catena-Poly[bis[(η²-1-allyl-3-aminopyridinium)copper(I)]-di-μ-chloro-copper(I)-di-μ-chloro-copper(I)-di-μ-chloro]

Crystals of the title π-complex, [Cu₄Cl₆(C₈H₁₁N₂)₂]_n, were obtained by means of alternating-current electrochemical synthesis. The structure consists of infinite copper–chlorine chains to which 1-allyl-3-amino­pyridinium moieties are attached via a η² Cu—(C=C) interaction. The two independent Cu atoms have distinct coordination environments. One is three-coordinate, surrounded by two chloro ligands and the olefinic bond, whereas the second copper center is surrounded by a tetrahedral arrangement of four Cl atoms. The lower basicity of 3-amino­pyridine as compared with 2- and 4-amino­pyridine lowers the capacity of the organic ligand for donating to N—H...Cl hydrogen bonds and results in the formation of a large inorganic fragment.

S1. Comment

π-complexes involving heterocyclic ligands have been investigated poorly. There have been only a few publications referring to copper(I) π-complexation with pyridine derivatives (for example, Munakata et al., 1987). The importance of metal complexes with heterocyclic ligands as compounds with potential biological activity (Ghiladi et al., 2001; Rhames et al., 2001) has led us to pursue a structural investigation of the copper(I) π-complexes with 1-allyl-4-aminopyridinium (Goreshnik et al., 2003a) and 1-allyl-2-aminopyridinium (Goreshnik et al., 2003b) cations. To complete the comparison of structural peculiarities of complexes with isomeric N-allylaminopyridinium cations, the copper(I) chloride π-complex, (I), with the 1-allyl-3-aminopyridinium cation has been obtained and structurally investigated.

The Cu and Cl atoms in (I) form infinite chains, propagating along [110]. These chains are composed of 4- and 8-membered cyclic subunits, with a common apex at atom Cu2 (Fig. 1). Both of the cyclic subunits are centrosymmetric; the four-membered cycle is essentially planar, while the eight-membered ring has a chair-like conformation. All Cl atoms act as bridges; atoms Cl1 and Cl2 connect pairs of Cu1 and Cu2 atoms in the eight-membered rings, whereas atom Cl3 bridges two Cu2 atoms in the four-membered ring. Atom Cu2 is tetrahedrally surrounded by four Cl atoms, whereas the trigonal-planar arrangement about atom Cu1 includes two Cl atoms and the olefinic bond of the allyl group of the 1-allyl-3-aminopyridinium ligand (Table 1). Because the coordination number is lower for atom Cu1 than for atom Cu2, the Cu1—Cl distances, of 2.2478 (14) and 2.2568 (14) Å, are noticeably shorter than the Cu2—Cl distances [2.3477 (15) – 2.4167 (15) Å].

For a numerical characterization of the effectiveness of the copper(I)-olefin interaction, the C—Cu—C angle provides the most suitable parameter, being dependent on both the C═C bond elongation and the Cu—(C═C) distance shortening. The Cu^I—(C═C) bond consists of two components. The [Cu(I)←L] σ donor–acceptor component – which is relatively insensitive to the olefinic bond orientation – is formed by the overlap of the occupied olefinic pπ orbital and the unoccupied 4s⁰ orbital of the Cu^I atom, and produces a shortening of the Cu—m distance (m is the mid-point of the C═C bond). The [Cu(I)→ L] π-dative component, based on electron transfer from the Cu^I 3d¹⁰ orbitals to the unoccupied antibonding orbital of the C═C group, which is strongly dependent on a proper olefinic group orientation in the metal coordination sphere, causes a lengthening of the C═ C bond. Therefore, both components increase the value of the C—Cu—C angle. Thus, shortening of the Cu—m distance and lengthening of the C═C bond, as well as an increase in the C—Cu—C angle, are the most informative values for estimating the effectiveness of the Cu—(C═C) interaction. An effective Cu—(C═C) interaction leads to a transformation of the copper coordination polyhedron from tetrahedral to trigonal-pyramidal, with the olefinic group in the basal plane and with concomitant lengthening of the central atom–axial ligand distance; this lengthening can proceed as far as the removal of the axial ligand from the metal coordination sphere, with the formation, as in the present structure, of a trigonal-planar copper environment.

The coordinated olefinic group, with a C═C distance of 1.344 (7) Å, is only slightly elongated as compared with the length of an uncoordinated C═ C bond. This value, as well as the C—Cu—C angle of 38.2 (2)° and a noteworthy 0.21 Å deviation of the olefinic C atoms from the Cl1/Cl2/m plane (corresponding to an 18° inclination of the C═C bond from the equatorial plane), reveal the low efficiency of the π interaction – that is, despite a rather effective σ-component [short Cu—m distance of 1.943 (6) Å], the π-dative component of the Cu—(C═C) interaction is less pronounced. Comparison of these values with the analogues in the structure of the copper(I) chloride π-complex with 1-allyl-4-aminopyridinium, where the Cu atom also possesses a trigonal-planar 2 C l + C═C environment [C—Cu—C = 38.0 (2)°, Cu—m = 1.950 (6) Å and C═C = 1.343 (6) Å], shows a similarly modest π interaction in both cases. The Cu—m distances are rather short for copper(I) π-complexes in general because of the absence of steric hindrance in the trigonal-planar metal environment, which includes two Cl atoms in addition to the C═C bond. The Cu1—C10(terminal) distance is, as usual, slightly shorter than the Cu1—C9 distance. All pyridine rings are strictly parallel to each other, but the shortest ring–ring distance (4.5 Å) indicates an absence of any aromatic π–π stacking. Infinite chains, formed by the CuLCl₂ and CuCl₄ subunits, are interconnected into a three-dimensional structure by weak N—H···Cl hydrogen bonds (Table 2 and Fig. 2). The H···Cl distances (2.75 and 2.83 Å) differ significantly from the values of 2.39–2.57 Å observed for the copper(I) chloride π-complex with 1-allyl-4-aminopyridinium, and 2.47–2.50 Å for the 1-allyl-2-aminopyridinium derivative. These π-complexes with N-allyl derivatives of aminopyridines, (2-H₂N—C₅H₄NC₃H₅)₂[Cu₂Cl₄] and (4-H₂N—C₅H₄NC₃H₅)[CuCl₂], possess structures with small inorganic fragments, Cu₂Cl₄ and CuCl₂, respectively, and rather strong N—H···Cl hydrogen bonds. We note that the progression from the simplest metal-containing fragment, CuCl₂⁻, in the complex with 1-allyl-4-aminopyridinium through Cu₂Cl₄²⁻ in the complex with 1-allyl-2-aminopyridinium to the complicated fragment (Cu₄Cl₆)_n in the present compound with 1-allyl-3-aminopyridinium corresponds to decreasing order of pK_a(base) values of the initial aminopyridines (9.25, 6.86 and 6.07, respectively). Thus, in (I), the electron-donor ability of the N atom of the NH₂ group is weaker, which may be responsible for the elongated N—H···Cl contacts here as compared with the 2-amino- and 4-aminopyridinium analogues. Moreover, a `chelating' ligand arrangement [a 1-allyl-2-aminopyridinium cation bonded to the same Cu<sub>2</sub>Cl<sub>4</sub><sup>2−</sup> dimer via a Cu—(C═C) interaction and by N—H···Cl contacts] or a `bridging' organization (a 1-allyl-4-aminopyridinium moiety connected to one of the Cu atoms through the C═C-bond and to a chloro ligand of an adjacent metal atom through N—H···Cl hydrogen bonds) also promotes the formation of effective hydrogen bonds. In such cases, the H atom effectively completes the coordination about the Cl atom, hindering a bridging function for the halogen and thus effectively impeding the further association of small inorganic fragments into larger ones. In the case of the 1-allyl-3-aminopyridinium complex, (I), the weakly hydrogen-bonding amine H atoms cannot compete with the Cu atoms for a place in the chlorine environment, which in turn enables the formation of the infinite copper–chlorine chains.

S2. Experimental

1-Allyl-3-aminopyridinium chloride was prepared from 3-aminopyridine (Aldrich) by a procedure similar to that used for obtaining 1-allyl-4-aminopyridinium chloride (Goreshnik et al., 2003a). Good quality crystals of the title compound were obtained using the alternating-current electrochemical technique (Mykhalichko & Mys'kiv, 1998) starting from 1-allyl-3-aminopyridinium chloride and copper(II) chloride. To an ethanol solution (2 ml) of CuCl₂^.2H₂O (1 mmol) was added an ethanol solution (2 ml) of 1-allyl-3-aminopyridinium chloride (1.2 mmol). The solution was placed into a small test tube and copper-wire electrodes in cork were inserted. After applying 0.30 V alternating current (frequency 50 Hz) for some days, colorless crystals of the title compound appeared on the copper electrodes. The density, measured by flotation in a chloroform–bromoform mixture, is 2.0 Mg m³.

S3. Refinement

The highest difference peak is located 0.92 Å from atom Cu1. All H atoms were allowed to ride on their parent atoms [C—H = 0.93 and 0.97 \%A and U_iso(H) = 1.2U_eq(C,N)].

Computing details

Data collection: CAD-4 Software (Enraf–Nonius, 1989); cell refinement: CAD-4 Software; data reduction: Corinc (Dräger & Gattow, 1971); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: Diamond (Bergerhoff, 1996); software used to prepare material for publication: enCIFer (Allen et al., 2004).

Figures

	Fig. 1. Copper–chloro chains and ligands in the structure of (I).
	Fig. 2. Hydrogen-bonding in the structure of (I).

catena-Poly[bis{[η²-3-(3-amino-1-pyridinio)propene]copper(I)}-di-µ-chloro- copper(I)-di-µ-chloro-copper(I)-di-µ-chloro]

Crystal data

[Cu4Cl6(C8H11N2)2]	Z = 1
Mr = 737.24	F(000) = 364
Triclinic, P1	Dx = 2.020 Mg m^−3 Dm = 2.000 Mg m^−3 Dm measured by flotation
Hall symbol: -P 1	Cu Kα radiation, λ = 1.54178 Å
a = 8.4148 (12) Å	Cell parameters from 25 reflections
b = 8.7310 (16) Å	θ = 35–45°
c = 9.8916 (16) Å	µ = 10.14 mm^−1
α = 102.177 (16)°	T = 295 K
β = 104.587 (12)°	Plate, colourless
γ = 113.166 (13)°	0.24 × 0.20 × 0.04 mm
V = 606.1 (2) Å^3

Data collection

Enraf–Nonius CAD-4 diffractometer	2004 reflections with I > 2σ(I)
Radiation source: rotating anode	Rint = 0.106
Graphite monochromator	θmax = 73.4°, θmin = 4.9°
θ/2ω scans	h = −10→0
Absorption correction: numerical (de Meulenaer & Tompa, 1965)	k = −9→10
Tmin = 0.19, Tmax = 0.696	l = −11→12
2615 measured reflections	3 standard reflections every 60 min
2443 independent reflections	intensity decay: 5%

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)] = 0.060	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.175	H-atom parameters constrained
S = 1.06	w = 1/[σ^2(Fo^2) + (0.1252P)^2 + 0.1886P] where P = (Fo^2 + 2Fc^2)/3
2443 reflections	(Δ/σ)max < 0.001
136 parameters	Δρmax = 1.28 e Å^−3
0 restraints	Δρmin = −0.95 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. A full-matrix least-squares refinement based on F² was carried out for the positional and thermal parameters for all atoms, anisotropic mode of the refinement - excluding H-atoms. The highest peak is located 0.92 Å from Cu1. For H atoms in NH₂ group the coordinates 'ride' on the coordinates of the N atom. The same shifts are applied to the coordinates of all three atoms, and all of them contribute to the derivative calculation. Hydrogen atoms of pyridine ring refined as a a riding model.

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

	x	y	z	Uiso*/Ueq
Cu1	0.37372 (10)	0.08635 (10)	0.55036 (8)	0.0357 (3)
Cu2	0.83984 (13)	0.32969 (13)	0.47343 (11)	0.0541 (3)
Cl1	0.67770 (15)	0.28543 (16)	0.64312 (13)	0.0356 (3)
Cl2	0.68444 (17)	0.04525 (17)	0.28167 (13)	0.0413 (3)
Cl3	0.83960 (16)	0.55051 (16)	0.37308 (14)	0.0389 (3)
N1	0.2456 (5)	0.2954 (5)	0.2040 (4)	0.0320 (8)
C2	0.0691 (7)	0.2630 (7)	0.1697 (5)	0.0375 (10)
H2	0.0103	0.2350	0.2356	0.045*
C3	−0.0290 (7)	0.2704 (7)	0.0370 (6)	0.0394 (11)
C4	0.0648 (9)	0.3151 (8)	−0.0560 (6)	0.0507 (14)
H4	0.0059	0.3270	−0.1433	0.061*
C5	0.2467 (10)	0.3425 (10)	−0.0204 (7)	0.0614 (18)
H5	0.3082	0.3688	−0.0851	0.074*
C6	0.3352 (8)	0.3305 (9)	0.1112 (6)	0.0489 (14)
H6	0.4563	0.3466	0.1355	0.059*
N7	−0.2074 (8)	0.2375 (9)	0.0043 (6)	0.0629 (15)
H7A	−0.2639	0.2213	−0.0841	0.076*
H7B	−0.2432	0.2122	0.0814	0.076*
C8	0.3429 (6)	0.2873 (6)	0.3489 (5)	0.0319 (9)
H8A	0.3258	0.3572	0.4288	0.038*
H8B	0.4753	0.3370	0.3691	0.038*
C9	0.2662 (6)	0.0981 (6)	0.3431 (5)	0.0311 (9)
H9	0.3168	0.0295	0.3054	0.037*
C10	0.1274 (7)	0.0235 (7)	0.3901 (5)	0.0350 (10)
H10A	0.0749	0.0897	0.4281	0.042*
H10B	0.0840	−0.0943	0.3845	0.042*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0288 (4)	0.0416 (5)	0.0373 (4)	0.0128 (3)	0.0123 (3)	0.0222 (3)
Cu2	0.0447 (5)	0.0533 (6)	0.0653 (6)	0.0175 (4)	0.0214 (4)	0.0326 (5)
Cl1	0.0250 (5)	0.0389 (6)	0.0410 (6)	0.0095 (5)	0.0124 (4)	0.0212 (5)
Cl2	0.0356 (6)	0.0434 (7)	0.0396 (6)	0.0088 (5)	0.0152 (5)	0.0228 (5)
Cl3	0.0270 (6)	0.0406 (6)	0.0487 (6)	0.0099 (5)	0.0140 (5)	0.0269 (5)
N1	0.030 (2)	0.0293 (19)	0.0306 (18)	0.0053 (16)	0.0117 (16)	0.0168 (15)
C2	0.037 (3)	0.042 (3)	0.035 (2)	0.016 (2)	0.015 (2)	0.020 (2)
C3	0.039 (3)	0.035 (2)	0.036 (2)	0.014 (2)	0.006 (2)	0.013 (2)
C4	0.059 (4)	0.050 (3)	0.033 (2)	0.018 (3)	0.007 (2)	0.023 (2)
C5	0.055 (4)	0.082 (5)	0.043 (3)	0.017 (3)	0.022 (3)	0.039 (3)
C6	0.033 (3)	0.064 (4)	0.047 (3)	0.012 (3)	0.018 (2)	0.030 (3)
N7	0.048 (3)	0.091 (4)	0.051 (3)	0.036 (3)	0.008 (2)	0.034 (3)
C8	0.024 (2)	0.033 (2)	0.031 (2)	0.0058 (18)	0.0074 (17)	0.0148 (17)
C9	0.032 (2)	0.035 (2)	0.033 (2)	0.0170 (19)	0.0114 (18)	0.0206 (18)
C10	0.031 (2)	0.031 (2)	0.040 (2)	0.0100 (19)	0.0096 (19)	0.021 (2)

Geometric parameters (Å, º)

Cu1—C10	2.048 (5)	C3—C4	1.378 (8)
Cu1—C9	2.064 (4)	C4—C5	1.389 (10)
Cu1—Cl1	2.2478 (14)	C4—H4	0.9300
Cu1—Cl2^i	2.2568 (14)	C5—C6	1.375 (8)
Cu2—Cl3	2.3477 (15)	C5—H5	0.9300
Cu2—Cl2	2.3841 (18)	C6—H6	0.9300
Cu2—Cl3^ii	2.3922 (16)	N7—H7A	0.8344
Cu2—Cl1	2.4167 (15)	N7—H7B	0.9251
Cu2—Cu2^ii	2.9506 (19)	C8—C9	1.501 (6)
N1—C2	1.333 (7)	C8—H8A	0.9700
N1—C6	1.338 (7)	C8—H8B	0.9700
N1—C8	1.492 (5)	C9—C10	1.344 (7)
C2—C3	1.392 (7)	C9—H9	0.9300
C2—H2	0.9300	C10—H10A	0.9300
C3—N7	1.348 (8)	C10—H10B	0.9300
C10—Cu1—C9	38.15 (19)	C3—C4—H4	119.8
C10—Cu1—Cl1	140.52 (14)	C5—C4—H4	119.8
C9—Cu1—Cl1	105.51 (14)	C6—C5—C4	119.5 (6)
C10—Cu1—Cl2^i	109.63 (14)	C6—C5—H5	120.3
C9—Cu1—Cl2^i	146.35 (14)	C4—C5—H5	120.3
Cl1—Cu1—Cl2^i	108.12 (5)	N1—C6—C5	119.4 (5)
Cl3—Cu2—Cl2	110.82 (6)	N1—C6—H6	120.3
Cl3—Cu2—Cl3^ii	103.01 (5)	C5—C6—H6	120.3
Cl2—Cu2—Cl3^ii	119.73 (6)	C3—N7—H7A	114.6
Cl3—Cu2—Cl1	115.89 (6)	C3—N7—H7B	108.7
Cl2—Cu2—Cl1	103.51 (5)	H7A—N7—H7B	134.7
Cl3^ii—Cu2—Cl1	104.32 (5)	N1—C8—C9	109.9 (4)
Cl3—Cu2—Cu2^ii	52.18 (4)	N1—C8—H8A	109.7
Cl2—Cu2—Cu2^ii	133.23 (6)	C9—C8—H8A	109.7
Cl3^ii—Cu2—Cu2^ii	50.83 (4)	N1—C8—H8B	109.7
Cl1—Cu2—Cu2^ii	123.23 (7)	C9—C8—H8B	109.7
Cu1—Cl1—Cu2	118.67 (6)	H8A—C8—H8B	108.2
Cu1^i—Cl2—Cu2	89.96 (5)	C10—C9—C8	122.8 (4)
Cu2—Cl3—Cu2^ii	76.99 (5)	C10—C9—H9	118.6
C2—N1—C6	121.9 (4)	C8—C9—H9	118.6
C2—N1—C8	118.4 (4)	C10—C9—Cu1	70.3 (3)
C6—N1—C8	119.6 (4)	C8—C9—Cu1	110.6 (3)
N1—C2—C3	121.3 (5)	C9—C10—Cu1	71.6 (3)
N1—C2—H2	119.3	C9—C10—H10A	120.0
C3—C2—H2	119.3	Cu1—C10—H10A	109.5
N7—C3—C4	122.3 (5)	C9—C10—H10B	120.0
N7—C3—C2	120.5 (5)	Cu1—C10—H10B	89.0
C4—C3—C2	117.2 (5)	H10A—C10—H10B	120.0
C3—C4—C5	120.5 (5)
C10—Cu1—Cl1—Cu2	−52.9 (3)	N7—C3—C4—C5	−177.9 (7)
C9—Cu1—Cl1—Cu2	−34.05 (16)	C2—C3—C4—C5	3.1 (9)
Cl2^i—Cu1—Cl1—Cu2	144.79 (6)	C3—C4—C5—C6	−2.2 (11)
Cl3—Cu2—Cl1—Cu1	90.30 (8)	C2—N1—C6—C5	3.3 (9)
Cl2—Cu2—Cl1—Cu1	−31.23 (8)	C8—N1—C6—C5	−178.3 (6)
Cl3^ii—Cu2—Cl1—Cu1	−157.23 (6)	C4—C5—C6—N1	−1.1 (11)
Cu2^ii—Cu2—Cl1—Cu1	150.51 (6)	C2—N1—C8—C9	71.2 (6)
Cl3—Cu2—Cl2—Cu1^i	−156.23 (6)	C6—N1—C8—C9	−107.3 (5)
Cl3^ii—Cu2—Cl2—Cu1^i	84.13 (6)	N1—C8—C9—C10	−93.3 (5)
Cl1—Cu2—Cl2—Cu1^i	−31.35 (6)	N1—C8—C9—Cu1	−172.6 (3)
Cu2^ii—Cu2—Cl2—Cu1^i	146.65 (7)	Cl1—Cu1—C9—C10	−160.6 (3)
Cl2—Cu2—Cl3—Cu2^ii	−129.23 (7)	Cl2^i—Cu1—C9—C10	21.4 (4)
Cl3^ii—Cu2—Cl3—Cu2^ii	0.0	C10—Cu1—C9—C8	118.6 (5)
Cl1—Cu2—Cl3—Cu2^ii	113.23 (7)	Cl1—Cu1—C9—C8	−42.0 (3)
C6—N1—C2—C3	−2.3 (8)	Cl2^i—Cu1—C9—C8	140.0 (3)
C8—N1—C2—C3	179.3 (5)	C8—C9—C10—Cu1	−102.3 (4)
N1—C2—C3—N7	−179.9 (5)	Cl1—Cu1—C10—C9	30.2 (4)
N1—C2—C3—C4	−1.0 (8)	Cl2^i—Cu1—C10—C9	−167.6 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N7—H7A···Cl1^iii	0.83	2.83	3.618 (5)	158
N7—H7B···Cl2^iv	0.93	2.75	3.629 (6)	160

Symmetry codes: (iii) x−1, y, z−1; (iv) x−1, y, z.