A novel five-coordinate cadmium phenanthroline thiosulfate

The structure of the novel cadmium phenanthroline thio­sulfate poly­[[(1,10-phenanthroline-κ²N,N′)­cadmium(II)]-μ₃-thio­sulfato-κ³S:S:O], [Cd(S₂O₃)(C₁₂H₈N₂)]_n, with a pentacoordinated Cd centre, is reported. It forms linear chains built up around a 2₁ axis and is isostructural with the known bi­pyridine homologue. The structure is also compared with a previously reported closely related mono­aqua monohydrated phase, where the Cd²⁺ cation is hexacoordinated. The incidence of weak C—H...O interactions in the determination of its general packing properties is discussed.

S1. Comment

The dithionite anion is quite unstable even in the absence of air and it can gradually decompose, breaking up easily into thiosulfate plus pyrosulfite (Remy, 1956). During an exploration of the Cd⁺²-dithionite-phenanthroline system, and as part of a search for a synthetic route to the elusive cadmium dithionite complexes, we unwittingly obtained the title novel anhydrous five-coordinate cadmium phenanthroline thiosulfate, (I). The compound is polymeric and crystallizes in the form of double chains, or strips, built up around the 2₁ axis running along a. This motif is not unusual, being shared by a number of related compounds, viz. the aqua monohydrated six-coordinate cadmium phenanthroline (phen) thiosulfate, (II) (Baggio et al., 1998) and the anhydrous cadmium bipyridine (bpy) thiosulfate, (III) (Baggio et al., 1997). In spite of belonging to an enanthiomorphic class (222), no definite handedness could be ascribed to the structure of (I), the best model for refinement being a racemic twin with a 0.43 (7):0.57 (7) ratio. \sch

A displacement ellipsoid plot of the ensemble (I) is shown in Fig 1. The bonds to the five-coordinate Cd centre are provided by two N atoms from the chelating dinitrogenated base, and two S atoms and one O atom from three different thiosulfate groups. The anion acts in two different bridging modes: as a short bridge through the terminal S1 atom (shared by two different Cd centres) and as a long bridge through the whole S1—S2—O3 arm. The geometry of the anion is normal for this type of coordination. Comparison of (I) with the closely related structures (II) and (III) reveals that, beyond the overall similarities, there are some minor subtle points differentiating them.

Structure (II) presents a six-coordinate Cd centre surrounded by the same ligands as in (I) but with the sixth place occupied by one aqua molecule and with a stabilizing hydration water molecule. In spite of the obvious differences that the larger coordination number introduces, the general structural trend is the same in both compounds: there are one-dimensional chains built up along one of the crystallographic axes, the axial length along the chains being defined by the doubling of the motif through the 2₁ axis, and with interleaving of the phen groups normal to this axis in the usual gear-like mode. As expected, the larger coordination number in (II) results in an elongation of the coordination bonds (Table 2). The effect is reflected in the concomitant enlargement of the associated cell parameter, which in (II) is ~8% larger than in (I) [7.051 (2) versus 6.520 (1) Å]. The relative weakening of the coordination bonds can be quantitatively analyzed in terms of the `bond valence' (Brown & Altermatt, 1985) associated with each of these interactions, those corresponding to bonds in (II) being consistently smaller than their homologues in (I) (Table 2). In both cases, the sum around the cation (2.013 and 2.045) is consistent with the divalent character of Cd. These differences in coordination strength propagate to the thiosulfate group: the larger involvement in coordination of atom S1 in structure (I) slightly weakens the S1—S2 bond in the anion, and this is reflected in its consequent enlargement and the associated evenness of the S—O bond lengths compared with those in (II) (Table 2).

Compound (III) is the bpy homologue of (I). Although it presents an almost exactly isostructural double chain (see Fig 2 for an overlap view) and a very similar density [2.16, versus 2.15 Mgm⁻³ in (I)], it crystallizes in a different space group (P2₁/n). Even though all the strips run in a unique crystallographic 2₁ screw-axis direction in both unit cells [the a axis in (I) and the b axis in (III)], two different orientations for the strip widths appear in the former (Fig. 3) while a single one appears in the latter, due to the different symmetry-element dispositions. This enables different ways of interaction between neighbouring chains. In fact, the weak C—H···O bonds present in the structures (Table 3) involve some H atoms which exist in just one of the ligands but not in the other. Thus, atom H4 in bpy has no counterpart in phen and atom H5A (C5) in phen has no counterpart in bpy, both H atoms being actively engaged in C—H···O bonds. Thus it seems that it is the different geometry (and, accordingly, the external hydrogen `shield' of each ligand) which favours one or the other packing mode. This is not a novel fact; we have recently reported (Harvey et al., 2003) a very similar situation where the presence (or absence) of some H atoms in the bpy or phen ligands in two otherwise absolutely isostructural compounds determined differences in weak interactions leading to measurable effects on some crystallographic properties, viz. the cell dimensions. In the present case, these modifications are more extensive, involving not only the cell parameters but also the crystal system and space group as well. The planar aromatic groups stack in the usual gear-like mode, leading to the classical 6.5 Å spacing. Here, however, the offset is rather large (Fig. 3), with almost no overlapping areas along the normal to the aromatic planes.

S2. Experimental

In a trial to obtain a cadmium dithionite, a methanolic solution of phenanthroline monohydrate was allowed to diffuse into a water solution of cadmium acetate dihydrate and sodium dithionite (all concentrations being 0.025M). Due to the unplanned dithionite decomposition, colourless prisms of the title thiosulfate, (I), suitable for X-ray diffraction, appeared after a few days.

S3. Refinement

All H atoms in the structure were defined by the stereochemistry and they were accordingly located at their calculated positions riding on their host atoms, with C—H = 0.93 Å and U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1988); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: MSC/AFC Diffractometer Control Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP in SHELXTL/PC (Sheldrick,1994); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A view of the polymeric unit of (I). Displacement ellipsoids are drawn at the 40% probability level and H atoms have been omitted for clarity. The independent part of the structure is shown as full ellipsoids. For symmetry codes, refer to Table 1.
	Fig. 2. A comparison of (I) and (III) through the overlap of the corresponding double chains. Structure (I) is denoted by solid lines and (III) by dashed lines. Note the almost perfect match between chain cores. For symmetry codes, refer to Table 1.
	Fig. 3. A schematic packing view of (I) down the chain direction.

(1,10-phenantholine-κ²N,N')(µ₃-thiosulfato-κ³S:S:O)cadmium(II)

Crystal data

[Cd(S2O3)(C12H8N2)]	F(000) = 792
Mr = 404.72	Dx = 2.148 Mg m^−3
Orthorhombic, P212121	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 25 reflections
a = 6.5200 (13) Å	θ = 7.5–15°
b = 10.172 (2) Å	µ = 2.09 mm^−1
c = 18.871 (4) Å	T = 293 K
V = 1251.6 (4) Å^3	Needle, colourless
Z = 4	0.50 × 0.15 × 0.15 mm

Data collection

Rigaku AFC-7S diffractometer	2013 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.018
Graphite monochromator	θmax = 27.5°, θmin = 2.2°
ω/2θ scans	h = −1→8
Absorption correction: ψ-scan MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1988)	k = −1→13
Tmin = 0.35, Tmax = 0.73	l = −1→24
2276 measured reflections	3 standard reflections every 150 reflections
2093 independent reflections	intensity decay: <3%

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)] = 0.031	H-atom parameters constrained
wR(F^2) = 0.140	w = 1/[σ^2(Fo^2) + (0.0894P)^2 + 7.6222P] where P = (Fo^2 + 2Fc^2)/3
S = 1.01	(Δ/σ)max = 0.008
2093 reflections	Δρmax = 1.21 e Å^−3
182 parameters	Δρmin = −1.04 e Å^−3
0 restraints	Absolute structure: Flack (1983)
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.43 (7)

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.

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

	x	y	z	Uiso*/Ueq
Cd	0.68554 (10)	0.35218 (6)	0.44820 (3)	0.0310 (2)
S1	1.0076 (3)	0.3703 (2)	0.52507 (11)	0.0318 (4)
S2	1.2289 (3)	0.46992 (19)	0.46632 (10)	0.0289 (4)
O1	1.2529 (14)	0.4036 (7)	0.3985 (3)	0.0493 (19)
O2	1.1586 (12)	0.6055 (7)	0.4621 (4)	0.0481 (17)
O3	1.4146 (10)	0.4554 (7)	0.5101 (3)	0.0385 (14)
N1	0.7066 (13)	0.5455 (7)	0.3847 (4)	0.0316 (15)
N2	0.7294 (12)	0.2975 (7)	0.3296 (4)	0.0289 (14)
C1	0.6982 (16)	0.6676 (9)	0.4119 (5)	0.042 (2)
H1A	0.6820	0.6776	0.4606	0.050*
C2	0.7129 (18)	0.7810 (9)	0.3694 (6)	0.047 (3)
H2A	0.7068	0.8643	0.3897	0.057*
C3	0.7361 (17)	0.7667 (11)	0.2989 (6)	0.047 (3)
H3A	0.7453	0.8410	0.2703	0.057*
C4	0.7464 (14)	0.6424 (10)	0.2683 (5)	0.0362 (18)
C5	0.7762 (17)	0.6216 (12)	0.1938 (5)	0.048 (3)
H5A	0.7873	0.6934	0.1635	0.057*
C6	0.7881 (16)	0.4989 (11)	0.1675 (5)	0.043 (2)
H6A	0.8086	0.4878	0.1191	0.052*
C7	0.7702 (14)	0.3843 (10)	0.2118 (4)	0.0347 (19)
C8	0.7736 (17)	0.2551 (11)	0.1851 (5)	0.045 (2)
H8A	0.7885	0.2398	0.1367	0.055*
C9	0.7548 (15)	0.1534 (12)	0.2310 (5)	0.044 (2)
H9A	0.7561	0.0672	0.2146	0.053*
C10	0.7335 (15)	0.1794 (9)	0.3033 (5)	0.038 (2)
H10A	0.7218	0.1086	0.3343	0.046*
C11	0.7437 (13)	0.4027 (9)	0.2851 (4)	0.0292 (17)
C12	0.7343 (13)	0.5335 (9)	0.3127 (5)	0.0303 (18)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd	0.0341 (3)	0.0341 (3)	0.0247 (3)	0.0010 (3)	0.0016 (2)	0.0042 (2)
S1	0.0296 (9)	0.0348 (10)	0.0310 (9)	0.0003 (9)	0.0008 (8)	0.0102 (8)
S2	0.0336 (10)	0.0273 (8)	0.0257 (9)	−0.0017 (8)	0.0018 (8)	0.0011 (7)
O1	0.067 (5)	0.051 (4)	0.030 (3)	−0.008 (4)	0.016 (3)	−0.013 (3)
O2	0.051 (4)	0.035 (3)	0.059 (4)	0.006 (3)	0.003 (4)	0.014 (3)
O3	0.032 (3)	0.046 (3)	0.038 (3)	0.005 (3)	−0.001 (3)	−0.001 (3)
N1	0.034 (4)	0.028 (3)	0.033 (3)	0.004 (3)	−0.002 (3)	0.001 (3)
N2	0.032 (4)	0.027 (3)	0.027 (3)	0.005 (3)	0.003 (3)	0.001 (3)
C1	0.042 (5)	0.042 (5)	0.042 (4)	−0.003 (5)	−0.004 (4)	−0.004 (4)
C2	0.045 (6)	0.023 (4)	0.075 (7)	−0.007 (4)	−0.008 (6)	0.005 (4)
C3	0.040 (6)	0.043 (5)	0.059 (6)	−0.006 (5)	−0.009 (5)	0.009 (5)
C4	0.032 (4)	0.038 (4)	0.039 (4)	0.001 (4)	−0.002 (4)	0.000 (4)
C5	0.043 (5)	0.063 (6)	0.037 (5)	0.012 (5)	0.001 (4)	0.028 (5)
C6	0.038 (5)	0.060 (6)	0.031 (4)	0.003 (5)	−0.006 (4)	0.013 (4)
C7	0.027 (4)	0.051 (5)	0.026 (4)	0.000 (4)	0.001 (3)	0.003 (3)
C8	0.040 (6)	0.061 (6)	0.035 (5)	0.000 (5)	−0.001 (4)	−0.011 (4)
C9	0.034 (4)	0.054 (5)	0.044 (5)	−0.003 (5)	0.001 (4)	−0.026 (5)
C10	0.035 (5)	0.034 (4)	0.046 (5)	0.002 (4)	0.009 (4)	0.009 (4)
C11	0.025 (4)	0.041 (4)	0.022 (3)	0.002 (3)	−0.002 (3)	−0.001 (3)
C12	0.022 (4)	0.036 (4)	0.033 (4)	0.001 (4)	−0.002 (3)	0.007 (3)

Geometric parameters (Å, º)

Cd—S1^i	2.593 (2)	C3—C4	1.393 (15)
Cd—S1	2.559 (2)	C3—H3A	0.9300
Cd—N1	2.306 (7)	C4—C12	1.391 (12)
Cd—N2	2.323 (7)	C4—C5	1.434 (13)
Cd—O3^ii	2.363 (7)	C5—C6	1.345 (16)
S1—S2	2.083 (3)	C5—H5A	0.9300
S2—O2	1.455 (7)	C6—C7	1.439 (13)
S2—O1	1.455 (6)	C6—H6A	0.9300
S2—O3	1.473 (7)	C7—C11	1.407 (12)
N1—C1	1.345 (12)	C7—C8	1.408 (14)
N1—C12	1.376 (11)	C8—C9	1.356 (16)
N2—C10	1.300 (11)	C8—H8A	0.9300
N2—C11	1.364 (11)	C9—C10	1.397 (13)
C1—C2	1.408 (13)	C9—H9A	0.9300
C1—H1A	0.9300	C10—H10A	0.9300
C2—C3	1.347 (17)	C11—C12	1.430 (13)
C2—H2A	0.9300
N1—Cd—S1^i	150.7 (2)	C2—C3—H3A	119.5
N2—Cd—S1^i	91.91 (18)	C4—C3—H3A	119.5
O3^ii—Cd—S1^i	87.55 (18)	C12—C4—C3	118.0 (8)
S1—Cd—S1^i	108.66 (5)	C12—C4—C5	118.8 (9)
N1—Cd—N2	72.4 (2)	C3—C4—C5	123.2 (10)
N1—Cd—O3^ii	85.5 (3)	C6—C5—C4	120.4 (9)
N2—Cd—O3^ii	132.4 (2)	C6—C5—H5A	119.8
N1—Cd—S1	100.6 (2)	C4—C5—H5A	119.8
N2—Cd—S1	117.5 (2)	C5—C6—C7	122.2 (9)
O3^ii—Cd—S1	107.52 (17)	C5—C6—H6A	118.9
S2—S1—Cd	107.57 (10)	C7—C6—H6A	118.9
O2—S2—O1	115.1 (5)	C11—C7—C8	118.6 (9)
O2—S2—O3	112.7 (4)	C11—C7—C6	118.3 (9)
O1—S2—O3	111.0 (5)	C8—C7—C6	123.1 (9)
O2—S2—S1	105.8 (3)	C9—C8—C7	118.8 (9)
O1—S2—S1	108.5 (3)	C9—C8—H8A	120.6
O3—S2—S1	102.8 (3)	C7—C8—H8A	120.6
C1—N1—C12	117.6 (8)	C8—C9—C10	119.3 (10)
C1—N1—Cd	125.9 (6)	C8—C9—H9A	120.3
C12—N1—Cd	116.4 (6)	C10—C9—H9A	120.3
C10—N2—C11	119.3 (7)	N2—C10—C9	123.3 (9)
C10—N2—Cd	126.3 (6)	N2—C10—H10A	118.3
C11—N2—Cd	114.4 (5)	C9—C10—H10A	118.3
N1—C1—C2	122.4 (9)	N2—C11—C7	120.7 (8)
N1—C1—H1A	118.8	N2—C11—C12	120.2 (7)
C2—C1—H1A	118.8	C7—C11—C12	119.2 (8)
C3—C2—C1	118.8 (10)	N1—C12—C4	122.2 (8)
C3—C2—H2A	120.6	N1—C12—C11	116.6 (8)
C1—C2—H2A	120.6	C4—C12—C11	121.2 (8)
C2—C3—C4	120.9 (10)

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