To determine the temperature dependence of oxidation and spin state of the metal center coordinated with cyanide NC -, variable temperature FT-IR measurements were carried out for 1•2DMF•H 2 O and 1•2DMF•in the temperature range of 300 -100 K (Figures ). At 300 K, two sharp absorption bands were observed at 2114 cm -1 and 2131 cm -1 , which are characteristic of  (CN) stretching vibration coming from the free cyanide of building block and bridging cyanide of Mo V -CN-Fe II HS, respectively. Upon cooling the sample from 300 K to 100 K, the position of the free cyanide remains the same whereas the stretching vibration of bridging  (CN) shifts to a lower frequency of 2127 cm -1 suggesting the possibility of Mo V -C≡N-Fe II LS moiety. The changes that occurred in the  (CN) stretching vibration upon cooling were also reversible upon heating to 300 K (Fig. ). This study reveals that there is a thermal dependency of the spin states of the system in the temperature range of 300 -100 K, which is further confirmed by magnetic measurement (vide infra).