{CoIIIMnIII}n corrugated chains based on heteroleptic cyanido metalloligands

Abstract

The use of the cyanide-bearing complexes PPh₄[Co^III(4,4′-dmbipy)(CN)₄] and PPh₄[Co^II(dmphen)(CN)₃] as metalloligands towards [Mn(salen)(H₂O)]ClO₄ affords one-dimensional coordination polymers with the formulas {[Mn^III(salen)(μ-NC)₂Co^III(4,4-dmbipy)(CN)₂]·H₂O}_n (1) and {[Mn^III(salen)(μ-NC)₂Co^III(dmphen)(CN)₂]}_n (2) [PPh₄⁺ = tetraphenylphosphonium cation, 4,4′-dmbipy = 4,4′-dimethyl-2,2′-bipyridine, dmphen = 2,9-dimethyl-1,10-phenanthroline and H₂salen = N,N′-ethylenebis(salicylideneimine)]. Compounds 1 and 2 were structurally characterized. Their structures consist of neutral chains with regular alternating [Mn(salen)]⁺ and [Co^III(4,4′-dmbipy)(CN)₄]⁻ (1)/[Co^III(dmphen)(CN)₄]⁻ (2) moieties, the latter ones acting as bis-monodentate ligands towards the Mn(III) units through two of their four cyanide groups. During the synthesis, the cobalt(II) ion of the starting [Co^II(dmphen)(CN)₃]⁻ metalloligand is oxidized to Co(III) and it takes an additional cyanide ligand to transform into {Co^III(dmphen)(CN)₄} in 2. Magnetic studies have been carried out on 1 and 2 in the temperature range 1.9–300 K which yielded local negative zero-field splitting parameters of −3.26 (1) and −4.38 cm⁻¹ (2). Frequency-dependent alternating current susceptibility signals under an external applied magnetic field (dc) were clearly observed for 1 and 2 indicating slow magnetic relaxation, that is, Single Ion Magnet (SIM) behaviour. The energy barriers (E_a) to reverse the magnetization direction under an applied dc magnetic field of 2000 Oe were 12.0(2) (1) and 9.4(3) cm⁻¹ (2), whereas the values of the pre-exponential factor (τ_o) were 1.40(2) × 10⁻⁸ (1) and 2.5(2) × 10⁻⁸ s (2).