Abstract
Single-crystal X and Q band EPR of a hydrogen-bridged l-dimensional Cu(II) complex, [Cu(stpy)2(CH3COO)2(H2O)2] [CU(stpy)2(CH3COO) 2(H2O)], containing both octahedral and square pyramidal geometries in the same unit cell, has been studied at 300 K. EPR of powder samples at X band frequencies at 300 K and 77 K show exchange-narrowed resonance. The peak-to-peak linewidths of the signals are 80 G and 85 G, respectively. However, at Q band frequencies it exhibits an axially symmetric spectrum with spin Hamiltonian parameters g|| = 2.303 and g⊥ = 2.077, corresponding to an |x2 − y2〉 ground state. Single-crystal X band EPR spectra show a single resonance line for all the orientations, indicating the complex to be in the strong exchange regime. On the other hand, Q band spectra exhibit two lines corresponding to the weak exchange regime. An estimate of the interchain-site exchange coupling constant J′ = 0.0125(3) cm−1 also reveals weak coupling between the magnetically distinct Cu(II) centres. The ratio of J′/J = 8.25 × 10−2 is low enough to make the interactions almost l-dimensional, in agreement with X-ray data. EPR linewidth and lineshape analyses also support l-dimensional behaviour of the system.