Self-assembled polymetallic square grids ([2 × 2] M₄, [3 × 3] M₉) and trigonal bipyramidal clusters (M₅)—structural and magnetic properties

Abstract

New self-assembled grids and clusters are reported, with square [2 6 2] M 4 (M = Mn(II) 4 , Cu(II) 4 ), trigonal-bipyramidal Mn(II) 5 , and square [3 6 3] M 9 (M = Mn(II), Cu(II)) examples. These are based on a series of ditopic and tritopic hydrazone ligands involving pyridine, pyrimidine and imidazole end groups. In all cases the metal centres are bridged by hydrazone oxygen atoms with large (>125u) bridge angles, leading to antiferromagnetic exchange for all the Mn systems (J = 22 to 25 cm 21 ), which results in S = 0 (Mn 4 ), and S = 5/2 (Mn 5 , Mn 9 ) ground states. The copper systems have a 90u alternation of the Jahn-Teller axes within the Cu 4 and Cu 8 grid rings (Cu 9 ), which leads to magnetic orbital orthogonality, and dominant ferromagnetic coupling. For the Cu 9 grid antiferromagnetic exchange between the ring and the central copper leads to a S = 7/2 ground state, while for the Cu 4 grids S = 4/2 ground states are observed. The magnetic data have been treated using isotropic exchange models in the cases of the Cu 4 and Cu 9 grids, and the Mn 5 clusters. However due to the enormity of a fully isotropic calculation a simplified model is used for the Mn 9 grid, in which the outer Mn 8 ring is treated as the equivalent of an isolated magnetic chain, with no coupling to the central metal ion.

Anion-tuning of supramolecular gel properties

“…In addition to weakening gels and causing gel-tosol transitions, anions can be used to enhance gelation. 12,90,93,198 salts shows how the anion has an important role in templating the assembly that leads to gelation. [202][203][204] The silver coordinates to the pyridyl functionality in a linear fashion resulting in either a cisoid (meta groups on pyridyl groups are cis to each other in relation to the N Ag N bond) or transoid (meta groups on pyridyl groups are trans to each other in relation to the N Ag N bond) arrangement depending on the identity of the anion present in solution.…”

“…Vancomycin, an antibiotic, has been used to both strengthen a gel and cause a transformation from gel to sol. 88,93 With compound 1.11, the interaction with vancomycin causes an improvement in the gelation ability. 93 In contrast compound 1.12 breaks down from a gel to a sol upon the addition of vancomycin.…”

“…88,93 With compound 1.11, the interaction with vancomycin causes an improvement in the gelation ability. 93 In contrast compound 1.12 breaks down from a gel to a sol upon the addition of vancomycin. 88 In both these cases the interaction between the D-ala-D-ala residues and the vancomycin are important for these tuning abilities.…”

“…54,61,77,78,88,93,98,[123][124][125][126][127][128][129][130][131][132][133][134][135] There have been some classical host:guest systems developed that can be used as LWMGs. An interesting host:guest system of cucurbit [7]uril (1.8) in acidic water was shown by Kim et al 1.8 to only gel in aqueous solutions at pH values below its pK a , which was determined to be 2.2 by a simple titration method.…”

Development of biradical ligands toward [2×2] molecular grids

“…Selfassembly of four ligands and four metal ions will afford a [2×2] molecular grid. There are a few ingredients in our molecular design, as follows: (i) A pyrimidine bridging ligand can serve as a ferromagnetic coupler between transition metal spins [1,12,13].…”