Bis(tetraethylammonium) bis(dimethylformamide)tetrakis(μ-N,2-dioxidobenzene-1-carboximidato)pentacopper(II)

The title compound, (C8H20N)2[Cu5(C7H4NO3)4(C3H7NO)2], abbreviated as (TEA)2[CuII(12-MCCuII N(shi)-4](DMF)2 [where TEA is tetraethylammonium, shi3− is salicylhydroximate (or N,2-dioxidobenzene-1-carboximidate) and DMF is N,N-dimethylformamide], contains five CuII ions. Four of the CuII ions are members of a metallacrown ring (MC), while the fifth CuII is bound in a central cavity. Two of the ring CuII ions are five-coordinate with distorted square-pyramidal geometry. The coordination sphere is composed of two shi3− ligands and one DMF molecule. The other two ring CuII ions and the central CuII ion are four-coordinate with square-planar geometry. The coordination spheres of these ions are only composed of shi3− ligands. The charge of the [CuII(12-MCCuII N(shi)-4]2− unit is balanced by two uncoordinated TEA+ countercations. The structure shows severe static disorder with the metallacrown, the tetraethylammonium cations and the DMF solvent molecule all disordered over each of two mutually exclusive sites, with occupancy rates for the major moieties of 0.6215 (6) for the metallacrown, 0.759 (3) for the tetraethylammonium ion and 0.537 (6) for the DMF molecules. The metallacrown unit is located on a crystallographic inversion center and disordered about a non-crystallographic twofold axis. The DMF molecule and the tetraethylammonium ion are disordered about a non-crystallographic twofold axis and pseudo-inversion center, respectively.


Experimental
Crystal data (C 8

Comment
Since the identification of metallacrowns (MC) in 1989 , these inorganic crown ether analogues have proved to be very diverse molecules (Mezei et al., 2007;Pecoraro et al., 1997). Metallacrowns can behave as single-molecule magnets, have potential use as MRI contrast agents, and can selectively bind cations or anions (Mezei et al., 2007). In addition to being inorganic structural and functional analogues of crown ethers, the naming scheme for the two molecules is very similar. For example, the name 12-MC-4 indicates that there are 12 atoms in the metallacrown ring and there are 4 oxygen atoms in the ring that can potentially bind to a central metal ion. A complete nomenclature description for metallacrowns can be found in Pecoraro et al. (1997).
Copper(II) 12-MC-4 structures are common (Mezei et al., 2007), and the structures tend to be fairly planar. The planar structures are generated by placing the ring Cu II ions at 90 o relative to each other. This placement is typically achieved by selection of a ligand, such as salicylhydroxamic acid, that can form fused five-and six-membered chelate rings. However, planar structures have been observed for other sized fused chelate rings (Mezei et al., 2007). One planar Cu II [12-MC Cu II -4] 2+ has been used to build a two-dimensional chiral solid (Bodwin & Pecoraro, 2000).
Compound 1 is fairly planar, which is typical of Cu II 12-MC-4 structures ( Fig. 1-3; Macrae et al., 2006). The structure consists of a [Cu II -N-O] repeat unit around the MC ring, and the MC binds a Cu II in the central cavity. Cu1 is located in the central cavity and is four-coordinate with square planar geometry. Cu2, Cu3, Cu2 i and Cu3 i compose the MC ring (symmetry operator (i): -x + 1, -y + 1, -z + 1). Cu2 is five-coordinate with distorted square pyramidal geometry with τ equal to 0.02 (τ = 0 for square pyramidal geometry and τ = 1 for trigonal bipyramidal geometry (Addison et al., 1984). The basal portion of the geometry is composed of two shi 3ligands that bind with oxygen and nitrogen atoms. The apical position is filled by a DMF molecule which binds with an oxygen atom (O7 and O7b). The Cu2-O7 bond distance is 2.763 (14) Å, and the Cu2-O7b bond distance is 2.696 (17) Å. Cu3 is four-coordinate with square planar geometry, and the coordination is composed of two shi 3ligands that bind with oxygen and nitrogen atoms. An uncoordinated TEA countercation is located in the lattice. In addition, the structure of 1 shows severe static disorder as the metallacrown, TEA, and DMF are disordered over two mutually exclusive sites (Figs. 4-6, Farrugia, 1997 (Gibney et al., 1994). However, in 2 all of the ring Cu II ions are four-coordinate with square planar geometry. The geometry about the ring Cu II ions in 2 is different compared to 1. In 1 the DMF molecules are bound to two of the ring Cu II ions, which gives these Cu II ions a distorted square pyramidal geometry (Fig. 2). In 2 the DMF molecule does not bind to any of the Cu II ions, but instead the DMF is present only in the lattice (Gibney et al., 1994).

Refinement
The structure of 1 shows severe static disorder. The anionic metallacrown, the tetraethylammonium and the solvent DMF molecules all show disorder over each two mutually exclusive sites with different occupancy ratios. The refined values are 0.6215 (6) to 0.3785 (6) for the metallacrown, 0.759 (3) to 0.241 (1) for the tetraethylammonium ions and 0.537 (6) to 0.463 (6) for the DMF molecules. The metallacrown is disordered by a non-crystallographic two-fold axis, as is the DMF molecule. The tetraethylammonium is disordered by a pseudo-inversion center. Equivalent bonds in disordered sections of the molecules were restrained to be similar (standard deviation 0.02 Å). The atom O7 and O7b were restrained to be approximately isotropic (standard deviation 0.01 Å 2 ), and the ADPs of the atoms C18b and C22, O7 and O7b, and N4 and N4b were each constrained to be the same. Aromatic benzene rings were constrained to resemble ideal hexagons with C-C distances of 1.39 Ångstroms.
Hydrogen atoms were placed in calculated positions with C-H = 0.95 (aromatic), 0.98 (methyl) and 0.99 Å (methylene) and were refined with Uĩso~(H) = 1.5 U eq (C) for methyl H atoms and 1.2 U eq (C) for methylene and aromatic moieties. Fig. 1. Single-crystal X-ray structure (top view) of (TEA) 2 [Cu(12-MC Cu II N(shi) -4)](DMF) 2 (1). The thermal ellipsoid plot of 1 is at a 50% probability level with the disordered portions of the molecule shown only at the higher occupancy positions. All non-carbon atoms are labeled. Hydrogen atoms and the lattice TEA have been omitted for clarity (symmetry operator (i): -x + 1, -y + 1, -z + 1). Color scheme for all figures: orange -Cu II , red -oxygen, bluenitrogen, and gray -carbon. Fig. 2. Single-crystal X-ray structure (side view) of 1. The DMF is coordinated to Cu2 with a Cu II -O7 distance of 2.763 (14) Å. The thermal ellipsoid plot of 1 is at a 50% probability level with the disordered portions of the molecule shown only at the higher occupancy positions. Cu2 and O7 are labeled to highlight the DMF molecules bonded to the metallacrown. Hydrogen atoms and the lattice TEA have been omitted for clarity (symmetry operator (i): -x + 1, -y + 1, -z + 1).  . Single-crystal X-ray structure (top view) of 1. The thermal ellipsoid plot of 1 is at a 50% probability level. All disordered atoms of the MC are shown. The metallacrown is disordered over two mutually exclusive sites by a non-crystallographic twofold axis. The refined occupancy ratio is 0.6215 (6) to 0.3785 (6). All copper atoms are labeled. Hydrogen atoms, the DMF molecules, and the lattice TEA have been omitted for clarity (symmetry operator (i): -x + 1, -y + 1, -z + 1).

Fig. 5.
Single-crystal X-ray structure of the TEA countercation with all disordered atoms shown. The thermal ellipsoid plot is at a 50% probability level. The tetraethylammonium is disordered over two mutually exclusive sites by a pseudo-inversion center. The refined occupancy ratio is 0.759 (3) to 0.241 (1). Hydrogen atoms have been omitted for clarity. Fig. 6. Single-crystal X-ray structure of the DMF molecule with all disordered atoms shown. The thermal ellipsoid plot is at a 50% probability level. The DMF is disordered over two mutually exclusive sites by a non-crystallographic twofold axis. The refined occupancy ratio is 0.537 (6) to 0.463 (6). Hydrogen atoms have been omitted for clarity.
Crystal data (C 8

Special details
Experimental. The structure of 1 shows severe static disorder. The anionic metallacrown, the tetraethylammonium, and the solvent DMF molecules all show disorder over each two mutually exclusive sites with different occupancy ratios. The refined values are 0.6215 (6) to 0.3785 (6) for the metallacrown, 0.759 (3) to 0.241 (1) for the tetraethylammonium ions and 0.537 (6) to 0.463 (6) for the DMF molecules. The metallacrown is disordered by a non-crystallographic two fold axis, as is the DMF molecule. The tetraethylammonium is disordered by a pseudo-inversion center. Equivalent bonds in disordered sections of the molecules were restrained to be similar (standard deviation 0.02 Å). The atom O7 and O7b were restrained to be approximately isotropic (standard deviation 0.01 Å 2 ), and the ADPs of the atoms C18b and C22, O7 and O7b, and N4 and N4b were each constrained to be the same. Aromatic benzene rings were constrained to resemble ideal hexagons with C-C distances of 1.39 Å.