Ligand directed self-assembly of polymetallic [nxn] (n = 2,3,4) grid platforms: synthesis, structure and magnetism

Abstract

Metallo-supramolecular [n × n] Mn₂ transition metal grid arrays (with n = 2, 3 and 4) were synthesized by self-assembly reactions with new ditopic imidazole hydrazone, tritopic picolinic dihydrazone and tetratopic pyridazine bis(hydrazone) ligands. Mono-, di-, trinuclear, [2×2] M₄ grid and trigonal-bipyramidal clusters formed by self-assembly reactions between the ditopic ligands and metal salts. Their structural characterizations suggest a possible route to the self-assembly of [2×2] M₄ grid and trigonal-bipyramidal architectures. Homometallic [3×3] M₉ (M = Mn(II), Co(II), Cu(II) and Zn(II)) and heterobimetallic [3×3] Mn(II)₅Cu(II)₄, Mn(II)₅Zn(II)₄ and Mn(II)Cu(II)₈ grids, based on a [M₉-(μ-O₁₂)] core framework were synthesized. Their structural characterizations, in particular the identification of the Jahn-Teller axes, leading to strict orbital orthogonality and ferromagnetism in the Cu(II) containing complexes, formed the basis for magnetic interpretation and modeling. [3×3] Mn(II)₉, Cu(II)₉ and Co(II)₅Co(III)₄ grids synthesized by self-assembly reactions between metal salts and tritopic ligands with quinoline-type endpieces, leading to extended structural motifs through intermolecular face-to-face and edge-to-face π-π interactions are also reported. 4×[2×2] M₁₆ (M = Mn(II), Co(II), Cu(II) and Cu(II)₁₂ Cu(I)₄) grids were synthesized, and their magnetic properties modeled as compartmental [2×2] M₄-(μ-Ohydrazone)₄ squares for the Mn(II)₁₆ and Co(II)₁₆ in complexes. The structural characterization of the Jahn-Teller axes leading to a combination of orthogonal and non-orthogonal orbital connections for both of the Cu₁₆ grids allowed for fairly simple magnetic models to be devised.