Rotaxane-like Complex Consisting of 1D and 2D Cyano-Bridged Coordination Polymers: Fe(4-methylpyrimidine)₂[Au(CN)₂]₂·Fe(4-methylpyrimidine)₂(H₂O)₂[Au(CN)₂]·[Au(CN)₄]

Coordination polymers showing the spin-crossover (SCO) phenomenon have attracted considerable attention because of their tunable properties and potential applications as sensors or switching materials. Although many of these polymers have been reported, examples with mixed-valence metal ions and N-heteroaromatic ligands other than pyridine-, pyrazine-, and bipyridine-type ligands are scarce. In this study, we synthesized a novel cyano-bridged coordination polymer, Fe(4-methylpyrimidine) 2 [Au(CN) 2 ] 2 ·Fe(4-methylpyrimidine) 2 (H 2 O) 2 [Au(CN) 2 ]·[Au(CN) 4 ] (complex 1 ), with a rotaxane-like structure. This polymer comprised monovalent Au atoms in a two-dimensional Soma–Iwamoto-type {Fe(4-methylpyrimidine) 2 [Au(CN) 2 ] 2 } n layer as well as a one-dimensional {Fe(4-methylpyrimidine) 2 (H 2 O) 2 [Au(CN) 2 ]} n n + cationic chain and trivalent Au atoms in the zero-dimensional [Au(CN) 4 ] − anion. Complex 1 showed a half SCO phenomenon above 300 K. The Fe K-edge X-ray absorption fine structure (XAFS) spectrum of complex 1 revealed that some of the Fe sites were in a low-spin state at room temperature, while all of the Fe sites were in a high-spin state at 395 K. The Au L 3 -edge XAFS spectrum of complex 1 revealed that monovalent and trivalent Au sites were present at room temperature and 398 K.