Template co-condensation of 2,3-dicyano-5,7-diphenyl-6H-1,4-diazepine 1 with 10-fold molar excess of phthalodinitrile 2 in the presence of Mg^II propoxide or butoxide in the corresponding alcohol leads to a mixture of Mg^II-diazepinoporphyrazines 3–6 from which the low symmetry 3:1 species 3, which contains three annulated benzene and one 1,4-diazepine rings, is separated by column chromatography as the aquo complex, [2,4-diphenyltribenzo[b,g,l][1,4]diazepino[2,3-q]porphyrazinato(aquo)magnesium(ii)], [Bz₃DzPzMg(H₂O)]. The complex 3 can be demetalated in acetic or trifluoroacetic acids under mild conditions with formation of the corresponding free-base [Bz₃DzPzH₂] 3a. This latter is also formed by co-cyclotetramerization of the same precursors 1 and 2 in the presence of sodium ethoxide in ethanol or lithium butoxide in butanol followed by demetalation of the intermediate disodium or dilithium salts in acid medium. The constitution and structure of the obtained compounds were established on the basis of elemental analysis, mass spectrometry, and ¹H NMR spectra. The variable temperature ¹H NMR measurements provide evidence that in porphyrazines 3 and 3a the 1,4-diazepine ring exists predominantly in the 6H-form over a wide temperature range. The free energy of activation for the inversion of the 1,4-diazepine ring determined for 3 is 45.6 ± 1.7 kJ mol^–1. Solution UV-visible spectra measurements in acidic media (CH₂Cl₂/CF₃COOH) provide evidence that the Mg^II complex 3 is easily protonated on the meso-N atom of the porphyrazine macrocycle followed by slow demetallation with formation of the free base 3a in its neutral form or as a species protonated on the diazepine ring.