Modulation of the ring size and nuclearity of metallamacrocycles via the steric effect of ligands: Preparation and characterization of 18-membered hexanuclear, 24-membered octanuclear, and 30-membered decanuclear manganese metal lad iazamacrocycles with alpha- and beta-branched N-acylsalicylhydrazides

Abstract

Hexanuclear, octanuclear, and decanuclear manganese metalladiazamacrocycles have been prepared by reacting a series of pentaclentate ligands, N-acylsalicylhydrazides (N-(3-methylbutanoyl)salicylhydrazide (H(3)3-mbshz), N-(phenylacetyl)salicylhydrazide (H(3)pashz), N-(3,3-dimethylbutanoyl)salicylhydrazide (H(3)3-dmbshz), N-(2-methy(propanoyl)salicylhydrazide (H(3)2-mpshz), N-((R,S)-2-methylbutanoyl)salicylhydrazide (H3RS-2-mbshz), N-((S)-2-methylbutanoyl)salicylhydrazide (H3S-2-mbshz), and N-(2,2-dimethylpropanoyl)salicylhydrazide (H(3)2-dmpshz)), with manganese(ll) acetate tetrahydrate. The self-assembled, supramolecular complexes assume a nearly planar cyclic structure with an -(Mn-N-N)(n) backbone and measure similar to 2.1, similar to 2.3, and similar to 2.6 nm in outer diameters for n = 6, 8, and 10, respectively. The chiralities of the manganese centers on the metalladiazamacrocycle occur in alternating (...)Delta Delta Delta Delta(...) configurations. While beta-branched N-acylsalicylhydrazides (H(3)3-mbshz, H(3)pashz, H(3)3-dmbshz) with a sterically flexible C alpha. methylene group yield 18-membered hexanuclear manganese metalladiazamacrocycles of S-6 point group symmetry, alpha-branched N-acylsalicylhydrazides lead to 24-membered octanuclear manganese metalladiazamacrocycles or 30-membered decanuclear manganese metalladiazamacrocycles depending on the size of the N-acyl substituents. The alpha-branched H(3)2-mpshz ligand with the sterically least demanding isopropyl tail at the N-acyl position yields a 24-membered octanuclear manganese metalladiazamacrocycle of S-8 point group symmetry, but other a-branched N-acylsalicylhydrazides such as H3RS-2-mbshz, H3S-2-mbshz, and H32-dmpshz lead to 30-membered decanuclear manganese metalladiazamacrocycles of S-10 point group symmetry. The magnetic properties of the metalladiazamacrocycles are characterized by a weak antiferromagnetic exchange interaction, with J(eff) = -8.5 to -3.8 K between the Mn3+ ion spins with S = 2 in the cyclic system.