Magnetic properties of an Fe(II) meso-tetra(4-pyridyl)porphyrin network

Magnetic properties of Fe(II) meso-tetra(4-pyridyl)porphyrin [Fe(TpyP)], a recently discovered metalloporphyrin network, were investigated using magnetic susceptibility M (T) H, isothermal magnetization M (H), and heat capacity C (T) measurements. The crystal structure of Fe(TpyP) at room temperature is orthorhombic with a space group Cmca (No. 64). This network gives rise to an unprecedented two-dimensional paddle-wheel-like pattern (a 44 topology). The results of M (T) H on powder samples of Fe(TpyP) show that the effective moment μeff of Fe2+ is 5.52 μB at 340 K, close to the expected value for a high spin Fe2+ (S=2) ion. μeff increases to 5.90 μB as T decreases to the range of 170 K<T<220 K, and then decreases monotonically as T decreases further. The behavior of μeff in the high temperature region may be attributed to a positive Fe2+ - Fe2+ coupling. The low field (H≤4 kG) M (T) H data reveal an anomalous behavior of this compound in the low temperature region which seems spin-glass-like. A small hysteresis was observed in M (H) measured at 2 K. No anomaly was seen in the C (T) data from 1.6 to 25 K.