Abstract
A heterometallic metal-organic framework (MOF) of [Cd(6)Ca(4)(BTB)(6)(HCOO)(2)(DEF)(2)(H(2)O)(12)]∙DEF∙xSol (1, H(3)BTB = benzene-1,3,5-tribenzoic acid; DEF = N,N'-diethylformamide; xSol. = undefined solvates within the pore) was prepared by solvothermal reaction of Cd(NO(3))(2)·4H(2)O, CaO and H(3)BTB in a mixed solvent of DEF/H(2)O/HNO(3). The compatibility of these two divalent cations from different blocks of the periodic table results in a solid-state structure consisting of an unusual combination of a discrete V-shaped heptanuclear cluster of [Cd(2)Ca](2)Ca' and an infinite one-dimensional (1D) chain of [Cd(2)CaCa'](n) that are orthogonally linked via a corner-shared Ca(2+) ion (denoted as Ca'), giving rise to an unprecedented branched-chain secondary building unit (SBU). These SBUs propagate via tridentate BTB to yield a three-dimensional (3D) structure featuring a corner-truncated P4(1) helix in MOF 1. This outcome highlights the unique topologies possible via the combination of carefully chosen s- and d-block metal ions with polydentate ligands.