Order-Disorder, Symmetry Breaking, and Crystallographic Phase Transition in a Series of Bis(trans-thiocyanate)iron(II) Spin Crossover Complexes Based on Tetradentate Ligands Containing 1,2,3-Triazoles

Maksym Seredyuk; Kateryna Znovjyak; Francisco Javier Valverde-Muñoz; M Carmen Muñoz; Volodymyr M Amirkhanov; Igor O Fritsky; José Antonio Real

doi:10.1021/acs.inorgchem.3c00830

Order-Disorder, Symmetry Breaking, and Crystallographic Phase Transition in a Series of Bis(trans-thiocyanate)iron(II) Spin Crossover Complexes Based on Tetradentate Ligands Containing 1,2,3-Triazoles

Inorg Chem. 2023 Jun 12;62(23):9044-9053. doi: 10.1021/acs.inorgchem.3c00830. Epub 2023 May 25.

Authors

Maksym Seredyuk^{1

2}, Kateryna Znovjyak², Francisco Javier Valverde-Muñoz¹, M Carmen Muñoz³, Volodymyr M Amirkhanov², Igor O Fritsky², José Antonio Real¹

Affiliations

¹ Instituto de Ciencia Molecular (ICMol)/Departamento de Química Inorgánica, Universidad de Valencia, 46980 Paterna, Valencia, Spain.
² Department of Chemistry, Taras Shevchenko National University of Kyiv, 64/13, Volodymyrska Street, 01601 Kyiv, Ukraine.
³ Departamento de Fisica Aplicada, Universitat Politècnica de València, Camino de Vera s/n, 46022 Valencia, Spain.

Abstract

We report herein a series of neutral trans-thiocyanate mononuclear spin crossover (SCO) complexes, [Fe^IIL(NCS)₂] (1-4), based on tetradentate ligands L obtained by reaction of N-substituted 1,2,3-triazolecarbaldehyde with 1,3-propanediamine or 2,2-dimethyl-1,3-diaminopropane [L = N¹,N³-bis((1,5-dimethyl-1H-1,2,3-triazol-4-yl)methylene)propane-1,3-diamine/-2,2-dimethylpropane-1,3-diamine, 1/2 and N¹,N³-bis((1-ethyl/1-propyl-1H-1,2,3-triazol-4-yl)methylene)-2,2-dimethylpropane-1,3-diamine, 3/4]. The thermal-induced SCO behavior is characterized by abrupt transitions with an average critical temperature (ΔT_1/2)/hysteresis loop width (ΔT_hyst) in the range 190-252/5-14 K, while the photo-generated metastable high-spin (HS) phases are characterized by T_LIESST temperatures in the range 44-59 K. Single crystal analysis shows that except 1, all compounds experience reversible symmetry breaking coupled with the thermal SCO. Furthermore, 4 experiences an additional phase transition at ca. 290 K responsible for the coexistence of two HS phases quenched at 10 K through LIESST and TIESST effects. The molecules form hexagonally packed arrays sustained by numerous weak CH···S and C···C/S···C/N···C bonds involving polar coordination cores, while non-polar pendant aliphatic substituents are segregated inside, occupying hexagonal channels. Energy framework analysis of complexes with one step SCO transition (1, 2, and 4) shows a correlation between the cooperativity and the amplitude of changes in the molecule-molecule interactions in the lattice at the SCO transition.