cis–trans Isomerism among the Octahedral Diaquabis(optically active C-substituted ethylenediamine)nickel(II) Complexes and Their Thermal Reaction Products. An Explanation for a Variety in Colors and Stereochemistry of Lifschitz Complexes

Abstract

The solid-phase thermal reactions of trans-diaquabis(diamine)nickel(II) complexes (trans-[Ni(diamine)2(H2O)2]X2) were investigated by means of TG/DTA and DSC, and high-temperature electronic spectrometry, where the diamine is an optically active diamine such as (1S,2S)-1,2-diphenyl-1,2-ethanediamine or (S)-4-methyl-1,2-pentanediamine, and X is Cl−, Br−, or NO3−. Several complexes were peculiarly transformed into cis-[NiX2(diamine)2] upon thermal deaquation-anation, and then isomerized to trans-[NiX2(diamine)2] upon further heating. The results were in contrast to the reactions of the complexes with the corresponding racemic diamines which underwent a simple deaquation-anation, retaining an original trans configuration. The differences must come from a slight difference in the conformation of diamine ligands between trans-[Ni(R-diamine)(S-diamine)(H2O)2]X2 which is obtained for the rac-diamines and trans-[Ni(R- or S-diamine)2(H2O)2]X2 which is obtained for the optically active diamines.

Porous Manganese(II) 3-(2-Pyridyl)-5-(4-Pyridyl)-1,2,4-Triazolate Frameworks: Rational Self-Assembly, Supramolecular Isomerism, Solid-State Transformation, and Sorption Properties

“…The reversible crystal-to-crystal and crystal-to-amorphous interconversions between 1 and 2 are novel as they involve breakage and formation of coordination and hydrogen bonds, trans-cis conversion of stereo configuration, and rearrangement of molecules in the crystal lattices, 27 though trans-cis conversion of metal complexes have been studied extensively by adsorption spectroscopy in solution or solid state. [28][29][30][31][32][33][34] Thermal Stability. 3b 3 0.5DMF 3 3H 2 O shows a slow weight loss of DMF and H 2 O molecules below 240 °C (observed: 16.8%, calculated: 15.4%), and no further weight loss below 400 °C until decomposition.…”

“…Therefore, discrete 1 and 2 are stable at relatively low temperatures while polymeric 3 prefer higher temperatures. The reversible crystal-to-crystal and crystal-to-amorphous interconversions between 1 and 2 are novel as they involve breakage and formation of coordination and hydrogen bonds, trans - cis conversion of stereo configuration, and rearrangement of molecules in the crystal lattices, though trans - cis conversion of metal complexes have been studied extensively by adsorption spectroscopy in solution or solid state. − …”