This Paper reports the first examples of O-P-O bridged Mn-2(salen)(2) (salen = N,N'-bis(salicylidene)-ethylenediamine) chain compounds, namely, [Mn-2(salen)(2)(2-FC6H4PO3H)](ClO4)center dot 1/2CH(3)OH (1) and [Mn-2(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 center dot center dot center dot O-Mn torsion angle over the O-P-O bridge, which are 96.6 and 1.9 degrees 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 Mn-2(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.