A new three-dimensional anionic cadmium(II) dicyanamide network

A new cadmium dicyanamide complex, poly[tetra­methyl­phos­pho­nium [μ-chlorido-di-μ-dicyanamido-κ⁴N¹:N⁵-cad­mium(II)]], [(CH₃)₄P][Cd(NCNCN)₂Cl], was synthesized by the reaction of tetra­methyl­phospho­nium chloride, cadmium nitrate tetra­hydrate and sodium dicyanamide in aqueous solution. In the crystal structure, each Cd^II atom is octa­hedrally coordinated by four terminal N atoms from four anionic dicyanamide (dca) ligands and by two chloride ligands. The dicyanamide ligands play two different roles in the building up of the structure; one role results in the formation of [Cd(dca)Cl]₂ building blocks, while the other links the building blocks into a three-dimensional structure. The anionic framework exhibits a solvent-accessible void of 673.8 ų, amounting to 47.44% of the total unit-cell volume. The cavities in the network are occupied by pairs of tetra­methyl­phospho­nium cations.

S1. Introduction

The engineering of metal–organic polymeric networks to produce compounds with multidimensional network structures is at the forefront of modern research (Palacio & Miller, 2000; Jensen et al., 2000; Batten, 2001). There are numerous reports in which N-donor bridging ligands are used to form infinite polymeric frameworks (Olenyuk et al., 1999; Rosi et al., 2003). In particular, the pseudohalide ligand dicyanamide [dca, N(CN)₂^-] has received considerable attention due to its polydentate character and bridging ability, yielding a variety of novel structures (Batten & Murray, 2003).

A notable feature of metal–dca coordination polymers is the ability of cations to template anionic [M(dca)₃]^- networks (Biswas et al., 2006). The prime cases of previously reported three-dimensional metal dicyanamide networks are the neutral binary systems. MX₂ with X^- = [N(CN)₂]^- and M = Cr²⁺, Mn²⁺, Co²⁺, Ni²⁺ or Cu²⁺ have gained increased inter­est because of the rutile-like structures containing chains of doubly bridged metal atoms with M(NCNCN)M units (Batten et al., 1999; Manson et al., 1999; Kurmoo & Kepert, 1998). On the other hand, the isomorphous (Ph₄E)[Mn(dca)₃] (E = P or As) structures are characterized by two-dimensional anionic sheets composed of metal atoms that are bridged by M(dca)₂M bridges in one direction and single dca bridges in the other (Schlueter et al., 2004, 2005; Raebiger et al., 2001). In the present paper, we report the use of the tetra­methyl­phospho­nium cation as a template for the formation of a new structure. The tetra­methyl­phospho­nium cation was selected because it offers the promise of a closely related series with finely tunable sizes. In particular, in the present title compound, {[(CH₃)₄P][Cd(NCNCN)₂]}_n, (I), a novel corrugated three-dimensional anionic framework has been obtained.

S2. Experimental

S2.1. Synthesis and crystallization

An aqueous solution (10 ml) of tetra­methyl­phospho­nium chloride (0.253 g, 2 mmol) was added slowly to an aqueous solution containing cadmium nitrate tetra­hydrate (0.617 g, 2 mmol) and sodium dicyanamide (0.534 g, 6 mmol) affording a colourless solution. Upon standing at room temperature for several days, suitable colourless single crystals were obtained upon slow solvent evaporation [yield 85%; m.p. 477–478 K (with decomposition)].

S2.2. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. All methyl H atoms were positioned geometrically and refined as riding, with C—H = 0.96 Å and U_iso(H) = 1.2U_eq(C). A soft U^ij similarity restraint was applied tor atoms C23, C43 and N33.

S3. Results and discussion

The independent unit in salt (I) is composed of a Cd^II cation, two dicyanamide and one chloride anions, complemented by an external (CH₃)₄P⁺ counter-ion (Fig. 1).

The Cd^II atom is six-coordinated by four terminal N atoms from four anionic dca ligands and two chloride ligands, adopting a distorted o­cta­hedrally coordinated geometry (Fig. 1). Each Cd^II atom is joined to two neighbouring Cd^II atoms through two single dca2 bridges and to another two Cd^II atoms through a double dca3 bridge and a double chloride bridge, respectively. The Cd—N bond lengths range from 2.313 (3) to 2.368 (3) Å and the cis-N—Cd—N angles range from 86.59 (1) to 90.79 (1)° , with a trans angle of 175.20 (11)°, all in good agreement with values found in the other Cd^II complexes with six-coordinated geometry (Biswas et al., 2006). Additionally, the Cd^II atoms do not coordinate linearly to the dicyanamide ligands, with Cd1—N12—C22, Cd1—N13—C23, Cd1—N53ⁱⁱⁱ—C43ⁱⁱⁱ and Cd1—N52ⁱⁱ—C42ⁱⁱ bond angles of 175.8 (3), 173.1 (3), 130.7 (2) and 149.2 (3)°, respectively [symmetry codes: (ii) x-1/2, -y+3/2, z-1/2; (iii) -x+1, -y+1, -z+1]. The N12—C22, C22—N32 and N33—C23 bond lengths (Table 2) indicate triple- and single-bond character, as is typical for bridging [N(CN)₂]^- ligands. All bond lengths and angles within the dicyanamide ligands are typical of the bridging mode, i.e. M—N···C—N—C···N—M.

It is worth noting that there are two types of dca molecules which play different roles in the formation of the three-dimensional network. One, with trailing number 3 (denoted dca3), is involved in the [Cd(dca)Cl]₂ nuclei, while the other (dca2) links these nuclei into a three-dimensional structure (Fig. 2b). The Cd^II atoms are alternately connected in one direction by double chloride bridges and M(dca)₂M bridges, and in the other direction by single dca bridges and chloride bridges. As shown in Fig. 2(a), dca3 double bridges two Cd^II atoms into a dimer, forming a 12-membered Cd₂(dca)₂ ring. In addition, two Cl atoms double bridge two Cd^II atoms, forming a four-membered ring. The Cd···Cd distance across dca2 is 8.323 (2) Å, while the shortest Cd···Cd contact across dca3 is 7.564 (1) Å. This phenomenon of the present compound is different from the two-dimensional anionic cadmium tris-dicyanamide compound (Et₄N)[Cd(N(CN)₂)₃]·0.75H₂O (Biswas et al., 2006), where the metal atoms are connected in one direction by double M(dca)₂M bridges and in the other by single dca bridges. It is also noticeable that the planes of the fused Cd/Cl/Cd/Cl rings in the molecule are strictly parallel along the a axis, with an inter­planar spacing of 6.43 (7) Å.

It should be pointed out that the three-dimensional anionic framework in (I) exhibits a void space of 673.8 ų, 47.44% of the unit-cell volume. Additionally, the tetra­methyl­phospho­nium cations occur in pairs within cavities in this anionic network, and presenting two different orientations, as shown in Fig. 2(b). The distance between the two P atoms is 6.828 (2) Å. This marks a difference with the related ((Ph₄E)[Mn(dca)₃] (E = P or As) structures, where the two-dimensional anionic [Mn(dca)₃]^- sheets are separated by layers of Ph₄E⁺ cations (van der Werff et al., 2001). In the present work, the equivalent two-dimensional network appears somewhat corrugated and stack up effectively and cooperatively forming the covalently linked 3hree-dimensional framework, as illustrated in Fig. 3, while the (intestitial) tetra­methyl­phospho­nium cations do not participate in any significant supra­molecular inter­actions, though are obviously important for stabilizing the structure.

Thus, the dca-based complex (I) described herein presents a new three-dimensional anionic network and analysis suggests that this pseudohalide ligand will continue to be a rich source of inter­esting coordination polymers.

Related literature

For related literature, see: Batten (2001); Batten & Murray (2003); Batten et al. (1999); Biswas et al. (2006); Jensen et al. (2000); Kurmoo & Kepert (1998); Manson et al. (1999); Olenyuk et al. (1999); Palacio & Miller (2000); Raebiger et al. (2001); Rosi et al. (2003); Schlueter et al. (2004, 2005); Werff et al. (2001).

Computing details

Data collection: CrystalClear (Rigaku, 2005); cell refinement: CrystalClear (Rigaku, 2005); data reduction: CrystalClear (Rigaku, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg & Putz, 2005); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. The coordination environment of the Cd^II atom in (I). Displacement ellipsoids are drawn at the 30% probability level. [Symmetry codes: (i) -x+1, -y+1, -z+2; (ii) x-1/2, -y+3/2, z-1/2; (iii) -x+1, -y+1, -z+1.]
	Fig. 2. (a) A single anionic network in the structure of (I). All the H atoms have been omitted for clarity. Note the corrugation of the anionic network. (b) Two cations contained inside a single anionic cavity in the structure of (I).
	Fig. 3. The packing view of coordination polymer of (I). H atoms have been omitted for clarity.

Poly[tetramethylphosphonium [µ-chlorido-di-µ-dicyanamido-κ⁴N¹:N⁵-cadmium(II)]]

Crystal data

(C4H12P)[Cd(C2N3)2Cl]	F(000) = 728
Mr = 371.07	Dx = 1.735 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 8983 reflections
a = 8.8694 (18) Å	θ = 3.0–27.5°
b = 17.827 (4) Å	µ = 1.83 mm^−1
c = 9.4062 (19) Å	T = 298 K
β = 107.25 (3)°	Block, colourless
V = 1420.4 (6) Å^3	0.20 × 0.20 × 0.20 mm
Z = 4

Data collection

Rigaku SCXmini diffractometer	2781 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.031
Graphite monochromator	θmax = 27.5°, θmin = 3.0°
ω scans	h = −11→11
Absorption correction: multi-scan (CrystalClearl Rigaku, 2005)	k = −22→23
Tmin = 0.694, Tmax = 0.701	l = −7→12
9731 measured reflections	3 standard reflections every 180 reflections
3255 independent reflections	intensity decay: none

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)] = 0.031	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.073	H-atom parameters constrained
S = 1.16	w = 1/[σ^2(Fo^2) + (0.0312P)^2 + 0.2889P] where P = (Fo^2 + 2Fc^2)/3
3255 reflections	(Δ/σ)max = 0.002
158 parameters	Δρmax = 0.58 e Å^−3
12 restraints	Δρmin = −0.78 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	0.42282 (3)	0.572939 (11)	0.84954 (2)	0.03673 (9)
Cl1	0.69792 (9)	0.51416 (4)	0.98770 (9)	0.04572 (19)
P1	0.55686 (10)	0.86634 (5)	0.74252 (9)	0.04223 (19)
N12	0.4563 (4)	0.66832 (15)	1.0229 (3)	0.0573 (8)
N32	0.4936 (4)	0.77058 (17)	1.2007 (3)	0.0644 (9)
N52	0.6778 (4)	0.87420 (17)	1.2280 (3)	0.0592 (8)
N13	0.3774 (4)	0.48435 (17)	0.6608 (3)	0.0633 (8)
N33	0.3352 (5)	0.3817 (2)	0.4878 (4)	0.0919 (12)
N53	0.4582 (4)	0.35308 (16)	0.2967 (3)	0.0594 (8)
C11	0.5409 (5)	0.8529 (2)	0.5514 (4)	0.0595 (9)
H11A	0.5424	0.8002	0.5309	0.089*
H11B	0.6280	0.8770	0.5291	0.089*
H11C	0.4436	0.8743	0.4910	0.089*
C21	0.5765 (5)	0.9627 (2)	0.7882 (5)	0.0728 (12)
H21A	0.4857	0.9894	0.7282	0.109*
H21B	0.6698	0.9821	0.7695	0.109*
H21C	0.5845	0.9691	0.8915	0.109*
C31	0.3857 (4)	0.8306 (2)	0.7769 (4)	0.0619 (10)
H31A	0.3916	0.8391	0.8793	0.093*
H31B	0.3777	0.7778	0.7565	0.093*
H31C	0.2944	0.8556	0.7138	0.093*
C41	0.7255 (4)	0.8171 (3)	0.8537 (4)	0.0781 (13)
H41A	0.7389	0.8271	0.9570	0.117*
H41B	0.8176	0.8335	0.8286	0.117*
H41C	0.7110	0.7643	0.8353	0.117*
C22	0.4790 (4)	0.71707 (17)	1.1038 (3)	0.0405 (7)
C42	0.5937 (4)	0.82407 (17)	1.2103 (3)	0.0411 (7)
C23	0.3672 (4)	0.43761 (19)	0.5788 (4)	0.0501 (8)
C43	0.4049 (4)	0.36966 (17)	0.3878 (4)	0.0460 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd1	0.04542 (15)	0.02919 (13)	0.03541 (13)	0.00443 (9)	0.01173 (10)	−0.00156 (8)
Cl1	0.0385 (4)	0.0458 (4)	0.0541 (4)	0.0032 (3)	0.0157 (3)	0.0078 (3)
P1	0.0388 (4)	0.0504 (5)	0.0388 (4)	−0.0001 (3)	0.0137 (3)	−0.0071 (3)
N12	0.073 (2)	0.0403 (15)	0.0601 (18)	−0.0058 (14)	0.0215 (16)	−0.0148 (14)
N32	0.077 (2)	0.0621 (19)	0.069 (2)	−0.0263 (17)	0.0448 (18)	−0.0312 (16)
N52	0.0614 (18)	0.0565 (18)	0.0591 (18)	−0.0183 (15)	0.0170 (15)	−0.0200 (14)
N13	0.084 (2)	0.0556 (18)	0.0516 (17)	−0.0071 (17)	0.0225 (16)	−0.0185 (15)
N33	0.121 (3)	0.078 (2)	0.107 (3)	−0.048 (2)	0.079 (2)	−0.052 (2)
N53	0.085 (2)	0.0469 (16)	0.0573 (18)	−0.0042 (15)	0.0376 (17)	−0.0038 (14)
C11	0.069 (2)	0.065 (2)	0.0481 (19)	−0.0114 (19)	0.0225 (18)	−0.0111 (17)
C21	0.084 (3)	0.059 (2)	0.073 (3)	−0.015 (2)	0.020 (2)	−0.021 (2)
C31	0.055 (2)	0.065 (2)	0.074 (3)	0.0061 (18)	0.0316 (19)	0.019 (2)
C41	0.052 (2)	0.114 (4)	0.060 (2)	0.026 (2)	0.0042 (19)	−0.017 (2)
C22	0.0430 (17)	0.0383 (16)	0.0441 (16)	−0.0044 (13)	0.0189 (14)	−0.0026 (14)
C42	0.0470 (17)	0.0432 (17)	0.0347 (15)	−0.0027 (14)	0.0142 (13)	−0.0122 (13)
C23	0.056 (2)	0.0488 (18)	0.0508 (19)	−0.0079 (15)	0.0239 (16)	−0.0061 (16)
C43	0.061 (2)	0.0310 (15)	0.0517 (18)	−0.0066 (14)	0.0250 (16)	−0.0026 (13)

Geometric parameters (Å, º)

Cd1—Cl1	2.6191 (11)	N33—C43	1.287 (5)
Cd1—Cl1^i	2.6218 (9)	N33—C23	1.289 (4)
Cd1—N12	2.313 (3)	N53—C43	1.134 (4)
Cd1—N13	2.321 (3)	C11—H11A	0.9600
Cd1—N52^ii	2.333 (3)	C11—H11B	0.9600
Cd1—N53^iii	2.368 (3)	C11—H11C	0.9600
P1—C31	1.763 (4)	C21—H21A	0.9600
P1—C21	1.767 (4)	C21—H21B	0.9600
P1—C11	1.777 (3)	C21—H21C	0.9600
P1—C41	1.781 (4)	C31—H31A	0.9600
N12—C22	1.133 (4)	C31—H31B	0.9600
N32—C42	1.288 (4)	C31—H31C	0.9600
N32—C22	1.299 (4)	C41—H41A	0.9600
N52—C42	1.144 (4)	C41—H41B	0.9600
N13—C23	1.120 (4)	C41—H41C	0.9600
N12—Cd1—N13	175.20 (11)	P1—C11—H11A	109.5
N12—Cd1—N52^ii	87.41 (1)	P1—C11—H11B	109.5
N13—Cd1—N52^ii	88.56 (12)	H11A—C11—H11B	109.5
N12—Cd1—N53^iii	90.79 (1)	P1—C11—H11C	109.5
N13—Cd1—N53^iii	86.59 (1)	H11A—C11—H11C	109.5
N52^ii—Cd1—N53^iii	90.06 (11)	H11B—C11—H11C	109.5
N12—Cd1—Cl1	92.20 (8)	P1—C21—H21A	109.5
N13—Cd1—Cl1	91.84 (9)	P1—C21—H21B	109.5
N52^ii—Cd1—Cl1	179.59 (8)	H21A—C21—H21B	109.5
N53^iii—Cd1—Cl1	90.06 (9)	P1—C21—H21C	109.5
N12—Cd1—Cl1^i	90.75 (8)	H21A—C21—H21C	109.5
N13—Cd1—Cl1^i	92.04 (9)	H21B—C21—H21C	109.5
N52^ii—Cd1—Cl1^i	92.47 (8)	P1—C31—H31A	109.5
N53^iii—Cd1—Cl1^i	177.10 (8)	P1—C31—H31B	109.5
Cl1—Cd1—Cl1^i	87.42 (3)	H31A—C31—H31B	109.5
Cd1—Cl1—Cd1^i	92.58 (3)	P1—C31—H31C	109.5
C31—P1—C21	109.5 (2)	H31A—C31—H31C	109.5
C31—P1—C11	108.81 (19)	H31B—C31—H31C	109.5
C21—P1—C11	110.5 (2)	P1—C41—H41A	109.5
C31—P1—C41	109.5 (2)	P1—C41—H41B	109.5
C21—P1—C41	109.4 (2)	H41A—C41—H41B	109.5
C11—P1—C41	109.18 (19)	P1—C41—H41C	109.5
C22—N12—Cd1	175.8 (3)	H41A—C41—H41C	109.5
C42—N32—C22	121.1 (3)	H41B—C41—H41C	109.5
C42—N52—Cd1^iv	149.2 (3)	N12—C22—N32	174.5 (4)
C23—N13—Cd1	173.1 (3)	N52—C42—N32	174.1 (3)
C43—N33—C23	123.7 (3)	N13—C23—N33	171.3 (4)
C43—N53—Cd1^iii	130.7 (2)	N53—C43—N33	173.6 (4)

Symmetry codes: (i) −x+1, −y+1, −z+2; (ii) x−1/2, −y+3/2, z−1/2; (iii) −x+1, −y+1, −z+1; (iv) x+1/2, −y+3/2, z+1/2.