Intermolecular Antiferromagnetic Interactions Research Articles

Novel Trinuclear Copper(II) Complex: Crystal Structure at 100 K and Magnetic Properties of (R, S)-di[(6,7-dimethoxy-isoquinolin-1-yl)-(3,4-dimethoxy-phenyl)-methanolato]-tetra(2-hydroxybenzoato)-diaqua-tricopper dihydrate, [Cu3(C7H5O3)4(C20H20NO5)2(H2O)2]·2(H2O)

The crystal structure of [Cu3(C7H5O3)4(C20H20NO5)2(H2O)2]·2(H2O) (1) and analysis of temperature and field dependence of magnetic susceptibility is reported in this work. The structure of 1 is composed of trinuclear complex units and water molecules. The middle copper atom occupies the center of symmetry. N, O-bonded (6,7-dimethoxy-isoquinolin-1-yl)-(3,4-di­methoxy-phenyl)-methanolato ligands, 2-hydroxybenzoates with bridging carboxylic groups, and oxo-bridged water molecules connect the middle Cu(II) atom with the terminal copper atoms. Two 2-hydroxybenzoates coordinate the terminal copper atoms via one carboxylic oxygen and an O atom of the hydroxyl group. The analysis of copper coordination by bond-valence sum approach and relevant structural correlation is consistent with hexacoordinated Cu(II) centers. Cu···Cu separation is 3.0269(3) Å. The magnetism of 1 shows a strong ferromagnetic interaction between the neighboring metallic centers accompanied by very weak antiferromagnetic intermolecular interactions. The complex units are mutually held by π···π stack interactions of 2-hydroxybenzoates and hydrogen bonds.Graphical A new N,O bonded ligands, (R, S)-[(6,7-dimethoxy-isoquinolin-1-yl)-(3,4-dimethoxy-phenyl)-methanolate] coordinate the terminal atoms of the trinuclear copper(II) complex.

Heterometallic {Fe18M6} (M = Y, Gd, Dy) Pivalate Wheels Display Solvent-Induced Polymorphism

A new series of heterometallic wheels, isolated as [Fe18M6(piv)12(Htea)18(tea)6(N3)6]·n(solvent) (MIII = Y (1a, 1b), Gd (2a, 2b), and Dy (3a, 3b); Hpiv = pivalic acid, H3tea = triethanolamine), forms by the reaction of trinuclear μ3-oxo-linked or hexanuclear μ-OH-linked Fe(III) pivalate clusters with rare earth nitrates, H3tea, and azide ligands in MeOH/MeCN or EtOH/MeCN media under ultrasonic irradiation. Single-crystal X-ray diffraction showed that wheels 1a–3a prepared from MeOH/MeCN solutions crystallize in the triclinic space group P1̅ and have Ci symmetry, whereas wheels 1b–3b received from EtOH/MeCN solution crystallize in the trigonal space group R3̅ and have C3i symmetry. Magnetic studies reveal medium antiferromagnetic exchange interactions within the Fe3 trimeric unit (with the exchange coupling parameters of JFe3 = −13.1 cm–1 for 1a, JFe3 = −11.6 cm–1 for 1b) and weak intermolecular antiferromagnetic exchange interactions (λmf = −0.366 mol cm–3 and −0.368 mol cm–3 (zJmf = −0.19 cm–1), respectively). This leads to spin ground states of S = 5/2 for each {Fe3} unit. Substitution of diamagnetic Y(III) centers by paramagnetic Ln(III) centers (in 2a/2b by Gd(III) and in 3a/3b by Dy(III) centers) results in ferromagnetic exchange interactions between the Fe(III) and Ln(III) centers in addition to the predominant antiferromagnetic Fe···Fe interactions in 1a/1b.

Zinc(II) and copper(II) complexes with benzothiadiazole Schiff-base ligands

The ligand (2-[4-(2,1,3-benzothiadiazole)imino]methyl-phenol) HL1 containing the electron poor benzothiadiazole (BTD) unit, conveniently prepared by condensation of 4-amino-2,1,3-benzothiadiazole and salicylaldehyde, has been structurally characterized by single crystal X-ray diffraction. Two energy minima have been determined, by DFT calculations, for HL1 and for its ortho-vanillin analogue HL2, corresponding either to the conformer observed in the solid state or to the chelating tridentate form. TD-DFT calculations have been performed on HL1 and HL2 in order to assign their experimental UV–visible absorption bands. Reaction of HL1 and HL2 with copper (II) hexafluoroacetylacetonate (hfac), zinc (II) hexafluoroacetylacetonate or zinc (II) acetate provided the neutral complexes [Cu(L1)(hfac)] (1), [Zn(L1)2] (2), [Cu(L2)2] (3) and [Zn(L2)2] (4) which were structurally characterized, with a focus on the coordination sphere of the metal centre and on the intermolecular interactions. The UV–visible absorption properties of the Zn(II) complexes 2 and 4 have been experimentally and theoretically investigated and compared to those of the ligands. Finally, the cryomagnetic study of 1 and 3 in the temperature range 2.0–295.0 K reveals a Curie-Weiss law behaviour with very weak intermolecular antiferromagnetic interactions in the low temperature region.

Halo‐Substituted Blatter Radicals and Their Role in Modulating Magnetic Interaction in Metal Complexes: A Combined Experimental and Theoretical Study

AbstractHerein, we report the synthesis, structure, and magnetic properties of three new halo‐substituted benzotriazinyl radicals (Rad3a‐3c where a=Cl, b=Br, c=I) and two metal complexes [M(hfac)2(Rad3c)⋅CHCl3](M=Cu(II) (1), Zn(II) (2) and hfac: hexafluoroacetylacetonate) as representative examples. Structural analyses disclose that all the radicals are isostructural. Compared to the reported benzotriazinyl radicals, the N4 atom of pyridine flips opposite to the spin bearing (N1) centre, and it is stabilized by secondary C−H⋅⋅⋅N interaction. The π⋅⋅⋅π stacking interaction between the spin bearing centre and pyridyl ring decreases as the size of the halogen increases from ‐Cl to ‐I. The stacking distance is substantially longer than the other coordinating benzotriazinyl radicals reported so far. The dc magnetic studies reveal the presence of strong intermolecular antiferromagnetic exchange interaction between the radical dimers, which decreases in the order of Rad3a→Rad3b→Rad3c. Complex 1 shows a strong intramolecular through‐bond metal‐radical ferromagnetic interaction, whereas a weak intermolecular through‐space radical⋅⋅⋅radical antiferromagnetic exchange interaction is observed in complex 2. Furthermore, the broken symmetry (BS)‐DFT calculations were performed to get more insight into the exchange interaction for all the radicals and metal complexes.

Crystal structure, magnetic properties and luminescent behavior of four mononuclear lanthanide-radical complexes

Four mononuclear lanthanide complexes based on a long nitronly nitroxide radical NIT-PhOPyrim, [Ln(hfac)3(NIT-PhOPyrim)(H2O)] (Ln(Ⅲ) = Gd 1, Tb 2, Dy 3, Er4; hfac = hexafluoroacetylacetonate; NIT-PhOPyrim = 2-[4-(pyrimidin-2-yloxy)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been synthesized and characterized. Single crystal X-ray diffraction analyses revealed that these four complexes are isomorphic in which each Ln(Ⅲ) ion is eight-coordinated by six oxygen atoms from three hfac ligands, one oxygen atom from one water molecule and one oxygen atom from the NO group of NIT-PhOPyrim ligand. Particularly, the coordinated water molecules were connected other mononuclear units through their hydrogen bonds into tetra-nuclear complexes and/or dimers. Variable temperature magnetization of complex 1 was shown the ferromagnetic interaction between Gd(III) ion and nitroxide radical, while weak intermolecular antiferromagnetic interactions through hydrogen bonds. Alternating-current (ac) magnetic susceptibility of complexes 2–4 revealed no magnetic relaxation behavior. Furthermore, Tb complex can detect Fe3+anion with a high sensitivity and selectivity through the fluorescence quenching effect.

Thermally Induced Reversible Metal-to-Metal Charge Transfer in Mixed-Valence {Fe III 4 Fe II 4 } Cubes

Thermally Induced Reversible Metal-to-Metal Charge Transfer in Mixed-Valence {Fe ^III ₄ Fe ^II ₄ } Cubes

Nickel(II) complexes with 2-Hfur and N-donors: The magnetic effects of the structural variations, thermal properties and antimycobacterial activity against Mycolicibacterium smegmatis

New complexes of nickel(II) with 2-furoic acid (2-Hfur) and different N-donor ligands of the composition [Ni(fur)2(phen)(H2O)2]·H2O (1) (phen = 1,10-phenantroline), [Ni(fur)2(2,2′-bpy)] (2, 2,2′-bpy = 2,2′-bipyridine), [Ni(fur)2(4,4′-bpy)(CH3OH)2]n (3, 4,4′-bpy = 4,4′-bipyridine), [Ni(fur)2(pz)4]·2MeCN (4) (pz = pyrazole) have been synthesized. The structure of the compounds was established by single crystal X-ray diffraction analysis. Complexes 1, 2, and 4 are mononuclear, complex 3 is a 1D coordination polymer. The DC magnetic susceptibility data measured for 2 and 3 are indicative of antiferromagnetic exchange interactions between the metal centers, which proved to be negligibly weak in 2 and more pronounced in 3. A quantum-chemical analysis of intermolecular (for 2) and intra- and interchain (for 3) magnetic exchange pathways confirms these findings, revealing the presence of magnetic chains formed by a network of very weak intermolecular antiferromagnetic exchange interactions in the crystal of 2 and a strengthening of antiferromagnetic exchange coupling in the polymeric chains of 3. Thermal behavior of 1 and 2 was studied by simultaneous thermal analysis (STA). According to PXRD data, the final thermolysis product of complex 2 is metal Ni nanocrystals (d = 14.7(3) nm). Analysis of the results of biological activity of 1–4in vitro against Mycolicibacterium smegmatis showed a low sensitivity of the mycobacterial wall to Ni2+ cations.

A rare isostructural series of 3d-4f cyanido-bridged heterometallic squares obtained by assembling [FeIII{HB(pz)3}(CN)3]- and LnIII ions: synthesis, X-ray structure and cryomagnetic study.

A new series of cyanido-bridged {FeIIILnIII}2 neutral molecular squares of general formula [Fe{HB(pz)3}(CN)(μ-CN)2Ln(NO3)2(pyim)(Ph3PO)]2·2CH3CN [Ln = Ce (1), Pr (2), Nd (3), Gd (4), Tb (5), Dy (6) and Er (7); {HB(pz)3}- = hydrotris(pyrazolyl)borate, pyim = 2-(1H-imidazol-2-yl)pyridine and Ph3PO = triphenylphosphine oxide] were obtained by reacting the low-spin [Fe{HB(pz)3}(CN)3]- species with the preformed [LnIII(pyim)(NO3)2(pyim)(Ph3PO)]+ complex anions (generated in situ by mixing the nitrate salt of each Ln(III) ion with pyim and Ph3PO molecules). Single-crystal X-ray diffraction studies show that 1-7 are isostructural compounds that crystallize in the triclinic P1̄ space group. Their crystal structures consist of centrosymmetric cyanido-bridged {FeIIILnIII}2 molecular squares where two [Fe{HB(pz)3}(CN)3]- units adopt bis-monodentate coordination modes towards two [LnIII(pyim)(NO3)2(pyim)(Ph3PO)]+ moieties. The cis-oriented convergent sites from both low-spin FeIII and LnIII fragments form a quasi square-shaped molecule in which the 3d and 4f ions alternatively occupy the corners of the square. Both FeIII ions show a distorted octahedral surrounding (C3v symmetry), whereas the LnIII ions exhibit a distorted muffin-like geometry (Cs symmetry) in 1-7. The intramolecular FeIII⋯LnIII distances across the two cyanido-bridges range from ca. 5.48/5.46 up to ca. 5.58/5.61 Å. The molecular squares in 1-7 are interlinked through hydrogen bonds, weak π⋯π stacking and very weak C-H⋯π type interactions into three-dimensional supramolecular networks. The analysis of the solid-state direct-current (dc) magnetic susceptibility data of 1-7 in the temperature range 1.9-300 K reveals the occurrence of weak intra- and intermolecular antiferromagnetic interactions. The small intramolecular antiferromagnetic couplings in 4 compare well with those previously reported for parent systems. Although the coexistence of the spin-orbit coupling (SOC) of the low-spin iron(III) and lanthanide(III) ions in the remaining compounds together with the ligand field effects mask the visualization and make difficult the evaluation of the possible magnetic interactions in them, we were able to do it through a SOC model applied on exact or effective Hamiltonians. Frequency-dependent alternating current magnetic susceptibility signals in the temperature range 2.0-9.0 K under zero and non-zero static fields were observed for 5-7 which indicate slow magnetic relaxation (SMM) behavior. The usual absence of χ''M maxima moved us to estimate their energy barriers through ln(χ''M/ χ'M) vs. 1/T plots, obtaining values from 25 to 40 cm-1.

An electrically conducting molecular crystal composed of a magnetic iron(iii) complex (S = 1/2) with a large aromatic ligand, 1,2-naphthlalocyanine (C4h isomer): towards the development of molecular spintronics.

The field of molecular spintronics has gained significant attention for the development of second-generation spintronic devices. Therefore, an electrically conducting molecular crystal, Ph4P[FeIII(1,2-Nc)(CN)2]2 (Ph4P = tetraphenylphosphonium and 1,2-Nc = C4h isomer of 1,2-naphthalocyanine), was fabricated as a new coordination compound with a strong π-d interaction. Furthermore, it is a mixed-valence compound with a local spin of S = 1/2 at the center of the conduction path. Crystal structure analysis revealed that Ph4P[FeIII(1,2-Nc)(CN)2]2 was isostructural to its non-magnetic analogue Ph4P[CoIII(1,2-Nc)(CN)2]2 but possessed higher electrical resistivity, indicating that the strong intramolecular π-d interaction is present in the [FeIII(1,2-Nc)(CN)2] unit. Although the magnetic interaction between π-conduction electrons and FeIII-d spins (π-d interaction) is crucial for the emergence of a negative magnetoresistance effect, the negative magnetoresistance effect of Ph4P[FeIII(1,2-Nc)(CN)2]2 was significantly smaller (-6% at 30 K under a static 9 T magnetic field) than those of Ph4P[FeIII(Pc)(CN)2]2 (-32%) and Ph4P[FeIII(tbp)(CN)2]2 (-13%) analogues (Pc = phthalocyanine and tbp = tetrabenzoporphyrin). This small negative magnetoresistance effect of Ph4P[FeIII(Pc)(CN)2]2 could be ascribed to the weak intermolecular antiferromagnetic interaction between its d spins. Hence, this study showed that constructing a molecular design for strengthening the intermolecular antiferromagnetic interaction is key to enhancing the negative magnetoresistance effect.

Secondary Metal Coordination Using a Tetranuclear Complex as Ligand Leading to Hexanuclear Complexes with Enhanced Thermal Barriers for Electron Transfer

Postsynthesis of the paramagnetic square-shaped complex {[(Tp*Me)Fe(μ-CN)2(CN)][Co(dmbpy)2]}2(BPh4)2·6MeCN·H2O [1, Tp*Me = tris(3,4,5-trimethylpyrazole)-borate; dmbpy = 4,4′-dimethyl-2,2′-bipyridin...

A series of mononuclear lanthanide complexes constructed by Schiff base and β-diketonate ligands: synthesis, structures, magnetic and fluorescent properties

The Schiff base H2bcsdt (H2bcsdt = N1,N3-bis(5-chlorosalicyladehyde) diethylenetriamine) and the β-diketonate Hdbm (Hdbm = dibenzoylmethane) have been employed as a ligand and a pro-ligand to construct a series of Ln(III) complexes. Five mononuclear compounds were synthesized under solvothermal conditions. Single-crystal X-ray diffraction analyses reveal that they are formulated as [Ln(bcsdt)(dbm)(H2O)]·MeCN (Ln = Gd (1), Tb (2), Dy (3), Ho (4), Er (5)). The metal ions in complexes 1–5 are all eight-coordinated and display a similar capped triangular dodecahedron (D2h) geometry. The fluorescent and magnetic properties of 1–5 were investigated. Complex 2 exhibits an intense green luminescence emission which is characteristic of the Tb(III) ion. Weak intermolecular antiferromagnetic interactions were determined in 2–5.

An investigation into the magnetic interactions in a series of Dy2 single-molecule magnets.

Three di-nuclear DyIII complexes [Dy2(H2L)2(tfa)]·Cl·3DMF (1), [Dy2(H2L)2(MeO)(SCN)]·MeOH (2) and [Dy2(H2L)2(MeOH)Cl]·Cl·2MeOH (3) were synthesized and structurally and magnetically characterized. The Dy1/Dy2 centers in these complexes are all nine-coordinate with spherical capped square antiprism (local C4v symmetry) environments. All complexes display single-molecule magnet (SMM) behavior under zero applied dc field with their properties dependent on the nature of the magnetic interactions between the DyIII ions. Ab initio calculations substantiate that all DyIII ions show a weakly axial crystal-field environment with the exception of one of the DyIII ions in complex 2. The ground Kramers doublets show modest amounts of quantum tunneling of magnetization that gets blocked by the interaction between the DyIII ions, leading to a thermally activated slow relaxation of magnetization. The interaction between the ions is ferromagnetic and mostly originates from the dipolar interaction. However, anti-ferromagnetic intermolecular interaction plays an important role and in the case of complex 2 it is sufficiently strong to mask the ferromagnetic intramolecular interaction.

Triplet Diradical-Cation Salts Consisting of the Phenothiazine Radical Cation and a Nitronyl Nitroxide.

The spin-spin and magnetic properties of two (nitronyl nitroxide)-(di-p-anisylamine-phenothiazine) diradical cation salts, (DAA-PTZ)+ -NN⋅MBr4 - (M=Ga, Fe), have been investigated. These diradical-cation species were prepared by the cross-coupling of iodophenothiazine DAA-PTZ-I with NN-AuPPh3 followed by oxidation with the thianthrenium radical cation (TA+ ⋅MBr4 - ). These salts were found to be highly stable under aerobic conditions. For the GaBr4 salt, large ferromagnetic intramolecular and small antiferromagnetic intermolecular interactions (J1 /kB =+320 K and J2 /kB =-2 K, respectively) were observed. The magnetic property of the Fe3+ salt was analyzed by using a six-spin model assuming identical intramolecular exchange interaction (J3 /kB =+320 K) and the other exchange interactions (J4 /kB =-7 K and J5 /kB =-4 K). A significant color change was observed in the UV/Vis/NIR absorption spectra upon electrochemical oxidation of the doublet DAA-PTZ-NN to the triplet (DAA-PTZ)+ -NN.

Probing through-space and through-bond magnetic exchange couplings in a new benzotriazinyl radical and its metal complexes.

The synthesis and characterization of a new chelating benzotriazinyl radical (Rad2) are described. Crystallographic studies coupled with SQUID magnetometry on Rad2 reveal the presence of discrete radical pairs which are antiferromagnetically coupled. The reaction of Rad2 with the 3d transition metal complexes M(hfac)2·xH2O (hfac- = hexafluoroacetylacetonate) led to mononuclear metal complexes of general formula M(hfac)2(Rad2) [M = Zn(ii) (1); Ni(ii) (2) and Co(ii) (3)] whose structures have been determined by single crystal X-ray diffraction. Compounds 1-3 are isostructural and crystallize in the monoclinic space group P21/n with two molecules in the asymmetric unit. In the case of the Zn(ii) complex (1) through-space intermolecular radicalradical antiferromagnetic exchange interactions viaπ*π* contacts are observed, whereas strong intramolecular through-bond metal-radical ferromagnetic interactions [J = +59.3(9) cm-1] are observed for the Ni(ii) complex (2). For the Co(ii) complex (3), computational and magnetic studies reveal substantial zero field splitting and ferromagnetic metal-radical interactions.

Determination of Large Zero-Field Splitting in High-Spin Co(I) Clathrochelates.

Zero-field splitting (ZFS) of three high-spin Co(I) ( S = 1) clathrochelate complexes was determined by frequency-domain Fourier-transform THz-EPR (FD-FT THz-EPR). The following axial and rhombic ZFS values ( D and E, respectively) were determined: [N( n-Bu)4]CoI(GmCl2)3(BPh)2 (1, D/ hc = +16.43(1) cm-1, E/ hc = 0.0(1) cm-1), [P(Me2N)4]CoI(GmCl2)3(BPh)2 (2, D/ hc = +16.67(4) cm-1, E/ hc = 0.0(1) cm-1), and [P(C6H5)4]CoI(GmCl2)3(BPh)2 (3, D/ hc = +16.72(2) cm-1, E/ hc = 0.24(3) cm-1). Complementary susceptibility χ T measurements and quantum chemistry calculations on 1 revealed hard-axis-type magnetic anisotropy and allowed for a correlation of ZFS and the electronic structure. Increased rhombicity of 3 as compared to 1 and 2 was assigned to symmetry changes of the ligand structure induced by the change of the counterion. 1 and 3 exhibited temperature-dependent ZFS values. Possible reasons for this phenomenon, such as structural changes and weak chain-like intermolecular antiferromagnetic interactions, are discussed.

Syntheses, crystal structures, spectroscopic and magnetic properties of two trinuclear iron complexes with carboxylate and oximate mixed-bridge ligands

Two trinuclear oxo-centered iron(III) complexes [Fe3(μ3-O)Salox(L1)5(MeOH)2] (1) and [Fe3(μ3-O)Salox(L1)5(EtOH)2]·2EtOH·2H2O (2) (Salox = salicylaldoxime, L1 = o-nitrobenzoic acid) have been synthesized, and their X-ray crystal structures, spectroscopic properties (IR, UV–Vis, fluorescence), and magnetic properties have been characterized. In each complex, the three Fe(III) centers of the [Fe3O] moieties are joined together by a μ3-O unit to form an isosceles triangle, and each metal center has a distorted octahedral coordination geometry. The fluorescence emission intensities for the two complexes are much higher than those of the free proligands, suggesting that the [Fe3O] structural unit increases the rigidity of the ligands after coordination, and the enlarged conjugate system reduces the frontier orbitals energy gap. The nature of magnetic coupling within complexes 1 and 2 indicates both intramolecular strong and intermolecular weak antiferromagnetic interactions.

Transition metal coordination complexes based on V-shaped bis-triazole ligand: syntheses, structures, and properties

Hydrothermal reactions of 1,3-bis(1,2,4-triazol-1-yl)benzene (btb) and M(NO3)2 (M = Co2+ (1), Cu2+ (2)) afforded two new coordination polymers, [Co(btb)2(NO3)(H2O)]n·NO3·H2O (1) and [Cu(btb)2(NO3)2]n (2), respectively. Single-crystal X-ray diffraction reveals that 1 crystallizes in the space group P21/m and 2 crystallizes in the space group Pī, both showing a double-stranded chain structure. The 1-D chains are interconnected via π⋯π interactions to lead to 2-D ladder-like supramolecular architectures. In addition, magnetic behavior and thermal stability of 1 and 2 have been investigated. For 1, weak antiferromagnetic interactions are observed at low temperature, and the data obey the Curie–Weiss law χM = C/(T−θ), with C = 3.22 cm3·mol−1·K and θ = −10.39 K. For 2, the decrease of the χT vs. T curve at low temperature is the result of intermolecular antiferromagnetic magnetic interactions.

Evaluation of the Giant Ferromagnetic π-d Interaction in Iron-Phthalocyanine Molecule.

The interaction between itinerant π and localized d electrons in metal-phthalocyanines, namely, Jπd interaction, is considered as responsible for the giant negative magnetoresistance observed in several phthalocyanine-based conductors, among many other important physical properties. Despite the fundamental and technological importance of this on-site intramolecular interaction, its giant ferromagnetic nature has been only recently demonstrated by the experiments conducted by Murakawa et al. in the neutral radical [Fe(Pc)(CN)2]·2CHCl3 ( Phys. Rev. B 2015 , 92 , 054429 ). In this article, we present the theoretical evaluation of this interaction combining wave function-based electronic calculations on isolated Fe(Pc)(CN)2 molecules and density functional theory-based periodic calculations on the crystal. Our calculations confirm the ferromagnetic nature of the π-d interaction, with a coupling constant as large as Jπd/kB = 570 K, in excellent agreement with the experiments, and the presence of intermolecular antiferromagnetic interactions driven by the π-π overlap of neighboring phthalocyaninato molecules. The analysis of the wave function of the ground state of the Fe(Pc)(CN)2 molecule provides the clues of the origin of this giant ferromagnetic π-d interaction.

Copper(II) complexes based on tripodal pyrazolyl amines: Synthesis, structure, magnetic properties and anticancer activity

The Cu(II) complexes [Cu(bpdmpz)Cl]ClO4 (1), [Cu(bdmpzp)Cl]ClO4 (2-ClO4), [Cu(bdmpzp)Cl]PF6 (2-PF6) and [Cu(tdmpza)Cl]ClO4 (3), bpdmpzp=[bis[((2-pyridylmethyl)-di(3,5-dimethyl-1H-pyrazolyl)methyl)]amine, bdmpzp=[bis((di(3,5-dimethyl-1H-pyrazolyl)methyl)-(2-pyridylmethyl)]amine and tdmpza=tris[di(3,5-dimethyl-1H-pyrazolyl)-methyl)]amine were synthesized and characterized by elemental analysis, magnetic and conductivity measurements, electrospray-ionization mass spectrometry, infrared and electronic spectroscopy, and X-ray crystallography. The magnetic properties of the complexes, measured at variable temperature, revealed weak antiferromagnetic intermolecular interactions. The cytotoxicity of the complexes 1, 2-ClO4, 3, and 4 ([Cu(bedmpzp)Cl]PF6, where bedmpzp=[bis(3,5-dimethyl-1H-pyrazol-1-yl-1-ethyl)-(2-pyridylmethyl)]amine), was investigated against four human cancer cell lines: A2780 (ovarian), A2780R (cisplatin-resistant variant), HOS (aggressive bone tumors), CaCo2 (epithelial colorectal adenocarcinoma) and on healthy human hepatocytes. The complex 4 was the most cytotoxic one, with IC50=1.4μM (A2780), 8.3μM (A2780R), 4.7μM (HOS) and 10.8μM (CaCo2). The mass spectrometry-based interaction studies, involving selected sulfur-containing biomolecules and small model proteins, revealed pro-oxidant effects of complexes 1 and 4 and differences in stability of both complexes in the mixtures containing the model protein cytochrome c after 24h incubation, complex 1 formed 1:1 adduct, the formation of which was accompanied by the loss of one dimethylpyrazole pendant arm from the bpdmpz ligand, while the complex 4 composition remained intact and the complex formed both 1:1 and 1:2 adducts (cytochrome c vs. Cu(II)-complex).

Crystallographic Insights into the Synthesis and Magnetic Properties of Oxoverdazyl Radicals Functionalized by Benzoic Acid

The synthesis and crystallization of two verdazyl radicals, 1,5‐dimethyl‐3‐(4′‐carboxyphenyl)‐6‐oxoverdazyl HIMe and 1,5‐diisopropyl‐3‐(4′‐carboxyphenyl)‐6‐oxoverdazyl HIiPr, are described. The electrochemical studies reveal that the oxidation of the two radicals is reversible, whereas their reduction is irreversible. The EPR spectrum of both radicals essentially exhibits a nine‐line pattern related to the mean hyperfine interaction of the unpaired electron with the nitrogen atoms of the verdazyl cycle. The single‐crystal X‐ray diffraction of the intermediates towards HIiPr allows a fine description of the cyanoborane adduct, which is the key intermediate of this synthesis. The verdazyl radicals themselves are obtained as single crystals. In the case of HIiPr, depending on the solvent, two polymorphs are crystallized. The structure resolution reveals that, in the solid state, the organization of the verdazyl radicals is governed by both H‐bonding and π–π interactions and is reminiscent of the H‐bonded structures that can be present in solution. Within the 1D π stacks observed in the three compounds, the verdazyl–verdazyl distance varies from 4.88 Å in HIMe to 7.90 Å in HaIiPr. This modulation of the distance strongly influences the antiferromagnetic intermolecular exchange interaction between π‐stacked radicals, which goes from J = –90 cm–1 (H = –JΣSiSi+1) for HIMe to –12.96(3) cm–1 for HbIiPr and –0.92 cm–1 for HaIiPr.