Gravar-mail: Crystal structures of the three closely related compounds: bis[(1H-tetrazol-5-yl)methyl]nitramide, triaminoguanidinium 5-({[(1H-tetrazol-5-yl)methyl](nitro)amino}methyl)tetrazol-1-ide, and diammonium bis[(tetrazol-1-id-5-yl)methyl]nitramide monohydrate