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.