A three-dimensional network of cadmium

The title complex, poly­[bis­[N-(2-amino­ethyl)-N-methyl-1,2-ethane­di­amine]­hexa-μ-thio­cyanato-tricadmium(II) monohydrate], [Cd₃(NCS)₆(medien)₂]_n·nH₂O [medien is N,N-bis(2-amino­ethyl)­methyl­amine, C₅H₁₆N₃], adopts a three-dimensional inorganic polymeric network structure. Two cadmium centres (Cd1 and Cd2) are linked to each other via thio­cyanate bridges. The environment of the Cd1 atom involves only S atoms, making it soft, whereas the environment of the Cd2 atom involves only N atoms, making it hard.

S1. Comment

In attempts to build molecular materials with interesting properties, such as catalysis clathration etc., much attention has been given to the synthesis of one-, two- and three-dimensional extended solids involving cadmium. Rigid bridged ligands are frequently employed to construct these materials (Abrahams et al., 1994; Soma et al., 1994; Fujita et al., 1994; Yuge & Iwamoto, 1995). The ambidentate thiocyanate ion which is usually S-bonded to a soft and N-bonded to a hard metal centre can also act as a bridging bidendate ligand to satisfy the coordination number of the metal ion, although the thiocyanate anion has not been widely used in the construction of inorganic polymeric networks. In order to synthesize uncharged three-dimensional polymers where channels remain unblocked by anions and free for solvent inclusion, we have chosen cadmium(II) thiocyanate as an effective building block. Cadmium is well suited for this as its d¹⁰ configuration permits a wide variety of symmetries and coordination numbers. Recently, we reported the syntheses of the inorganic polymer [Cd₃(dien)₂(µ-NCS)₆]_n^.nH₂O (dien is diethylenetriamine), (II) (Mondal et al., 1999), by utilizing fully the bridging potential of the anion. The structure of complex (II) is a polymeric network which contains solvent-filled channels. Channel-containing solids have been and continue to be investigated intensively because of their potential applications, viz. as heterogeneous catalysts and molecular sieves. As part of a continuing investigation into control over the channels, we are currently studying the corresponding cadmium compounds. In this paper, we report the structure of the title Cd^II complex (I), where medien [medien is N,N-bis(2-aminoethyl)methylamine] ligands replace the dien ligands of complex (II).

The structure determination of (I) reveals that the polymer has the stoichiometry [Cd₃(µ-NCS)₆(medien)₂]^.H₂O, with the occurrence of infinite Cd2—N1—C1—S1—Cd1— zigzag chains forming a three-dimensional network. Water molecules are accommodated in interstitial sites which are nearly rectangular and have a volume of 341.0 ų (Spek, 1998). Each Cd1 atom is connected to six Cd2 atoms by thiocyanate bridges. Three N1 atoms, two symmetry-related N2 atoms and one N3 atom complete the CdN₆ chromophore. The geometry around the Cd1 atom is a trigonally distorted octahedron and that around the Cd2 atom is a distorted octahedron.

It should be noted that each Cd2 atom, coordinated by the N atoms of the medien ligand, is invariably linked with the hard N atom of the thiocyanate ion. In other words, the N atoms of the medien ligand `harden' Cd2 and so the thiocyanate bonds to it preferentially through the N atom. Conversely, the soft end of each thiocyanate ion (i.e. the S atom) is cordinated to Cd1 making it `soft'. Thus, the thiocyanate S atoms are clubbed together around Cd1. Each Cd ion is coordinated by N– or S-donor atoms only, and both hard and soft metal centres are generated in the same compound. There are six branches emanating from the Cd1 centre. In each branch, Cd2 is connected to Cd1 via thiocyanate bridges. Every such Cd2 atom produces two other branches which are connected via an thiocyanate bridge to two other Cd1 atoms, each of which in turn produces five other branchings. The sequence in one branch can be written as Cd1—S1—C1—N1—Cd2—N1—C1^vi—S1^vi—Cd1^vi [symmetry code: (vi) 1 − x, z − 1/2, 3/2 − z]. The Cd2—N and Cd1—S distances are comparable to corresponding values in analogous octahedrally coordinated Cd complexes. The thiocyanate ligands are almost linear [177.7 (10)°]. Other bond distances and angles in the ligand are close to expected values.

S2. Experimental

Bis(2-aminoethyl)methylamine (2 mmol) in methanol was added dropwise with stirring to Cd(NCS)₂ (3 mmol) dissolved in methanol (10 ml). A sticky oily layer separated at the bottom of the container. The supernatant solution was filtered and the filtrate was kept in a CaCl₂ desiccator for a few days at \approx 300 K giving the title polymer as shining transparent crystals in 34% isolated yield. Elemental analyses supported the unusual stoichiometry of the compound.

S3. Refinement

Since the site symmetry of Cd2 is 3, three sites of coordinating thiocyanate N1 atoms are accordingly related by symmetry. The primary N atoms, N2 and the secondary N3 atoms are in general positions, there being three symmetry-related sites for each of them. These six sites (3 + 3) were envisaged to be occupied by three groups of two N2 atoms with occupancy 2/3 and one N3 atom with occupancy 1/3 leading to a threefold disorder about the [111] direction. Although the geometry of this model looked reasonable at the isotropic level of refinement, the R1 value of ~0.25 was too high and there were many peaks in the difference map which could not be incorporated in the model. A twin model was then proposed such that the crystal is composed of two twin domains with the reciprocal lattices of these two components being coincident: I(hkl) = (1-α)I(hkl) + αI(hk¯l). In SHELXL93 (Sheldrick, 1993), this is incorporated into the least-squares refinement by the twin matrix (010/100/001). Application of this twin law in the isotropic refinement resulted in a drastic drop in the R1 factor to 0.118. Anisotropic refinement was carried out for all non-H atoms, except for the disordered water O atom, with DFIX constraints for the C—N and C—C distances of the medien ligand and EADP constraints for the C2 and C3 atoms. The water H atoms were located from a difference synthesis but their positions were not refined. Other H atoms were allowed to ride on their attached C or N atoms. At convergence, the value for the BASF(α) parameter was 0.4883.

Computing details

Data collection: XSCANS (Siemens, 1995); cell refinement: XSCANS; data reduction: SHELXTL (Sheldrick, 1995); program(s) used to solve structure: SHELXS86 (Sheldrick, 1985); program(s) used to refine structure: SHELXL93 (Sheldrick, 1993); molecular graphics: ZORTEP (Zsolnai, 1995); software used to prepare material for publication: SHELXL93.

Figures

	Fig. 1. A ZORTEP (Zsolnai, 1995) view of the title complex showing the Cd1 and Cd2 octahedra (50% probability level). Only one of the three possible orientations of the medien ligand is shown.
	Fig. 2. A view of [Cd3(µ-NCS)6(medien)2]^.H2O showing the water-molecule-filled channels. For clarity, the medien ligand has been omitted.

poly[Bis((2-aminomethyl)methylamine)(µ-hexathiocyanato) triccadmium(II) 1.0 water solvate

Crystal data

[Cd3(NCS)6(C5H15N3)2]·H2O	Mo Kα radiation, λ = 0.71073 Å
Mr = 938.10	Cell parameters from 27 reflections
Cubic, Pa3	θ = 5.1–12.5°
a = 15.0766 (9) Å	µ = 2.24 mm^−1
V = 3427.0 (4) Å^3	T = 293 K
Z = 4	Octahedron, colourless
F(000) = 1840	0.64 × 0.48 × 0.46 mm
Dx = 1.818 Mg m^−3

Data collection

Siemens P4 diffractometer	902 reflections with I > 2σ(I)
Radiation source: sealed tube	Rint = 0.038
Graphite monochromator	θmax = 25.0°, θmin = 1.4°
ω scans	h = −1→17
Absorption correction: integration (North et al., 1968)	k = −1→17
Tmin = 0.450, Tmax = 0.498	l = −1→17
4244 measured reflections	3 standard reflections every 97 reflections
1010 independent reflections	intensity decay: 3.4%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full with fixed elements per cycle	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.044	H-atom parameters constrained
wR(F^2) = 0.129	Calculated w = 1/[σ^2(Fo^2) + (0.0279P)^2 + 3.3796P] where P = (Fo^2 + 2Fc^2)/3
S = 1.04	(Δ/σ)max = −0.036
1067 reflections	Δρmax = 0.73 e Å^−3
78 parameters	Δρmin = −0.66 e Å^−3
24 restraints	Extinction correction: SHELXL93, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: Patterson	Extinction coefficient: 0.0046 (5)

Special details

Experimental. The Cd and S atoms were located by the Patterson method (SHELX86; Sheldrick, 1985). The rest of the molecule was obtained by standard Fourier methods.

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.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Cd1	0.5	0.5	0.5	0.0426 (3)
S1	0.4740 (2)	0.5231 (2)	0.67669 (13)	0.0625 (6)
C1	0.5476 (6)	0.4550 (6)	0.7179 (5)	0.053 (2)
N1	0.6010 (7)	0.4097 (7)	0.7476 (5)	0.085 (3)
Cd2	0.69516 (4)	0.30484 (4)	0.80484 (4)	0.0719 (4)
N2	0.7884 (8)	0.1908 (9)	0.8798 (8)	0.066 (3)	0.6667
H1N	0.8307	0.2149	0.9144	0.080*	0.6667
H2N	0.7560	0.1519	0.9114	0.080*	0.6667
N3	0.7286 (14)	0.2102 (12)	0.6986 (11)	0.063 (6)	0.3333
C2	0.824 (2)	0.1529 (19)	0.8012 (12)	0.165 (9)	0.6667
H2A	0.8582	0.1016	0.8185	0.197*	0.6667
H2B	0.8644	0.1956	0.7759	0.197*	0.6667
C3	0.7593 (18)	0.1229 (12)	0.7255 (18)	0.165 (9)	0.6667
H3A	0.7903	0.0924	0.6781	0.197*	0.6667
H3B	0.7114	0.0860	0.7475	0.197*	0.6667
C4	0.6535 (18)	0.174 (3)	0.651 (3)	0.086 (10)	0.3333
H4A	0.5995	0.1971	0.6752	0.103*	0.3333
H4B	0.6536	0.1105	0.6557	0.103*	0.3333
H4C	0.6576	0.1904	0.5893	0.103*	0.3333
O	−0.014 (6)	0.038 (4)	−0.039 (5)	0.092 (14)*	0.1667
H1W	0.0100	0.0515	0.0026	0.110*	0.1667
H2W	−0.0026	−0.0100	−0.0515	0.110*	0.1667

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd1	0.0426 (3)	0.0426 (3)	0.0426 (3)	0.0007 (3)	0.0007 (3)	0.0007 (3)
S1	0.0707 (15)	0.0698 (14)	0.0470 (10)	0.0075 (10)	0.0039 (12)	−0.0050 (12)
C1	0.060 (5)	0.062 (5)	0.039 (4)	−0.010 (4)	−0.009 (4)	0.009 (4)
N1	0.098 (7)	0.096 (7)	0.060 (5)	−0.012 (6)	−0.012 (5)	0.013 (5)
Cd2	0.0719 (4)	0.0719 (4)	0.0719 (4)	0.0154 (3)	0.0154 (3)	−0.0154 (3)
N2	0.070 (8)	0.067 (7)	0.063 (7)	−0.006 (7)	−0.010 (6)	0.013 (7)
N3	0.091 (15)	0.065 (14)	0.031 (9)	−0.006 (12)	−0.005 (11)	−0.022 (9)
C2	0.192 (17)	0.140 (13)	0.162 (16)	0.087 (13)	−0.026 (14)	−0.033 (13)
C3	0.192 (17)	0.140 (13)	0.162 (16)	0.087 (13)	−0.026 (14)	−0.033 (13)
C4	0.050 (14)	0.12 (2)	0.091 (19)	0.008 (16)	−0.046 (14)	−0.054 (18)

Geometric parameters (Å, º)

Cd1—S1^i	2.715 (2)	Cd2—N3^vii	2.20 (2)
Cd1—S1^ii	2.715 (2)	Cd2—N1^vii	2.293 (10)
Cd1—S1^iii	2.715 (2)	Cd2—N1^vi	2.293 (10)
Cd1—S1	2.715 (2)	Cd2—N2^vii	2.492 (12)
Cd1—S1^iv	2.715 (2)	Cd2—N2	2.492 (12)
Cd1—S1^v	2.715 (2)	Cd2—N2^vi	2.492 (12)
S1—C1	1.634 (9)	N2—C2	1.42 (2)
C1—N1	1.148 (12)	N3—C3^vii	1.41 (2)
N1—Cd2	2.293 (10)	N3—C4	1.45 (2)
Cd2—N3	2.203 (17)	N3—C3	1.45 (2)
Cd2—N3^vi	2.20 (2)	C2—C3	1.56 (2)
S1^i—Cd1—S1^ii	88.04 (10)	N3^vi—Cd2—N2^vii	74.1 (6)
S1^i—Cd1—S1^iii	91.97 (10)	N3^vii—Cd2—N2^vii	75.7 (6)
S1^ii—Cd1—S1^iii	180.0	N1^vii—Cd2—N2^vii	174.6 (4)
S1^i—Cd1—S1	88.03 (10)	N1—Cd2—N2^vii	81.3 (4)
S1^ii—Cd1—S1	91.97 (10)	N1^vi—Cd2—N2^vii	84.4 (4)
S1^iii—Cd1—S1	88.03 (10)	N3—Cd2—N2	75.7 (6)
S1^i—Cd1—S1^iv	91.97 (10)	N3^vii—Cd2—N2	74.1 (6)
S1^ii—Cd1—S1^iv	88.03 (10)	N1^vii—Cd2—N2	84.4 (4)
S1^iii—Cd1—S1^iv	91.97 (10)	N1—Cd2—N2	174.6 (4)
S1—Cd1—S1^iv	180.0	N1^vi—Cd2—N2	81.3 (4)
S1^i—Cd1—S1^v	180.0	N2^vii—Cd2—N2	100.3 (4)
S1^ii—Cd1—S1^v	91.97 (10)	N3—Cd2—N2^vi	74.1 (6)
S1^iii—Cd1—S1^v	88.03 (10)	N3^vi—Cd2—N2^vi	75.7 (6)
S1—Cd1—S1^v	91.97 (10)	N3^vii—Cd2—N2^vi	40.3 (6)
S1^iv—Cd1—S1^v	88.03 (10)	N1^vii—Cd2—N2^vi	81.3 (4)
C1—S1—Cd1	101.2 (3)	N1—Cd2—N2^vi	84.4 (4)
N1—C1—S1	177.7 (10)	N1^vi—Cd2—N2^vi	174.6 (4)
C1—N1—Cd2	172.8 (9)	N2^vii—Cd2—N2^vi	100.3 (4)
N3—Cd2—N1^vii	144.7 (6)	N2—Cd2—N2^vi	100.3 (3)
N3^vi—Cd2—N1^vii	111.3 (6)	C2—N2—Cd2	96.3 (12)
N3^vii—Cd2—N1^vii	108.3 (5)	C3^vii—N3—C4	96 (3)
N3—Cd2—N1	108.3 (5)	C3^vii—N3—C3	111 (3)
N3^vi—Cd2—N1	144.7 (6)	C4—N3—C3	93 (3)
N3^vii—Cd2—N1	111.3 (6)	C3^vii—N3—N2^vii	115 (2)
N1^vii—Cd2—N1	93.8 (3)	C3^vii—N3—Cd2	119.3 (12)
N3—Cd2—N1^vi	111.3 (6)	C4—N3—Cd2	115.3 (19)
N3^vi—Cd2—N1^vi	108.3 (5)	C3—N3—Cd2	117.2 (11)
N3^vii—Cd2—N1^vi	144.7 (6)	N2—C2—C3	120 (2)
N1^vii—Cd2—N1^vi	93.8 (3)	N3—C3—C2	98.0 (17)
N1—Cd2—N1^vi	93.8 (3)

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