The diethyl ester of o-phenylenebis(oxamic acid) (opbaH2Et2) was treated with an excess of RNH2 in MeOH to cause the exclusive formation of the respective o-phenylenebis(N(R)-oxamides) (opboH4R2, R = Me , Et , (n)Pr ) in good yields. Treatment of with half an equivalent of [Cu2(AcO)4(H2O)2] or one equivalent of [Ni(AcO)2(H2O)4] followed by the addition of four equivalents of [(n)Bu4N]OH resulted in the formation of mononuclear bis(oxamidato) type complexes [(n)Bu4N]2[M(opboR2)] (M = Ni, R = Me , Et , (n)Pr ; M = Cu, R = Me , Et , (n)Pr ). By addition of two equivalents of [Cu(pmdta)(NO3)2] to MeCN solutions of , novel trinuclear complexes [Cu3(opboR2)(L)2](NO3)2 (L = pmdta, R = Me , Et , (n)Pr ) could be obtained. Compounds have been characterized by elemental analysis and NMR/IR spectroscopy. Furthermore, the solid state structures of and have been determined by single-crystal X-ray diffraction studies. By controlled cocrystallization, diamagnetically diluted and (1%) in the host lattice of and (99%) (@ and @), respectively, in the form of single crystals have been made available, allowing single crystal ESR studies to extract all components of the g-factor and the tensors of onsite (Cu)A and transferred (N)A hyperfine (HF) interaction. From these studies, the spin density distribution of the [Cu(opboEt2)](2-) and [Cu(opbo(n)Pr2)](2-) complex fragments of and , respectively, could be determined. Additionally, as a single crystal ENDOR measurement of @ revealed the individual HF tensors of the N donor atoms to be unequal, individual estimates of the spin densities on each N donor atom were made. The magnetic properties of were studied by susceptibility measurements versus temperature to give J values varying from -96 cm(-1) () over -104 cm(-1) () to -132 cm(-1) (). These three trinuclear Cu(II)-containing bis(oxamidato) type complexes exhibit J values which are comparable to and slightly larger in magnitude than those of related bis(oxamato) type complexes. In a summarizing discussion involving experimentally obtained ESR results (spin density distribution) of and , the geometries of the terminal [Cu(pmdta)](2+) fragments of determined by crystallographic studies, together with accompanying quantum chemical calculations, an approach is derived to explain these phenomena and to conclude if the spin density distribution of mononuclear bis(oxamato)/bis(oxamidato) type complexes could be a measure of the J couplings of corresponding trinuclear complexes.

Large separation of magnetic levels and slow relaxation in metal complexes are desirable properties of single-molecule magnets (SMMs). Spin-phonon coupling (interactions of magnetic levels with phonons) is ubiquitous, leading to magnetic relaxation and loss of memory in SMMs and quantum coherence in qubits. Direct observation of magnetic transitions and spin-phonon coupling in molecules is challenging. We have found that far-IR magnetic spectra (FIRMS) of Co(PPh 3 ) 2 X 2 (Co-X; X = Cl, Br, I) reveal rarely observed spin-phonon coupling as avoided crossings between magnetic and u-symmetry phonon transitions. Inelastic neutron scattering (INS) gives phonon spectra. Calculations using VASP and phonopy programs gave phonon symmetries and movies. Magnetic transitions among zero-field split (ZFS) levels of the S = 3/2 electronic ground state were probed by INS, high-frequency and -field EPR (HFEPR), FIRMS, and frequency-domain FT terahertz EPR (FD-FT THz-EPR), giving magnetic excitation spectra and determining ZFS parameters (D, E) and g values. Ligand-field theory (LFT) was used to analyze earlier electronic absorption spectra and give calculated ZFS parameters matching those from the experiments. DFT calculations also gave spin densities in Co-X, showing that the larger Co(II) spin density in a molecule, the larger its ZFS magnitude. The current work reveals dynamics of magnetic and phonon excitations in SMMs. Studies of such couplings in the future would help to understand how spinphonon coupling may lead to magnetic relaxation and develop guidance to control such coupling.

Treatment of the diethyl ester of o-phenylenebis(oxamic acid) (opbaH(2)Et(2), 1) with 5/6 equivalent of MeNH(2) in abs. EtOH results in the exclusive formation of the ethyl ester of o-phenylene(N′-methyl oxamide)(oxamic acid) (opooH(3)EtMe, 2) in ca. 50% yield. Treatment of 2 with four equivalents of [Me(4)N]OH followed by the addition of Cu(ClO(4))(2)·6H(2)O gave [Me(4)N](2)[Cu(opooMe)]·H(2)O (3A) in ca. 80% yield. As 3A appears to be a hygroscopic solid, the related [(n)Bu(4)N](+) salts [(n)Bu(4)N](2)[M(opooMe)]·H(2)O (M = Cu (3B), Ni (4)) have been synthesized. By addition of two equivalents of [Cu(pmdta)(NO(3))(2)] to a MeCN solution of 3B the novel asymmetric trinuclear complex [Cu(3)(opooMe)(pmdta)(2)](NO(3))(2) (5) could be obtained in ca. 90% yield. Compounds 2, 3A, 3B, 4 and 5 have been characterized by elemental analysis and NMR/IR spectroscopy. Furthermore, the solid state structures of 3A in the form of [Me(4)N](2)[Cu(opooMe)]·MeOH (3A′), 3B in the form of [(n)Bu(4)N](2)[Cu(opooMe)] (3B′), 4 in the form of [(n)Bu(4)N](2)[Ni(opooMe)]·1.25H(2)O (4′) and 5 in the form of [Cu(3)(opooMe)(pmdta)(2)] (NO(3))(2)·3MeCN (5′), respectively, have been determined by single-crystal X-ray diffraction studies. By controlled cocrystallization, diamagnetically diluted 3B (1%) in the host lattice of 4 (99%) in the form of single crystals have been made available, allowing single crystal EPR studies to extract all components of the g-factor and the tensors of onsite (Cu)A and transferred (N)A hyperfine interaction. Out of these studies the spin density distribution of the [Cu(opooMe)](2-) complex fragment could be determined. The magnetic properties of 5 were studied by susceptibility measurements versus temperature. An intramolecular J parameter of -65 cm(-1) has been obtained, unexpectedly, as 5 should possess two different J values due to its two different spacers between the adjacent Cu(II) ions, namely an oxamate (C(2)NO(3)) and an oxamidate (C(2)N(2)O(2)) fragment. This unexpected result is explained by a summarizing discussion of the experimentally obtained EPR results (spin density distribution) of 3B, the geometries of the terminal [Cu(pmdta)](2+) fragments of 5 determined by X-ray crystallographic studies and accompanying quantum chemical calculations of the spin density distribution of the mononuclear [Cu(opooMe)](2-) and of the magnetic exchange interactions of trinuclear [Cu(3)(opooMe)(pmdta)(2)](2+) complex fragments.

Metallocorroles wherein the metal ion is Mn III and formally Fe IV are studied here using fieldand frequency-domain electron paramagnetic resonance techniques. The Mn III corrole, Mn(tpfc) (tpfc = 5,10,15-tris(pentafluorophenyl)corrole trianion), exhibits the following S = 2 zero-field splitting (zfs) parameters: D = −2.67(1) cm −1 , |E| = 0.023(5) cm −1 . This result and those for other Mn III tetrapyrroles indicate that when D ≈ − 2.5 ± 0.5 cm −1 for 4-or 5coordinate and D ≈ − 3.5 ± 0.5 cm −1 for 6-coordinate complexes, the ground state description is [Mn III (Cor 3− )] 0 or [Mn III (P 2− )] + (Cor = corrole, P = porphyrin). The situation for formally Fe IV corroles is more complicated, and it has been shown that for Fe(Cor)X, when X = Ph (phenyl), the ground state is a spin triplet best described by [Fe IV (Cor 3− )] + , but when X = halide, the ground state corresponds to [Fe III (Cor •2− )] + , wherein an intermediate spin (S = 3 / 2 ) Fe III is antiferromagnetically coupled to a corrole radical dianion (S = 1 / 2 ) to also give an S = 1 ground state. These two valence isomers can be distinguished by their zfs parameters, as determined here for Fe(tpc)X, X = Ph, Cl (tpc = 5,10,15triphenylcorrole trianion). The complex with axial phenyl gives D = 21.1(2) cm −1 , while that with axial chloride gives D = 14.6(1) cm −1 . The D value for Fe(tpc)Ph is in rough agreement with the range of values reported for other Fe IV complexes. In contrast, the D value for Fe(tpc)Cl is inconsistent with an Fe IV description and represents a different type of iron center. Computational studies corroborate the zfs for the two types of iron corrole complexes. Thus, the zfs of metallocorroles can be diagnostic as to the electronic structure of a formally high oxidation state metallocorrole, and by extension to metalloporphyrins, although such studies have yet to be performed.

The treatment of the diethyl ester of o-phenylenebis(oxamic acid) (opbaH(2)Et(2)) with 2/3 of an equivalent of MeNH(2) in MeOH does not result in the formation of the methyl ester of o-phenylene(N'-methyloxamide)(oxamic acid) (opooH(3)Me, 1) in pure state, as reported previously. The colourless crude material formed by this reaction was confirmed to be composed of 1 (89% content), the dimethyl ester of o-phenylenebis(oxamic acid) (opbaH(2)Me(2), 2, 6%), 1,4-dihydro-2,3-quinoxalinedione (3, 3%) and o-phenylenebis(N'-methyloxamide) (opboH(4)Me(2), 4, 1%), respectively. The identities of 1-4 have been verified by IR, (1)H and (13)C NMR spectroscopy as well as elemental analysis. In addition, the solid state structures of 1 and 2·2DMSO, respectively, were determined by single-crystal X-ray diffraction studies. Successive recrystallization of the crude material from MeOH and MeOH : THF (1 : 1), respectively, does not give pure 1, but a mixture of 1 and 2. It is shown further that out of this mixture pure bis(oxamato) complexes cannot be obtained, as previously reported. Instead, treatment of the mixture with Ni(II) or Cu(II) salts, followed by the addition of [(n)Bu(4)N]OH, results in the formation of two mixtures of [(n)Bu(4)N](2)[Ni(opba)] (5) and [(n)Bu(4)N](2)[Ni(opooMe)] (6) as well as [(n)Bu(4)N](2)[Cu(opba)] (7) and [(n)Bu(4)N](2)[Cu(opooMe)] (8), respectively. The simultaneous formation of 5/6 and 7/8, respectively, has been verified by crystallization of the obtained mixtures and X-ray diffraction studies of the obtained single crystals. Co-crystallization of mixtures of 5/6 (99 mass%) and 7/8 (1 mass%), respectively, results in the formation of single-crystals of diamagnetically diluted 7 in the host lattice of 5 (7@5) accompanied by single-crystal formation of diamagnetically diluted 8 in the host lattice of 6 (8@6), as verified by EPR spectroscopy. It is finally shown that the ethyl ester of o-phenylene(N'-methyloxamide)(oxamic acid) (opooH(3)Et, 9), a homologue of 1, can be obtained in pure state by the treatment of opbaH(2)Et(2) with 5/6 of an equivalent of MeNH(2) in EtOH.

The metal−metal-bonded molecule [Bu 4 N]-[( H L) 2 Fe 6 (dmf) 2 ] (Fe 6 ) was previously shown to possess a thermally isolated spin S = 19 / 2 ground state and found to exhibit slow magnetization relaxation below a blocking temperature of ∼5 K [J. Am. Chem. Soc. 2015, 137, 13949−13956]. Here, we present a comprehensive spectroscopic investigation of this unique singlemolecule magnet (SMM), combining ultrawideband field-swept high-field electron paramagnetic resonance (EPR) with frequencydomain Fourier-transform terahertz EPR to accurately quantify the spin Hamiltonian parameters of Fe 6 . Of particular importance is the near absence of a 4th-order axial zero-field splitting term, which is known to arise because of quantum mechanical mixing of spin states on account of the relatively weak spin−spin (superexchange) interactions in traditional polynuclear SMMs such as the celebrated Mn 12 -acetate. The combined high-resolution measurements on both powder samples and an oriented single crystal provide a quantitative measure of the isolated nature of the spin ground state in the Fe 6 molecule, as well as additional microscopic insights into factors that govern the quantum tunneling of its magnetization. This work suggests strategies for improving the performance of polynuclear SMMs featuring direct metal−metal bonds and strong ferromagnetic spin−spin (exchange) interactions.

We have applied the pulse ELDOR detected NMR (EDNMR) technique to determine the tensors of the transferred Cu (S = 1/2) - (14)N (I = 1) hyperfine (HF) interaction in single crystals of diamagnetically diluted mononuclear o-phenylenebis(N(R)-oxamide) complexes of [(n)Bu4N]2[Cu(opboR2)] (R = Et 1, (n)Pr 2) (1%) in a host lattice of [(n)Bu4N]2[Ni(opboR2)] (R = Et 3, (n)Pr 4) (99%) (1@3 and 2@4)). To facilitate the analysis of our EDNMR data and to analyze possible manifestations of the nuclear quadrupole interaction in the EDNMR spectra, we have treated a model electron-nuclear system of the coupled S = 1/2 and I = 1 spins using the spin density matrix formalism. It appears that this interaction yields a peculiar asymmetry of the EDMR spectra that manifests not only in the shift of the positions of the EDNMR lines that correspond to the forbidden EPR transitions, as expected, but also in the intensities of the EDNMR lines. The symmetric shape of the experimental spectra suggests the conclusion that, in the studied complexes, the quadrupole interaction is negligible. This has simplified the analysis of the spectra. The HF tensors of all four N donor atoms could be accurately determined. On the basis of the HF tensors, an estimate of the spin density transferred from the central paramagnetic Cu(II) ion to the N donor atoms reveals its unequal distribution. We discuss possible implications of our estimates for the magnetic exchange paths and interaction strengths in respective trinuclear complexes [Cu3(opboR2) (pmdta)2](NO3)2 (R = Et 6, (n)Pr 7).

The synthesis, structure, and magnetic properties of two mononuclear cobalt(ii) complexes [Co(LSal,2-Ph)2] (1) and [Co(LNph,2-Ph)2] (2) are reported. The utilized sterically demanding Schiff-base ligands HLSal,2-Ph (2-(([1,1'-biphenyl]-2-ylimino)methyl)phenol) and HLNph,2-Ph (1-(([1,1'-biphenyl]-2-ylimino)methyl)naphthalen-2-ol) lead to a strong distortion of the [N2O2] coordination environment in the complexes 1 and 2, which can be primarily attributed to the variation in the dihedral angle between the planes of the two chelate ligands. Magnetic susceptibility and FD-FT THz-EPR measurements as well as ab initio calculations reveal that both complexes exhibit an easy-axis type of anisotropy. For both compounds frequency-dependent ac susceptibility measurements show an out-of-phase susceptibility under applied static fields of 400 and 1000 Oe. A detailed analysis of the underlying relaxation process is given, revealing significant differences in the contributions of Orbach, Raman, and direct processes within the observed temperature range. Fitting of the magnetic data leads to a spin-reversal barrier of 49 cm-1 for 1 at an applied field of 1000 Oe. For 2 the barrier is not well defined by the analysis of the relaxation times and is, therefore, approximated by the experimental barrier derived from FD-FT THz-EPR measurements (62.8 cm-1). The results from ab initio calculations and FD-FT THz-EPR measurements show that the distortion of the coordination sphere in complexes 1 and 2 from the pseudotetrahedral towards a square-planar coordination geometry leads to an increase in both the axial (D) and the rhombic zero-field splitting (E).