Tetrakis[μ2-1,1,1,3,3,3-hexafluoro-2-(trifluoromethyl)propan-2-olato]tetrakis(μ3-2-methylpropan-2-olato)octacopper(I)

The structure of the title ocyacopper cluster contains two C16H18Cu4F18O4 units linked through a center of inversion by weak Cu—O bonds.


Chemical context
The structural chemistry of perfluoroalkoxides has been the subject of much recent interest because of the increased acidity caused by perfluorination. Metal complexes of such species often show enhanced volatility, which makes them useful precursors to ceramic materials (Bradley, 1989) and other applications. Because of their interesting properties, metal complexes of these ligands have been studied extensively. Focusing on copper complexes, with suitable variants of these ligands complexes have been used to demonstrate that optically active complexes can be obtained (Cripps & Willis, 1975a,b). Further studies involving both perfluorinated alkoxides and copper have demonstrated their ability to obtain heterometallic complexes containing both Cu and Ba (Purdy & George 1991;Borup et al., 1997) and in the use of such compounds in the oxycupration of tetrafluoroethylene (Ohashi et al., 2017). Of particular interest are the alkoxide complexes of copper(I), which often form cluster compounds (Purdy & George 1995;Borup et al., 1997;Purdy & George 1998;Anson et al., 2005;Lieberman et al., 2015). Within this set of compounds, there are those that form tetra-Cu I squares bridged along the edges by oxygen donors (Greiser & Weiss, 1976;McGeary et al., 1992;Terry et al., 1996;Lopes et al., 1997;Nikitinsky et al., 2000;Hå kansson et al., 2000;Krossing, 2012;Bellow et al., 2015). In view of the interesting chemistry exhibited by these alkoxide complexes containing Cu I , the synthesis of a mixed alkoxide complex was attempted and resulting structure of the compound is reported. ISSN (Fig. 1) contains an almost square-planar Cu 4 metallic core linked by bridging tert-butyl and perfluorinated tert-butyl groups with Cu-Cu distances ranging from 2.7108 (4) to 2.7612 (4) Å and Cu-Cu-Cu angles ranging from 89.459 (10) to 90.025 (11) (see Table 1). The two types of ligand are arranged around the square so that each is adjacent (cis) rather than opposed (trans) with Cu-O distances ranging from 1.8758 (16) to 1.9168 (15) Å . The coordination environment of all the Cu atoms in the asymmetric unit are different. Two of them have a two-coordinate linear geometry (Cu1 and Cu3), while two have a three-coordinate T-shaped geometry (Cu2 and Cu4). These metrical parameters are in the range found for other Cu I structures with this type of core. The four oxygen donors form a plane [r.m.s. deviation of only 0.0158 (7) Å ] and both Cu1 and Cu3 are in this plane while Cu2 and Cu4 deviate from this plane by 0.153 (1) and 0.129 (1) Å , respectively. Both the t-butyl and perfluorinated t-butyl groups deviate from this plane, as shown by the Cu-O-C angles which range from 118.57 (12) to 120.57 (12) for the t-butyl groups and 125.64 (14) to 127.62 (14) for the perfluorinated t-butyl groups, with this larger value reflecting the increased steric bulk of the latter. For both the t-butyl and perfluorinated t-butyl groups, this deviation is on the same side of the Cu 4 O 4 plane to allow for the association of the two C 16 H 18 Cu 4 F 18 O 4 units into the dimer mentioned above (see   Symmetry code: (i) Àx þ 1; Ày þ 1; Àz þ 1.

Figure 1
Molecular diagram for the major component of 1 showing the atom labeling. Atomic displacement parameters are at the 30% level.

Supramolecular features
In addition to the weak Cu-O interactions associating the C 16 H 18 Cu 4 F 18 O 4 units into dimers, there are also intradimer C-HÁ Á ÁF interactions (see Table 2 and Fig. 2). These dimers are further linked by weak interdimer C-HÁ Á ÁF and FÁ Á ÁF interactions. While intradimer FÁ Á ÁF are numerous, there are very few interdimer C-HÁ Á ÁF or FÁ Á ÁF interactions, which reflects the fact that this compound was originally isolated by sublimation from the reaction mixture. The overall packing is shown in Fig. 3.

Database survey
In the literature there are six examples of structures containing a square-planar Cu 4 O 4 arrangement and they divide into two groups. In the first group, this Cu 4 O 4 arrangement is isolated owing to the steric bulk of the O substituents [JUVKUG (McGeary et al., 1992); ZUTCIA (Terry et al., 1996); QEMCUG (Nikitinsky et al., 2000); GEQCUC (Krossing, 2012),] while in the second group these units associate into dimers [CUTBUX (Greiser & Weiss, 1976); CUTBUX01 (Hå kansson et al., 2000)]. Interestingly, in these two groups, one contains a structure where all the substituents are t-butyl groups [two polymorphs of the tertbutyl derivative (Greiser & Weiss, 1976;Hå kansson et al., 2000)] and thus the C 16 H 36 Cu 4 O 4 units associate into dimers, while the other group contains a structure where all the substituents are perfluorinated t-butyl groups and this has an isolated C 16 F 36 Cu 4 O 4 unit. Thus 1, which has two of each type in a cis arrangement, has just enough steric freedom to associate into these dimeric units. The dimerization of 1 and those for both CUTBUX and CUTBUX01 have the same arrangement where they associate via a crystallographic center of inversion (see Fig. 2).

Synthesis and crystallization
Copper(I) t-butoxide (0.25 g) was mixed with perfluoro-tbutanol (1.02 g) in a small amount of dry heptane under an inert atmosphere, and stirred for 4 d. The mixture was pumped to dryness and sublimed under vacuum at 333-373 K. A portion was sealed into an NMR tube with C 6 D 6 , and the spectrum shows both normal and fluorinated t-butyl groups. After many years, the NMR tube was opened and crystals were isolated.

Figure 3
Packing diagram viewed along the a axis.
to be disordered and was refined with two equivalent conformations with occupancies of 0.74 (3) 2 -1,1,1,3,3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (