| Summary: | Two novel <i>1D</i> heterobimetallic compounds {[Mn<sup>III</sup>(SB<sup>2+</sup>)M<sup>III</sup>(CN)<sub>6</sub>]·4H<sub>2</sub>O}<sub>n</sub> (SB<sup>2+</sup> = N,N′-ethylenebis(5-trimethylammoniomethylsalicylideneiminate) based on orbitally degenerate cyanidometallates [Os<sup>III</sup>(CN)<sub>6</sub>]<sup>3−</sup> (<b>1</b>) and [Ru<sup>III</sup>(CN)<sub>6</sub>]<sup>3−</sup> (<b>2</b>) and Mn<sup>III</sup> Schiff base complex were synthesized and characterized structurally and magnetically. Their crystal structures consist of electrically neutral, well-isolated chains composed of alternating [M<sup>III</sup>(CN)<sub>6</sub>]<sup>3−</sup> anions and square planar [Mn<sup>III</sup>(SB<sup>2+</sup>)]<sup>3+</sup> cations bridged by cyanide groups. These -ion magnetic anisotropy of Mn<sup>III</sup> centers. These results indicate that the presence of compounds exhibit single-chain magnet (SCM) behavior with the energy barriers of Δ<i>τ<sub>1</sub></i>/<i>k</i><sub>B</sub> = 73 K, Δ<i>τ<sub>2</sub></i>/<i>k</i><sub>B</sub> = 41.5 K (<b>1</b>) and Δ<i>τ<sub>1</sub></i>/<i>k</i><sub>B</sub> = 51 K, Δ<i>τ<sub>2</sub></i> = 27 K (<b>2</b>). Blocking temperatures of <i>T</i><sub>B</sub> = 2.8, 2.1 K and magnetic hysteresis with coercive fields (at 1.8 K) of 8000, 1600 Oe were found for <b>1</b> and <b>2</b>, respectively. Theoretical analysis of the magnetic data reveals that their single-chain magnet behavior is a product of a complicated interplay of extremely anisotropic triaxial exchange interactions in M<sup>III</sup>(4d/5d)–CN–Mn<sup>III</sup> fragments: −<i>J<sub>x</sub>S</i><sub>M</sub><i><sup>x</sup>S</i><sub>Mn</sub><i><sup>x</sup></i>−<i>J<sub>y</sub>S</i><sub>M</sub><i><sup>y</sup>S</i><sub>Mn</sub><i><sup>y</sup></i>−<i>J<sub>z</sub>S</i><sub>M</sub><i><sup>z</sup>S</i><sub>Mn</sub><i><sup>z</sup></i>, with opposite sign of exchange parameters <i>J<sub>x</sub></i> = −22, <i>J<sub>y</sub></i> = +28, <i>J<sub>z</sub></i> = −26 cm<sup>−1</sup> and <i>J<sub>x</sub></i> = −18, <i>J<sub>y</sub></i> = +20, <i>J<sub>z</sub></i> = −18 cm<sup>−1</sup> in <b>1</b> and <b>2</b>, respectively) and single orbitally degenerate [Os<sup>III</sup>(CN)<sub>6</sub>]<sup>3−</sup> and [Ru<sup>III</sup>(CN)<sub>6</sub>]<sup>3−</sup> spin units with unquenched orbital angular momentum in the chain compounds <b>1</b> and <b>2</b> leads to a peculiar regime of slow magnetic relaxation, which is beyond the scope of the conventional Glaubers’s <i>1D</i> Ising model and anisotropic Heisenberg model.
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