1,3,5,7-Tetrakis(tetrazol-5-yl)-adamantane: the smallest tetrahedral tetrazole-functionalized ligand and its complexes formed by reaction with anhydrous M(ii)Cl2 (M = Mn, Cu, Zn, Cd)

Abstract

1,3,5,7-Tetrakis(tetrazol-5-yl)-adamantane (H₄L) was probed as a building block for the synthesis of tetrazolato/halido coordination polymers with open-network structures. MCl₂ (M = Cu, Cd, Zn, Mn) was reacted with H₄L in DMF at 70 °C to yield [Cu₄Cl₄L(DMF)₅]·DMF, 1; [Cd₄Cl₄L(DMF)₇]·DMF, 2; [Zn₃Cl₂L(DMF)₄]·2DMF, 3 and [Mn₂L(DMF)₂(MeOH)₄]·DMF·2MeOH·2H₂O, 4. 1 and 2 (Fddd) are nearly isostructural and have zeolitic structures with a {4³·6²·8}, gis or gismondine underlying net, where the role of the tetrahedral nodes is served by the coordination bonded clusters and the adamantane moiety. 3 (P2₁/n) has a porous structure composed of coordination bonded layers with a (4·8²) fes topology joined via trans-{Zn(tetrazolate)₂(DMF)₄} pillars with an overall topology of {4·6²}{4·6⁶·8³}, fsc-3,5-Cmce-2. 4 (Pca2₁) is composed of stacked {Mn₂L} hexagonal networks. In 1 and 2 the ligand fulfills a symmetric role of a tetrahedral building block, while in 3 and 4 it fulfills rather a role of an effective trigonal unit. Methanol-exchanged and activated 1 displayed an unusual type IV isotherm with H2 type hysteresis for N₂ sorption with an expected uptake at high P/P₀, but with a smaller S_BET = 505.5 m² g⁻¹ compared to the calculated 1789 m² g⁻¹, which is a possible result of the framework's flexibility. For H₂ sorption 0.79 wt% (1 bar, 77 K) and 0.06 wt% (1 bar, RT) uptake and Q_st = −7.2 kJ mol⁻¹ heat of adsorption (77 K) were recorded. Weak antiferromagnetic interactions were found in 1 and 4 with J₁ = −9.60(1), J₂ = −17.2(2), J₃ = −2.28(10) cm⁻¹ and J = −0.76 cm⁻¹ respectively. The formation of zeolitic structures in 1 and 2, the concept of structural ‘imprinting’ of rigid building blocks, and design opportunities suggested 4 as a potential hexafunctionalized biadamantane building block.