the length of the ligand.

S1. Comment

Designed synthesis of metal-organic coordination polymers by employing various metal centres and polyfunctional ligands has attracted increasing interest in recent years because of their novel electronic, optical, magnetic and catalytic properties (Janiak, 2003; Kitagawa, et al., 2004). In the case of reaction systems containing inorganic moieties, the coordination polymers may form in an organic–inorganic hybrid fashion. Coordinate covalent bonds or non-covalent interactions, such as hydrogen bonds and π–π interactions, are useful tools to connect inorganic and organic components (Graham & Pike, 2000; Mitzi, et al., 1995). The choice of metal coordination units as building blocks is crucial to the assembly of the supramolecular networks since their geometric and topological characteristics determine the structures of products. The Cu^I halide/organoamine system is of interest because of the preference for the formation of predictable copper(I) halide motifs, including zigzag chain (Wang et al., 2005), rack chain (Begley et al., 1994) and staircase (Blake, Brooks, Champness, Cooke, Crew et al., 1999; Aakeröy et al., 2000), which can be propagated through the coordination of organic N-donor ligands to form network structures. It has been demonstrated that the ligand geometry can affect the type of Cu^I halide framework. For example, the Cu^I halide polymers in a staircase form have been observed for linear bidentate ligands such as pyrazine (pyz) and 4,4'-bipyridine (bpy) (Kawata et al., 1998; Lu et al., 1999), while a tridentate triazine ligand results in the formation of the columnar polymer (Blake, Brooks, Champness, Cooke, Deveson et al., 1999). This led us to examine the effects of 1,2-bis(4-pyridyl)ethylene (bpe), a longer analog of 4,4'-bipyridine, on the structure of Cu^I halide hybrid polymer. We report here the structure of [(CuCl)₂(bpe)]_n, (I), which exhibits an organic–inorganic layered structure formed by the assembly of the one-dimensional CuCl1 staircase and the bridging ligand.

Compound (I) was prepared as described below, and the resulting dark-yellow crystals suggested that (I) is a cuprous product; this was established by crystal structure analysis. The formations of the coordination polymer [Cu₄(1,4-C₆H₄(COO)₂)₃(bpy)₂], with mixed-valence Cu^I/Cu^II subunits from the Cu^II salt under a similar solvothermal condition (Lo et al., 2000), and the polymer [(CuCl)₂(bpy)], from hydrothermal reaction of Cu^II chloride (Lu et al., 1999), have shown that both ethanol and aromatic amine may act as reducing agents for Cu^II reduction at high temperature.

In the structure of (I), as shown in Fig. 1, atom Cu1 is coordinated to three Cl1 atoms and an N atom from the bpe ligand in a distorted-tetrahedral environment (Table 1), showing the typical character of the monovalent Cu ion. Each Cl1 atom binds three Cu atoms in a µ₃-fashion, thus generating a polymeric CuCl1 staircase-like chain. The bpe ligand is planar, with an inversion centre lying on the middle of the ethylene bond. The polymeric CuCl1 chains arranged parallel to each other are interconnected through the bridging bpe molecules into a two-dimensional layered network (Fig. 2). The bridging ligands are stacked in such a way that π–π interactions between the pyridine rings may be maximized with a centroid-to-plane separation of 3.46 Å, which further stabilizes the network structure.

There are three types of Cu···Cu separations that are structurally significant. One is the shortest contact of 2.975 (2) Å between Cu1 and Cu1ⁱ (see Fig. 2 for symmetry code) within the CuCl1 staircase, which implies a weak Cu···Cu interaction. This interaction seems to be enhanced as the size of the bridging ligand decreases, as indicated by the corresponding values of 2.936 (1) Å in [(CuCl)₂(bpy)] (Lu et al., 1999) and 2.889 (2) Å in [(CuCl)₂(pyz)] (Kawata et al., 1998). The second is the separation of Cu1 and Cu1ⁱⁱ of 3.796 (1) Å along the staircase, which corresponds to the short axis of the unit cell. This distance is a good match with π–π interaction between the bridging ligands. In the case of [(CuI)₂(bpe)] (Blake, Brooks, Champness, Cooke, Crew et al., 1999), the corresponding distance is a little longer [4.1000 (8) Å], leading to a relatively weak π–π interaction between the pyridine rings with a centroid-to-plane distance of 3.59 Å. The third is the separation of Cu1 and Cu1ⁱⁱⁱ between the adjacent CuCl1 staircases [13.377 (5) Å]. A comparison with the corresponding values of 11.099 and 6.781 Å in [(CuCl)₂(bpy)] and [(CuCl)₂(pyz)], respectively, shows that the separation of the CuCl1 staircases can be effectively governed by the length of the bridging ligands. This distance can also be extended by the use of hydrogen-bonded dimeric ligands (Aakeröy et al., 2000). Thus it presents a predictable and adjustable aspect of this family of structures.

The two-dimensional networks are stacked along the c axis at c = 0 and 0.5. Adjacent sheets are staggered with respect to each other by half a translation along the b axis so that the ethylene C6 atom is located near the Cl1 atom from the neighbouring sheet to form a weak C—H···Cl1 contact. The H···Cl(−x, −1/2 + y, 1/2 − z) distance of 2.95 Å is at the limit of van der Waals radii (Bondi, 1964), but the C—H···Cl1 angle of 157° is within the range of acceptable values for hydrogen bonds (Taylor & Kennard, 1982). This C—H···Cl1 interaction may benefit the stacking of the planar sheets in an ABAB fashion.

In summary, the two-dimensional hybrid network with CuCl1 staircase as building block and bpe ligand as spacer can be readily constructed from the reduction reaction of Cu^II under solvothermal conditions. The results indicate that the structural motif is stable and repeatable and it is possible to control the separations of Cu atoms by changing the size of ligands and thus lead to changes in properties of the compounds.

S2. Experimental

A mixture of Cu(BF₄)₂ (0.2 mmol), bpe(0.2 mmol), HCl1 (0.2 mmol) in water (9 ml) and ethanol (3 ml) was stirred, adjusted to a pH of 9.6 with triethylamine, then transferred and sealed in a 25 ml Teflon-lined reaction vessel, which was heated at 433 K for three days. The vessel was cooled to room temperature at a rate of 10 K h⁻¹. The resulting dark-yellow plate-like crystals were filtered off, washed and dried in air (yield 34%).

S3. Refinement

H atoms were located from difference maps and treated as riding atoms, with C—H distances of 0.93 Å and with U_iso(H) = 1.2U_eq(parent).

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SMART; data reduction: SAINT (Bruker, 2003); 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. Structure of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) −x, 1 − y, 1 − z; (ii) 1 − x, 1 − y, 1 − z; (iii) 1 − x, −y, 1 − z.] No symmetry codes are indicated
	Fig. 2. A view of the two-dimensional network, showing the one-dimensional CuCl staircases linked by the bpe ligands. [Symmetry codes: (i) 1 − x, 1 − y, 1 − z; (ii) 1 + x, y, z; (iii) 1 − x, −y, 1 − z.]

Poly[µ₂-trans-1,2-bis(4-pyridyl)ethylene-di-µ₃-chloro-dicopper(I)]

Crystal data

[Cu2Cl2(C12H10N2)]	F(000) = 376
Mr = 380.20	Dx = 2.026 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 619 reflections
a = 3.7965 (11) Å	θ = 2.3–22.2°
b = 15.078 (5) Å	µ = 3.82 mm^−1
c = 10.972 (4) Å	T = 293 K
β = 97.082 (6)°	Plate, dark-yellow
V = 623.3 (4) Å^3	0.36 × 0.26 × 0.15 mm
Z = 2

Data collection

Bruker SMART APEX CCD area-detector diffractometer	1238 independent reflections
Radiation source: fine-focus sealed tube	840 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.053
ϕ and ω scans	θmax = 26.1°, θmin = 2.3°
Absorption correction: multi-scan (SAINT; Bruker, 2003)	h = −4→4
Tmin = 0.332, Tmax = 0.604	k = −18→18
3304 measured reflections	l = −13→10

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)] = 0.055	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.120	H-atom parameters constrained
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0513P)^2] where P = (Fo^2 + 2Fc^2)/3
1238 reflections	(Δ/σ)max < 0.001
82 parameters	Δρmax = 0.49 e Å^−3
0 restraints	Δρmin = −0.42 e Å^−3

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

	x	y	z	Uiso*/Ueq
Cu1	0.2722 (2)	0.43705 (5)	0.55941 (7)	0.0603 (3)
Cl1	0.1807 (4)	0.50141 (9)	0.34369 (11)	0.0397 (4)
N1	0.3155 (11)	0.3068 (3)	0.5309 (4)	0.0368 (11)
C1	0.4863 (14)	0.2531 (3)	0.6147 (5)	0.0409 (13)
H1	0.5857	0.2779	0.6887	0.049*
C2	0.5246 (15)	0.1637 (3)	0.5988 (5)	0.0416 (14)
H2	0.6439	0.1294	0.6612	0.050*
C3	0.3840 (14)	0.1246 (3)	0.4887 (5)	0.0334 (12)
C4	0.2072 (14)	0.1800 (4)	0.4020 (5)	0.0401 (13)
H4	0.1050	0.1569	0.3273	0.048*
C5	0.1805 (14)	0.2691 (3)	0.4249 (5)	0.0425 (14)
H5	0.0632	0.3049	0.3639	0.051*
C6	0.4197 (16)	0.0299 (3)	0.4602 (5)	0.0431 (14)
H6	0.3258	0.0101	0.3827	0.052*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0775 (7)	0.0358 (4)	0.0653 (6)	0.0075 (4)	0.0001 (4)	−0.0096 (4)
Cl1	0.0404 (8)	0.0426 (8)	0.0345 (7)	0.0021 (6)	−0.0019 (5)	−0.0002 (6)
N1	0.040 (3)	0.026 (2)	0.044 (3)	0.004 (2)	0.004 (2)	−0.004 (2)
C1	0.045 (4)	0.038 (3)	0.038 (3)	0.004 (3)	−0.004 (3)	−0.008 (2)
C2	0.047 (4)	0.040 (3)	0.037 (3)	0.004 (3)	0.002 (3)	0.006 (3)
C3	0.029 (3)	0.033 (3)	0.038 (3)	0.001 (2)	0.002 (2)	−0.004 (2)
C4	0.047 (4)	0.037 (3)	0.035 (3)	0.002 (3)	−0.003 (3)	−0.006 (2)
C5	0.054 (4)	0.033 (3)	0.039 (3)	0.004 (3)	−0.002 (3)	0.001 (2)
C6	0.053 (4)	0.038 (3)	0.037 (3)	0.002 (3)	0.000 (3)	0.000 (2)

Geometric parameters (Å, º)

Cu1—N1	1.999 (4)	C2—C3	1.391 (7)
Cu1—Cl1^i	2.3235 (16)	C2—H2	0.9300
Cu1—Cl1^ii	2.4003 (17)	C3—C4	1.377 (7)
Cu1—Cl1	2.5420 (17)	C3—C6	1.471 (7)
Cu1—Cu1^ii	2.9752 (17)	C4—C5	1.371 (7)
Cu1—Cu1^i	2.9848 (17)	C4—H4	0.9300
N1—C1	1.331 (6)	C5—H5	0.9300
N1—C5	1.339 (6)	C6—C6^iii	1.347 (10)
C1—C2	1.370 (7)	C6—H6	0.9300
C1—H1	0.9300
N1—Cu1—Cl1^i	122.94 (13)	C5—N1—Cu1	121.5 (3)
N1—Cu1—Cl1^ii	111.45 (13)	N1—C1—C2	124.1 (5)
Cl1^i—Cu1—Cl1^ii	106.96 (6)	N1—C1—H1	118.0
N1—Cu1—Cl1	103.53 (13)	C2—C1—H1	118.0
Cl1^i—Cu1—Cl1	104.47 (5)	C1—C2—C3	119.5 (5)
Cl1^ii—Cu1—Cl1	106.04 (5)	C1—C2—H2	120.2
N1—Cu1—Cu1^ii	119.66 (13)	C3—C2—H2	120.2
Cl1^i—Cu1—Cu1^ii	116.67 (5)	C4—C3—C2	116.4 (5)
Cl1^ii—Cu1—Cu1^ii	55.20 (4)	C4—C3—C6	119.5 (4)
Cl1—Cu1—Cu1^ii	50.84 (4)	C2—C3—C6	124.1 (5)
N1—Cu1—Cu1^i	128.50 (14)	C5—C4—C3	120.6 (5)
Cl1^i—Cu1—Cu1^i	55.55 (5)	C5—C4—H4	119.7
Cl1^ii—Cu1—Cu1^i	117.54 (5)	C3—C4—H4	119.7
Cl1—Cu1—Cu1^i	48.91 (4)	N1—C5—C4	123.1 (5)
Cu1^ii—Cu1—Cu1^i	79.14 (4)	N1—C5—H5	118.5
Cu1^i—Cl1—Cu1^ii	106.96 (6)	C4—C5—H5	118.5
Cu1^i—Cl1—Cu1	75.53 (5)	C6^iii—C6—C3	123.9 (6)
Cu1^ii—Cl1—Cu1	73.96 (5)	C6^iii—C6—H6	118.0
C1—N1—C5	116.4 (4)	C3—C6—H6	118.0
C1—N1—Cu1	122.1 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C6—H6···Cl1^iv	0.93	2.95	3.824 (6)	157

Symmetry code: (iv) −x, y−1/2, −z+1/2.