[MIII2MII3] (n+) trigonal bipyramidal cages based on diamagnetic and paramagnetic metalloligands.

A family of five [MIII2MII3] (n+) trigonal bipyramidal cages (M(III) = Fe, Cr and Al; M(II) = Co, Zn and Pd; n = 0 for 1-3 and n = 6 for 4-5) of formulae [Fe2Co3L6Cl6] (1), [Fe2Zn3L6Br6] (2), [Cr2Zn3L6Br6] (3), [Cr2Pd3L6(dppp)3](OTf)6 (4) and [Al2Pd3L6(dppp)3](OTf)6 (5) (where HL is 1-(4-pyridyl)butane-1,3-dione and dppp is 1,3-bis(diphenylphosphino)propane) are reported. Neutral cages 1-3 were synthesised using the tritopic [M(III)L3] metalloligand in combination with the salts Co(II)Cl2 and Zn(II)Br2, which both act as tetrahedral linkers. The assembly of the cis-protected [Pd(II)(dppp)(OTf)2] with [M(III)L3] afforded the anionic cages 4-5 of general formula [MIII2PdII3](OTf)6. The metallic skeleton of all cages describes a trigonal bipyramid with the M(III) ions occupying the two axial sites and the M(II) ions sitting in the three equatorial positions. Direct current (DC) magnetic susceptibility, magnetisation and heat capacity measurements on 1 reveal weak antiferromagnetic exchange between the Fe(III) and Co(II) ions. EPR spectroscopy demonstrates that the distortion imposed on the {MO6} coordination sphere of [M(III)L3] by complexation in the {MIII2MII3} supramolecules results in a small, but measurable, increase of the zero field splitting at M(III). Complete active space self-consistent field (CASSCF) calculations on the three unique Co(II) sites of 1 suggest DCo ≈ -14 cm(-1) and E/D ≈ 0.1, consistent with the magnetothermal and spectroscopic data.