2 = 4; 1606 independent reflections with I > 30(I): four-circle diffractometer, Cu,., 3" I 2 6 I 115". Lorentz, polarization, and adsorption corrections and corrections for linear decay were applied to the 3766 independent reflections collected. Anomalous dispersion corrections were applied for Co, K, and Na. The 35 non-hydrogen atoms were located using the SHELXTL Direct Methods programs and the hydrogen atom positions were located. Final cycles of least-squares refinement, which employed anisotropic thermal parameters for non-hydrogen atoms and isotropic parameters for hydrogen atoms, gave R, = 0.053, R, = 0.058. Further details of the crystal structure investigation may be obtained from the Director of the Cambridge Crystallographic Data Centre, University Chemical Laboratory, Lensfield Road, Cambridge CB2 1 EW (England). by quoting the full literature citation. 17) The twist angle T and the pyramidalization terms x, and xN were obtained from the primary torsion angles wl, w 2 , and w , as follows: T = (wl + w2)/2; xN = (w2 -0) + n) mod 2 ~; xc = (w, -IU, + n) mod 2x. Here we use the modified twist angle, ?: Z = (T) modn [3 a]. 7 maximizes at 2 90" and can be interpreted as the angle between the idealized positions ofthe pn orbitals on C and N. The pyramidalization terms maximize at 60".