Iron(II) Spin Crossover Complex with the 1,2,3-Triazole-Containing Linear Pentadentate Schiff-Base Ligand and the MeCN Monodentate Ligand

Abstract

A mononuclear iron(II) complex bearing the linear pentadentate N5 Schiff-base ligand containing two 1,2,3-triazole moieties and the MeCN monodentate ligand, [FeIIMeCN(L3-Me-3Ph)](BPh4)2·MeCN·H2O (1), have been prepared (L3-Me-3Ph = bis(N,N′-1-Phenyl-1H-1,2,3-triazol-4-yl-methylideneaminopropyl)methylamine). Variable-temperature magnetic susceptibility measurements revealed an incomplete one-step spin crossover (SCO) from the room-temperature low-spin (LS, S = 0) state to a mixture of the LS and high-spin (HS, S = 2) species at the higher temperature of around 400 K upon first heating, which is irreversible on the consecutive cooling mode. The magnetic modulation at around 400 K was induced by the crystal-to-amorphous transformation accompanied by the loss of lattice MeCN solvent, which was evident from powder X-ray diffraction (PXRD) studies and themogravimetry. The single-crystal X-ray diffraction studies showed that the complex is in the LS state (S = 0) between 296 and 387 K. In the crystal lattice, the complex-cations and B(1)Ph4− ions are alternately connected by intermolecular CH···π interactions between the methyl group of the MeCN ligand and phenyl groups of B(1)Ph4− ions, forming a 1D chain structure. The 1D chains are further connected by P4AE (parallel fourfold aryl embrace) interactions between two neighboring complex-cations, constructing a 2D extended structure. B(2)Ph4− ions and MeCN lattice solvents exist in the spaces of the 2D layer. DFT calculations verified that the 1,2,3-triazole-containing ligand L3-Me-3Ph gives a stronger ligand field around the octahedral coordination environment of the iron(II) ion than the analogous imidazole-containing ligand H2L2Me (= bis(N,N′-2-methylimidazol-4-yl-methylideneaminopropyl)methylamine) of the known compound [FeIIMeCN(H2L2Me)](BPh4)1.5·Cl0.5·0.5MeCN (2) reported by Matsumoto et al. (Nishi, K.; Fujinami, T.; Kitabayashi, A.; Matsumoto, N. Tetrameric spin crossover iron(II) complex constructed by imidazole⋯chloride hydrogen bonds. Inorg. Chem. Commun. 2011, 14, 1073–1076), resulting in the much higher spin transition temperature of 1 than that of 2.

Structural studies into the spin crossover behaviour of Fe(abpt)2(NCS)2 polymorphs B and D

“…1 Spin crossover compounds display a reversible high spin (HS) to low spin (LS) transition at a metal centre, which can be induced by external stimuli such as temperature, pressure 2 or light irradiation 3,4 and can occur in both solution and the solid state. The phenomenon is relatively common for 3d 4 -3d 7 metal centres. 5 While many of the spin crossover complexes that have been studied are octahedral Fe(II) complexes with nitrogen [5][6][7][8][9][10] ligands, other examples include Fe(III) 4,[11][12][13][14] , Co(II) [15][16][17] and Ni(II) 18 .…”

“…The phenomenon is relatively common for 3d 4 -3d 7 metal centres. 5 While many of the spin crossover complexes that have been studied are octahedral Fe(II) complexes with nitrogen [5][6][7][8][9][10] ligands, other examples include Fe(III) 4,[11][12][13][14] , Co(II) [15][16][17] and Ni(II) 18 . The change in electronic structure, as a result of the spin crossover, can result in changes in properties including molecular structure, colour and magnetism.…”

Solvent Coligand-Induced Spin State Variation in Iron(II) Complexes Bearing Pentadentate N5 Ligand Toward the Construction of an N5O Spin Crossover Center

“…The spectra also showed characteristic bands at ca. 1610 and 1637 cm –1 for 1 and 1638 cm –1 for 3 , corresponding to the CN stretching vibration of the pentadentate Schiff-base ligand L 3‑Me‑3 Me , , whereas the spectrum of 2 showed strong broad band at around 1590–1690 cm –1 (the peak top is 1656 cm –1 ), which is assignable to the CO stretching vibration of the monodentate DMF ligand . In addition, the spectrum of 3 showed the characteristic band at ca.…”

“…Recently, we have reported an iron­(II) SCO complex with N 6 donor atoms from the 1,2,3-triazole-containing pentadentate ligand L 3‑Me‑3 Ph and the monodentate solvent ligand MeCN, [Fe II (L 3‑Me‑3 Ph )­MeCN]­(BPh 4 ) 2 ·MeCN·H 2 O (L 3‑Me‑3 Ph = bis­( N , N ′-1-phenyl-1 H -1,2,3-triazol-4-yl-methylideneaminopropyl)­methylamine) . This iron­(II) complex shows heating-induced irreversible SCO from the LS to a mixture of the LS and HS species at the higher temperature of around 400 K. These results make us to hypothesize that such a 1,2,3-triazole-containing pentadentate ligand system can utilize a monodentate solvent ligand having a weaker ligand field for exhibiting SCO in the iron­(II) system.…”

Synthesis and Applications of New Spin Crossover Compounds

“…The 1,2,3-triazole-containing polydentate ligand iron(II) SCO family into a linear pentadentate ligand system was reported. This was shown in an abrupt and incomplete HT SCO at approximately 400 K while the SCO transition was irreversible due to the crystal-to-amorphous transformation in association with the loss of the lattice MeCN solvent molecules [11]. A series of SCO Fe(II) complexes based on dipyridyl-N-alkylamine and thiocyanate ligands were investigated, and the higher SCO transition temperature explained the more pronounced linearity of the Fe-N-C angles in the crystal recently indicated by experimental and theoretical magneto-structural research [12].…”