Spin state modulation in cobalt(II) terpyridine complexes by co-crystallization with 1,3,5-triiodo-2,4,6-trifluorobenzene

Reversible water molecule-induced spin state inter-conversion for the mononuclear cobalt(II) complex [Co(terpy)2]I2·2H2O (1, terpy = 2,2′:6′,2′′-terpyridine) is reported along with its co-crystallization with 1,3,5-triiodo-2,4,6-trifluorobenzene (TITFB) to yield three types of halogen bonded frameworks, [Co(terpy)2][(TITFB)I2] (2), [Co(terpy)2][(TITFB)2I2] (3) and [Co(terpy)2][(TITFB)4(MeOH)I2] (4) (TITFB = 1,3,5-triiodo-2,4,6-trifluorobenzene). The magnetic properties of 1–4 have been investigated. While 1 exhibits gradual spin crossover (SCO) behavior, de-solvated [Co(terpy)2]I2 (1′) exhibits abrupt SCO behavior (T1/2 = 120 K) attributed to a change in its intermolecular interactions on dehydration. The crystal structures as well as the magnetic properties of 1 and 1′ can be switched reversibly via single-crystal to single-crystal (SCSC) transformations via hydration/dehydration processes. Co-crystallization of [Co(terpy)2]I2 with TITFB resulted in three types of halogen-bonded frameworks (2–4). While 2 exhibits incomplete abrupt spin transition (T1/2 = 56 K), 3 and 4 show incomplete gradual SCO behavior (attributed to stabilization of the LS state). The observed SCO behaviors are in accord with the structural distortions occurring in the respective [Co(terpy)2]2+ cations and resulting from their intermolecular interactions with the surrounding frameworks. These results illustrate the manner by which co-crystallization leading to halogen-bonded co-crystals in the present study can result in spin state modulation in SCO complexes

Supramolecular Modulation of Spin Crossover in an Fe(II) Dinuclear Triple Helicate

A spin-crossover (SCO) active dinuclear Fe(II) triple helicate of the form [Fe2L3]4+ was combined with additional supramolecular components in order to manipulate the interhelical separation and steric congestion and to study the magneto-structural effects on the ensuing composite materials. A more separated array of SCO units produced more extensive spin-transitions, while a tightly arranged lattice environment stabilized the low-spin state. This study highlights the important interplay between crystal packing, intermolecualr interactions, and the magentic behavior of SCO materials.</p

A large dinuclear Fe(II) triple helicate demonstrating a two-step spin crossover

Reported herein, the synthesis as well as the structural and magnetic characterisation of the largest reported dinuclear Fe(II) triple helicate system to exhibit spin crossover—and also a rare example of a 273° helical twist using aromatic spacers—is presented, with exploration of the two-step spin-transition observed

A mixed-spin spin-crossover thiozolylimine [Fe4L6]8+ cage

The self-assembly of a mixed-spin [Fe4L6]8+ tetrahedral cage is reported. The cage undergoes temperature induced spin-crossover with a 29 K hystereisis. Variable temperature X-ray photoelectron spectroscopy (VT-XPS), combined with SQUID data, allowed differentiation between the surface and bulk magnetic properties

Unique spin crossover pathways differentiated by scan rate in a new dinuclear Fe(II) triple helicate : mechanistic deductions enabled by synchrotron radiation studies

The achievement of targeted properties in spin crossover (SCO) materials is complicated by often unpredictable cooperative interactions in the solid state. Herein, we report a dinuclear Fe(II) triple helicate 1 , (single crystals ( 1 ·4(MeCN)5.75(H 2 O)Et 2 O), and air dried bulk samples 1 ·6H 2 O and desolvated 1 ), which represents a rare example of a SCO system possessing two distinct magnetic behaviours that depend upon the thermal scan rate. Desolvated 1 was seen to undergo spin transition (ST) which was complete following slow cooling (1 K min −1 ), but incomplete ST (corresponding to 50% conversion) on fast cooling (10 K min −1 ). The incomplete ST observed in the latter case was accompanied by a higher temperature onset of ST, differing from TIESST (Temperature-Induced Excited Spin-State Trapping) materials. The two SCO pathways have been shown to arise from the interconversion between two structural phases ( a and b ), with both phases having associated high spin (HS) and low spin (LS) states. SCXRD (Single Crystal X-ray Diffraction) experiments of 1 ·4(MeCN)5.75(H 2 O)Et 2 O using controlled cooling rates and a synchrotron light source enabled short collection times (2-3 minutes per dataset) which has enabled the identification of a mechanism by which the slow-cooled material may fully relax. In contrast, fast-cooled materials exhibit disordered arrangements of multiple structural phases, which has in turn revealed that the [HS-LS] ↔ [LS-HS] equilibria are controllable in the solid by varying the scan rate. Such behaviour has been previously observed in solution studies, but its control in solids has not been reported up to now. This study demonstrates how intermolecular cooperativity can allow multiple distinct magnetic behaviours, and provides some insight into how [HS-LS] ↔ [LS-HS] equilibria can be controlled in the solid state, which may assist in the design of next-generation logic and signalling devices

Unique Spin Crossover Pathways Differentiated by Scan Rate in a New Dinuclear Fe(II) Triple Helicate: Mechanistic Deductions Enabled by Synchrotron Radiation Studies

The achievement of targeted properties in spin crossover (SCO) materials is complicated by often unpredictable cooperative interactions in the solid state. Herein, we report a dinuclear Fe(II) triple helicate 1, which is a rare example of a SCO material possessing two distinct magnetic behaviors that depend upon the thermal scan rate. Desolvated 1 was seen to undergo spin transition (ST) which was complete following slow cooling (1 K min-1), but incomplete ST (corresponding to 50% conversion) on fast cooling (10 K min-1). The incomplete ST observed in the latter case was accompanied by a higher temperature onset of ST, differing from TIESST (Temperature-Induced Excited Spin-State Trapping) materials. The two SCO pathways have been shown to arise from the interconversion between two structural phases (a and b), with both phases having associated high spin (HS) and low spin (LS) states. SCXRD (Single Crystal X-ray Diffraction) experiments using controlled cooling rates and a synchrotron light source enabled short collection times (2-3 minutes per dataset) which has enabled the identification of a mechanism by which the slow-cooled material may fully relax. In contrast, fast-cooled materials exhibit disordered arrangements of multiple structural phases, which has in turn revealed that the [HS-LS] ↔ [LS-HS] equilibria are controllable in the solid by varying the scan rate. Such behavior has been previously observed in solution studies, but its control in solids has not been reported up to now. This study demonstrates how intermolecular cooperativity can allow multiple distinct magnetic behaviors, and provides some insight into how [HS-LS] ↔ [LS-HS] equilibria can be controlled in the solid state, which may assist in the design of next-generation logic and signaling devices