Towards Dual‐Functionality Spin‐Crossover Complexes

Abstract

The multistep synthesis of a versatile new 4‐substituted 3,5‐bis(2‐pyridyl)‐1,2,4‐triazole (Rdpt) ligand, 4‐[4‐(2‐aminomethyl)phenyl]‐3,5‐bis(2‐pyridyl)‐4 H‐1,2,4‐triazole (apdpt), is reported, which features a reactive aminomethyl para‐substituent on the phenyl group that points “out of the back” of the triazole. This enables further functionalisation under mild conditions by using a range of esters to form an amide link. Specifically, this proof of principle study demonstrates the synthesis of apdpt successfully appended with gold‐binding thioctic acid (tpdpt), graphene‐binding/emissive pyrene/propylpyrene (prdpt/pbdpt), and a Langmuir–Blodgett film‐forming polyethylene glycol (PEG) tail (pgdpt). These ligands are subsequently reacted with [Fe(pyridine)4(NCBH3)2] to give the mononuclear iron(II) complexes [Fe(Rdpt)2(NCBH3)2]⋅solvent, in which Rdpt/solvent is tpdpt/2.5 H2O (1), prdpt/0.5 CHCl3⋅H2O (2), and pbdpt/0.5 CHCl3⋅2 H2O (3), as red powders. Magnetic studies on these powders indicate that the complexes undergo only very gradual and incomplete spin crossover, from completely or mostly high spin at 300 K, to half or three‐quarters high spin at 50 K. Gold nanoparticles are successfully functionalised with the thioctic acid tpdpt ligand to give tpdpt@Au with an average diameter (as determined by TEM) of (3.1±0.7) nm. Preliminary studies on the two pyrene systems in dimethylformamide show that upon excitation at λ=345 nm the blue fluorescence observed for the free ligands is retained, essentially unaffected, in the respective complexes.

1,7-Dipyrene-Containing Aza-BODIPYs: Are Pyrene Groups Effective as Ligands To Promote and Direct Complex Formation with Common Nanocarbon Materials?

“…Installation of the pyrene substituents into 5a – e was motivated by the potential to promote assembly of intermolecular complexes with nanocarbon electron acceptors. The hypothesis that the pyrene motif would successfully provide an effective conduit for association and charge transfer was based on prior reports of other donor–acceptor complexes observed in solution. − The energetics of electron transfer from the 5a – e photoexcited states to a nanocarbon acceptor can be estimated from the spectroscopic and electrochemical measurements following a standard approach. − One-electron transfer is energetically favorable in all cases, with Δ G ranging from −0.2 eV for 5d to −0.5 eV for 5e . Changes in static and time-resolved absorption and static fluorescence with addition of C 60 , C 70 , (6,5)-SWCNT, and graphene were measured as potential indicators of charge transfer and quantitative evidence of complex formation.…”

Abrupt Spin Crossover Behavior in a Linear N1,N2-Triazole Bridged Trinuclear Fe(II) Complex

“…Based on the ligand 4-((1H-pyrrol-2-yl)methylene-amino)-4H-1,2,4-triazole (pyrtrz), a group of two crystalline coordination Fe II 6 ]·10H 2 O·2CH 3 OH (C2), has been synthesized and magnetically characterized. An abrupt spin transition (T 1/2 = 120 K) was found in compound 2, which was confirmed and explored by the magnetic susceptibility, Mössbauer spectra and structural measurements.…”

“…Currently, special attention is given to SCO compounds exhibiting pronounced cooperative behavior. Here, the mononuclear system [Fe(bpp) 2 ] 2+ (bpp = 2,6-di{pyrazol-1-yl}pyridine) [1][2][3][4], as well as the triazole-based mono-/bi-nuclear [Fe 2 (PMAT) 2 ] 4+ system [5][6][7][8], are among the most frequently reported compounds. Recently, we could enlarge the family of binuclear systems showing multiple SCO steps with reports on thiadiazole and oxadiazole complexes for which the cooperativity was studied in detail [9,10].…”

“…This family of compounds shows the attempt and endeavor to explore the famous 1D coordination polymers of general formula [Fe(Rtrz) 3 ](X) 2 (Rtrz = 4-subsitituted-1,2,4-triazole, X − = standard monoanions): some of which displayed wide thermal hysteresis loops around room temperature [11][12][13][14][15][16]. Compared to the typical molecular system mentioned above [1][2][3][4][5][6][7][8][9][10], the triazole-based compounds bear benefits of expanding the discrete nuclearities to multinuclear or 1D polymeric complexes, which is of vital importance…”

Hysteretic Thermal Spin-Crossover and Symmetry Breaking in Heteroleptic Fe(II) Complexes Using Alkyl Chain Substituted 2,2’-Dipyridylamine Ligands

“…A number of studies have focussed on utilising the conformational changes of alkyl chain containing materials to: probe the relationship between SCO and thermotropic liquid crystal behaviour; [17][18][19][20] develop dual functioning SCO-active materials such as those found in Langmuir-Blodgett films; 21 and study biomimetic models of phospholipid membranes. 22…”