6533b826fe1ef96bd1284631

RESEARCH PRODUCT

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

subject

description

Reaction of the ligand 2,2,2-tris(2-aza-3-((5-akloxy)(6-methyl)(2-pyridyl))prop-2-enyl)ethane (C n -tameMe) with Fe(X) 2 . sH 2 O salts afforded a series of spin crossover metallomesogens with general formula [Fe(C n -tame)](X) 2 . sH 2 O (s ≥ 0), with n = 6, 10, 12, 14, 16, 17, 18, or 20 and X =ClO 4 - or BF 4 -. Single crystal X-ray measurements have been performed on the [Fe(C 6 -tameMe)](ClO 4 ) 2 (C 6 -1) derivative at 100 K. The complex C 6 -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 C n -tameMe ligand. The average Fe-N im and Fe-N py bond distance is 1.918(2) A and 2.084(2) A, 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(C 18 -tameMe)](ClO 4 )2 (C 18 -1) and the series [Fe(C n -tameMe)](BF 4 ) 2 (n = 10,12,14,16,17,18, 20) (C n -2) series show thermally driven spin crossover and mesomorphism above 300 K. The thermotropic behavior of compounds C n -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 BF 4 - or ClO 4 - anions. This gives rise to a mesophase with molten alkyl chains but with restricted movement through the ionic layer. Compounds C n -2 show thermochromic properties, they are dark violet in the LS state (T 275 K, Cr, S x ). These bi-functional materials combine spin state change and mesomorphic behavior in a narrow interval of temperatures, 300-375 K.