Discovering the Complex Chemistry of a Simple Ni^II/H₃L System: Magnetostructural Characterization and DFT Calculations of Di- and Polynuclear Nickel(II) Compounds

The simple nickel(II) acetate/H3L system (H3L = 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) presents an unusually complicated reactivity scheme, which strongly depends on the Ni(OAc)2/H3L molar ratio and on the pH of the medium. Thus, in addition to the formerly reported compounds [Ni2L(OAc)(H2O)2][Ni2L(OAc)(H2O)(HOAc)]·3.25H2O, 1·3.25H2O; [{Ni3L(OAc)(OH)(H2O)(MeOH)2}(CO3){Ni2L(OAc)(MeOH)2}]·2.7H2O·1.5MeOH, 2·2.7H2O·1.5MeOH; and [Ni3L(OAc)2(OH)(H2O)(MeOH)2]·3H2O·0.5MeOH, 3·3H2O·0.5MeOH, this system can also yield some other complexes as [Ni2L(o-O−C6H4−CHO)(H2O)]·1.75H2O, 4·1.75H2O; [Ni2L(OH)(H2O)(MeOH)]·3H2O·1.5MeOH, 5·3H2O·1.5MeOH; [Ni2L(OAc)(MeOH)2]·H2O·3MeOH, 6·H2O·3MeOH; and [{Ni2L(MeOH)}(CO3){Ni2L(MeOH)2}]·4.75H2O·2MeOH, 7·4.75H2O·2MeOH. A detailed study of the reaction scheme that allows obtaining all of these complexes is presented herein, as well as the structural characterization of the novel compounds 4·1.75H2O to 7·4.75H2O·2MeOH. X-ray analyses show that all of them present stereoisomery in the solid state. In this way, 6·H2O·3MeOH appears particularly interesting, as its molecular and supramolecular chirality is only controlled by hydrogen bonds. Magnetic studies of 5·3H2O to 7·4.75H2O·2MeOH are also discussed, and the complicated magnetic superexchange pathway shown by 7·4.75H2O·2MeOH is analyzed in light of DFT calculations.