To apply to magnetic memory device of nanodispersed spin crossover complex, we have studied the magnetic properties of hetero-spin crossover complex of [Fe(Htrz)3x(4-NHtrz)3−3x](BF4)2nH2O in emulsion polymerization of trifluoroethylmethacrylate using poly (vinyl alcohol) as a protective colloid. Effect of central transition metal ion of CoII ions on the spin crossover complex in the emulsion polymerization was investigated. The experimental results can be explained by theoretical consideration of electron density between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and Fe-N bond lengths, magnetic parameters, g-factor using density functional theory. This result was thought to have arisen from ligand field theory with a slight distribution of bond-length based on a slight exchange interaction due to a miner Jahn-Teller effect.