Iron(II) Metallomesogens Exhibiting Coupled Spin State and Liquid Crystal Phase Transitions near Room Temperature

Reaction of the ligand 2,2,2‐tris(2‐aza‐3‐((5‐akloxy)(6‐methyl)(2‐pyridyl))prop‐2‐enyl)ethane (Cn‐tameMe) with Fe(X)2 · sH2O salts afforded a series of spin crossover metallomesogens with general formula [Fe(Cn‐tame)](X)2 · sH2O (s ≥ 0), with n = 6, 10, 12, 14, 16, 17, 18, or 20 and X = ClO4− or BF4−. Single crystal X‐ray measurements have been performed on the [Fe(C6‐tameMe)](ClO4)2 (C6‐1) derivative at 100 K. The complex C6‐1 crystallizes in the triclinic system and adopts the Pbca space group. The iron(II) ion is in a distorted octahedral environment shaped by three imine and three pyridine nitrogen atoms of the Cn‐tameMe ligand. The average Fe–Nim and Fe–Npy bond distance is 1.918(2) Å and 2.084(2) Å, respectively, which are characteristic for the Fe(II) ion in the LS state. Neighbor molecules are packed in a head‐to‐head fashion forming a layered microsegregated structure. Ionic layer is composed of cationic spin crossover head‐groups and perchlorate anions, whereas alkyl tails are arranged into a non‐polar hydrocarbon layer. The complex [Fe(C18‐tameMe)](ClO4)2 (C18‐1) and the series [Fe(Cn‐tameMe)](BF4)2 (n = 10, 12, 14, 16, 17, 18, 20) (Cn‐2) series show thermally driven spin crossover and mesomorphism above 300 K. The thermotropic behavior of compounds Cn‐2 depends on the chain length defined by n. A common structural feature among all homologues of the series is a similar layered structure and adoption on melting of a smectic mesophase at ca. 350–375 K. Formation of the mesophase is due to the melting of the alkyl chains rather than a rearrangement of the ionic bilayers composed of polar SCO cations and BF4− or ClO4− anions. This gives rise to a mesophase with molten alkyl chains but with restricted movement through the ionic layer. Compounds Cn‐2 show thermochromic properties, they are dark violet in the LS state (T 275 K, Cr, SX). These bi‐functional materials combine spin state change and mesomorphic behavior in a narrow interval of temperatures, 300–375 K. Reaction of the ligand 2,2,2‐tris(2‐aza‐3‐((5‐akloxy)(6‐methyl)(2‐pyridyl))prop‐2‐enyl)ethane (Cn‐tameMe) with iron(II) salts has afforded two series of spin crossover metallomesogens Cn‐1 (n = 6, 18; ClO4−) and Cn‐2 (n = 10–20; BF4−) that show thermally driven spin crossover and mesomorphism above 300 K. The thermotropic behavior and temperature of the magnetic anomaly of compounds Cn‐2 depend on the chain length defined by n.