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 4(4) topology). The results of M(T)/H on powder samples of Fe(TpyP) show that the effective moment mu(eff) of Fe2+ is 5.52 mu(B) at 340 K, close to the expected value for a high spin Fe2+ (S=2) ion. mu(eff) increases to 5.90 mu(B) as T decreases to the range of 170 K < T < 220 K, and then decreases monotonically as T decreases further. The behavior of mu(eff) 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.