To understand fully the spin-state switching phenomenon and the electronic and spin-states of the iron centres present in both complexes 1•2DMF•H2O and 1•2DMF, 57 Fe Mössbauer spectroscopic studies were carried out for both solvated and desolvated sample at 5, 90, 120 and 300 K (Figure , Figure -25, Table ). ) was observed and the LS-Fe II (δ = 0.53 mm s -1 , ΔEQ = 0.24 mm s -1 ) peak intensity decreases (HS/LS ratio 36.7/63.3). Upon further increasing the temperature to 120 K, the HS-Fe II intensity (δ = 1.13 mm s -1 , ΔEQ = 2.81 mm s -1 ) increases and LS-Fe II intensity (δ = 1.13 mm s -1 , ΔEQ = 2.81 mm s -1 ) decreases further with a HS /LS ratio of 57.9/42.1. Finally at 300 K, the amount of HS Fe II ions increases notably (δ = 1.13 mm s -1 , ΔEQ = 2.81 mm s -1 ) with presence of small amount of residual LS-Fe II ion (δ = 1.13 mm s -1 , ΔEQ = 2.81 mm s -1 ) with a HS /LS ratio of 63.5/36.5. The relative amounts of Fe II LS/Fe II HS ions derived from the Mössbauer spectroscopic studies, as depicted in Table for 1•2DMF.H2O and 1•2DMF were in good agreement with the magnetic studies (vide infra).