A novel two-dimensional network cadmium(II) coordination polymer containing one 1,4-bis­(1,2,4-triazol-1-yl)butane and double dicyanamide bridges

In the crystal structure of the title complex, poly[μ-1,4-bis­(1,2,4-triazol-1-yl)butane-di-μ-1,5-dicyanamido-cadmium(II)], [Cd(C₂N₃)₂(C₈H₁₂N₆)]_n or [Cd(dca)₂(btb)]_n, where dca is dicyanamide and btb is 1,4-bis­(1,2,4-triazol-1-yl)butane, each Cd^II atom occupies a center of symmetry and is in a six-coordinated distorted octa­hedral environment. Four N atoms from four dca ligands fill the equatorial positions, and two N atoms from two btb ligands occupy the axial positions. The dca ligands adopt an end-to-end coordination mode and link the Cd^II atoms to form a 12-membered Cd(dca)₂Cd ring, and neighboring rings extend along the b axis to form a [Cd(dca)₂]_n chain. The btb ligands, acting as bridging bidentate ligands, link the Cd^II atoms of adjacent one-dimensional [Cd(dca)₂]_n chains, forming a rhombic two-dimensional network.

S1. Comment

Metal coordination polymers with multidimensionality have attracted great interest in coordination chemistry because of their intriguing structural topologies and their interesting applications as functional materials (Batten & Robson, 1998; Blake et al., 1999).

The structural motifs of coordination polymers rest on several factors, such as the central atom, the performance of the ligands, the counter-ions, the solvent systems and the reaction conditions. The ligand is no doubt the key factor of manipulating the topologies of the coordination polymers. A flexible ligand, which can adopt various conformations, may induce coordination polymers with novel topologies or supramolecular isomers (Carlucci et al., 2004; Li et al., 2005).

The dicyanamide ligand, [N(CN)₂]^-, is a remarkably versatile building block for the construction of coordination polymers (Riggio et al., 2001; Li et al., 2003). However the structurally characterized cadmium(II) dicyanamide complexes are relatively few (Luo, Hong, Cao et al., 2002; Luo, Hong, Weng et al., 2002; Luo et al., 2003; Gao et al., 2002). The combination of the flexible ligand 1,4-bis(1,2,4-triazol-1-yl)butane (btb) and dicyanamide (dca) can give rise to novel motifs. In the present work, we report the crystal structure of a novel two-dimensional network polymer, viz. [Cd(dca)₂(btb)]_n, (I).

The structure of (I) consists of uniform neutral chains in which neighboring Cd^II atoms are connected through two end-to-end dca bridges, and btb ligands link the chains forming a two-dimensional network (Fig. 1). Each Cd^II atom occupies a center of symmetry. The coordination geometry of the Cd^II atom is distorted octahedral, being coordinated by four N atoms of four dca ligands in the equatorial plane and two N atoms of the triazole rings of two btb ligands at the axial positions. This coordination environment is similar to those observed in [Cd(dca)₂(bpp)]_n, (II) [bpp is 1,3-bis(4-pyridyl)propane; Gao et al., 2002], and [Cd(dca)₂(dadpm)]_n (dadpm is 4,4^/-diaminodiphenylmethane; Luo et al., 2003). The N—Cd—N bond angles are in the range 89.50(6)–91.29 (6)°, close to 90°. The Cd—N_dca bond lengths and Cd—N_btb bond lengths (Table 1) in (I) are similar to corresponding values reported in [Cd(dca)₂(bpp)]_n and [Cd(dca)₂(dadpm)]_n.

The dca ligand adopts an end-to-end coordination mode. Two dca ions link two Cd^II atoms to form a 12-membered Cd(dca)₂Cd ring, and neighboring rings share Cd^II atoms to form a [Cd(dca)₂]_n chain along the b axis. The Cd···Cd distance in these chains is 7.627 (2) Å, corresponding to the b axis translation, which is similar to the corresponding distances 7.597 Å in [Cd(dca)₂(dadpm)]_n (Luo et al., 2003) and 7.67 Å in [Cd(dca)₂(pyridine)₂]_n (Luo, Hong, Weng et al., 2002).

Free dca possesses C_2v symmetry, while dca in (I) possesses pseudo-C_2v symmetry, with the nitrile C—N bond lengths of 1.146 (3) Å (for N5—C5) and 1.152 (3) Å (for N6—C6). The C5—N4—C6 bond angle is 121.75 (19)°, corresponding to an amide N atom with sp²-hybrid orbitals; the N5—C5—N4 and N6—C6—N4 angles are 173.1 (2) and 172.8 (2)°, respectively, corresponding to atoms N5, C5, C6 and N6 having sp-hybridization.

Each btb ligand has an extended geometry in which the N(CH₂)₄N chain has an all anti geometry and has its plane steeply inclined, by 80.0 (2)°, to the triazole ring planes. The r.m.s. deviation of the triazole ring atoms from the mean plane is 0.0031 (11) Å.

The btb ligands, acting as bridging bidentate ligands, link the Cd^II atoms of adjacent one-dimensional [Cd(dca)₂]_n chains, resulting in a rhombic two-dimensional network. The Cd···Cd distance between Cd atoms separated by a btb ligand is 14.304 (3) Å. The two-dimensional sheets are stacked in parallel along the a axis (Fig. 2). The shortest Cd···Cd distance between adjacent sheets is 6.424 (2) Å, corresponding to the a axis translation.

Although some interesting Cd^II–dca complexes have been reported, a Cd^II–dca complex forming such a two-dimensional network has not been observed previously. For example, the structure of (II) consists of uniform sinusoidal chains in which adjacent Cd atoms are triply linked by two dca and one bpp bridges. The intrachain cadmium–cadmium separation of (II) is 7.26 Å, shorter than the value 7.627 (2) Å in (I).

S2. Experimental

A water–methanol solution (20 ml, 1:1 v/v) of btb (0.096 g, 0.50 mmol) and Na(dca) (0.089 g, 1.0 mmol) was added to one leg of an H-shaped tube and a water–methanol solution (20 ml, 1:1 v/v) of Cd(NO₃)₂·4H₂O (0.155 g, 0.5 mmol) was added to the other leg of the tube. Colorless crystals suitable for X-ray analysis were obtained after about two months. The product is stable in ambient atmosphere and insoluble in most common inorganic and organic solvents. Analysis found: C 32.95, H 2.73, N 38.42%; calculated for C₁₂H₁₂CdN₁₂: C 33.00, H 2.77, N 38.49%.

S3. Refinement

H atoms were placed in idealized positions and refined as riding, with C—H distances of 0.95 (triazole) and 0.99 Å (butane), and with U_iso(H) = 1.2 U_eq(C).

Computing details

Data collection: CrystalClear (Rigaku, 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, 1998); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The two-dimensional network of (I), with displacement ellipsoids drawn at the 50% probability level and all atoms of the asymmetric unit labelled. H atoms have been omitted for clarity.
	Fig. 2. A view of the stacked sheets along the a axis in (I).

poly[di-µ-1,5-dicyanamido-µ-1,4-bis(1,2,4-triazol-1-yl)butane-cadmium(II)]

Crystal data

[Cd(C2N3)2(C8H12N6)]	Z = 1
Mr = 436.75	F(000) = 216
Triclinic, P1	Dx = 1.684 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 6.4236 (17) Å	Cell parameters from 2027 reflections
b = 7.627 (2) Å	θ = 3.1–25.4°
c = 9.814 (3) Å	µ = 1.29 mm^−1
α = 104.424 (6)°	T = 193 K
β = 96.634 (2)°	Block, colorless
γ = 108.810 (5)°	0.34 × 0.22 × 0.16 mm
V = 430.6 (2) Å^3

Data collection

Rigaku Mercury CCD diffractometer	1565 independent reflections
Radiation source: fine-focus sealed tube	1561 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.016
ω scans	θmax = 25.4°, θmin = 3.1°
Absorption correction: multi-scan (Jacobson, 1998)	h = −7→7
Tmin = 0.668, Tmax = 0.820	k = −9→8
4239 measured reflections	l = −11→11

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)] = 0.017	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.045	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0301P)^2 + 0.1146P] where P = (Fo^2 + 2Fc^2)/3
1565 reflections	(Δ/σ)max = 0.001
116 parameters	Δρmax = 0.51 e Å^−3
0 restraints	Δρmin = −0.54 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
Cd1	1.0000	0.0000	0.0000	0.02069 (8)
N1	0.6758 (2)	0.1760 (2)	0.35438 (16)	0.0202 (3)
N2	0.7938 (3)	0.0952 (2)	0.42601 (17)	0.0252 (3)
N3	0.8720 (3)	0.0788 (2)	0.20759 (16)	0.0223 (3)
N4	0.6464 (4)	0.3633 (3)	−0.2021 (2)	0.0507 (6)
N5	0.7972 (3)	0.1544 (3)	−0.10310 (19)	0.0309 (4)
N6	0.6867 (3)	0.6989 (2)	−0.08579 (19)	0.0312 (4)
C1	0.5097 (3)	0.2488 (3)	0.4144 (2)	0.0231 (4)
H1A	0.4675	0.1923	0.4923	0.028*
H1B	0.3724	0.2037	0.3381	0.028*
C2	0.5937 (3)	0.4681 (3)	0.4739 (2)	0.0224 (4)
H2A	0.6428	0.5265	0.3981	0.027*
H2B	0.7247	0.5143	0.5550	0.027*
C3	0.9080 (3)	0.0378 (3)	0.3329 (2)	0.0240 (4)
H3	1.0071	−0.0267	0.3518	0.029*
C4	0.7236 (3)	0.1642 (3)	0.2253 (2)	0.0238 (4)
H4	0.6604	0.2104	0.1557	0.029*
C5	0.7325 (3)	0.2603 (3)	−0.1428 (2)	0.0263 (4)
C6	0.6752 (3)	0.5411 (3)	−0.1337 (2)	0.0260 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd1	0.03077 (13)	0.02118 (12)	0.01825 (11)	0.01737 (9)	0.00987 (8)	0.00737 (8)
N1	0.0253 (8)	0.0222 (8)	0.0187 (8)	0.0139 (6)	0.0084 (6)	0.0073 (6)
N2	0.0287 (8)	0.0325 (9)	0.0224 (8)	0.0171 (7)	0.0086 (6)	0.0128 (7)
N3	0.0291 (8)	0.0251 (8)	0.0190 (8)	0.0159 (7)	0.0094 (6)	0.0073 (6)
N4	0.0907 (17)	0.0347 (11)	0.0282 (10)	0.0394 (11)	−0.0132 (10)	0.0020 (8)
N5	0.0426 (10)	0.0282 (9)	0.0300 (9)	0.0224 (8)	0.0056 (7)	0.0110 (8)
N6	0.0376 (10)	0.0235 (9)	0.0347 (10)	0.0142 (7)	0.0044 (7)	0.0101 (8)
C1	0.0251 (9)	0.0262 (10)	0.0249 (10)	0.0149 (8)	0.0133 (7)	0.0085 (8)
C2	0.0251 (9)	0.0255 (10)	0.0210 (9)	0.0139 (8)	0.0086 (7)	0.0066 (7)
C3	0.0268 (10)	0.0297 (10)	0.0248 (10)	0.0175 (8)	0.0096 (7)	0.0130 (8)
C4	0.0309 (10)	0.0300 (10)	0.0194 (9)	0.0192 (8)	0.0101 (7)	0.0097 (8)
C5	0.0359 (11)	0.0229 (10)	0.0195 (9)	0.0142 (8)	0.0022 (8)	0.0023 (8)
C6	0.0317 (10)	0.0277 (11)	0.0228 (9)	0.0154 (8)	0.0006 (8)	0.0113 (8)

Geometric parameters (Å, º)

Cd1—N3	2.2985 (16)	N5—C5	1.146 (3)
Cd1—N5	2.3210 (17)	N6—C6	1.152 (3)
Cd1—N6^i	2.3867 (18)	C1—C2	1.513 (3)
N1—C4	1.326 (2)	C1—H1A	0.9900
N1—N2	1.357 (2)	C1—H1B	0.9900
N1—C1	1.469 (2)	C2—C2^ii	1.531 (3)
N2—C3	1.314 (2)	C2—H2A	0.9900
N3—C4	1.322 (2)	C2—H2B	0.9900
N3—C3	1.355 (2)	C3—H3	0.9500
N4—C6	1.296 (3)	C4—H4	0.9500
N4—C5	1.302 (3)
N3—Cd1—N5^iii	90.50 (6)	N1—C1—H1B	108.9
N3—Cd1—N5	89.50 (6)	C2—C1—H1B	108.9
N3—Cd1—N6^i	89.74 (6)	H1A—C1—H1B	107.7
N5—Cd1—N6^i	91.29 (6)	C1—C2—C2^ii	110.04 (19)
N3—Cd1—N6^iv	90.26 (6)	C1—C2—H2A	109.7
C4—N1—N2	109.89 (15)	C2^ii—C2—H2A	109.7
C4—N1—C1	127.96 (16)	C1—C2—H2B	109.7
N2—N1—C1	121.98 (15)	C2^ii—C2—H2B	109.7
C3—N2—N1	102.71 (15)	H2A—C2—H2B	108.2
C4—N3—C3	103.25 (15)	N2—C3—N3	114.14 (17)
C4—N3—Cd1	125.66 (13)	N2—C3—H3	122.9
C3—N3—Cd1	130.85 (13)	N3—C3—H3	122.9
C6—N4—C5	121.75 (19)	N3—C4—N1	110.00 (16)
C5—N5—Cd1	167.33 (17)	N3—C4—H4	125.0
C6—N6—Cd1^v	131.87 (15)	N1—C4—H4	125.0
N1—C1—C2	113.45 (15)	N5—C5—N4	173.1 (2)
N1—C1—H1A	108.9	N6—C6—N4	172.8 (2)
C2—C1—H1A	108.9
C4—N1—N2—C3	−0.1 (2)	N3^iii—Cd1—N5—C5	−91.3 (8)
C1—N1—N2—C3	175.55 (17)	N6^i—Cd1—N5—C5	178.4 (8)
N5^iii—Cd1—N3—C4	−174.94 (16)	N6^iv—Cd1—N5—C5	−1.6 (8)
N5—Cd1—N3—C4	5.06 (16)	Cd1^v—Cd1—N5—C5	12.9 (7)
N6^i—Cd1—N3—C4	−86.23 (16)	Cd1^vi—Cd1—N5—C5	82.0 (8)
N6^iv—Cd1—N3—C4	93.77 (16)	C4—N1—C1—C2	−81.5 (2)
Cd1^v—Cd1—N3—C4	41.40 (15)	N2—N1—C1—C2	103.71 (19)
Cd1^vi—Cd1—N3—C4	20.80 (11)	N1—C1—C2—C2^ii	176.76 (18)
N5^iii—Cd1—N3—C3	−1.56 (17)	N1—N2—C3—N3	0.7 (2)
N5—Cd1—N3—C3	178.44 (17)	C4—N3—C3—N2	−0.9 (2)
N6^i—Cd1—N3—C3	87.14 (17)	Cd1—N3—C3—N2	−175.40 (13)
N6^iv—Cd1—N3—C3	−92.86 (17)	C3—N3—C4—N1	0.8 (2)
Cd1^v—Cd1—N3—C3	−145.23 (17)	Cd1—N3—C4—N1	175.65 (12)
Cd1^vi—Cd1—N3—C3	−165.8 (2)	N2—N1—C4—N3	−0.5 (2)
N3—Cd1—N5—C5	88.7 (8)	C1—N1—C4—N3	−175.79 (17)

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