Tetra-μ3-iodido-tetrakis[(tri-n-butylphosphane-κP)copper(I)]

The title complex, [Cu4I4(C12H27P)4], crystallizes with six molecules in the unit cell and with three independent one-third molecule fragments, completed by application of the relevant symmetry operators, in the asymmetric unit. The tetranuclear copper core shows a tetrahedral geometry (site symmetry 3..). The I atoms also form a tetrahedron, with I⋯I distances of 4.471 (1) Å. Both tetrahedra show an orientation similar to that of a pair of self-dual platonic bodies. The edges of the I-tetrahedral structure are capped to the face centers of the Cu-tetrahedron and vice versa. The Cuface⋯I distances are 2.18 Å (averaged) and the Iface⋯Cu distances are 0.78 Å (averaged). As a geometric consequence of these properties there are eight distorted trigonal–bipyramidal polyhedra evident, wherein each trigonal face builds up the equatorial site and the opposite Cu⋯I positions form the axial site. As expected, the n-butyl moieties are highly flexible, resulting in large elongations of their anisotropic displacement parameters. Some C atoms of the n-butyl groups were needed to fix alternative discrete disordered positions.

The title complex, [Cu 4 I 4 (C 12 H 27 P) 4 ], crystallizes with six molecules in the unit cell and with three independent onethird molecule fragments, completed by application of the relevant symmetry operators, in the asymmetric unit. The tetranuclear copper core shows a tetrahedral geometry (site symmetry 3..). The I atoms also form a tetrahedron, with IÁ Á ÁI distances of 4.471 (1) Å . Both tetrahedra show an orientation similar to that of a pair of self-dual platonic bodies. The edges of the I-tetrahedral structure are capped to the face centers of the Cu-tetrahedron and vice versa. The Cu face Á Á ÁI distances are 2.18 Å (averaged) and the I face Á Á ÁCu distances are 0.78 Å (averaged). As a geometric consequence of these properties there are eight distorted trigonal-bipyramidal polyhedra evident, wherein each trigonal face builds up the equatorial site and the opposite CuÁ Á ÁI positions form the axial site. As expected, the n-butyl moieties are highly flexible, resulting in large elongations of their anisotropic displacement parameters. Some C atoms of the n-butyl groups were needed to fix alternative discrete disordered positions.
Furthermore, complex [n-Bu 3 PCuI] 4 has the largest I-Cu-I angle and the smallest Cu-I-Cu angle as compared to the other complexes (Churchill & Kalra, 1974;Medina et al., 2005). Due to this very strong distortion the structure could be better described as two interpenetrating copper and iodine tetrahedrons.

Refinement
H atoms were only partly located in difference fourier map, because of the strong disordered behaviour of the n-butyl moieties. They are refined with fixed individual displacement parameters using a riding model with C-H ranging [U(H) = 1.2 U eq (C) for methylene groups and [U(H) = 1.5 U eq (C) for methyl groups] from 0.98 to 0.99 Å. In addition, the methyl groups are allowed to rotate but not to tip. A free refinement of the anisotropic displacement parameters of the nbutyl moieties was not possible, so an ISOR = 0.01 instruction for all carbons was established, which solves this problem.
The carbon atoms C17, C18, C21, C28, C37 and C38 were identified as discrete disordered atoms. -C40 were also fixed by the DFIX command by the same conditions as above.
Nevertheless it was not possible to prevent the detection of some B-alerts in the checkcif utility. There are two short intermolecular H···H distances of 1.76 Å and 1.95 Å and also a large U eq (max)/U eq (min) ratio of the carbon atoms. The C -C bond precision is 0.0205 Å, which is low. All these diagnostic results have their reason in the high flexibility of the n-butyl moieties in context to the high electron density localized on the heavy elements (iodine) at the rigid core of the system. Even the terminal carbons show a large elongation of their displacement parameters which is also a sign of the dynamic behaviour of the n-butyl moieties. The detection of the large Hirshfeld Test value of bond C23-C24 (7.5 su) yields in the difficulties resolving the discrete disorder positions by the same reasons. Possible tetrameric core structures based on cubane (1) or open-step framework (2).

Figure 2
ORTEP-style plot-view of complex [n-Bu 3 PCuI] 4 in the solid state of one conformer.

Figure 3
Packing diagram of the unit cell.

Tetra-µ 3 -iodido-tetrakis[(tri-n-butylphosphane-κP)copper(I)]
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.62 e Å −3 Δρ min = −1.16 e Å −3 Absolute structure: Flack (1983), 6695 Friedel pairs Absolute structure parameter: −0.02 (2) 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 F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.