Bis(μ-hexa­methyl­enetetr­amine)­bis(aqua­di­bromo­cadmium)­di­aqua­di­bromo­cadmium dihydrate

The title compound, poly­[[di­aqua­di­bromo­cadmium-μ-(1,3,5,7-tetra­aza­tri­cyclo[3.3.1.1^3,7]decane-N¹:N⁵)-aqua­cad­mium-di-μ-bromo-aqua­cadmium-μ-(1,3,5,7-tetra­aza­tri­cyclo[3.3.1.1^3,7]decane-N¹:N⁵)-di-μ-bromo] dihydrate], [Cd₃­Br₆­(C₆­H₁₂­N₄)₂­(H₂O)₄]·­2H₂O, is made up of two-dimensional neutral rectangular coordination layers. Each rectangular subunit is enclosed by a pair of Cd₃(μ₂-Br)₆(H₂O)₃ fragments and a pair of (μ₂-hmt)Cd(H₂O)₂Br₂(μ₂-hmt) fragments as sides (hmt is hexa­methyl­enetetr­amine). The unique Cd^II atom in the Cd₂Br₂ ring in the Cd₃(μ₂-Br)₆(H₂O)₃ fragment is in a slightly distorted octahedral CdNOBr₄ geometry, surrounded by one hmt ligand [2.433 (5) Å], one aqua ligand [2.273 (4) Å] and four Br atoms [2.6409 (11)–3.0270 (14) Å]. The Cd^II atom in the (μ₂-hmt)Cd(H₂O)₂Br₂(μ₂-hmt) fragment lies on an inversion center and is in a highly distorted octahedral CdN₂O₂Br₂ geometry, surrounded by two trans-related N atoms of two hmt ligands [2.479 (5) Å], two trans-related aqua ligands [2.294 (4) Å] and two trans-related Br atoms [2.6755 (12) Å]. Adjacent two-dimensional coordination sheets are connected into a three-dimensional network by hydrogen bonds involving lattice water mol­ecules, and the aqua, bromo and hmt ligands belonging to different layers.

S1. Comment

Hexamethylenetetramine (hmt) as a potential polydendate ligand has been of interest in recent years (Miyamae et al., 1988; Mak, 1984; Pickardt & Droas, 1985). These compounds may exhibit interesting topological structures. We and others have recently reported some interesting two- and three-dimensional non-interpenetrating open-networks constructed µ-4-hmt ligand (Bertelli et al., 1997; Carlucci et al., 1997; Tong et al., 1999). We describe herein the crystal structure of the title compound, (I), with a two-dimensional rectangle-like network, in which hmt acts in a µ₂ bridging mode. \sch

The title complex is made up of two-dimensional neutral layers of rectangular subunits and lattice water molecules. As shown in Fig.1, each rectangular subunit is enclosed by a pair of Cd₃(µ₂-Br)₆(H₂O)₃ fragments and a pair of Cd(H₂O)₂Br₂(µ₂-hmt)₂ fragments as sides. The Cd(H₂O)₂Br₂(µ₂-hmt)₂ fragment has inversion symmetry with octahedral coordination by two trans-related monodentate bromo atoms [Cd1—Br1 2.6755 (12) Å], two trans-related aqua ligands [Cd1—O2W 2.294 (4) Å] and two trans-related nitrogen atoms [Cd1—N2 2.479 (5) Å] from different hmt ligands. The Cd2 atom in Cd₃(µ₂-Br)₆(H₂O)₃ fragment is in a highly distorted octahedral geometry and coordinated by four bromo atoms [2.6409 (11)–3.0270 (14) Å], one aqua [2.273 (4) Å] and one hmt ligand [2.433 (5) Å]. Along the a direction, the Cd^II atoms share common Br atoms at the corners to form Cd(µ₂-Br)₂(H₂O) infinite chains, similar to that in the related compounds (Rogers et al., 1993, 1996; Krishnan et al., 1991). These chains are further interlinked by (µ₂-hmt)-CdBr₂(H₂O)₂-(µ₂-hmt) fragments, resulting in a two-dimensional coordination rectangular layer. The hmt ligand acts in a µ₂-mode and bridges two Cd^II atoms belonging to two types of Cd^II atoms. The Cd—Br(µ₂-mode) bonds are not equivalent. The Cd—Br(µ₂-mode) bonds are largely inequivalent compared to those [2.668 (3) and 2.780 (4) Å] found in a related compound, catena-[(µ₂-nicotinato-O,O',N)-µ₂-aquacadmium(II)] (Zhang et al., 1996).

The structure of (I) differs significantly from that of a closely related compound, namely bis(µ₂-hexamethylenetetramine)bis(diiodocadmium)diaquadiiodocadmium dihydrate, in which the Cd^II atoms have an octahedral or tetrahedral coordinate geometry, resulting in a three-dimensional coordination network (Mak, 1981, 1982; Pickardt, 1981).

It is also noteworthy that the extensive interlayer hydrogen bonds between the adjacent layers may play a role in consolidating the crystal architecture. Each O1W ligand forms one hydrogen bond with a lattice water molecule and one interlayer hydrogen bond with the hmt ligand belonging to the adjacent layer. Each O2W ligand donates only one hydrogen bond, which is with the lattice water molecule. Interestingly, each lattice water molecule forms two acceptor hydrogen bonds with two aqua ligands and two donor hydrogen bonds with two bromo ligands [O1W···O3W 2.812 (7), O2W···O3Wⁱ 2.837 (7), O3W···Br1ⁱⁱ 3.332 (5) and O3W···Br3ⁱⁱⁱ 3.415 (5), O1W···N3ⁱⁱ 2.771 (7), O2W—Br1ⁱ 3.522 (5) Å; symmetry codes: (i) −x, −y, −z; (ii) x, y − 1, z; (iii) x − 1, y, z]. These hydrogen bonds extend the two-dimensional coordination layers into three-dimensional molecular networks (Fig. 2).

S2. Experimental

To a solution (5 cm³) of CdBr₂·4H₂O (1 mmol), a solution (5 cm³) of hmt (1 mmol) was slowly added with stirring at 323 K for 15 min. The resulting solution was allowed to stand in air at room temperature, colorless crystals were deposited within several days (90% yield).

Computing details

Data collection: R3M Software (Siemens, 1990); cell refinement: R3M Software; data reduction: R3M Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 1998); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. ORTEP (Sheldrick, 1998) plot (35% probability displacement ellipsoids) of the coordination layer with rectangular cavities in (I).
	Fig. 2. Perspective view of the molecular packing of (I).

bis(µ₂-hexamethylenetetramine)bis(aquadi(µ₂-bromo)- cadmium)diaquadibromocadmium dihydrate

Crystal data

[Cd3Br6(C6H12N4)2(H2O)4]·2H2O	Z = 1
Mr = 1205.15	F(000) = 566
Triclinic, P1	Dx = 2.533 Mg m^−3
a = 7.577 (2) Å	Mo Kα radiation, λ = 0.71073 Å
b = 8.030 (2) Å	Cell parameters from 25 reflections
c = 13.464 (3) Å	θ = 7.5–15°
α = 76.60 (3)°	µ = 9.63 mm^−1
β = 89.17 (3)°	T = 293 K
γ = 82.60 (3)°	Block, colorless
V = 790.2 (3) Å^3	0.3 × 0.2 × 0.16 mm

Data collection

Siemens R3m diffractometer	2716 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.000
Graphite monochromator	θmax = 27.6°, θmin = 1.6°
ω scan	h = 0→9
Absorption correction: ψ scan semi-empirical (using intensity measurements) absorption based on ψ scan (North et al., 1968)	k = −10→10
Tmin = 0.112, Tmax = 0.214	l = −17→17
3630 measured reflections	2 standard reflections every 150 reflections
3630 independent reflections	intensity decay: none

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)] = 0.043	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.104	Calculated w = 1/[σ^2(Fo^2) + (0.0557P)^2 + 0.0981P] where P = (Fo^2 + 2Fc^2)/3
S = 1.03	(Δ/σ)max = 0.002
3630 reflections	Δρmax = 1.00 e Å^−3
161 parameters	Δρmin = −0.93 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0046 (5)

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	0.0000	0.0000	0.0000	0.02334 (18)
Cd2	0.23094 (7)	−0.43802 (7)	0.44138 (3)	0.02542 (15)
Br1	−0.19458 (11)	0.29096 (11)	0.02279 (6)	0.0431 (2)
Br2	−0.10841 (10)	−0.27189 (10)	0.44681 (6)	0.0362 (2)
Br3	0.58513 (10)	−0.64476 (10)	0.41609 (5)	0.03300 (19)
N1	0.2884 (7)	−0.1805 (7)	0.3157 (3)	0.0187 (11)
N2	0.1977 (7)	−0.0043 (7)	0.1460 (3)	0.0188 (11)
N3	0.2941 (7)	0.1291 (7)	0.2770 (4)	0.0248 (12)
N4	0.5083 (7)	−0.0491 (7)	0.2004 (4)	0.0235 (12)
C1	0.2605 (9)	−0.0233 (9)	0.3558 (4)	0.0258 (14)
H1A	0.3392	−0.0369	0.4132	0.080*
H1B	0.1404	−0.0070	0.3788	0.080*
C2	0.4719 (8)	−0.2008 (9)	0.2789 (5)	0.0235 (14)
H2A	0.4931	−0.3021	0.2519	0.080*
H2B	0.5523	−0.2155	0.3356	0.080*
C3	0.1679 (8)	−0.1577 (8)	0.2264 (4)	0.0197 (13)
H3A	0.0469	−0.1434	0.2483	0.080*
H3B	0.1852	−0.2585	0.1988	0.080*
C4	0.4778 (9)	0.1030 (9)	0.2435 (5)	0.0287 (15)
H4A	0.5584	0.0900	0.2999	0.080*
H4B	0.5006	0.2027	0.1923	0.080*
C5	0.3839 (8)	−0.0262 (9)	0.1142 (4)	0.0239 (14)
H5A	0.4055	0.0742	0.0632	0.080*
H5B	0.4044	−0.1242	0.0841	0.080*
C6	0.1737 (9)	0.1481 (8)	0.1898 (4)	0.0243 (14)
H6A	0.0530	0.1646	0.2117	0.080*
H6B	0.1937	0.2483	0.1382	0.080*
O1W	0.1851 (7)	−0.5399 (6)	0.3011 (3)	0.0309 (11)
H1WA	0.2082	−0.6661	0.2970	0.080*
H1WB	0.0601	−0.5648	0.2914	0.080*
O2W	0.1886 (6)	0.1593 (7)	−0.1054 (3)	0.0368 (12)
H2WA	0.1897	0.2597	−0.1249	0.080*
H2WB	0.1887	0.1225	−0.1597	0.080*
O3W	−0.1538 (7)	−0.5112 (7)	0.2116 (4)	0.0421 (13)
H3WA	−0.1330	−0.4801	0.1439	0.080*
H3WB	−0.2595	−0.5699	0.2300	0.080*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd1	0.0218 (4)	0.0251 (4)	0.0232 (3)	−0.0016 (3)	−0.0004 (2)	−0.0066 (3)
Cd2	0.0284 (3)	0.0250 (3)	0.0238 (2)	−0.0087 (2)	−0.00364 (18)	−0.00442 (19)
Br1	0.0433 (5)	0.0393 (5)	0.0509 (5)	0.0089 (4)	−0.0098 (3)	−0.0258 (4)
Br2	0.0270 (4)	0.0315 (4)	0.0459 (4)	−0.0054 (3)	0.0043 (3)	0.0002 (3)
Br3	0.0347 (4)	0.0340 (4)	0.0324 (3)	−0.0033 (3)	−0.0088 (3)	−0.0119 (3)
N1	0.020 (3)	0.018 (3)	0.019 (2)	−0.004 (2)	−0.0049 (19)	−0.006 (2)
N2	0.019 (3)	0.016 (3)	0.020 (2)	0.001 (2)	−0.0007 (19)	−0.004 (2)
N3	0.031 (3)	0.021 (3)	0.026 (3)	−0.005 (3)	−0.001 (2)	−0.010 (2)
N4	0.017 (3)	0.026 (3)	0.028 (3)	−0.002 (2)	−0.002 (2)	−0.009 (2)
C1	0.034 (4)	0.025 (4)	0.020 (3)	−0.005 (3)	0.000 (2)	−0.006 (3)
C2	0.011 (3)	0.025 (4)	0.034 (3)	0.001 (3)	−0.005 (2)	−0.007 (3)
C3	0.018 (3)	0.023 (3)	0.020 (3)	−0.006 (3)	−0.003 (2)	−0.007 (2)
C4	0.028 (4)	0.031 (4)	0.032 (3)	−0.011 (3)	−0.004 (3)	−0.012 (3)
C5	0.020 (3)	0.027 (4)	0.023 (3)	−0.001 (3)	0.000 (2)	−0.004 (3)
C6	0.030 (4)	0.017 (3)	0.026 (3)	0.000 (3)	−0.004 (2)	−0.005 (3)
O1W	0.039 (3)	0.020 (3)	0.037 (2)	0.002 (2)	−0.012 (2)	−0.014 (2)
O2W	0.035 (3)	0.029 (3)	0.041 (3)	−0.003 (2)	0.010 (2)	0.000 (2)
O3W	0.042 (3)	0.045 (4)	0.041 (3)	−0.001 (3)	−0.003 (2)	−0.016 (3)

Geometric parameters (Å, º)

Cd1—O2W	2.294 (4)	N1—C3	1.483 (7)
Cd1—O2W^i	2.294 (4)	N2—C6	1.467 (8)
Cd1—N2	2.479 (5)	N2—C5	1.469 (8)
Cd1—N2^i	2.479 (5)	N2—C3	1.479 (7)
Cd1—Br1	2.6755 (12)	N3—C4	1.462 (8)
Cd1—Br1^i	2.6755 (12)	N3—C6	1.465 (8)
Cd2—O1W	2.273 (4)	N3—C1	1.469 (8)
Cd2—N1	2.433 (5)	N4—C4	1.460 (9)
Cd2—Br3^ii	2.6409 (11)	N4—C5	1.469 (7)
Cd2—Br2^iii	2.7287 (13)	N4—C2	1.469 (8)
Cd2—Br2	2.7482 (13)	O1W—N3^iv	2.771 (7)
Cd2—Br3	3.0270 (14)	O1W—O3W	2.812 (7)
Br2—Cd2^iii	2.7287 (13)	O2W—O3W^i	2.837 (7)
Br3—Cd2^ii	2.6409 (11)	O3W—Br1^iv	3.332 (5)
N1—C2	1.471 (7)	O3W—Br3^v	3.415 (5)
N1—C1	1.475 (8)
O2W—Cd1—O2W^i	180.0	C2—N1—C1	108.5 (5)
O2W—Cd1—N2	88.47 (17)	C2—N1—C3	107.2 (4)
O2W^i—Cd1—N2	91.53 (17)	C1—N1—C3	109.0 (5)
O2W—Cd1—N2^i	91.53 (17)	C2—N1—Cd2	110.6 (4)
O2W^i—Cd1—N2^i	88.47 (17)	C1—N1—Cd2	112.8 (3)
N2—Cd1—N2^i	180.0	C3—N1—Cd2	108.6 (3)
O2W—Cd1—Br1	90.06 (13)	C6—N2—C5	107.0 (5)
O2W^i—Cd1—Br1	89.94 (13)	C6—N2—C3	108.8 (4)
N2—Cd1—Br1	91.75 (13)	C5—N2—C3	108.3 (5)
N2^i—Cd1—Br1	88.25 (13)	C6—N2—Cd1	116.8 (4)
O2W—Cd1—Br1^i	89.94 (13)	C5—N2—Cd1	109.1 (3)
O2W^i—Cd1—Br1^i	90.06 (13)	C3—N2—Cd1	106.5 (3)
N2—Cd1—Br1^i	88.25 (13)	C4—N3—C6	108.9 (5)
N2^i—Cd1—Br1^i	91.75 (13)	C4—N3—C1	108.7 (5)
Br1—Cd1—Br1^i	180.0	C6—N3—C1	109.1 (5)
O1W—Cd2—N1	83.48 (17)	C4—N4—C5	108.8 (5)
O1W—Cd2—Br3^ii	157.16 (13)	C4—N4—C2	108.7 (5)
N1—Cd2—Br3^ii	91.96 (12)	C5—N4—C2	108.5 (5)
O1W—Cd2—Br2^iii	86.88 (12)	N3—C1—N1	110.9 (5)
N1—Cd2—Br2^iii	167.46 (11)	N4—C2—N1	111.7 (5)
Br3^ii—Cd2—Br2^iii	99.99 (4)	N2—C3—N1	111.5 (5)
O1W—Cd2—Br2	96.00 (13)	N4—C4—N3	110.8 (5)
N1—Cd2—Br2	85.88 (13)	N4—C5—N2	111.7 (5)
Br3^ii—Cd2—Br2	106.02 (4)	N3—C6—N2	112.0 (5)
Br2^iii—Cd2—Br2	87.17 (4)	Cd2—O1W—N3^iv	126.4 (2)
O1W—Cd2—Br3	76.72 (13)	Cd2—O1W—O3W	122.6 (2)
N1—Cd2—Br3	95.03 (13)	N3^iv—O1W—O3W	95.3 (2)
Br3^ii—Cd2—Br3	81.43 (4)	Cd1—O2W—O3W^i	132.2 (2)
Br2^iii—Cd2—Br3	90.53 (4)	O3W^i—O2W—Br1^i	167.6 (2)
Br2—Cd2—Br3	172.48 (3)	O1W—O3W—Br1^iv	118.1 (2)
Cd2^iii—Br2—Cd2	92.83 (4)	O1W—O3W—Br3^v	103.18 (17)
Cd2^ii—Br3—Cd2	98.57 (4)	Br1^iv—O3W—Br3^v	113.62 (16)

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