Molecules of copper(II) l-sparteine dinitrate are mixed four- and five-coordinate in one crystalline phase and only four-coordinate in another

A neutral complex of Cu(lI) with the chiral bidentate nitrogen-chelating alkaloid (-)-sparteine, with nitrate groups occupying the remaining coordination sites, has been prepared and characterized. Solution conductivity measurements indicate that both nitrate groups are coordinated to copper to give a neutral molecule. Optical and electron-spin-resonance spectra in toluene/CHCl3, did not show a clear picture of the coordination geometry. A frozen-glass ESR spectrum showed the same evidence for mixed species, with the predominant species characterized by a very low A(11) value of 118 G. Crystals 1 and 2 of Cu(C15H26N2)(NO3)(2) were grown by two methods: 1 at 25 degrees C from saturated acetonitrile, and 2 at 5 degrees C from ethanol/dichloromethane under CCl4, vapor. Their structures were determined by X-ray crystallography. Crystals 1 were monoclinic, space group P2(1), with a = 7.851(6), b = 14.408(10), c = 16.079(10) Angstrom, beta = 97,93(6)degrees, V = 1801(2) Angstrom and Z = 4. Crystals 2 were orthorhombic, space group P2(1)2(1)2(1), with a = 7.863(4), b = 12.410(4), c = 18.050(6)Angstrom, V = 1761(1) Angstrom(3) and Z = 4. Two different coordination geometries are present in 1: four-coordinate pseudo-tetrahedral with two monodentate nitrates, and five-coordinate distorted square-pyramidal with one bidentate nitrate occupying an axial and an equatorial position. In 2, only four-coordinate molecules are found; their structure is almost the same as the four-coordinate molecules in 1, These results indicate the near electronic energy equivalence of four and five-coordination about copper(II) in this compound. Furthermore, crystal 1 is a rare example of a pure compound which displays two different coordination numbers in the same crystal structure.