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 diagonal:)<br>. Included below are references and links to discussions of the old definition<br> With the popularity of personal computers it became easier to examine the finer details of magic cubes. Also more and more work was being done with higher dimension magic Hypercubes. For example, John Hendricks constructed the world's first Nasik magic tesseract in 2000. Classed as a perfect magic tesseract by Hendricks definition. A magic hypercube of dimension "n" is perfect if all pan-n-agonals sum correctly. Then all lower dimension hypercubes contained in it are also perfect.<br> For dimension 2, The Pandiagonal Magic Square has been called "perfect"