Antiferromagnetic resonance (AFMR) is used to characterize the canted antiferromagnetic state and to probe magnetostructural correlations within a series of layered solids including KMnPO4. H2O, four manganese alkylphosphonates, Mn(O3PCnH2n+l). H2O (n = 3-6), and manganese phenylphosphonate. All samples were investigated as powders. A complete set of magnetic parameters, determined from AFMR and SQUID magnetometry, are presented for each material. The high field electron magnetic resonance facility at the National High Magnetic Field Laboratory in Tallahassee, Florida, was used to acquire AFMR spectra. Source frequencies ranged from 24 to 380 GHz, and the magnetic field range was 0-14.5 T. Correlations between the magnetic exchange and the electronic structure of the bridging ligand as well as measurements of the magnetic anisotropy in the ordered state are determined from analysis of the frequency and field dependence of the AFMR signals.