Polymorphic Derivatives of Ni^II and Co^II Mesocates with 3D Networks and “Brick and Mortar” Structures: Preparation, Structural Characterization, and Cryomagnetic Investigation of New Single-Molecule Magnets

Abstract

In this work we describe the preparation, spectroscopic, thermal and structural characterization, and cryomagnetic investigation of four new polymorphic derivatives of the [M2(H2mpba)3]2– mesocate of formulas {[K2(dmf)2(H2O)2]­[M2(H2mpba)3]·2H2O} n (M = Co (1), Ni (2)) and [M­(tppz)2]­[M2(H2mpba)3]·9H2O (M = Co (3), Ni (4)) (H4mpba = 1,3-phenylenebis­(oxamic) acid), tppz = 2,3,5,6-tetrakis­(2-pyridyl)­pyrazine). Pairs 1/2 and 3/4 are isomorphous compounds exhibiting a triple-stranded dinuclear motif, [M2(H2mpba)3]2–. 1 and 2 exhibit a three-dimensional network with [M2(H2mpba)3]2– mesocates interlinked by potassium­(I) ions. 3 and 4 present a brick and mortar network, where the “brick” is [M2(H2mpba)3]2– + [M­(tppz)2]2+ and the “mortar” refers to water molecules, where the electroneutrality of the motif is achieved by the [M­(tppz)2]2+ cationic complex. The dc magnetic data for 1–4 in the temperature range 1.9–300 K reveal the occurrence of magnetically isolated high-spin cobalt­(II) of the mesocate units in 1 and 3 plus a thermally induced spin crossover behavior of the [Co­(tppz)2]2+ unit in 3, whereas 2 and 4 exhibit Curie law behavior. Out-of-phase ac signals are observed for 1 and 3 at temperatures below 14 K under zero and nonzero applied dc fields, which are characteristic of the occurrence of slow magnetic relaxation in these systems, thus being new examples of single-molecule magnets (SMMs).

Intensity and lifetime ratiometric luminescent thermometer based on a Tb(iii) coordination polymer

“…During the synthesis of 1 , several experiments were conducted. This is because it is widely recognized that factors such as temperature, molar ratio of reagents, geometric characteristics, and coordination sites of the organic ligands 27–30 can have a significant impact on crystal growth. Moreover, the choice of synthetic strategies, such as stirring, 9,31 diffusion, 32 solvothermal (particularly when mixed organic solvents are employed), 8 and hydrothermal (used when water is the only solvent), 22,33 can also influence the process.…”

Nickel, copper, and zinc dinuclear helicates: how do bulky groups influence their architecture?

“…Our study was completed with Ni 2+ , whose electronic configuration is d 8 . The preferential coordination spheres of Ni 2+ are six-coordinate (octahedral geometry) 19,50 or four-coordinate complexes with planar-square if the ligand-field is strong. 51 However, there are also some examples of tetrahedral geometries.…”

Insertion of single-ion magnets based on mononuclear Co(ii) complexes into ferromagnetic oxalate-based networks

“…The values for the pre-exponential factor and activation energy are consistent with those of the other Co( ii ) complexes showing this behavior. 34–36…”