Studies of Er(iii)–W(v) compounds showing nonlinear optical activity and single-molecule magnetic properties

Abstract

Self-assembly of Er(III) ions with octacyanidotungstate(V) in the presence of pure N,N-dimethylacetamide (dma) resulted in the formation of one-dimensional zigzag chain {[Er^III(dma)₅][W^V(CN)₈]}_n (1). Coordination polymer 1 crystallizes in the non-centrosymmetric space group P2₁ and it exhibits second harmonic generation (SHG) effect with SH susceptibility of 5.8 × 10⁻¹¹ esu. Interestingly, the treatment of 1 with small amount of water results in the generation of another complex salt [Er^III(dma)₅(H₂O)₂]·[W^V(CN)₈]·dma·H₂O (2) which crystallizes in centrosymmetric space groups of P2₁/n, disqualifying the occurrence of SHG phenomenon. On the other hand, the elimination of cyanido-bridges and formation of seven-coordinated erbium(III) centre resulted in magnetic field induced single molecule magnet (SMM) behaviour with effective energy barrier of 28.6(3) K for 2. Finally, self-assembly of Er(III) with octacyanidotungstate(V) in water/dma mixture gave a complex salt [Er^III(dma)₄(H₂O)₃]·[W^V(CN)₈]·dma·3H₂O (3) similar to 2. Dynamic magnetic studies reveal that 3 is also showing slow magnetic relaxation, however, the substitution of single dma by water molecule induces the change in the local geometry of Er(III) centre leading to weak SMM properties for 3.