Effect of Structural Isomerism on Magnetic Dynamics: from Single-Molecule Magnet to Single-Chain Magnet

This
Paper reports the first examples of O–P–O bridged
Mn2(salen)2 (salen = N,N'-bis­(salicylidene)­ethylenediamine) chain compounds,
namely,
[Mn2(salen)2(2-FC6H4PO3H)]­(ClO4)·1/2CH3OH (1) and [Mn2(salen)2(4-FC6H4PO3H)]­(ClO4) (2). The phosphonate
ligands adopt a syn-anti bidentate bridging mode
in 1 and a syn-syn bidentate bridging
mode in 2, originated from the isomeric phosphonate ligands.
The different bridging modes cause a significant change in the Mn–O···O–Mn
torsion angle over the O–P–O bridge, which are 96.6
and 1.9° for 1 and 2, respectively.
As a result, the antiferromagnetic (AF) exchange couplings mediated
through the O–P–O pathway are extremely weak in 1, and the overall magnetic behaviors are dominated by the
Mn2(salen)2 moieties. Single-molecule magnetic
behavior is observed in 1. For compound 2, the AF interaction over the O–P–O bridge is much
stronger. The coexistence of metamagnetism and single-chain magnetic
behavior is observed for 2.