Crystal structures of the isomorphous tris(hexafluoroacetylacetonato)copper(II) and tris(hexafluoroacetylacetonato)magnesium salts of monoprotonated 1,8-bis(dimethylamino)naphthalene

Abstract

Three-dimensional X-ray crystal structure analyses have been carried out on the compounds [C₁₄H₁₉N₂]+[(CF₃·CO·CH·CO·CF₃)₃M]^–(M = Mg or Cu). Both have Z= 4 in a monoclinic unit cell with space group P2₁/n and dimensions: (M = Mg)a= 12·775, b= 21·268, c= 13·594 Å, β= 99° 10′; (M = Cu)a= 12·878, b= 21·00, c= 13·620 Å, β= 98° 44′. A full-matrix refinement gave R values of 0·095 for 1998 observations (Mg) and 0·108 for 2478 observations (Cu).

In the cation the proton lies in the plane of the naphthalene ring between the two nitrogen atoms which are slightly displaced on opposite sides of the ring, and are 2·60(1)(Mg) and 2·65(2)(Cu)Å apart; the proton appears closer to one nitrogen in the magnesium and the other nitrogen in the copper complex. With a standard deviation of 0·15 Å it is not possible to distinguish between a proton in a double potential well and a proton equidistant from the nitrogen atoms.

In the anions all six chelate rings show delocalisation. The magnesium ion is octahedrally co-ordinated by oxygen atoms, mean Mg–O 2·06(2)Å. For copper there appears to be a tetragonal distortion, four short bonds, mean Cu–O 2·01 (2)Å, and two long ones at 2·16(3) and 2·20(3)Å. The evidence for accepting the significance of this is discussed.