Biology uses phosphate as accumulator-emitters of energy due to the easiness that phosphate offers for changing from ionic state to covalent state and vice verse.
When changing covalent phosphate to ionic phosphate an important energy emission takes place due to the difference of molecular volume from a state to another.
Usually, covalent molecules have much more volume and therefore they contain much more energy, whereas the ionic molecules are smaller (here, due to the decrease that phosphorous suffers when losing five orbits) and they contain less energy.
It is due to the characteristic and property of all atoms and molecules of containing the same energy density. If its volume increases they absorb energy; if it diminishes they emit energy. (See Law of Universal Balance).
Many molecules can give or to admit electrons maintaining their structure almost invariable and therefore without to need neither to emit too much energy.
Tetras are example of it, which can change from a single bond to double bond or vice verse.
When they pass from double to single bond they catch four electrons, and if they pass from single to double bond they give four electrons.
Molecules with this connection type are usually used by biology as accumulator-emitters of electrons. For example Adenine, Guanine or Nicotinamide..
Therefore if we form a molecular group with sugars (to obtain energy), phosphates (to extract and to transfer energy) and electrons accumulator-emitters molecules (to propitiate the molecular works) we will have an authentic package of energy for biology development.