Template Assembly of Spin Crossover One‐Dimensional Nanowires

Abstract

Spin crossover [1] (SCO) is an important example of molecular switching, [2] which can be realized by a wide variety of external stimuli. [3][4][5][6] Many applications have been explored, including sensor [7] and display [8] technologies, and data storage. [9] Much effort has been expended to develop the assembly of SCO complexes in materials and impressive results have been achieved with monodisperse nanoparticles, [10] nanocrystals, [11] thin films, [12] micro-and nanopatterned media, [13] Langmuir-Blodgett (LB) films, [14] and hysteretic soft-media assemblies. [15] Progress in this area was recently reviewed by Bousseksou et al., and the link between size morphology and switching characteristics was also examined. [16] However a striking absence from this list is the 1D nanowire. Magnetic nanowires [17] have been cited by the magnetic recording industry as being important in overcoming difficulties in domain wall motion, [18] and reliable thin-film etching [18b, 19] and template-assisted electrodeposition [20] routes to nanowires of magnetic metals have been established. However, preparation of nanowires of functional molecules by such methods is not possible, and wet chemistry routes are better employed. Melt-assisted template assembly methods have been effective for polymers [21] and in favorable cases, nanowires of functional polymers show novel optical properties, including wave guiding [22] and lasing. [23] These nanowires are prepared by adding molten polymer to a nano-porous template, such as anodic aluminum oxide (AAO), followed by acidic or basic template dissolution. Preparation of polymer nanowires is also possible by using solutionassisted template wetting, [24] and this method can be extended to include small molecules, [25] but the acidic or basic treatment means that it is less suitable for fragile small molecules that would not survive dissolution of the template. However, by appropriate modification, insolubility in acids or bases may be conferred on functional small molecules such as mononuclear SCO complexes. To this end, we have investigated the potential of alkylated derivatives [26] of Wilsons [Fe(sal 2trien)] [27] complex, where sal 2 trien is the hexadentate N 4 O 2 bisimino ligand formed by condensation of salicylaldehyde with N 1 ,N 2 -bis(2-aminoethyl)-1,2-ethanediamine, to form nanowires by template assembly in nanoporous AAO, and describe herein the first reported SCO nanowires formed from [Fe III L](BF 4 ) 0.8 Br 0.2 (1).Alkylated ligand L was prepared by substitution of the amines on sal 2 trien with 1-bromododecane, [28] and crystallization in the presence of Fe(BF 4 ) 2 ·6 H 2 O produced the mixed anion salt 1 with some bromide remaining from the ligand synthesis. Structural analysis of rod-shaped crystals of 1 showed packing by intercalation of the ligand C 12 chains (Figure 1), and close association of the coordination centers Figure 1. Molecular structure of 1, and structure of 1 at 100 K showing intercalation of C 12 ligand chains and p-p interactions between phen...

Solution and solid state properties of Fe(III) complexes bearing N-ethyl-N-(2-aminoethyl)salicylaldiminate ligands

“…This included the discovery of several new examples of SCO compounds [3,[9][10][11], the explanation of different types of SCO profiles [4,12] and the modification of SCO compounds to increase cooperativity and to direct their application into materials science [13]. Scientists have developed SCO networks [14][15][16], frameworks [17][18][19], gels [20][21][22], liquid crystals [23][24][25], nanoparticles and nanocrystals [26][27][28][29], nanowires [30], thin films [31][32][33] and have also applied patterning techniques to fabricate SCO devices [34]. Among complexes displaying SCO, [Fe(salEen) 2 ] + derivatives (salEen = N-ethyl-N-(2-aminoethyl)salicylaldiminate) are known to undergo thermal SCO sensitive to unit cell contents and supramolecular packing in the crystal [35].…”

Anion Influence on Spin State in Two Novel Fe(III) Compounds: [Fe(5F-sal2333)]X

“…The results of our studies into spin state choices with various metal-ligand combinations, including those reported here, are summarized in Table 1. LS, HS, SCO [15][16][17][18][19][20][21][22][23][24] LS, HS, SCO [4,24] LS [24][25][26] HS, SCO [24,25] a G.G. Morgan unpublished results. In both Fe(III) and Mn(III) complexes, three possible spin arrangements are possible in mononuclear complexes.…”

“…It has long been known that the R-Sal 2 -222 ligand family promotes SCO in iron(III) in addition to stabilizing both HS and LS complexes across a temperature range [15][16][17][18][19][20][21][22][23][24]. The Fe(III) R-Sal 2 -222 complexes have, in recent years, been extensively developed as new switchable materials due to the ease of derivatization which has led to the synthesis of ionic liquids [27], liquid crystals [28], Langmuir-Blodgett film formation with amphiphilic complexes [6,29], and preparation of templated nanowires [21]. We have also observed SCO in Fe(III) complexes from the R-Sal 2 -232 ligand type [4], but the majority of this class of compound remains HS from room temperature down to 5 K. In contrast, the R-Sal 2 -323 ligand type has been shown by Reedjik [26] to promote the LS state in iron (III).…”

Robust Room Temperature Hysteresis in an FeIII Spin Crossover Metallomesogen

“…[9] The C12 alkylated complex also allows for the formation of nanowires by template methods. [10] Here we report the physical and magnetic properties of the C18 alkylated complex (1) above 300 K where it exhibits a liquid crystalline phase and opening of a scan-rate dependent hysteresis window centered at 310 K.…”