The effect of the large cation matrix and delocalization of electronic density on the switchable behaviour of heterotrimetallic cyanido-bridged FexMn9−xW6 clusters

Abstract

Multimetallic coordination clusters offer significant potential for exhibiting unique structural forms and functional behaviour driven by site-selective metal-ion embedment and the ability to combine specific sets of metal ions within the coordination skeleton. In this work, we present {Fe^II_xMn^II_9−x[W^V(CN)₈]₆(MeOH)₂₄}·nMeOH (x = 2–7 (2–7); n = 15, 18), an Fe_xMn_9−xW₆ cyanido-bridged cluster series combining (i) Fe(II) cations and cyanido-bridged Fe(II)–W(V) pairs as components, ensuring spin-crossover (SCO) and electron-transfer (ET) switchable behaviour, respectively, and (ii) 6-coordinate complexes of Mn(II), forming a large cation matrix due to their exceptionally long bonds. On cooling from RT, 2–4 revealed a complete ^HSFe^II → ^LSFe^II SCO transition at the central [Fe(μ-NC)₆] moieties below 200 K. In contrast, 5–7 exhibited ^HSFe^IIW^V → ^HSFe^IIIW^IV ET with thermal hysteresis (6, 7) near 200 K, triggered by SCO at higher temperatures. The reversible spin or valence state changes are coupled with structural transitions and are tuneable with the 3d metal ion composition, as evidenced by comprehensive temperature-dependent data involving SCXRD, PXRD, and SQUID measurements, IR spectroscopy, and ⁵⁷Fe Mössbauer spectroscopy. The observed switchable behavior is discussed regarding the significant matrix effects of Mn(II) and the degree of electronic density delocalization along the Fe–W subnetworks of the cyanido-bridged framework. This work significantly expands the switchable 15-nuclear trimetallic six-capped body-centered cubic cluster library.