Dinuclear helicate and tetranuclear cage assembly using appropriately designed ditopic triazole-azine ligands

Abstract

Architecture, helicate or cage, is controlled by choice of meta vs. para phenylene linker in new, robust, ditopic triazole-pyrimidine ligands.

Correlations between ligand field Δo, spin crossover T1/2 and redox potential Epa in a family of five dinuclear helicates

“…So, whilst the same linker is used, both bidentate ligand binding sites are changed from featuring azine-triazole to azole-triazole binding pockets. The five new ditopic ligands of azole-triazole, 2-imidazole L 2NHIm-meta , 4-imidazole L 4NHIm-meta , 1methyl-4-imidazole L 4NMeIm-meta , 4-oxazole L 4OIm-meta and 4thiazole L 4SIm-meta , were synthesised by refluxing the previously reported ethylated bis-thioamide 57 In the same way, the analogous dinuclear Ni(II) helicates were prepared and isolated by vapour diffusion of diethyl ether into the MeCN reaction solutions. After air drying, 1 Ni -5 Ni were obtained, as analytically pure pale violet/pink powders (Figure S9, ESI), as the following solvatomorphs, all hydrates, in 50-96% yield:…”

“…The octahedral distortion parameters (sum of deviations of the 12 cis angles from 90°) of the Fe(II) centres in 1-5 lie in a narrow range, 56.8-62.0° (Table 1 and S1 (60.3°), and falls in the range seen for all of the SCO-active helicates reported in the literature (51-70°). 11,57 The intrahelicate Fe•••Fe distances in 1-5 lie between 9.971-10.323 Å (Table 1), which falls in the range of 9-12 Å reported for seven of the literature examples SCO-active Fe(II) helicates 17, 19-21, 26, 60 (exception ~ 4Å (L7/L8), 24,25 ~15 Å (L10/L11) 23 and 19 Å (L12), 16 Figure S1, ESI).…”

“…Such ligands have included (Figure 2): mono-and bis-dentate Rdpt, 48 bis-terdentate PMRT/PSRT 11,[49][50][51] and the related PMTD/PMOD [52][53][54] or TMTD 55 all of which have been reported in the literature to form SCO active Fe(II) complexes. Recently, we reported that our general synthetic strategy for accessing Rdpt ligands 38,56 could be extended to access the first examples of ditopic azine-triazole analogues 57 and of azole-triazole monotopic Rat ligands. 58 The first four ditopic azine-triazole ligands prepared, L npym-meta and L npym-para (Figure 2), 57 featured n-pyrimidine-triazole binding sites linked by either meta-(for helicates) or para-(for tetrahedral cages) substituted phenylene linkers.…”

“…Recently, we reported that our general synthetic strategy for accessing Rdpt ligands 38,56 could be extended to access the first examples of ditopic azine-triazole analogues 57 and of azole-triazole monotopic Rat ligands. 58 The first four ditopic azine-triazole ligands prepared, L npym-meta and L npym-para (Figure 2), 57 featured n-pyrimidine-triazole binding sites linked by either meta-(for helicates) or para-(for tetrahedral cages) substituted phenylene linkers. All four of the structurally characterised iron(II) complexes, both helicates and cages, of these first ditopic Rat ligand systems were found to be LS.…”

“…All four of the structurally characterised iron(II) complexes, both helicates and cages, of these first ditopic Rat ligand systems were found to be LS. 57 Clearly, the ligand field of these new robust ditopic Rat ligands needs to be reduced in order to enable SCO. With this goal in mind, very recently, we reported the first examples of monotopic azoletriazole L 4NMe/SIm ligands (Figure 2), which, as expected, imposed a weaker ligand field: [Fe(L 4NMeIm ) 3 ](BF 4 ) 2 is HS whereas [Fe(L 4SIm ) 3 ](BF 4 ) 2 is SCO-active in both the solid state and in MeCN solution.…”