Low-dimensional compounds containing cyano groups. II. catena-Poly[[(2,2′-bipyridine-κ²N:N′)(dicyanamido-κN)copper(II)]-μ-dicyanamido-κ²N:N′]

The crystal structure of the title compound, [Cu(C₂N₃)₂(C₁₀H₈N₂)]_n, is formed by neutral zigzag chains of the [–NC–N–CN–Cu{(bpy)N(CN)₂}–NC–N–CN–] type run­ning along the c axis (bpy is 2,2′-bi­pyridine). The Cu atoms in the chains are pentacoordinated in the form of a distorted tetragonal pyramid, with a CuN₅ chromophore. The coordination sites are occupied by two N atoms of one bpy mol­ecule in the basal plane [Cu—N 2.018 (4) and 2.025 (2) Å] and by three terminal N atoms of two dicyan­amide ligands. One of the dicyan­amide ligands is coordinated in a monodentate fashion through a nitrile N atom in the basal plane [Cu—N 1.963 (4) Å]. The second acts as an end-to-end bridging ligand to a neighbouring Cu atom and is coordinated by one nitrile N atom in the basal plane [Cu—N 2.001 (2) Å], while the second nitrile N atom occupies the apical position [Cu—N 2.159 (2) Å] and originates from the bridge connecting another Cu atom. The shortest intrachain Cu...Cu distance is 8.212 (1) Å, as a consequence of the large bridging ligand, whereas the minimum interchain distance between Cu atoms is only 5.77 (7) Å, because of the interdigitation of the chains.

S1. Comment

The dicyanamide anion, [N(CN)₂]^- (dca), can be coordinated to a central metal atom either monodentately, through a nitrile or amide N atom, or as a bidentate, tridentate or even tetradentate bridging ligand, with the participation of two or three donor N atoms. Nevertheless, monodentate coordination of dca through the amide N atom is rather improbable and, to date, no crystal structure of such a compound is known (Kohout et al., 2000). On the other hand, structures of several molecular and ionic compounds with dca monodentately coordinated through the nitrile N atom have been reported. These compounds contain either six-coordinate central atoms and are of the general formula [ML₄(dca)₂], e.g. [Ni(4Meim)₄(dca)₂] (4Meim is 4-methylimidazole; Kožíšek et al., 1996), [Cu(phen]₂(dca)₂] (phen is 1,10-phenanthroline; Potočňák et al., 1995) and [Cu(NITpPy)₂(H₂O)₂(dca)₂] (NITpPy is the nitronyl nitroxide radical; Dasna et al., 2001), or five-coordinate central atoms and have the general formula [ML₄(dca)]X, e.g. [Cu(phen)₂(dca)]C(CN)₃ (Potočňák et al., 1996), [Cu(bpy)₂(dca)]C(CN)₃ (bpy is 2,2'-bipyridine; Potočňák, Dunaj-Jurčo, Mikloš & Jäger, 2001) and [Cu(bpy)₂(dca)]BF₄ (Potočňák, Dunaj-Jurčo, Mikloš et al., 2001), in which L may be four monodentate or two bidentate ligands and X is a -1 anion.

As a consequence of a possible bridging function of dca, there has been unusual interest in this ligand during recent years, especially in connection with the preparation of magnetic materials. Among them, weak ferromagnets of the general formula α-[M(dca)₂], with a three-dimensional rutile-type structure, have attracted great attention because of the ability of dca to act as a molecular-based magnet precursor, with several transition metal ions octahedrally coordinated by tridentate dca ligands (Batten et al., 1998; Jensen, Batten, Fallon, Hockless et al., 1999; Jensen, Batten, Fallon, Moubaraki et al., 1999; Kurmoo & Kepert, 1998; Manson et al., 1998). If the two dca ligands are tetrahedrally coordinated only through the nitrile N atoms, β-isomers of these compounds occur in the form of sheet-like structures (Jensen, Batten, Fallon, Hockless et al., 1999; Jensen, Batten, Fallon, Moubaraki et al., 1999).

When two coordination sites of hexacoordinated metallic centres are occupied by additional blocking ligands, the dca acts as a bidentate bridging ligand coordinated through the nitrile N atoms, and the resulting compounds contain [ML₂(dca)₂] units (L is one bidentate or two monodentate ligands; Manson et al., 1999; Escuer et al., 2000; van Albada et al., 2000; Jäger et al., 2001; Dasna et al., 2001; Sun et al., 2001). All these compounds are one-dimensional and contain chains in which two metallic centres are connected by a pair of dca ligands, forming double bridges. Moreover, if the ligands L can serve as additional bridges between central atoms, the above chains are connected by these ligands, giving a two-dimensional sheet (Jensen, Batten, Fallon, Hockless et al., 1999; Jensen, Batten, Fallon, Moubaraki et al., 1999; Jensen et al., 2001).

The [ML₂(dca)₂] units are also present in another type of one-dimensional structure. This type was previously observed in [M(bpym)(dca)₂]·H₂O (M is Mn, Fe or Co, and bpym is 2,2'-bipyrimidine; Marshall et al., 2000) and is formed by chains in which two hexacoordinate metallic centres are connected by only one bridging dca, whereas the second one remains monodentate. The one-dimensional structure of the title complex, [Cu(bpy)(dca)₂], (I), which we present herein as a part of our study on low-dimensional magnetic materials (Černák et al., 2001), is of this last type, but it contains five-coordinate central atoms and is similar to the very recently published structures of [Cu(dmbpy)(dca)₂] (dmbpy is 5,5'-dimethyl-2,2'-bipyridine; Kooijman et al., 2002) and [Cu(phen)(dca)₂] (phen is 1,10-phenanthroline; Luo et al., 2002). \sch

The structure of (I) (Fig. 1) is formed by neutral zigzag chains of the [–NC—N—CN—Cu{(bpy)N(CN)₂}-NC—N—CN–] type running along the c axis. The coordination sites of the Cu atoms in the chains are occupied by two N atoms of one bpy molecule [Cu1—N10 2.018 (4) and Cu1—N20 2.025 (2) Å] and three nitrile N atoms of two dicyanamide ligands. The shortest bond around the Cu atom is to the monodentately coordinated dicyanamide ligand, with Cu1—N2 1.963 (4) Å. The second dca acts as an end-to-end bridging ligand to a neighbouring Cu atom and is coordinated by one nitrile N atom (N5) at a distance of 2.001 (2) Å, while the second nitrile N atom (N6) originating from the bridge connecting another Cu atom is coordinated at the longest distance, at 2.159 (2) Å.

The chromophore of (I) is thus CuN₅ and the coordination polyhedron adopts the shape of a distorted tetragonal pyramid. Atoms N10 and N20 of the bpy molecule, atom N2 of the monodentate dca and atom N5 of the bridging dca occupy the basal plane, while atom N6 from the second end of the bridging dca is coordinated apically. Relatively small deviations of the bond angles around the Cu atom from the corresponding values for an ideal tetragonal pyramid indicate that the degree of distortion is not dramatic. This is confirmed by the value of the τ parameter (Addison et al., 1984), which is equal to 31.3 (the τ parameter is 100 for an ideal trigonal bipyramid and 0 for an ideal tetragonal pyramid).

As the angle between the two planar pyridine rings of the bpy molecule, originating from possible free rotation of the pyridine rings around their common single C—C bond, is only 5.0 (1)°, the whole bpy molecule is almost planar [the largest deviation of atoms from the mean plane is 0.078 (3) Å For which atom?]. Bond distances and angles within the bpy molecule are normal for aromatic heterocycles (Ref?) and range from 1.327 (4) to 1.401 (4) Å, while the single C—C bond distance is 1.486 (3) Å. The angles within the individual pyridine rings of the bpy molecule range from 118.0 (3) to 121.7 (2)°, while the angles including the two pyridine rings lie in a somewhat larger interval.

There are two independent dca ligands in the structure of (I). Although they differ in ligation, the values of the corresponding bond distances and angles are similar (Table 1). Inspection of the bond lengths shows that none of the three possible canonical formulae (Golub et al., 1986) properly describes the bonding mode of the dicyanamide. Both the N_nitrile≡C distances and the N_amide═C distances are close to N≡C triple (1.15 Å) and N═C double bonds (1.27 Å), respectively. The N_amide—C≡ N_nitrile angles are almost linear, while the values of the C—N_amide—C angles are somewhat larger than 120°. Both dca ligands are perfectly planar, the largest deviation of atoms from the mean plane being 0.009 (3) Å (for C5), and their bonding mode to the Cu atom (C≡N_nitrile—Cu) can be considered as angular.

A similar one-dimensional structure, with one bridging and one terminal dca, has been observed in [M(bpym)(dca)₂]·H₂O (M is Mn, Fe or Co, and bpym is 2,2'-bipyrimidine; Marshall et al., 2000). The complex consists of interdigitated zigzag chains, in which two hexacoordinated metallic centres are connected by one bridging dca ligand. Because of the interdigitation of the chains, the nearest interchain M···M distances are about 2 Å shorter than the nearest intrachain M···M distances, which range from 8.630 Å (Fe) to 8.983 Å (Mn). By analogy, the shortest intrachain Cu1···Cu1 distance in (I) is 8.212 (1) Å, as a consequence of the large bridging ligand, and because of the interdigitation of the chains (Fig. 2), the minimum interchain distance between Cu atoms is 5.77 (7) Å.

S2. Experimental

Crystals of (I) were prepared by mixing a 0.1 M aqueous solution of Cu(BF₄)₂ (5 ml) with a 0.1 M ethanolic solution of bpy (10 ml). To the resulting blue solution, a 0.1 M aqueous/ethanolic solution of KN(CN)₂ (6 ml) was added (all solutions were warmed before mixing). A mixture of blue crystals of [Cu(bpy)(dca)]BF₄ (for the structure, see Potočňák, Dunaj-Jurčo, Mikloš et al., 2001), and a small amount of green crystals of (I) appeared the next day. The crystals were filtered off, dried in air and mechanically separated under a microscope. Elemental analysis of (I): calculated for C₁₄H₈N₈Cu (M_r 351.82): C 47.80, H 2.29, N 31.85%; found: C 47.18, H 2.51, N 31.24%.

S3. Refinement

All H atoms were placed in calculated positions, with C—H = 0.93 Å, and refined using the appropriate riding models, with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: EXPOSE in IPDS (Stoe & Cie, 1999); cell refinement: CELL in IPDS (Stoe & Cie, 1999); data reduction: INTEGRATE in IPDS (Stoe & Cie, 1999); program(s) used to solve structure: SHELXS86 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The molecular structure of (I) with the atom-labelling scheme. Displacement ellipsoids are drawn at the 40% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. The stacking of the chains of (I) viewed down the a axis. H atoms have been omitted for clarity.

catena-Poly[[(2,2'-bipyridine-κ²N:N')(dicyanamide-κN)copper(II)]- µ-dicyanamide-κ²N:N']

Crystal data

[Cu(C10H8N2)(C2N3)2]	F(000) = 708
Mr = 351.82	Dx = 1.633 Mg m^−3
Monoclinic, Cc	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: C -2yc	Cell parameters from 7754 reflections
a = 8.6495 (18) Å	θ = 1.7–26.1°
b = 17.118 (4) Å	µ = 1.54 mm^−1
c = 10.568 (2) Å	T = 220 K
β = 113.85 (2)°	Prism, green
V = 1431.1 (5) Å^3	0.30 × 0.27 × 0.21 mm
Z = 4

Data collection

Stoe IPDS diffractometer	2491 independent reflections
Radiation source: fine-focus sealed tube	2434 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.028
φ scan	θmax = 25.9°, θmin = 2.8°
Absorption correction: numerical FACE in IPDS (Stoe & Cie, 1999)	h = −10→10
Tmin = 0.671, Tmax = 0.776	k = −20→20
5294 measured reflections	l = −12→12

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)] = 0.023	H-atom parameters constrained
wR(F^2) = 0.064	w = 1/[σ^2(Fo^2) + (0.0407P)^2 + 0.6066P] where P = (Fo^2 + 2Fc^2)/3
S = 1.09	(Δ/σ)max < 0.001
2491 reflections	Δρmax = 0.25 e Å^−3
208 parameters	Δρmin = −0.39 e Å^−3
2 restraints	Absolute structure: (Flack, 1983), 1224 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.012 (11)

Special details

Experimental. _diffrn_measurement_method D=70 mm, Φ 0–199.5°, ΔΦ 1.5°, 5 min/rec

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	−0.07395 (2)	−0.183633 (13)	−0.71806 (2)	0.03066 (10)
N10	−0.3290 (5)	−0.18665 (12)	−0.7987 (4)	0.0323 (7)
N20	−0.1092 (3)	−0.30078 (12)	−0.7266 (3)	0.0336 (6)
C11	−0.3984 (3)	−0.25867 (13)	−0.8158 (3)	0.0298 (5)
C12	−0.4277 (4)	−0.12434 (15)	−0.8421 (3)	0.0390 (6)
H12	−0.3785	−0.0752	−0.8326	0.047*
C13	−0.6031 (4)	−0.13072 (19)	−0.9014 (3)	0.0441 (7)
H13	−0.6704	−0.0864	−0.9307	0.053*
C14	−0.6749 (4)	−0.2032 (2)	−0.9161 (4)	0.0443 (7)
H14	−0.7919	−0.2085	−0.9542	0.053*
C15	−0.5725 (3)	−0.26869 (17)	−0.8740 (3)	0.0411 (6)
H15	−0.6195	−0.3184	−0.8845	0.049*
C21	−0.2736 (3)	−0.32352 (13)	−0.7709 (3)	0.0303 (6)
C22	0.0126 (4)	−0.35507 (18)	−0.6876 (3)	0.0447 (7)
H22	0.1248	−0.3395	−0.6572	0.054*
C23	−0.0251 (4)	−0.43418 (18)	−0.6915 (4)	0.0528 (10)
H23	0.0611	−0.4711	−0.6661	0.063*
C24	−0.1886 (5)	−0.45744 (16)	−0.7325 (4)	0.0510 (8)
H24	−0.2142	−0.5102	−0.7321	0.061*
C25	−0.3183 (4)	−0.40172 (15)	−0.7753 (3)	0.0398 (6)
H25	−0.4310	−0.4166	−0.8058	0.048*
C2	0.3182 (4)	−0.17978 (16)	−0.5806 (3)	0.0382 (6)
N2	0.1728 (5)	−0.19182 (16)	−0.6217 (5)	0.0477 (9)
N1	0.4790 (5)	−0.17500 (18)	−0.5413 (5)	0.0586 (10)
C3	0.5685 (4)	−0.11258 (16)	−0.4834 (3)	0.0426 (6)
N3	0.6617 (4)	−0.06218 (15)	−0.4330 (4)	0.0617 (8)
C5	−0.0472 (4)	−0.01411 (18)	−0.6014 (3)	0.0445 (7)
N5	−0.0680 (3)	−0.07777 (15)	−0.6359 (3)	0.0484 (6)
N4	−0.0121 (6)	0.05849 (19)	−0.5707 (4)	0.0804 (12)
C6	−0.0491 (3)	−0.09740 (14)	−0.9821 (3)	0.0338 (5)
N6	−0.0722 (3)	−0.13972 (14)	−0.9090 (3)	0.0437 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.02391 (16)	0.03166 (14)	0.03519 (17)	0.00042 (15)	0.01067 (13)	0.00155 (15)
N10	0.0292 (17)	0.0326 (14)	0.0361 (17)	0.0000 (9)	0.0143 (15)	0.0017 (8)
N20	0.0330 (18)	0.0359 (10)	0.0323 (12)	0.0022 (9)	0.0136 (14)	0.0010 (10)
C11	0.0295 (13)	0.0323 (12)	0.0287 (13)	0.0000 (9)	0.0129 (12)	0.0006 (9)
C12	0.0345 (15)	0.0342 (14)	0.0480 (17)	0.0028 (11)	0.0162 (14)	0.0013 (11)
C13	0.0285 (15)	0.0475 (16)	0.0507 (19)	0.0087 (12)	0.0100 (15)	−0.0040 (13)
C14	0.0211 (15)	0.0587 (17)	0.050 (2)	0.0004 (14)	0.0111 (16)	−0.0101 (16)
C15	0.0275 (14)	0.0446 (15)	0.0487 (18)	−0.0072 (11)	0.0130 (14)	−0.0085 (12)
C21	0.0298 (15)	0.0325 (12)	0.0302 (14)	0.0001 (9)	0.0139 (14)	0.0002 (9)
C22	0.0392 (18)	0.0465 (16)	0.0471 (19)	0.0153 (13)	0.0160 (16)	0.0103 (12)
C23	0.061 (2)	0.0383 (15)	0.060 (3)	0.0210 (13)	0.026 (2)	0.0085 (14)
C24	0.072 (2)	0.0273 (14)	0.055 (2)	0.0046 (14)	0.027 (2)	0.0028 (11)
C25	0.0472 (16)	0.0343 (13)	0.0388 (15)	−0.0038 (11)	0.0182 (14)	0.0005 (11)
C2	0.0282 (16)	0.0410 (16)	0.0415 (18)	0.0040 (10)	0.0102 (15)	0.0007 (10)
N2	0.0279 (19)	0.0478 (17)	0.062 (3)	−0.0015 (11)	0.0133 (18)	−0.0005 (13)
N1	0.0269 (17)	0.0531 (17)	0.087 (3)	0.0008 (12)	0.0139 (18)	−0.0168 (15)
C3	0.0373 (16)	0.0421 (14)	0.0493 (18)	0.0101 (12)	0.0185 (15)	0.0076 (12)
N3	0.0462 (15)	0.0441 (14)	0.080 (2)	−0.0021 (13)	0.0109 (17)	−0.0041 (14)
C5	0.0362 (15)	0.0534 (17)	0.0468 (16)	−0.0083 (12)	0.0198 (14)	−0.0175 (13)
N5	0.0365 (14)	0.0504 (14)	0.0519 (17)	−0.0028 (10)	0.0114 (14)	−0.0183 (11)
N4	0.117 (3)	0.0609 (18)	0.104 (3)	−0.0418 (19)	0.086 (3)	−0.0455 (18)
C6	0.0284 (13)	0.0347 (12)	0.0388 (15)	0.0044 (10)	0.0140 (12)	0.0029 (10)
N6	0.0468 (14)	0.0434 (12)	0.0470 (14)	0.0057 (10)	0.0253 (13)	0.0106 (10)

Geometric parameters (Å, º)

Cu1—N2	1.963 (4)	C15—H15	0.9300
Cu1—N5	2.001 (2)	C21—C25	1.389 (3)
Cu1—N6	2.159 (2)	C22—C23	1.389 (5)
Cu1—N10	2.018 (4)	C22—H22	0.9300
Cu1—N20	2.025 (2)	C23—C24	1.361 (5)
N10—C12	1.327 (4)	C23—H23	0.9300
N10—C11	1.351 (3)	C24—C25	1.401 (4)
N20—C22	1.339 (4)	C24—H24	0.9300
N20—C21	1.362 (4)	C25—H25	0.9300
C11—C15	1.387 (4)	N1—C2	1.283 (5)
C11—C21	1.486 (3)	N1—C3	1.316 (5)
C12—C13	1.392 (4)	N2—C2	1.171 (5)
C12—H12	0.9300	N3—C3	1.154 (4)
C13—C14	1.368 (5)	N4—C5	1.289 (4)
C13—H13	0.9300	N4—C6^i	1.291 (4)
C14—C15	1.386 (5)	N5—C5	1.140 (4)
C14—H14	0.9300	N6—C6	1.134 (3)
N2—Cu1—N5	90.46 (12)	C11—C15—C14	118.7 (3)
N2—Cu1—N10	172.06 (15)	C11—C15—H15	120.6
N5—Cu1—N10	92.19 (10)	C14—C15—H15	120.6
N2—Cu1—N20	93.72 (11)	N20—C21—C25	121.7 (2)
N5—Cu1—N20	153.26 (11)	N20—C21—C11	114.8 (2)
N10—Cu1—N20	80.60 (9)	C25—C21—C11	123.6 (2)
N2—Cu1—N6	95.29 (15)	N20—C22—C23	121.5 (3)
N5—Cu1—N6	94.67 (11)	N20—C22—H22	119.3
N10—Cu1—N6	91.95 (12)	C23—C22—H22	119.3
N20—Cu1—N6	111.18 (11)	C24—C23—C22	119.7 (3)
C12—N10—C11	119.9 (3)	C24—C23—H23	120.1
C12—N10—Cu1	124.5 (2)	C22—C23—H23	120.1
C11—N10—Cu1	115.5 (2)	C23—C24—C25	119.8 (3)
C22—N20—C21	119.3 (2)	C23—C24—H24	120.1
C22—N20—Cu1	126.0 (2)	C25—C24—H24	120.1
C21—N20—Cu1	114.58 (16)	C21—C25—C24	118.0 (3)
N10—C11—C15	121.1 (3)	C21—C25—H25	121.0
N10—C11—C21	114.4 (3)	C24—C25—H25	121.0
C15—C11—C21	124.5 (2)	N2—C2—N1	172.9 (3)
N10—C12—C13	121.6 (3)	C2—N2—Cu1	163.6 (3)
N10—C12—H12	119.2	C2—N1—C3	124.0 (3)
C13—C12—H12	119.2	N3—C3—N1	172.6 (3)
C14—C13—C12	119.0 (3)	N5—C5—N4	173.0 (3)
C14—C13—H13	120.5	C5—N5—Cu1	167.8 (2)
C12—C13—H13	120.5	C6^i—N4—C5	125.3 (3)
C13—C14—C15	119.7 (3)	N6—C6—N4^ii	171.0 (3)
C13—C14—H14	120.2	C6—N6—Cu1	158.2 (2)
C15—C14—H14	120.2

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