Bis[2-(methylamino)troponato]copper(II)

In the title compound, [Cu(C8H8NO)2], a strictly square-planar geometry about the CuII metal atom is observed. Substitution of an O atom with a methyl-functionalized N atom does not significantly alter the bond distances and angles in the copper(II) complex when compared with a similar bis(troponato)copper(II) complex. π–π stacking is observed between the tropolone rings, with interplanar distances of 3.5039 (16) and 3.2933 (15) Å, respectively. Additional stabilisation of the structure is accomplished through C—H⋯O hydrogen-bonding interactions.

In the title compound, [Cu(C 8 H 8 NO) 2 ], a strictly squareplanar geometry about the Cu II metal atom is observed. Substitution of an O atom with a methyl-functionalized N atom does not significantly alter the bond distances and angles in the copper(II) complex when compared with a similar bis(troponato)copper(II) complex.stacking is observed between the tropolone rings, with interplanar distances of 3.5039 (16) and 3.2933 (15) Å , respectively. Additional stabilisation of the structure is accomplished through C-HÁ Á ÁO hydrogen-bonding interactions.

Comment
Complexes containing tropolonato type derivatives have steadily increased over the last few decades (Roesky, 2000), with most of the work having involved the first and second row transition elements. This attention has been to a large extent due to the medical application of tropolone in radio-pharmaceuticals (Nepveu et al., 1993) andcatalyst precursors (Crous et al., 2005;Roodt et al., 2003). Functionalization of the tropolonato backbone (seven-membered ring) has also been investigated with a range of Rh I and Pd II complexes reported to date (Steyl et al., 2001;Steyl, 2005).
Heteroatom substitution of the tropolonato moiety has also been reported, most notably the O atoms are replaced with functionalized amino groups, resulting in either the 2-(aminotropone) or 1,2-(aminotropoimine) compounds (Roesky & Burgstein, 1999;Claramunt et al., 2004). Thus, a host of amino and anilino derivatives of tropolone have been reported (Roesky & Burgstein, 1999;Roesky, 2000;Claramunt et al., 2004). The addition of electron-donating or -withdrawing moieties to the N atom can significantly increase the application of these compounds in coordination chemistry. The most interesting observation concerning the Cu II metal centres in general is the difference in the coordination behaviour of the bidentate-O,O donor atoms compared to the N,N donor atom complexes; the geometrical conformation changes from a square planar (Starikova & Shugam, 1969;Byrn et al., 1993)  In an effort to further investigate these types of complexes, the crystal structure of [Cu(TropNMe) 2 ] is presented.

Refinement
All H atoms were positioned geometrically and allowed to ride on their parent atoms, with U iso (H) = 1.2U eq (parent) of the parent atom with a C-H distance of 0.93. The methyl H atoms were placed in geometrically idealized positions and constrained to ride on the parent atoms with U iso (H) = 1.5U eq (C) and at a distance of 0.96 Å. Fig. 1. Representation of the title compound, showing the numbering scheme and displacement ellipsoids (50% probability).

Special details
Experimental. First 80 frames repeated after collection for monitoring possible decay.
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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 > 2σ(F 2 ) is used only for calculating Rfactors(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.