$H_{3}^{+},C_{3}^{-},NO_3^{-},SO_{3},O_{3},SO_{2},NO_{2}^{-}$ and $C_{6}H_{6}$ make multicenter bonds, in which some electrons compose an delocalized bonding among several atoms together. Transition metals and complex compounds also donate electrons in order to make delcoalized bonds among them together. Many metal crystals have allotropic transformations and an abrupt change of the property at the allotropic temperature must mean ans atomic rearrangement by the three-dimensional crystallizing ${pi}-bondings$. The crystals may have many kinds of the crystallizing ${pi}-bondings$ but the ${pi}-bondings$ from square and hexagonal packings are more stable than any linear and triangular ones. The high melting points of the transition metals are attributed to mixed metallic-covalent bonding.