Lewis acids and bases ionic bonding. Classically, the term "Lewis acid" is restricted to trigonal planar species with an empty p orbital, such as BR where R can be an organic substituent or a halide. For the purposes of discussion, even complex compounds such as EtAlCl and AlCl are treated as trigonal planar Lewis acids. Metal ions such as Na, Mg, and Ce, which are invariably complexed with additional ligands, are often sources of coordinatively unsaturated derivatives that form Lewis adducts upon reaction with a Lewis base[citation needed]. Other reactions might simply be referred to as "acid-catalyzed" reactions. Some compounds, such as HO, are
Magic cube classes for many years. This is consistent with the perfect (nasik) definitions given above for the cube. In this dimension, there is no ambiguity because there are only two classes of magic square, simple and perfect. <br> In the case of 4 dimensions, the magic tesseract, Mitsutoshi Nakamura has determined that there are 18 classes. He has determined their characteristics and constructed examples of each. And in this dimension also, the "Perfect (nasik)" magic tesseract has all possible lines summing correctly and all cubes and squares contained in it are also nasik magic. Proper: A Proper magic cube is a magic