Lewis basicity of a chlorine atom bound to an aliphatic carbon atom as sensed by a quadruple chromium-chromium bond. Structures of M2(2,6-xylyl)NC(CH3)O4.2CH2Cl2, M = chromium, molybdenum. Journal of the American Chemical Society, (102)10:3475--3479, 1980. [PUMA: chromium quadruple basicity;crystal length bond chlorine structure]