Poly[dimethyl­diphenyl­phospho­nium [di-μ₄-iodido-tetra-μ₃-iodido-penta­copper(I)]]

The title compound, {(C₁₄H₁₆P)[Cu₅I₆]}_n, prepared from the reaction between copper powder, iodine and dimethyl­diphenyl­phospho­nium iodide in hydroxyacetone, features an anion that consists of a continuous two-dimensional Cu–I sheet [Cu—I = 2.5960 (14)–2.6994 (13) Å and Cu—I—Cu = 63.28 (5)–114.25 (5)°]. The cation, which lies on a mirror plane, is a typical dimethyl­diphenyl­phospho­nium ion. The structure shows a strong tendency towards segregation of the inorganic and organic parts of the structure into separate subspaces. The two-dimensional Cu–I sheet displays a pronounced subcell with pseudo-tetra­gonal symmetry that is broken by ordered vacancies on the Cu position. The symmetry is further reduced by the orientation of the inter­leaved organic counter-ion that is inclined with respect to the pseudo-mirror planes defined by the Cu–I sheet normal, perpendicular to the b axis.

S1. Comment

Copper(I) halide complexes are well known for their structural variations. They exist in several different oligo- and polymeric forms from discrete anion complexes to infinite chains and sheets. It is also well known that this wide variation is due to the ability of copper to adopt different local geometries, primarily trigonal planar and tetrahedral coordination. The type of the counter-ion is crucial for stabilizing different complexes. Typically, small counter-ions give rise to infinite chains or two- or three-dimensional Cu–I complexes, but discrete Cu–I anions are formed when a large or bulky counter-ion is employed. Other important facts that influence the type of compound formed is the synthesis temperature and the solvent employed.

The title compound, (I) (Fig. 1), crystallizes in the space group Ama2, but there is a pronounced pseudosymmetry, indicating further centring (Fmm2). This is caused by the peculiar nature of the two rather well separated parts of the structure. The title compound is layered, consisting of anionic nets of the composition {[Cu₅I₆]^-}_2∞ interleaved with organic layers hosting the dimethyldiphenylphosphonium (DMDPP) counter-ions. Unlike in the pure iodide, the organic moieties form a dense herringbone pattern, as might be expected from their shape. The {[Cu₅I₆]^-}_2∞ entity appears to be a new addition to the zoo of Cu–I species.

Naked two-dimensional Cu–I polymeric species are relatively rare. The archetype is found in the trigonal and rhombohedral forms of CuI itself (Keen & Hull, 1995; Shan et al., 2009), where electroneutral double layers display iodide surfaces that are separated by van der Waals gaps. There are also several examples of intercalation compounds with this basic motif (Cariati et al., 2001; Shibaeva & Lobkovskaya, 1988; Wu et al., 2008; Hartl & Brudgam, 1989; Mishra et al., 2007). In the title compound, however, the anionic net has an underlying tetragonal rather than trigonal symmetry. Cu atoms form a defect, almost square-planar arrangement, with iodide above and below, in an arrangement reminiscent of that formed by BiO in BiOCl (Keramidas et al., 1993). Defect-free, the layer would be charge neutral, but every sixth Cu position is missing in a regular manner giving rise to a superstructure in the layer. Along the a direction, the unit cell is trebled by the alternation of defect-free rows of Cu atoms and rows where every second Cu atom is missing. As a consequence, along the c direction the unit cell is doubled due to the alternation of defect-free rows and rows with every third Cu position missing. The missing 1/6 of the Cu positions thus generate a sixfold, 3 × 2 superstructure in the ac plane. To complicate matters further, the DMDPP counter-ions are stacked in a herringbone pattern along the c direction, and the relative positions of these rows are out of step along the a direction, generating a further doubling of the unit cell along a. Thus, overall the result is a 6 × 2 superstructure as seen in both the direct-space image and the reciprocal-space image in Fig. 2.

Since the scattering from the Cu₅I₆ layer completely dominates the diffraction pattern of the compound, this superstructuring is evident in the reconstructed reciprocal-lattice layer perpendicular to [010] in Fig. 2. The symmetry allowed by the defect-free CuI layer is 4/mmm, and the defects lower the local symmetry to mmm. Further, a slight tilting of the DMDPP molecules with respect to the normal of the plane defined by CuI violates the reflection perpendicular to c, and the space-group symmetry is reduced to Ama2. It is notable that the Cu positions are described by larger displacement ellipsoids than the I atoms. This reflects a common phenomenon in Cu–I cluster systems. The size mismatch between Cu and I leads to a large configurational freedom for Cu within the convex hull defined by the I positions. At room temperature, many polymeric species are ionic conductors. The Cu₅I₆ layer is subject to relaxation around the vacancies, and this together with the tendency of the DMDPP counter-ion to form dense, flat layers is probably responsible for the stabilization of this unique form of a bidimensional Cu–I anion. In Fig. 3, the unit-cell packing is shown (projected along c). Cu2 is located at the intersection of a mirror plane perpendicular to a and a pseudo-mirror plane perpendicular to c, facing two defects. There is room for the surrounding iodides to relax into, and since they are all related by symmetry (or pseudosymmetry), Cu2 displays the most homogeneous tetragonal coordination of all the three independent Cu-atom positions in the structure, with two bond distances of 2.652 (1) Å and two of 2.659 (1) Å. The position Cu3 faces Cu atoms in three directions and a defect on one side. The Cu3 position moves towards the defect and, as a consequence, the Cu3I₄ tetrahedron is highly irregular with two short bonds [2.604 (1) and 2.596 (1) Å] and two long bonds [2.691 (1) and 2.699 (1) Å]. Cu1 finally displays the most severe distortions of the tetrahedron. Like Cu3, it is displaced from the mirror plane, avoiding short Cu3···Cu3 contacts. It is the Cu the furthest away from the defects. Like for Cu3, there are two groups of distances, two short and two long, but the spread is larger: 2.603 (1), 2.617 (1), 2.698 (1) and 2.734 (1) Å. The distances from the defect to the surrounding iodides are 2.611 Å, well below the average Cu—I contacts for each of the Cu positions (2.663 Å for Cu1, 2.656 Å for Cu2 and 2.648 Å for Cu3). This indicates that the defects are a necessary condition for the stability of the layer at ambient conditions. It would be interesting to attempt the synthesis of similar compounds with larger, layer-forming counter-ions to dilute the cationic charge to create chemical pressure to reduce the number of defects. The limiting factor in determining the stability of the Cu–I layer may well be Cu—Cu contacts rather than Cu—I contacts. In the title compound, there is a number of short (below 3 Å) Cu···Cu distances. Cu2 and Cu3 each have two such contacts [2.803 (1) and 2.994 (1) Å, respectively] and, as a consequence, Cu1 has three. It may prove hard to increase these numbers significantly.

Related literature

For related literature, see: Cariati et al. (2001); Flack (1983); Hartl & Brudgam (1989); Keen & Hull (1995); Keramidas et al. (1993); Mishra et al. (2007); Shan et al. (2009); Shibaeva & Lobkovskaya (1988); Wu et al. (2008).

S2. Experimental

Dimethyldiphenylphosphonium iodide (3.98 mmol), iodine (5.03 mmol) and copper powder (20.02 mmol) were mixed and heated under reflux in hydroxyacetone (50 ml) under a nitrogen atmosphere. After 4 h, the solution became pale yellow, indicating the transformation of iodine to iodide. The mixture was filtered while hot and the solution kept in a refrigerator. Colourless crystals formed over the course of several days.

S3. Refinement

The structures were solved by charge flipping, giving the I-, Cu-, P- and a major part of the C-atom positions. Subsequently, the remaining C-atom positions were found using difference Fourier analysis. All non-H-atom positions were refined using full-matrix least-squares. Refinement was performed against F². The H atoms were located by geometric methods and were allowed to ride, with methyl C—H = 1.00 Å [U_iso(H) = 1.5U_eq(C)] and phenyl C—H = 0.95 Å [U_iso(H) = 1.2U_eq(C)]. The Flack parameter (Flack, 1983) was calculated, yielding a value close to 1/2, viz. 0.43 (4). Refining the compound as a single crystal in either of the two possible absolute structures, or as a racemic twin, leads to indistinguishable results. In the final refinement, a racemic twin model was used leading to the twin fraction 0.43 (4). The main electron residuals are around I atoms.

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2008); cell refinement: CrysAlis RED (Oxford Diffraction, 2008); data reduction: CrysAlis RED (Oxford Diffraction, 2008); program(s) used to solve structure: Superflip (Oszlányi & Sütő, 2004); program(s) used to refine structure: JANA2000 (Petricek et al., 2000); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: JANA2000 (Petricek et al., 2000).

Figures

	Fig. 1. Overview of the title compound. The a axis is horizontal and the b axis is vertical. All non-H atoms are shown as displacement ellipsoids at the 50% probability level. [Symmetry codes: (i) -1/2+x, 1-y, -1+z; (2i) -1/2+x, 1-y, z; (3i) 1.5-x, y, z; (4i) x, y, -1+z; (6i) 2-x, 1-y, 1+z; (7i) 1-x, 1-y, z; (8i) 2-x, 1-y, z; (9i) 2-x, 1-y, -1+z; (10i) -1/2+x, 1-y, 3+z; (11i) 1-x, 1-y, 1+z; (12i) -1.5-x, y, -1+z.]
	Fig. 2. The diffraction pattern of the title compound displays a pronounced subset of strong reflections (red square) corresponding to the square net of iodides. The smaller black rectangle indicates the true reciprocal cell. The a* direction shows a sixfold superstructure caused by two effects: (i) the absence of every third Cu position along the a direction in every second row along the b direction, as indicated by the triple arrow in black, and (ii) the out-of-step arrangement of the counter-ion herringbone stacks, as indicated by the double arrows in red. The doubling of the cell along c is caused by the Cu defects being localized to every second row of Cu positions, and by the counter-ion stacking. All non-H atoms are shown as displacement ellipsoids at the 50% probability level. [See Fig. 1 for symmetry codes; additionally, (13i) x, 1/2+y, -1/2+z; (14i) x, 1/2+y, 1/2+z; (16i) -1/2+x, 3/2-y, -1/2+z; (18i) 3/2-x, 1/2+y, 1/2+z; (20i) 3/2-x, 1/2-y, -1/2+z.]
	Fig. 3. On the left is shown a packing plot of the structure along c. The grey box signifies the section of the bounded projection along b (a single layer of counter-ions and one Cu–I sheet) shown on the right. For clarity in this projection, the Cu–I network has been cut away around the only counter-ion shown. The atoms are shown as displacement displacement ellipsoids at the 50% probability level. pSee Fig. 1 for symmetry codes; additionally, (5i) 1-x, 1/2-y, -1/2+z; (17i) -1/2+x, 3/2-y, 1/2+z; (19i) -1/2+x, 1/2-y, -1/2+z.]

Poly[dimethyldiphenylphosphonium [di-µ₄-iodido-tetra-µ₃-iodido-pentacopper(I)]]

Crystal data

(C14H16P)[Cu5I6]	F(000) = 2312
Mr = 1294.4	Dx = 3.423 Mg m^−3
Orthorhombic, Ama2	Mo Kα radiation, λ = 0.71069 Å
Hall symbol: A 2 -2a	Cell parameters from 9161 reflections
a = 18.2110 (5) Å	θ = 3.6–34.5°
b = 23.6861 (4) Å	µ = 11.61 mm^−1
c = 5.8206 (1) Å	T = 100 K
V = 2510.70 (9) Å^3	Flake, colourless
Z = 4	0.16 × 0.11 × 0.05 mm

Data collection

Oxford Diffraction Excalibur3 diffractometer with a Sapphire-3 CCD detector	5260 independent reflections
Radiation source: Enhance (Mo) X-ray source	3765 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.070
Detector resolution: 16.5467 pixels mm^-1	θmax = 34.6°, θmin = 3.6°
ω scans	h = −28→28
Absorption correction: gaussian (CrysAlis RED; Oxford Diffraction, 2008)	k = −37→37
Tmin = 0.274, Tmax = 0.593	l = −9→9
45244 measured reflections

Refinement

Refinement on F^2	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.041	Weighting scheme based on measured s.u.'s w = 1/[σ^2(I) + 0.0004I^2]
wR(F^2) = 0.065	(Δ/σ)max = 0.001
S = 1.02	Δρmax = 1.87 e Å^−3
5260 reflections	Δρmin = −2.73 e Å^−3
126 parameters	Absolute structure: Flack (1983)
0 restraints	Absolute structure parameter: 0.43 (4)

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
I1	0.75	0.568480 (18)	0.89346 (16)	0.01258 (17)
I2	0.92261 (2)	0.570810 (14)	1.40745 (16)	0.01377 (12)
I3	0.91865 (2)	0.431453 (13)	0.89358 (11)	0.01282 (12)
I4	0.75	0.441964 (18)	0.38605 (14)	0.01168 (14)
Cu1	0.84638 (4)	0.50594 (4)	1.1367 (3)	0.0198 (3)
Cu2	1	0.5	1.1508 (4)	0.0165 (3)
Cu3	0.84237 (4)	0.50221 (5)	0.6508 (3)	0.0200 (3)
P1	0.75	0.25993 (9)	0.7803 (4)	0.0132 (6)
C1	0.8295 (3)	0.2519 (2)	0.6042 (9)	0.0118 (16)
C2	0.8587 (4)	0.1981 (2)	0.5698 (11)	0.0169 (19)
C3	0.9161 (4)	0.1895 (3)	0.4182 (16)	0.027 (2)
C4	0.9455 (4)	0.2355 (3)	0.2952 (11)	0.021 (2)
C5	0.9157 (4)	0.2892 (3)	0.3302 (12)	0.021 (2)
C6	0.8574 (4)	0.2976 (2)	0.4851 (11)	0.0182 (19)
C11	0.75	0.2071 (4)	1.0072 (17)	0.024 (3)
C22	0.75	0.3275 (3)	0.9172 (18)	0.019 (3)
H2	0.838983	0.16691	0.651847	0.0203*
H3	0.935626	0.152709	0.396929	0.0319*
H4	0.984839	0.230068	0.190376	0.0249*
H5	0.935066	0.320492	0.248086	0.0253*
H6	0.837402	0.334233	0.507649	0.0219*
H11	0.705268	0.212013	1.104853	0.0361*	0.5
H12	0.749795	0.168559	0.937419	0.0361*
H13	0.794938	0.211814	1.104088	0.0361*	0.5
H21	0.705123	0.331295	1.015026	0.0284*	0.5
H22	0.794793	0.331245	1.015434	0.0284*	0.5
H23	0.750084	0.357867	0.797702	0.0284*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
I1	0.0141 (3)	0.00763 (17)	0.0160 (4)	0	0	0.0015 (4)
I2	0.0165 (2)	0.00968 (12)	0.0151 (3)	−0.00011 (13)	0.0003 (3)	0.0009 (2)
I3	0.01413 (19)	0.00834 (12)	0.0160 (3)	0.00002 (12)	−0.0007 (3)	−0.0017 (3)
I4	0.0148 (3)	0.00713 (16)	0.0131 (3)	0	0	0.0029 (3)
Cu1	0.0204 (4)	0.0145 (4)	0.0245 (5)	0.0015 (5)	−0.0007 (6)	−0.0031 (5)
Cu2	0.0168 (5)	0.0131 (4)	0.0197 (5)	−0.0016 (5)	0	0
Cu3	0.0223 (5)	0.0144 (4)	0.0234 (4)	−0.0022 (6)	−0.0014 (7)	0.0031 (5)
P1	0.0156 (12)	0.0097 (9)	0.0142 (11)	0	0	0.0013 (8)
C1	0.010 (3)	0.017 (3)	0.009 (3)	−0.001 (2)	−0.001 (2)	0.002 (2)
C2	0.019 (4)	0.015 (3)	0.017 (3)	−0.004 (2)	0.000 (3)	0.003 (2)
C3	0.027 (4)	0.011 (2)	0.041 (5)	0.004 (2)	0.001 (5)	−0.002 (4)
C4	0.013 (3)	0.029 (3)	0.020 (3)	0.003 (3)	0.004 (3)	−0.004 (3)
C5	0.020 (4)	0.024 (3)	0.019 (3)	−0.001 (3)	−0.004 (3)	0.010 (2)
C6	0.023 (4)	0.015 (3)	0.017 (3)	0.003 (3)	0.001 (3)	0.004 (2)
C11	0.027 (7)	0.029 (5)	0.016 (5)	0	0	−0.002 (4)
C22	0.022 (5)	0.016 (3)	0.019 (5)	0	0	−0.008 (4)

Geometric parameters (Å, º)

I1—Cu1	2.6981 (13)	C1—C6	1.382 (8)
I1—Cu3	2.6997 (13)	C2—C3	1.382 (10)
I2—Cu1	2.6022 (13)	C2—H2	0.950
I2—Cu2	2.6516 (14)	C3—C4	1.408 (10)
I2—Cu3^i	2.6042 (13)	C3—H3	0.950
I3—Cu1	2.6167 (13)	C4—C5	1.398 (9)
I3—Cu2	2.6594 (14)	C4—H4	0.950
I3—Cu3	2.5952 (13)	C5—C6	1.407 (10)
I4—Cu1^ii	2.7356 (13)	C5—H5	0.950
I4—Cu3	2.6908 (14)	C6—H6	0.950
Cu1—Cu2	2.8023 (8)	C11—H11	1.000
Cu1—Cu3	2.830 (3)	C11—H12	1.000
P1—C1	1.785 (6)	C11—H13	1.000
P1—C11	1.819 (10)	C22—H21	1.000
P1—C22	1.789 (8)	C22—H22	1.000
C1—C2	1.395 (8)	C22—H23	1.000
Cu1—I1—Cu1^iii	81.16 (4)	I2^ii—Cu3—I4	111.73 (7)
Cu1—I1—Cu3	63.25 (5)	I2^ii—Cu3—Cu1^ii	54.86 (4)
Cu1—I1—Cu3^iii	111.14 (4)	I2^ii—Cu3—Cu1	120.63 (5)
Cu1^iii—I1—Cu1	81.16 (4)	I3—Cu3—I4	107.70 (4)
Cu1^iii—I1—Cu3	111.14 (4)	I3—Cu3—Cu1^ii	123.37 (5)
Cu1^iii—I1—Cu3^iii	63.25 (5)	I3—Cu3—Cu1	57.47 (4)
Cu3—I1—Cu3^iii	77.08 (4)	I4—Cu3—Cu1^ii	57.22 (4)
Cu3^iii—I1—Cu3	77.08 (4)	I4—Cu3—Cu1	127.22 (5)
Cu1—I2—Cu2	64.46 (3)	Cu1^ii—Cu3—Cu1	175.49 (5)
Cu1—I2—Cu3^i	70.22 (5)	Cu1—Cu3—Cu1^ii	175.49 (5)
Cu2—I2—Cu3^i	102.12 (4)	C1—P1—C1^iii	108.5 (3)
Cu1—I3—Cu2	64.16 (3)	C1—P1—C11	110.1 (3)
Cu1—I3—Cu3	65.79 (5)	C1—P1—C22	110.6 (3)
Cu2—I3—Cu3	102.15 (4)	C1^iii—P1—C1	108.5 (3)
Cu1^ii—I4—Cu1^iv	79.82 (4)	C1^iii—P1—C11	110.1 (3)
Cu1^ii—I4—Cu3	66.98 (5)	C1^iii—P1—C22	110.6 (3)
Cu1^ii—I4—Cu3^iii	114.28 (4)	C11—P1—C22	107.0 (5)
Cu1^iv—I4—Cu1^ii	79.82 (4)	P1—C1—C2	119.3 (4)
Cu1^iv—I4—Cu3	114.28 (4)	P1—C1—C6	120.1 (5)
Cu1^iv—I4—Cu3^iii	66.98 (5)	C2—C1—C6	120.3 (5)
Cu3—I4—Cu3^iii	77.38 (4)	C1—C2—C3	120.9 (5)
Cu3^iii—I4—Cu3	77.38 (4)	C1—C2—H2	119.5
I1—Cu1—I2	109.92 (4)	C3—C2—H2	119.5
I1—Cu1—I3	114.43 (7)	C2—C3—C4	119.9 (6)
I1—Cu1—I4^i	99.51 (3)	C2—C3—H3	120.1
I1—Cu1—Cu2	133.82 (6)	C4—C3—H3	120.1
I1—Cu1—Cu3	58.40 (4)	C3—C4—C5	118.8 (6)
I1—Cu1—Cu3^i	121.65 (5)	C3—C4—H4	120.6
I2—Cu1—I3	117.22 (3)	C5—C4—H4	120.6
I2—Cu1—I4^i	110.37 (7)	C4—C5—C6	121.0 (6)
I2—Cu1—Cu2	58.62 (4)	C4—C5—H5	119.5
I2—Cu1—Cu3	129.59 (5)	C6—C5—H5	119.5
I2—Cu1—Cu3^i	54.92 (4)	C1—C6—C5	119.2 (5)
I3—Cu1—I4^i	103.66 (4)	C1—C6—H6	120.4
I3—Cu1—Cu2	58.66 (4)	C5—C6—H6	120.4
I3—Cu1—Cu3	56.74 (4)	P1—C11—H11	109.5
I3—Cu1—Cu3^i	122.19 (5)	P1—C11—H11^iii	109.5
I4^i—Cu1—Cu2	126.67 (6)	P1—C11—H12	109.5
I4^i—Cu1—Cu3	119.75 (5)	P1—C11—H12^iii	109.5
I4^i—Cu1—Cu3^i	55.80 (4)	P1—C11—H13	109.5
Cu2—Cu1—Cu3	93.06 (7)	P1—C11—H13^iii	109.5
Cu2—Cu1—Cu3^i	89.63 (6)	H11—C11—H12	109.5
Cu3—Cu1—Cu3^i	175.49 (5)	H11—C11—H12^iii	109.8
Cu3^i—Cu1—Cu3	175.49 (5)	H11—C11—H13	109.5
I2—Cu2—I2^v	111.42 (9)	H11^iii—C11—H12	109.8
I2—Cu2—I3	114.031 (12)	H11^iii—C11—H12^iii	109.5
I2—Cu2—I3^v	103.127 (11)	H11^iii—C11—H13^iii	109.5
I2—Cu2—Cu1	56.92 (3)	H12—C11—H13	109.5
I2—Cu2—Cu1^v	125.37 (6)	H12—C11—H13^iii	109.1
I2^v—Cu2—I2	111.42 (9)	H12^iii—C11—H13	109.1
I2^v—Cu2—I3	103.127 (11)	H12^iii—C11—H13^iii	109.5
I2^v—Cu2—I3^v	114.031 (12)	P1—C22—H21	109.5
I2^v—Cu2—Cu1	125.37 (6)	P1—C22—H21^iii	109.5
I2^v—Cu2—Cu1^v	56.92 (3)	P1—C22—H22	109.5
I3—Cu2—I3^v	111.48 (9)	P1—C22—H22^iii	109.5
I3—Cu2—Cu1	57.18 (3)	P1—C22—H23	109.5
I3—Cu2—Cu1^v	120.60 (6)	P1—C22—H23^iii	109.5
I3^v—Cu2—I3	111.48 (9)	H21—C22—H22	109.5
I3^v—Cu2—Cu1	120.60 (6)	H21—C22—H23	109.5
I3^v—Cu2—Cu1^v	57.18 (3)	H21—C22—H23^iii	109.3
Cu1—Cu2—Cu1^v	176.64 (11)	H21^iii—C22—H22^iii	109.5
Cu1^v—Cu2—Cu1	176.64 (11)	H21^iii—C22—H23	109.3
I1—Cu3—I2^ii	105.75 (4)	H21^iii—C22—H23^iii	109.5
I1—Cu3—I3	115.09 (7)	H22—C22—H23	109.5
I1—Cu3—I4	102.62 (3)	H22—C22—H23^iii	109.6
I1—Cu3—Cu1^ii	121.39 (5)	H22^iii—C22—H23	109.6
I1—Cu3—Cu1	58.34 (4)	H22^iii—C22—H23^iii	109.5
I2^ii—Cu3—I3	113.50 (3)

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