Chloridotris[μ2-2-(dimethylamino)ethanolato]-μ3-hydroxido-tri-μ2-trifluoroacetato-tetracopper(II) tetrahydrofuran solvate

The title compound, [Cu4(C2F3O2)3(C4H10NO)3Cl(OH)]·C4H8O or [Cu4(TFA)3(dmae)3Cl(OH)]·THF (dmae is dimethylaminoethanolate, TFA is trifluoroacetate and THF is tetrahydrofuran), has an approximate molecular threefold symmetry with three equivalent {Cu(dmae)(TFA)} units bridging between a Cu—Cl and a hydroxide unit, with the latter two lying on the molecular threefold axis. However, in the solid state, the tetranuclear complex has Ci symmetry. The Cu atom bonded to the Cl atom has a distorted tetrahedral geometry. The other three Cu atoms have distorted square-pyramidal geometries with an NO4 coordination environment. The bonds within the CuNO3 base of the pyramid range from 1.953 (2) to 2.033 (3) Å, while the apical Cu—O bonds are significantly longer, ranging from 2.286 (2) to 2.377 (2) Å. The square-pyramidal geometries are augmented by weak interactions towards a sixth O atom, forming a highly distorted octahedral coordination environment [long Cu—O distances = 2.712 (2)–2.824 (2) Å]. The hydroxide group is hydrogen bonded to the tetrahydrofuran solvent molecule. One of the –CF3 groups shows minor disorder over two positions, with a refined occupancy ratio of 0.894 (4):0.106 (5).

The title compound, [Cu 4 (C 2 F 3 O 2 ) 3 (C 4 H 10 NO) 3 Cl(OH)]Á-C 4 H 8 O or [Cu 4 (TFA) 3 (dmae) 3 Cl(OH)]ÁTHF (dmae is dimethylaminoethanolate, TFA is trifluoroacetate and THF is tetrahydrofuran), has an approximate molecular threefold symmetry with three equivalent {Cu(dmae)(TFA)} units bridging between a Cu-Cl and a hydroxide unit, with the latter two lying on the molecular threefold axis. However, in the solid state, the tetranuclear complex has C i symmetry. The Cu atom bonded to the Cl atom has a distorted tetrahedral geometry. The other three Cu atoms have distorted squarepyramidal geometries with an NO 4 coordination environment. The bonds within the CuNO 3 base of the pyramid range from 1.953 (2) to 2.033 (3) Å , while the apical Cu-O bonds are significantly longer, ranging from 2.286 (2) to 2.377 (2) Å . The square-pyramidal geometries are augmented by weak interactions towards a sixth O atom, forming a highly distorted octahedral coordination environment [long Cu-O distances = 2.712 (2)-2.824 (2) Å ]. The hydroxide group is hydrogen bonded to the tetrahydrofuran solvent molecule. One of the -CF 3 groups shows minor disorder over two positions, with a refined occupancy ratio of 0.894 (4):0.106 (5).

Comment
In recent years, there has been a considerable interest towards the synthesis of copper complexes; these complexes are extensively used in catalysis, enzymatic reactions, magnetism and molecular architecture (Coastamagna, Vargas et al., 1992). The present work is a continuation of earlier studies for the preparation and structure eludication of copper (II) complexes (Shahid et al., 2009). The motivation behind the synthesis of the title compound was to use it as a starting material for the synthesis of single source precursors for the deposition of thin films of copper oxides using aerosol assisted chemical vapor deposition (AACVD). We present here the synthesis and crystal structure of the title compound, [Cu 4 ((CH 3 ) 2 NCH 2 CH 2 O) 3 (F 3 CCOO) 3 (OH)Cl] or [Cu 4 (dmae) 3 (TFA) 3 (OH)Cl] (dmae = dimethylaminoethanolate, TFA = trifluoroacetate), which crystallized from THF as the mono solvate with the THF molecule tightly hydrogen bonded to the hydroxyl group.
The title compound has a slightly distorted molecular three fold symmetry with three equivalent Cu(dmae)(TFA) units bridging via their alcoholate oxygen atoms between a Cu-Cl and an hydroxyl unit with the latter two lying on a molecular pseudo threefold axis. The Cu atom bonded to the chlorine has a distorted tetrahedral geometry. The other three copper atoms have distorted square pyramidal geometries with a CNO 4 coordination environment from the dmae O and N atoms, the hydroxyl O atom and two TFA anions. The TFA anions are bridging between two neighboring copper ions with one of the oxygen atoms being part of the base of the pyramid of one copper ion, and the other being in the apical position of the neighboring copper ion. The bonds within the CuNO 3 bases of the pyramids are strong and quite similar in length with distances between 1.953 (2) and 2.033 (3) Å. The apical Cu-O bonds are significantly longer and between 2.286 (2) and 2.377 (2) Å, thus rendering the µ 2 -bridge of the TFA ions asymmetric. The square pyramidal geometries are augmented by weak interactions towards a fifth oxygen atom to form a highly distorted octahedral coordination environment (Cu-O distances: O3-Cu3 = 2.712 (2), O2-Cu2 = 2.780 (2), O1-Cu4 = 2.8240 (2) Å).
A similar motif as in the title compound was previously observed for two mixed metal copper-titanium complexes (Tahir et al., 2008). In these complexes the TFA anions were replaced by benzoate or 2-methyl-benzoate ligands, and the Cu-Cl unit was replaced by a titanium atom, which in turn was bonded to another larger Cu-Ti cluster. The [Cu 3 (dmae) 3 (TFA) 3 (OH)] unit in the title compound and the [Cu 3 ((CH 3 ) 2 NCH 2 CH 2 O) 3 (O 2 C-C 6 H 5 R) 3 (OH)] units in the Cu-Ti complexes (R = H, Me) are quite similar. In the 2-methyl-benzoate complexes the [Cu 3 ((CH 3 ) 2 NCH 2 CH 2 O) 3 (O 2 C-C 6 H 5 Me) 3 (OH)] unit is located on an actual crystallographic three fold axis. The carboxylate anions show coordination modes differing slightly from those observed in the title compound with some of the oxygen atoms being detached from the copper ions and interactions to the fifth oxygen atom, which are very weak in the title compound, being strengthened instead. The overall coordination environment -distorted square pyramidal CNO 4 geometries with an additional weak interaction towards a fifth oxygen atom -is however the same in all three compounds, which shows the idiosyncracy commonly observed for copper(II) to form strongly distorted and highly flexible octahedral geometries with a set of four strong bonds in a square planar arrangement and two apical ligands at variable distances. Indi-supplementary materials sup-2 vidual ligand atoms in these kinds of complexes can easily switch from tightly bound to only weakly coordinated as long as the overall coordination environment of the metal center is retained, and energy differences and activation barriers between the different arrangements that can be achieved that way are quite small. The difference in bonding arrangement in the three complexes in the solid state does thus probably not translate into a different chemical nature for the three complexes as the bonding environment around Cu(II) is very flexible and it can be assumed that in solution (i.e. upon release of packing effects) all complexes will attain the same connectivity pattern.
In the title compound the hydroxyl group is O-H···O hydrogen bonded to a tetrahydrofuran molecule (Table 1), which is embedded in a bowl shaped cleft of the complex formed by the three TFA ligands. No such host-guest behavior was observed for the other two related compounds (Tahir et al., 2008).

Experimental
Tetrameric N,N-dimethylaminoethanolato copper(II) chloride, [Cu(dmae)Cl] 4 was prepared according to a literature method (Anwander et al., 1997). The title compound was prepared as follows: 1.25 g (1.67 mmole) of [Cu(dmae)Cl] 4 in 20 ml THF were combined with 1.77 g (6.66 mmole) of Cu(F 3 CCOO) 2 in 10 ml THF followed by the addition of 0.297 g (3.33 mmole) N,N-dimethylaminoethanol. The reaction mixture was stirred for 3 h and filtered through a cannula to remove any undissolved species. The filtrate was evaporated to dryness under vacuum, the solid was re-dissolved in 5 ml THF and placed in a vial with rubber seal at room temperature for one week to give blue crystals suitable for single-crystal X-ray diffraction analysis. Yield: 86% m.p. 393-394 K. Elemental Analysis for Cu 4 ((CH 3 ) 2 NCH 2 CH 2 O) 3 (F 3 CCOO) 3 (OH)Cl % calc: C, 21.99 H, 3.97 N, 4.27, % found: C, 22.10 H, 3.90 N, 4.53.

Refinement
The fluorine atoms bonded to C14 were refined as disordered over two mutually exclusive positions with a refined occupancy ratio of 0.894 (4) to 0.106 (5). C-F bond distances within this CF 3 group were restrained to be the same within a standard uncertaincy of 0.02 Å and ADPs of the minor F atoms were constrained to be identical to those of the major moiety F atom opposite their position.
All hydrogen atoms were added in calculated positions with a C-H bond distances of 0.97 (methylene), 0.96 (methyl) and 1.00 Å (OH). They were refined with isotropic displacement parameteres U iso of 1.5 (methyl, OH) or 1.2 times U eq (methylene) of the adjacent carbon or oxygen atom. Fig. 1. Perspective view of the title compound with the atom numbering scheme. The displacement ellipsoids are at the 50% probability level and H atoms are drawn as small spheres of arbitrary radii. Fig. 2. Perspective view of the title compound, view down the pseudo three fold axis. The displacement ellipsoids are at the 50% probability level and H atoms are drawn as small spheres of arbitrary radii.

Special details
Experimental. The fluorine atoms bonded to C14 were refined as disordered over two mutually exclusive positions with a refined occupancy ratio of 0.894 (4) to 0.106 (5). C-f bond distances within this CF3 group were restrained to be the same within a standard uncertaincy of 0.02 Angstrom and ADPs of the minor F atoms were constrained to be identical to those of the major moiety F atom opposite their position.