Mind the gap: A complete, cooperative spin transition for a mononuclear Mn(III) complex is reported with an 8 K hysteresis window. Raman spectra collected at a single temperature in warming and cooling modes confirm the electronic bistability within the hysteresis loop. The source of the cooperativity is a disconnection in the hydrogen-bonded 1D chains that connect adjacent cations owing to an order-disorder transition in the PF(6)(-) counterion.

Six solvated salts of a mononuclear manganese(III) complex with a chelating hexadentate Schiff base ligand are reported. One member of the series, [MnL]PF(6)⋅0.5 CH(3)OH (1), shows a rare low-spin (LS) electronic configuration between 10-300 K. The remaining five salts, [MnL]NO(3)⋅C(2)H(5)OH(2), [MnL]BF(4)⋅C(2)H(5)OH(3), [MnL]CF(3)SO(3)⋅C(2)H(5)OH (4), [MnL]ClO(4)⋅C(2)H(5)OH (5) and [MnL]ClO(4)⋅0.5 CH(3)CN (6), all show gradual incomplete spin-crossover (SCO) behaviour. The structures of all were determined at 100 K, and also at 293 K in the case of 3-6. The LS salt [MnL]PF(6)⋅0.5 CH(3)OH is the only member of the series that does not exhibit strong hydrogen bonding. At 100 K two of the four SCO complexes (2 and 4) assemble into 1D hydrogen-bonded chains, which weaken or rupture on warming. The remaining SCO complexes 3, 5 and 6 do not form 1D hydrogen-bonded chains, but instead exhibit discrete hydrogen bonding between cation/counterion, cation/solvent or counterion/solvent and show no significant change on warming.

Eleven new mononuclear manganese(III) complexes prepared from two hexadentate ligands, L1 and L2, with different degrees of steric bulk in the substituents are reported. L1 and L2 are Schiff bases resulting from condensation of N,N'-bis(3-aminopropyl)ethylenediamine with 3-methoxy-2-hydroxybenzaldehyde and 3-ethoxy-2-hydroxybenzaldehyde respectively, and are members of a ligand series we have abbreviated as R-Sal2323 to indicate the 323 alkyl connectivity in the starting tetraamine and the substitution (R) on the phenolate ring. L1 hosts a methoxy substituent on both phenolate rings, while L2 bears a larger ethoxy group in the same position. Structural and magnetic properties are reported in comparison with those of a previously reported analogue with L1, namely, [MnL1]NO3, (1e). The BPh4(-) and PF6(-) complexes [MnL1]BPh4, (1a), [MnL2]BPh4, (2a), [MnL1]PF6, (1b'), and [MnL2]PF6, (2b), with both ligands L1 and L2, remain high-spin (HS) over the measured temperature range. However, the monohydrate of (1b') [MnL1]PF6·H2O, (1b), shows gradual spin-crossover (SCO), as do the ClO4(-), BF4(-), and NO3(-) complexes [MnL1]ClO4·H2O, (1c), [MnL2]ClO4, (2c), [MnL1]BF4·H2O, (1d), [MnL2]BF4·0.4H2O, (2d), [MnL1]NO3, (1e), and [MnL2]NO3·EtOH, (2e). The three complexes formed with ethoxy-substituted ligand L2 all show a higher T1/2 than the analogous complexes with methoxy-substituted ligand L1. Analysis of distortion parameters shows that complexes formed with the bulkier ligand L2 exhibit more deformation from perfect octahedral geometry, leading to a higher T1/2 in the SCO examples, where T1/2 is the temperature where the spin state is 50% high spin and 50% low spin. Spin state assignment in the solid state is shown to be solvate-dependent for complexes (1b) and (2e), and room temperature UV-visible and NMR spectra indicate a solution-state spin assignment intermediate between fully HS and fully low spin in 10 complexes, (1a)-(1e) and (2a)-(2e).

No 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...