Experimental and Theoretical Investigations of Magnetic Exchange Pathways in Structurally Diverse Iron(III) Schiff-Base Complexes

Abstract

The synthesis, and the structural and magnetic properties, of the following new iron(III) Schiff base complexes with the {O',N,O″}-chelating ligand H2L (2-hydroxyphenylsalicylaldimine) are reported: K[FeL2]·H2O (1), (Pr3NH)[FeL2]·2CH3OH (2), [FeL(bpyO2) (CH3OH)][FeL2]·CH3OH (3), [Fe2L3(CH3OH)]·2CH3OH·H2O (4), and [{Fe2L2}(μ-OH)2{FeL(bpyO2)}2][BPh4]2·2H2O (5), where Pr3NH(+) represents the tripropylammonium cation and bpyO2 stands for 2,2'-bipyridine-N-dioxide. A thorough density functional theory (DFT) study of magnetic interactions (the isotropic exchange) at the B3LYP/def-TZVP level of theory was employed, and calculations have revealed superexchange pathways through intramolecular/intermolecular noncovalent contacts (π-π stacking, C-H···O and O-H···O hydrogen bonds, diamagnetic metal cations) and/or covalent bonds ((μ-O(Ph), μ-OH) or bis(μ-O(Ph)) bridging modes), which helped us to postulate trustworthy spin Hamiltonians for magnetic analysis of experimental data. Within the reported family of compounds 1-5, the mediators of the antiferromagnetic exchange can be sorted by their increasing strength as follows: π-π stacking (J(DFT) = -0.022 cm(-1)/J(mag) = -0.025(4) cm(-1) in 2) < C-H···O contacts and π-π stacking (J(DFT) = -0.19 cm(-1)/J(mag) = -0.347(9)cm(-1) in 1) < O-H···O hydrogen bonds (J(DFT) = -0.53 cm(-1)/J(mag) = -0.41(1) cm(-1) in 3) < bis(μ-O(Ph)) bridge (J(DFT) = -13.8 cm(-1)/J(mag) = -12.3(9) cm(-1) in 4) < (μ-O(Ph), μ-OH) bridge (J(DFT) = -18.0 cm(-1)/J(mag) = -17.1(2) cm(-1) in 5), where J(DFT) and J(mag) are the isotropic exchange parameters derived from DFT calculations, and analysis of the experimental magnetic data, respectively. The good agreement between theoretically calculated and experimentally derived isotropic exchange parameters suggests that this procedure is applicable also for other chemical and structural systems to interpret magnetic data properly.

Late First-Row Transition-Metal Complexes Containing a 2-Pyridylmethyl Pendant-Armed 15-Membered Macrocyclic Ligand. Field-Induced Slow Magnetic Relaxation in a Seven-Coordinate Cobalt(II) Compound

“…36,58 Furthermore, the predictive role of such theoretical calculations can be utilized for trustworthy postulation of spin Hamiltonians for analysis of the experimental magnetic data. 59 Herein, we focused on calculations of magnetic anisotropy parameters (D and E) for Fe(II), Co(II), and Ni(II) complexes 2−4, which have higher pre-disposition for the ZFS. 60 We employed the ab initio calculations using ORCA software based on SA-CASSCF wave functions accompanied by NEVPT2.…”

Anion coordination directed synthesis patterns for [Ni4] aggregates: structural changes for thiocyanate coordination and ligand arm hydrolysis

“…Thus, the predictive role of DFT calculations in magnetochemistry was exploited with the aim to estimate principal parameters describing the exchange coupling in these systems. 28 Recently, we used such approach for polynuclear Ni(II) complexes with the great success. Please do not adjust margins Please do not adjust margins calculate parameters of the isotropic exchange J ab between the nickel(II) ions based on comparing the energy differences between the high spin (HS) and broken-symmetry (BS) spin states.…”

Solvent-induced structural diversity in tetranuclear Ni(ii) Schiff-base complexes: the first Ni4single-molecule magnet with a defective dicubane-like topology

“…Molecular structures of the complex anion in 2 (c) and view on a defective dicubane core of 2 (b). Bond distances (in Å) within the coordination polyhedra for 2: (Ni1-O1) = 2.0076 (19), (Ni1-O2A) = 2.0474(17), (Ni1-O3) = 2.1810(16), (Ni1-O4) = 2.0387(16), (Ni1-O6) = 2.1050(16), (Ni1-N1) = 2.030(5), (Ni2-O2) = 2.1396(15), (Ni2-O2A) = 2.0549(16), (Ni2-O3) = 2.0580(17), (Ni2-O4) = 2.9994(17), (Ni2-O5) = 2.0534(16), (Ni2-N2) = 1.989(2). bonding donors) and the adjacent O Sal atoms are of significant strength with donor⋯acceptor distances from a very narrow range (from 2.63 to 2.69 Å).…”