Syntheses and crystal structures of two magnesium-tetrazole compounds in salt and polymeric forms

Two alkaline earth-tetrazole compounds, namely catena-poly[[[triaquamagnesium(II)]-μ-5,5'-(azanediyl)ditetrazolato-κ(3)N(1),N(1'):N(5)] hemi{bis[μ-5,5'-(azanediyl)ditetrazolato-κ(3)N(1),N(1'):N(2)]bis[triaquamagnesium(II)]} monohydrate], {[Mg(C(2)HN(9))(H(2)O)(3)][Mg(2)(C(2)HN(9))(2)(H(2)O)(6)]0.5·H(2)O}n, (I), and bis[5-(pyrazin-2-yl)tetrazolate] hexaaquamagnesium(II), (C(5)H(3)N(6))[Mg(H(2)O)(6)], (II), have been prepared under hydrothermal conditions. Compound (I) is a mixed dimer-polymer based on magnesium ion centres and can be regarded as the first example of a magnesium-tetrazolate polymer in the crystalline form. The structure shows a complex three-dimensional hydrogen-bonded network that involves magnesium-tetrazolate dimers, solvent water molecules and one-dimensional magnesium-tetrazolate polymeric chains. The intrinsic cohesion in the polymer chains is ensured by N-H...N hydrogen bonds, which form R(2)(2)(7) rings, thus reinforcing the propagation of the polymer chain along the a axis. The crystal structure of magnesium tetrazole salt (II) reveals a mixed ribbon of hydrogen-bonded rings, of types R(2)(2)(7), R(2)(2)(9) and R(2)(4)(10), running along the c axis, which are linked by R(2)(4)(16) rings, generating a 4,8-c flu net.