Synthesis of Furo[3,2-b]pyrrole-5-carboxhydrazides and Their Cu, CO and Ni Complexes

Carboxhydrazides 3 were synthesized by reaction of substituted furo[3,2-b]pyrrole-5-carboxhydrazides 1 with 4-oxo-4H-chromene-2-carboxaldehyde 2 in the presence of 3-methyl-benzenesulfonic acid in ethanol. Carboxhydrazides 3 were used as ligands for synthesis of Cu, Co, and Ni complexes 4

Five mononuclear pentacoordinate Co(II) complexes with field-induced slow magnetic relaxation

Five related mononuclear pentacoordinate complexes of the formula [CoL³Cl2] show slow magnetic relaxation under small applied DC field; L³ – a tridentate N-donor ligand based upon dipyrazolpyridine with an alkyl tail. All of them exhibit a supramolecular assembly, either forming dimers or chains via π–π stacking. Moreover, they display two relaxation branches, one being typical for single molecule magnets of this class, τ ∼ 10−6 s, and the second one as slow as τ ∼ 0.5 s at T = 1.9 K

Spin Symmetry in Polynuclear Exchange-Coupled Clusters

The involvement of spin symmetry in the evaluation of zero-field energy levels in polynuclear transition metal and lanthanide complexes facilitates the division of the large-scale Hamiltonian matrix referring to isotropic exchange. This method is based on the use of an irreducible tensor approach. This allows for the fitting of the experimental data of magnetic susceptibility and magnetization in a reasonable time for relatively large clusters for any coupling path. Several examples represented by catena-[AN} and cyclo-[AN] systems were modeled. Magnetic data for 20 actually existing endohedral clusters were analyzed and interpreted

Energy Levels in Pentacoordinate d⁵ to d⁹ Complexes

Energy levels of pentacoordinate d5 to d9 complexes were evaluated according to the generalized crystal field theory at three levels of sophistication for two limiting cases of pentacoordination: trigonal bipyramid and tetragonal pyramid. The electronic crystal field terms involve the interelectron repulsion and the crystal field potential; crystal field multiplets account for the spin–orbit interaction; and magnetic energy levels involve the orbital– and spin–Zeeman interactions with the magnetic field. The crystal field terms are labelled according to the irreducible representations of point groups D3h and C4v using Mulliken notation. The crystal field multiplets are labelled with the Bethe notations for the respective double groups D’3 and C’4. The magnetic functions, such as the temperature dependence of the effective magnetic moment and the field dependence of the magnetization, are evaluated by employing the apparatus of statistical thermodynamics as derivatives of the field-dependent partition function. When appropriate, the formalism of the spin Hamiltonian is applied, giving rise to a set of magnetic parameters, such as the zero-field splitting D and E, magnetogyric ratio tensor, and temperature-independent paramagnetism. The data calculated using GCFT were compared with the ab initio calculations at the CASSCF+NEVPT2 level and those involving the spin–orbit interaction

Zero-Field Splitting in Hexacoordinate Co(II) Complexes

A collection of 24 hexacoordinate Co(II) complexes was investigated by ab initio CASSCF + NEVPT2 + SOC calculations. In addition to the energies of spin–orbit multiplets (Kramers doublets, KD) their composition of the spins is also analyzed, along with the projection norm to the effective Hamiltonian. The latter served as the evaluation of the axial and rhombic zero-field splitting parameters and the g-tensor components. The fulfilment of spin-Hamiltonian (SH) formalism was assessed by critical indicators: the projection norm for the first Kramers doublet N(KD1) > 0.7, the lowest g-tensor component g1 > 1.9, the composition of KDs from the spin states |±1/2> and |±3/2> with the dominating percentage p > 70%, and the first transition energy at the NEVPT2 level 4Δ1. Just the latter quantity causes a possible divergence of the second-order perturbation theory and a failure of the spin Hamiltonian. The data set was enriched by the structural axiality Dstr and rhombicity Estr, respectively, evaluated from the metal–ligand distances Co-O, Co-N and Co-Cl corrected to the mean values. The magnetic data (temperature dependence of the molar magnetic susceptibility, and the field dependence of the magnetization per formula unit) were fitted simultaneously, either to the Griffith–Figgis model working with 12 spin–orbit kets, or the SH-zero field splitting model that utilizes only four (fictitious) spin functions. The calculated data were analyzed using statistical methods such as Cluster Analysis and the Principal Component Analysis

Energy Levels in Pentacoordinate d5 to d9 Complexes

Energy levels of pentacoordinate d5 to d9 complexes were evaluated according to the generalized crystal field theory at three levels of sophistication for two limiting cases of pentacoordination: trigonal bipyramid and tetragonal pyramid. The electronic crystal field terms involve the interelectron repulsion and the crystal field potential; crystal field multiplets account for the spin–orbit interaction; and magnetic energy levels involve the orbital– and spin–Zeeman interactions with the magnetic field. The crystal field terms are labelled according to the irreducible representations of point groups D3h and C4v using Mulliken notation. The crystal field multiplets are labelled with the Bethe notations for the respective double groups D’3 and C’4. The magnetic functions, such as the temperature dependence of the effective magnetic moment and the field dependence of the magnetization, are evaluated by employing the apparatus of statistical thermodynamics as derivatives of the field-dependent partition function. When appropriate, the formalism of the spin Hamiltonian is applied, giving rise to a set of magnetic parameters, such as the zero-field splitting D and E, magnetogyric ratio tensor, and temperature-independent paramagnetism. The data calculated using GCFT were compared with the ab initio calculations at the CASSCF+NEVPT2 level and those involving the spin–orbit interaction

Diamagnetic cobalt(III)tris(o-ethylxanthate) and nickel(II)bis(o-ethylxanthate)

Diamagnetic [Co(xanth)3] and [Ni(xanth)2] complexes have been prepared by reaction of Co(II) and Ni(II) salts with potassium O-ethyl xanthate (Kxanth). The isolated Co(III) and Ni(II) complexes have been characterized by single-crystal X-ray crystallography, UV-VIS and IR spectroscopy, computational methods, and magnetic measurements

On new solvatomorphs of the metalloligand [Ni(o-van-en)]

The Schiff-base bis­(2-hydroxy-3-methoxybenzylidene)ethylenediamine, denoted H2(o-van-en), is a versatile two-compartment polydentate ligand that can bring different guests, such as a transition metal and a lanthanoid, into close proximity to produce novel complexes with potentially singular properties. The base, which is prepared by the condensation of o-vanillin with ethylenediamine, reacts with nickel(II) carbonate to yield a microcrystalline product which upon recrystallization from acetone, ethanol and isopropanol, yielded three solvatomorphs of [Ni(o-van-en)]. These products, the hydrate [Ni(o-van-en)]⋅nH2O (n = 1.17, 1), the ethanol–water solvate [Ni(o-van-en)]⋅H2O⋅EtOH (2) and the isopropanol-water solvate [Ni(o-van-en)]⋅H2O⋅iPrOH (3), all contain the molecular complex [Ni(o-van-en)], as characterized by single-crystal x-ray diffraction. The [Ni(o-van-en)] fragment, which has been developed as a metalloligand for the preparation of mixed-metal (Tr-Ln) complexes with novel magnetic properties, here forms solvatomorphs whose crystals display pronounced differences in morphology and stability. The Ni(II) center in each of the three solvatomorphs is coordinated by the (o-van-en)2- ligand in a square geometry with a cis-N2O2 donor set. Each solvatomorph contains water solvate molecules; and in addition, ethanol and isopropanol solvate molecules are present in 2 and 3, respectively. Full Interaction Maps were used for comparison of the intermolecular interactions, by way of understanding the factors leading to the different solvation behavior. A review of the known structures containing o-van-en fragments is used as a contextual backdrop for a discussion of the new solvatomorph structures. Calculations based on an energy-decomposition model are used to characterize the interactions within dimeric aggregates observed in the structures of 2 and 3.This work was supported by the Slovak grants APVV-18-0016 and VEGA (grant No. 1/0063/17). Funding from the Ministry of Science and Innovation (Spain) under grant PGC2018–093451-B-I00, from the European regional development fund (FEDER), and from the Diputación General de Aragón (Project M4, E11_20R) is gratefully acknowledged.Peer reviewe

Field induced slow magnetic relaxation in a zig-zag chain-like Dy(iii) complex with the ligand o-phenylenedioxydiacetato

The new complex [Dy(PDOA)(NO3)(H2O)2]n·nH2O (1) (H2PDOA is o-phenylenedioxydiacetic acid) was isolated from the reaction of dysprosium(III) nitrate and H2PDOA in a 1 : 1 molar ratio. Its crystal structure is formed of neutral zig-zag chains in which the nona-coordinated Dy(III) atoms (O9 donor set) are linked by PDOA ligands with a chelating-bridging coordination mode. DC and AC magnetic studies revealed that 1 behaves as a field-induced SMM with three relaxation channels. The derived values, considering the Orbach relaxation process, of the barrier to spin reversal and the extrapolated relaxation time are U/kB = 59.5 K and τ0 = 6.3 × 10−10 s, respectively. Ab initio calculations support the experimental results.Financial support from Slovak grant agencies (APPV-18-0016 and VEGA 1/0063/17) is gratefully acknowledged. We also thank the Ministerio de Ciencia e Innovación (Spain, Grant PGC2018-093451-B-I00), the European Union Regional Development Fund, FEDER, and the Diputación General de Aragón, Project M4, E11_20R.Peer reviewe

Slow magnetic relaxations in a ladder-type Dy(III) complex and its dinuclear analogue

The complex {[Dy(PDOA)(HO)]·2HO} (1) (HPDOA = 1,2-phenylenedioxydiacetic acid) was prepared from aqueous solution. Its crystal structure, built up of {-Dy-O-C-O-} chains interlinked by PDOA ligands yielding a ladder-like arrangement, was determined at 173 K. 1 exhibits slow magnetic relaxation under a small magnetic field B = 0.2 T with two (LF and HF) relaxation channels. The LF relaxation time at B = 0.2 T and T = 1.85 K is as slow as τ(LF) = 46 ms whereas the HF channel is τ(HF) = 1.4 ms. The mole fraction of the LF species is x = 0.76 at 1.85 K and it escapes progressively on heating. In the dinuclear analogue [Dy(PDOA)(HO)]·3.5HO (2) one PDOA ligand forms a bis(chelate) bridge between the two Dy(iii) atoms yielding a local structure analogous to that in 1; however its AC susceptibility data show slightly different quantitative characteristics of the single-molecule magnetic behaviour.Grant agencies (Slovakia: VEGA 1/0534/16, 1/0063/17 and 1/0131/16, and APVV-14-0078; Spain: MAT2015-68200-C2-1-P by the Ministerio de Ciencia e Innovación, European Union Regional Development Fund, FEDER, and Diputación General de Aragón (M4)) are acknowledged for their financial support.Peer Reviewe