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Reactions between 1,2-di(tetrazol-2-yl)ethane (ebtz), 1,6-di(tetrazol-2-yl)hexane (hbtz) or 1,1′-di(tetrazol-1-yl)methane (1ditz) and Fe(BF4)2 in the presence of adiponitrile (ADN), glutaronitrile (GLN) or suberonitrile (SUN) resulted in the formation of coordination polymers [Fe(μ-ebtz)2(μ-ADN)](BF4)2 (1), [Fe(μ-hbtz)2(μ-ADN)](BF4)2 (2), [Fe(μ-1ditz)2(GLN)2](BF4)2·GLN (3) and [Fe(μ-1ditz)2(μ-SUN)](BF4)2·SUN (4). It was established that the application of dinitriles allows an increase in the dimensionality of the ebtz and hbtz based systems while maintaining the structure of the polymeric units characteristic of previously studied mononitrile based analogues. In 3 and 4, regardless of the type of dinitrile coligand, the motif of 2D polymeric layers constituted by 1ditz molecules remains preserved. However, the dimensionality of 1ditz based networks is governed by the coordination modes of dinitriles. 3, based on a shorter molecule of glutaronitrile, crystallizes as a two-dimensional (2D) coordination polymer. In this compound, dinitriles coordinate monodentately or play the role of guest molecules. The substitution of glutaronitrile with suberonitrile enables the bridging of neighboring polymeric layers, resulting in a 3D network. The intentional selection of bis(tetrazoles) and dinitriles as building blocks has led, as expected, to obtaining systems with the structure of the first coordination sphere consisting of four tetrazole rings and two axially coordinated nitrile molecules. It created the conditions required for the occurrence of thermally induced spin crossover. Magnetic measurements and single crystal X-ray diffraction studies were used for the characterization of the spin crossover properties of 1–4. [ABSTRACT FROM AUTHOR]

Cooling [Fe(bbtr)3](BF4)2 (bbtr=1,4‐di(1,2,3‐triazol‐1‐yl)butane) triggers very slow spin crossover below 80 K (T1/2↓=76 K). The spin crossover (SCO) is accompanied by a hysteresis loop (T1/2↑=89 K). In contrast to isostructural perchlorate analogue [Fe(bbtr)3](ClO4)2 in which spin crossover during cooling is preceded by phase transition at TPT=126 K in tetrafluoroborate phase transition does not occur to the beginning of spin crossover (80 K). Studies of mixed crystals [Fe(bbtr)3](BF4)2(1‐x)(ClO4)2x (0.5≤x≤0.9) showed that a phase transition precedes spin crossover, however, for x≅0.46 intersection of T1/2(x) and TPT(x) dependencies takes place. The application of pressure of 1 GPa shifts the spin crossover in [Fe(bbtr)3](BF4)2 to a temperature above 270 K. High‐pressure studies of neat tetrafluoroborate and perchlorate, as well as mixed crystals [Fe(bbtr)3](BF4)2(1‐x)(ClO4)2x (0.1≤x≤0.9), revealed that at 295 K P1/2 value changes linearly with x indicating similar mechanism of spin crossover under elevated pressure in all systems under investigation. Variable pressure single crystal X‐ray diffraction studies confirmed that in contrast to thermally induced spin crossover undergoing differently in tetrafluoroborate and perchlorate an application of high pressure removes this differentiation leading to a similar mechanism depending at first on start spin crossover and then P‐3→P‐1 phase transition occurs. In this report we have shown that 2D coordination polymer [Fe(bbtr)3](BF4)2 (bbtr=1,4‐di(1,2,3‐triazol‐1‐yl)butane) treated to date as spin crossover silent shows thermally induced spin crossover phenomenon. Spin crossover in tetrafluoroborate is extremely slow. Determination of the spin crossover curve required carrying measurement in the settle mode‐cooling from 85 to 70 K took about 600 h (average velocity of change of temperature ca. 0.0004 K/min). [ABSTRACT FROM AUTHOR]

Cooling [Fe(bbtr)3](BF4)2 (bbtr=1,4‐di(1,2,3‐triazol‐1‐yl)butane) triggers very slow spin crossover below 80 K (T1/2↓=76 K). The spin crossover (SCO) is accompanied by a hysteresis loop (T1/2↑=89 K). In contrast to isostructural perchlorate analogue [Fe(bbtr)3](ClO4)2 in which spin crossover during cooling is preceded by phase transition at TPT=126 K in tetrafluoroborate phase transition does not occur to the beginning of spin crossover (80 K). Studies of mixed crystals [Fe(bbtr)3](BF4)2(1‐x)(ClO4)2x (0.5≤x≤0.9) showed that a phase transition precedes spin crossover, however, for x≅0.46 intersection of T1/2(x) and TPT(x) dependencies takes place. The application of pressure of 1 GPa shifts the spin crossover in [Fe(bbtr)3](BF4)2 to a temperature above 270 K. High‐pressure studies of neat tetrafluoroborate and perchlorate, as well as mixed crystals [Fe(bbtr)3](BF4)2(1‐x)(ClO4)2x (0.1≤x≤0.9), revealed that at 295 K P1/2 value changes linearly with x indicating similar mechanism of spin crossover under elevated pressure in all systems under investigation. Variable pressure single crystal X‐ray diffraction studies confirmed that in contrast to thermally induced spin crossover undergoing differently in tetrafluoroborate and perchlorate an application of high pressure removes this differentiation leading to a similar mechanism depending at first on start spin crossover and then P‐3→P‐1 phase transition occurs. In this report we have shown that 2D coordination polymer [Fe(bbtr)3](BF4)2 (bbtr=1,4‐di(1,2,3‐triazol‐1‐yl)butane) treated to date as spin crossover silent shows thermally induced spin crossover phenomenon. Spin crossover in tetrafluoroborate is extremely slow. Determination of the spin crossover curve required carrying measurement in the settle mode‐cooling from 85 to 70 K took about 600 h (average velocity of change of temperature ca. 0.0004 K/min). [ABSTRACT FROM AUTHOR]

Reactions between 1,2-di(tetrazol-2-yl)ethane (ebtz), 1,6-di(tetrazol-2-yl)hexane (hbtz) or 1,1'-di(tetrazol-1-yl)methane (1ditz) and Fe(BF 4 ) 2 in the presence of adiponitrile (ADN), glutaronitrile (GLN) or suberonitrile (SUN) resulted in the formation of coordination polymers [Fe(μ-ebtz) 2 (μ-ADN)](BF 4 ) 2 (1), [Fe(μ-hbtz) 2 (μ-ADN)](BF 4 ) 2 (2), [Fe(μ-1ditz) 2 (GLN) 2 ](BF 4 ) 2 ·GLN (3) and [Fe(μ-1ditz) 2 (μ-SUN)](BF 4 ) 2 ·SUN (4). It was established that the application of dinitriles allows an increase in the dimensionality of the ebtz and hbtz based systems while maintaining the structure of the polymeric units characteristic of previously studied mononitrile based analogues. In 3 and 4, regardless of the type of dinitrile coligand, the motif of 2D polymeric layers constituted by 1ditz molecules remains preserved. However, the dimensionality of 1ditz based networks is governed by the coordination modes of dinitriles. 3, based on a shorter molecule of glutaronitrile, crystallizes as a two-dimensional (2D) coordination polymer. In this compound, dinitriles coordinate monodentately or play the role of guest molecules. The substitution of glutaronitrile with suberonitrile enables the bridging of neighboring polymeric layers, resulting in a 3D network. The intentional selection of bis(tetrazoles) and dinitriles as building blocks has led, as expected, to obtaining systems with the structure of the first coordination sphere consisting of four tetrazole rings and two axially coordinated nitrile molecules. It created the conditions required for the occurrence of thermally induced spin crossover. Magnetic measurements and single crystal X-ray diffraction studies were used for the characterization of the spin crossover properties of 1-4.

Cooling [Fe(bbtr) 3 ](BF 4 ) 2 (bbtr=1,4-di(1,2,3-triazol-1-yl)butane) triggers very slow spin crossover below 80 K (T 1/2 ↓ =76 K). The spin crossover (SCO) is accompanied by a hysteresis loop (T 1/2 ↑ =89 K). In contrast to isostructural perchlorate analogue [Fe(bbtr) 3 ](ClO 4 ) 2 in which spin crossover during cooling is preceded by phase transition at T PT =126 K in tetrafluoroborate phase transition does not occur to the beginning of spin crossover (80 K). Studies of mixed crystals [Fe(bbtr) 3 ](BF 4 ) 2(1-x) (ClO 4 ) 2x (0.5≤x≤0.9) showed that a phase transition precedes spin crossover, however, for x≅0.46 intersection of T 1/2 (x) and T PT (x) dependencies takes place. The application of pressure of 1 GPa shifts the spin crossover in [Fe(bbtr) 3 ](BF 4 ) 2 to a temperature above 270 K. High-pressure studies of neat tetrafluoroborate and perchlorate, as well as mixed crystals [Fe(bbtr) 3 ](BF 4 ) 2(1-x) (ClO 4 ) 2x (0.1≤x≤0.9), revealed that at 295 K P 1/2 value changes linearly with x indicating similar mechanism of spin crossover under elevated pressure in all systems under investigation. Variable pressure single crystal X-ray diffraction studies confirmed that in contrast to thermally induced spin crossover undergoing differently in tetrafluoroborate and perchlorate an application of high pressure removes this differentiation leading to a similar mechanism depending at first on start spin crossover and then P-3→P-1 phase transition occurs. In this report we have shown that 2D coordination polymer [Fe(bbtr) 3 ](BF 4 ) 2 (bbtr=1,4-di(1,2,3-triazol-1-yl)butane) treated to date as spin crossover silent shows thermally induced spin crossover phenomenon. Spin crossover in tetrafluoroborate is extremely slow. Determination of the spin crossover curve required carrying measurement in the settle mode-cooling from 85 to 70 K took about 600 h (average velocity of change of temperature ca. 0.0004 K/min)., (© 2023 Wiley-VCH GmbH.)