Does the Solid-Liquid Crystal Phase Transition Provoke the Spin-State Change in Spin-Crossover Metallomesogens?
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- 作者：M. Seredyuk ; A. B. Gaspar ; V. Ksenofontov ; Y. Galyametdinov ; J. Kusz ; P. Gü ; tlich
- 刊名：Journal of the American Chemical Society
- 出版年：2008
- 出版时间：January 30, 2008
- 年：2008
- 卷：130
- 期：4
- 页码：1431 - 1439
- 全文大小：536K
- 年卷期：v.130,no.4(January 30, 2008)
- ISSN：1520-5126
文摘
Three types of interplay/synergy between spin-crossover (SCO) and liquid crystalline (LC) phasetransitions can be predicted: (i) systems with coupled phase transitions, where the structural changes associatedto the Cr
LC phase transition drives the spin-state transition, (ii) systems where both transitions coexist in thesame temperature region but are not coupled, and (iii) systems with uncoupled phase transitions. Here we presenta new family of Fe(II) metallomesogens based on the ligand tris[3-aza-4-((5-Cn)(6-R)(2-pyridyl))but-3-enyl]amine,with Cn = hexyloxy, dodecyloxy, hexadecyloxy, octadecyloxy, eicosyloxy, R = hydrogen or methyl (Cn-trenH orCn-trenMe), which affords examples of systems of types i, ii, and iii. Self-assembly of the ligands Cn-trenH andCn-trenMe with Fe(A)2·xH2O salts have afforded a family of complexes with general formula [Fe(Cn-trenR)](A)2·sH2O (s 
0), with A = ClO4-, F-, Cl-, Br- and I-. Single-crystal X-ray diffraction measurements have beenperformed on two derivatives of this family, named as [Fe(C6-trenH)](ClO4)2 (C6-1) and [Fe(C6-trenMe)](ClO4)2(C6-2), at 150 K for C6-1 and at 90 and 298 K for C6-2. At 150 K, C6-1 displays the triclinic space group P
,whereas at 90 and at 298 K C6-2 adopts the monoclinic P21/c space group. In both compounds the iron atomsadopt a pseudo-octahedral symmetry and are surrounded by six nitrogen atoms belonging to imino groups andpyridines of the ligands Cn-trenH and Cn-trenMe. The average Fe(II)-N bonds (1.963(2) Å) at 150 K denote thatC6-1 is in the low-spin (LS) state. For C6-2 the average Fe(II)-N bonds (2.007(1) Å) at 90 K are characteristic ofthe LS state, while at 298 K they are typical for the high-spin (HS) state (2.234(3) Å). Compound C6-1 and [Fe(C18-trenH)](ClO4)2 (C18-1) adopts the LS state in the temperature region between 10 and 400 K, while compoundC6-2 and [Fe(Cn-trenMe)](ClO4)2 (n = 12 (C12-2), 18 (C18-2)) exhibit spin crossover behavior at T1/2 centeredaround 140 K. The thermal spin transition is accompanied by a pronounced change of color from dark red (LS)to orange (HS). The light-induced excited spin state trapping (LIESST) effect has been investigated in compoundsC6-2, C12-2 and C18-2. The T1/2LIESST is 56 K (C6-2), 48 K (C16-2), and 56 K (C18-2). On the basis of differentialscanning calorimetry, optical polarizing microscopy, and X-ray diffraction findings for C18-1, C12-2, and C18-2 athigh temperature a smectic mesophase SX has been identified with layered structures similar to C6-1 and C6-2.The compounds [Fe(Cn-trenH)](Cl)2·sH2O (n = 16 (C16-3, s = 3.5, C16-4, s = 0.5, C16-5, s = 0), 18 (C18-3, s =3.5, C18-4, s = 0.5, C18-5, s = 0), 20 (C20-3, s = 3.5, C20-4, s = 0.5, C20-5, s = 0)) and [Fe(C18-tren)](F)2·sH2O(C18-6, s = 3.5, C18-7, s = 0) show a very particular spin-state change, while [Fe(C18-tren)](Br)2·3H2O (C18-8)together with [Fe(C18-tren)](I)2 (C18-9) are in the LS state (10-400 K) and present mesomorphic behavior likethat observed for the complexes C18-1, C12-2, and C18-2. In compounds Cn-3 50% of the Fe(II) ions undergospin-state change at T1/2 = 375 K induced by releasing water, and in partially dehydrated compounds (s = 0.5)the Cr
SA phase transition occurs at 287 K (C16-4), 301 K (C18-4) and 330 K (C20-4). For the fully dehydratedmaterials Cn-5 50% of the Fe(II) ions are in the HS state and show paramagnetic behavior between 10 and 400K. In the partially dehydrated Cn-4 the spin transition is induced by the change of the aggregate state of matter(solidliquid crystal). For compound C18-6 the full dehydration to C18-7 provokes the spin-state change of nearly50% of the Fe(II) ions. The compounds Cn-3 and C18-6 are dark purple in the LS state and become light purple-brown when 50% of the Fe(II) atoms are in the HS state.
LC phase transition drives the spin-state transition, (ii) systems where both transitions coexist in thesame temperature region but are not coupled, and (iii) systems with uncoupled phase transitions. Here we presenta new family of Fe(II) metallomesogens based on the ligand tris[3-aza-4-((5-Cn)(6-R)(2-pyridyl))but-3-enyl]amine,with Cn = hexyloxy, dodecyloxy, hexadecyloxy, octadecyloxy, eicosyloxy, R = hydrogen or methyl (Cn-trenH orCn-trenMe), which affords examples of systems of types i, ii, and iii. Self-assembly of the ligands Cn-trenH andCn-trenMe with Fe(A)2·xH2O salts have afforded a family of complexes with general formula [Fe(Cn-trenR)](A)2·sH2O (s 0), with A = ClO4-, F-, Cl-, Br- and I-. Single-crystal X-ray diffraction measurements have beenperformed on two derivatives of this family, named as [Fe(C6-trenH)](ClO4)2 (C6-1) and [Fe(C6-trenMe)](ClO4)2(C6-2), at 150 K for C6-1 and at 90 and 298 K for C6-2. At 150 K, C6-1 displays the triclinic space group P,whereas at 90 and at 298 K C6-2 adopts the monoclinic P21/c space group. In both compounds the iron atomsadopt a pseudo-octahedral symmetry and are surrounded by six nitrogen atoms belonging to imino groups andpyridines of the ligands Cn-trenH and Cn-trenMe. The average Fe(II)-N bonds (1.963(2) Å) at 150 K denote thatC6-1 is in the low-spin (LS) state. For C6-2 the average Fe(II)-N bonds (2.007(1) Å) at 90 K are characteristic ofthe LS state, while at 298 K they are typical for the high-spin (HS) state (2.234(3) Å). Compound C6-1 and [Fe(C18-trenH)](ClO4)2 (C18-1) adopts the LS state in the temperature region between 10 and 400 K, while compoundC6-2 and [Fe(Cn-trenMe)](ClO4)2 (n = 12 (C12-2), 18 (C18-2)) exhibit spin crossover behavior at T1/2 centeredaround 140 K. The thermal spin transition is accompanied by a pronounced change of color from dark red (LS)to orange (HS). The light-induced excited spin state trapping (LIESST) effect has been investigated in compoundsC6-2, C12-2 and C18-2. The T1/2LIESST is 56 K (C6-2), 48 K (C16-2), and 56 K (C18-2). On the basis of differentialscanning calorimetry, optical polarizing microscopy, and X-ray diffraction findings for C18-1, C12-2, and C18-2 athigh temperature a smectic mesophase SX has been identified with layered structures similar to C6-1 and C6-2.The compounds [Fe(Cn-trenH)](Cl)2·sH2O (n = 16 (C16-3, s = 3.5, C16-4, s = 0.5, C16-5, s = 0), 18 (C18-3, s =3.5, C18-4, s = 0.5, C18-5, s = 0), 20 (C20-3, s = 3.5, C20-4, s = 0.5, C20-5, s = 0)) and [Fe(C18-tren)](F)2·sH2O(C18-6, s = 3.5, C18-7, s = 0) show a very particular spin-state change, while [Fe(C18-tren)](Br)2·3H2O (C18-8)together with [Fe(C18-tren)](I)2 (C18-9) are in the LS state (10-400 K) and present mesomorphic behavior likethat observed for the complexes C18-1, C12-2, and C18-2. In compounds Cn-3 50% of the Fe(II) ions undergospin-state change at T1/2 = 375 K induced by releasing water, and in partially dehydrated compounds (s = 0.5)the CrSA phase transition occurs at 287 K (C16-4), 301 K (C18-4) and 330 K (C20-4). For the fully dehydratedmaterials Cn-5 50% of the Fe(II) ions are in the HS state and show paramagnetic behavior between 10 and 400K. In the partially dehydrated Cn-4 the spin transition is induced by the change of the aggregate state of matter(solidliquid crystal). For compound C18-6 the full dehydration to C18-7 provokes the spin-state change of nearly50% of the Fe(II) ions. The compounds Cn-3 and C18-6 are dark purple in the LS state and become light purple-brown when 50% of the Fe(II) atoms are in the HS state.