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 C m c a (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 μ eff of Fe 2 + is 5.52 μ B at 340 K , close to the expected value for a high spin Fe 2 + ( S = 2 ) ion. μ eff increases to 5.90 μ B as T decreases to the range of 170 K < T < 220 K , and then decreases monotonically as T decreases further. The behavior of μ eff in the high temperature region may be attributed to a positive Fe 2 + - Fe 2 + 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 .