Structural Phase Transition of Magnetic [Ni(dmit)₂]^- Salts Induced by Supramolecular Cation Structures of (M⁺)([12]crown-4)₂

Abstract

Sandwich-type supramolecular cation structures of (M(+))([12]crown-4)(2) complexes (M(+) = Li(+), Na(+), K(+), and Rb(+)) were introduced as countercations to the [Ni(dmit)(2)](-) anion, which bears an S = (1)/(2) spin, to form novel magnetic crystals (dmit(2-) = 2-thione-1,3-dithiole-4,5-dithiolate). The zigzag arrangement of Li(+)([12]crown-4)(2) cations in Li(+)([12]crown-4)(2)[Ni(dmit)(2)](-) salt induced weak intermolecular interactions of [Ni(dmit)(2)](-) dimers, whose magnetic spins were isolated from each other. The molecular arrangements of cations and anions in M(+)([12]crown-4)(2)[Ni(dmit)(2)](-) salts (M(+) = Na(+), K(+), and Rb(+)) were isostructural to each other. In the case of Na(+)([12]crown-4)(2)[Ni(dmit)(2)](-), the space group C2/m changed to C2/c with a lowering in temperature from 298 to 100 K. This structural change occurred at 222.5 K as a first-order phase transition. The space group C2/m (T = 298 K) in the salt K(+)([12]crown-4)(2)[Ni(dmit)(2)](-) also changed to C2/c (T = 100 K), which transition occurred at 270 K. Crystal structural analyses at 298 and 100 K revealed changes in both supramolecular cation conformation and [Ni(dmit)(2)](-) anion arrangements. The transition from C2/m to C2/c crystals generated a dipole moment in the Na(+)([12]crown-4)(2) and K(+)([12]crown-4)(2) structures, which were reconstructed to cancel the net dipole moment of the C2/c crystals. These cation transformations led to changes in intermolecular interactions between the [Ni(dmit)(2)](-) anions via structural rearrangements. The crystal structure of C2/c was stabilized in Rb(+)([12]crown-4)(2)[Ni(dmit)(2)](-) at 298 K. The [Ni(dmit)(2)](-) configuration in these salts with the C2/c space group was a one-dimensional uniform chain, which showed the temperature-dependent magnetic susceptibility of a one-dimensional linear Heisenberg antiferromagnetic chain.

Laser spectroscopic study on (dibenzo-24-crown-8-ether)–water and –methanol complexes in supersonic jets

“…Parallel to the experiments, we obtained stable conformers of DB24C8 by DFT calculations at the B3LYP/6-31+G* level. As was described in the experimental section, a conformational exploration was carried out to obtain the initial geometries by using the mixed torsional search with low-mode sampling 24 in MacroModel V.9.1 25 with 8 MMFF94s force field 26 . The 10000 initial geometries were generated, and following optimizations with PRCG algorithm gave more than one thousand conformers with a convergence threshold of 0.05 kJ mol -1 Å -1 .…”

“…5 18-crown-6-ether (18C6) forms an exceptionally stable 1 : 1 complex with K + with high symmetry (D 3d ). 1,6,7 CEs also show other types of encapsulation, in which a guest species is enclosed by two CE molecules, 8,9 or two guests are held by one CE molecule. 10,11 The preferential capture of K + by 18C6 was originally observed in condensed phase.…”

Water-mediated conformer optimization in benzo-18-crown-6-ether/water system

“…5 It is well known that 18-crown-6-ether (18C6) forms an exceptionally stable 1 : 1 complex with K + with high symmetry (D 3d ); the size of the K + ion is comparable with the cavity size of 18C6. 1,6,7 Crown ethers also show the type of encapsulation in which a guest species is enclosed by two crown ethers, 8,9 or two guests are held by one crown ether. 10,11 Compared with the encapsulation of atomic guests such as alkali metal ions, the encapsulation of polyatomic molecular guests is much more complicated because of a variety of intermolecular interactions.…”

Three ion–pair complexes containing bis(maleonitriledithiolate)copper(II) anion and substituted 2-aminopyridinium cations: Syntheses, crystal structures, and magnetic properties

“…Inorganic complex anions [M(mnt) 2 ] n-(M = Ni, Pd, Pt, Cu, Fe; mnt 2− = maleonitriledithiolate, n = 1 or 2) are especially interesting because they have been proved to be very useful and potential building block over the past few years and the overlapping of the neighboring anions are influenced by the size and configuration of the organic couter-cation as well as some non-covalent interactions such as weak p⋅⋅⋅π or π⋅⋅⋅π stacking interactions and H-bonding interactions [7][8][9][10][11][12][13]. In this area, one important branch is the design and synthesis of molecular solids containing the [Ni(mnt) 2 ] − anion and some organic cations due to their versatile magnetic properties such as ferromagnetism, magnetic transition from ferromagnetic to diamagnetic coupling, spin-Peierls-like transitions, and meta-magnetism [14][15][16][17][18][19].…”