FOX-7 and its cisoid and transoid 1,5-tautomers as well as magnesium composites of all have been investigated quantum chemically within the restrictions of density functional theory (B3LYP/6-311++G(d,p)). Certain physico-chemical and quantum chemical properties, energies, stabilities, calculated IR and UV-VIS spectra are discussed. The influence of magnesium atom is investigated. It has been found that in FOX-7 composites the magnesium is not a silent ingredient, but interacts with the organic constituents. (C) 2017 Published by Elsevier Ltd.