Ferro-vs.antiferromagnetic exchange between two Ni(ii) ions in a series of Schiff base heterometallic complexes: what makes the difference?

Olga Yu Vassilyeva, Elena A. Buvaylo, Vladimir N. Kokozay, Brian W. Skelton, Alexandre N. Sobolev, Alina Bieńko, Andrew Ozarowski

Research output: Contribution to journalArticle

Abstract

Three new NiII/ZnIIheterometallics, [NiZnL′2(OMe)Cl]2(1), [NiZnL′′(Dea)Cl]2·2DMF (2) and [Ni2(H3L′′′)2(o-Van)(MeOH)2]Cl·[ZnCl2(H4L′′′)(MeOH)]·2MeOH (3), containing three-dentate Schiff bases as well as methanol or diethanolamine (H2Dea) oro-vanillin (o-VanH), all deprotonated, as bridging ligands were synthesized and structurally characterized. The Schiff base ligands were producedin situfromo-VanH and CH3NH2(HL′), or NH2OH (HL”), or 2-amino-2-hydroxymethyl-propane-1,3-diol (H4L′′′); a zerovalent metal (Ni and Zn in1, Zn only in2and3) was employed as a source of metal ions. The first two complexes are dimers with a Ni2Zn2O6central core, while the third compound is a novel heterometallic cocrystal salt solvate built of a neutral zwitterionic ZnIISchiff base complex and of ionic salt containing dinuclear NiIIcomplex cations. The crystal structures contain either centrosymmetric (1and2) or non-symmetric di-nickel fragment (3) with Ni-Ni distances in the range 3.146-3.33 Å. The exchange coupling is antiferromagnetic for1,J= 7.7 cm−1, and ferromagnetic for2,J= −6.5 cm−1(using the exchange Hamiltonian in a formĤ=JŜ1Ŝ2). The exchange interactions in1and2are comparable to the zero-field splitting (ZFS). High-field EPR revealed moderate magnetic anisotropy of opposite signs:D= 2.27 cm−1,E= 0.243 cm−1(1) andD= −4.491 cm−1,E= −0.684 cm−1(2). Compound3stands alone with very weak ferromagnetism (J= −0.6 cm−1) and much stronger magnetic anisotropy withD= −11.398 cm−1andE= −1.151 cm−1. Attempts to calculate theoretically the exchange coupling (using the DFT “broken symmetry” method) and ZFS parameters (with theab initioCASSCF method) were successful in predicting the trends ofJandDamong the three complexes, while the quantitative results were less good for1and3.

Original languageEnglish
Pages (from-to)2841-2853
Number of pages13
JournalDalton Transactions
Volume50
Issue number8
DOIs
Publication statusPublished - 28 Feb 2021

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