Directed exciton transport highways in organic semiconductors.

Exciton bandwidths and exciton transport are difficult to control by material design. We showcase the intriguing excitonic properties in an organic semiconductor material with specifically tailored functional groups, in which extremely broad exciton bands in the near-infrared-visible part of the electromagnetic spectrum are observed by electron energy loss spectroscopy and theoretically explained by a close contact between tightly packing molecules and by their strong interactions. This is induced by the donor-acceptor type molecular structure and its resulting crystal packing, which induces a remarkable anisotropy that should lead to a strongly directed transport of excitons. The observations and detailed understanding of the results yield blueprints for the design of molecular structures in which similar molecular features might be used to further explore the tunability of excitonic bands and pave a way for organic materials with strongly enhanced transport and built-in control of the propagation direction.

Low-Dimensional Magnetism in Multivariate Copper/Zinc MOF-74 Materials Formed via Different Mechanochemical Methods.

MOF-74 is an archetypal magnetic metal-organic framework (MOF) family, with metal nodes bridged by 2,5-dioxido-1,4-benzenedicarboxylic acid (H4dobdc) and arranged into one of the simplest representations of the 1D Ising magnetic model. Recently, a novel mechano-synthetic approach opened a pathway toward a series of bimetallic multivariate (1:1) M1M2-MOF-74 materials, with the uniform distribution of metal cations in the oxometallic chains, offering a unique opportunity to investigate low-dimensional magnetism in these heterometallic MOFs. We explore here how different mechanochemical procedures affect the interaction between the metal nodes of the model system of three multivariate copper(II)/zinc(II)-MOF-74 materials, two of which were obtained through a template-controlled procedure, and the third one was obtained by recently developed mechanical MOF-alloying combined with subsequent accelerated aging. While the three Cu/Zn-MOF-74 products have almost identical powder X-ray diffraction (PXRD) diffractograms and Fourier transform infrared spectra, they differ significantly in their magnetic properties, as revealed through detailed magnetization and X-band and multifrequency high-field electron spin resonance measurements. The magnetic results of the three multivariate Cu/Zn-MOF-74s were compared to the properties of the monometallic Cu-MOF-74, which shows antiferromagnetic intrachain and weaker ferromagnetic interchain interactions. Energy-dispersive X-ray spectroscopy/scanning electron microscopy and solid-state nuclear magnetic resonance spectroscopy helped rationalize the observed differences in magnetization, and in situ synchrotron PXRD monitoring of template-controlled MOF formation revealed different reaction pathways when using the zinc or copper intermediates, involving even the fleeting occurrence of a rare MOF-74 polymorph.

Correction to: Optical Anisotropy and Momentum-Dependent Excitons in Dibenzopentacene Single Crystals.

[This corrects the article DOI: 10.1021/acsomega.2c01987.].

Charge-Compensated N-Doped π-Conjugated Polymers: Toward both Thermodynamic Stability of N-Doped States in Water and High Electron Conductivity.

The understanding and applications of electron-conducting π-conjugated polymers with naphtalene diimide (NDI) blocks show remarkable progress in recent years. Such polymers demonstrate a facilitated n-doping due to the strong electron deficiency of the main polymer chain and the presence of the positively charged side groups stabilizing a negative charge of the n-doped backbone. Here, the n-type conducting NDI polymer with enhanced stability of its n-doped states for prospective "in-water" applications is developed. A combined experimental-theoretical approach is used to identify critical features and parameters that control the doping and electron transport process. The facilitated polymer reduction ability and the thermodynamic stability in water are confirmed by electrochemical measurements and doping studies. This material also demonstrates a high conductivity of 10-2  S cm-1  under ambient conditions and 10-1  S cm-1  in vacuum. The modeling explains the stabilizing effects  for various dopants. The simulations show a significant doping-induced "collapse" of the positively charged side chains on the core bearing a partial negative charge. This explains a decrease in the lamellar spacing observed in experiments. This study fundamentally enables a novel pathway for achieving both thermodynamic stability of the n-doped states in water and the high electron conductivity of polymers.

Optical Anisotropy and Momentum-Dependent Excitons in Dibenzopentacene Single Crystals.

High-quality single crystals of the organic semiconductor (1,2;8,9)-dibenzopentacene were grown via physical vapor transport. The crystal structure-unknown before-was determined by single-crystal X-ray diffraction; polarization-dependent optical absorption measurements display a large anisotropy in the ac plane of the crystals. The overall Davydov splitting is ∼110 meV, which is slightly lower than that in the close relative pentacene (120 meV). Momentum-dependent electron energy-loss spectroscopy measurements show a clear exciton dispersion of the Davydov components. An analysis of the dispersion using a simple 1D model indicates smaller electron- and hole-transfer integrals in dibenzopentacene as compared to pentacene. The spectral weight distribution of the excitation spectra is strongly momentum-dependent and demonstrates a strong momentum-dependent admixture of Frenkel excitons, charge-transfer excitons, and vibrational modes.

Highly efficient modulation doping: A path toward superior organic thermoelectric devices.

We investigate the charge and thermoelectric transport in modulation-doped large-area rubrene thin-film crystals with different crystal phases. We show that modulation doping allows achieving superior doping efficiencies even for high doping densities, when conventional bulk doping runs into the reserve regime. Modulation-doped orthorhombic rubrene achieves much improved thermoelectric power factors, exceeding 20 µW m-1 K-2 at 80°C. Theoretical studies give insight into the energy landscape of the heterostructures and its influence on qualitative trends of the Seebeck coefficient. Our results show that modulation doping together with high-mobility crystalline organic semiconductor films is a previosly unexplored strategy for achieving high-performance organic thermoelectrics.

A mononuclear iron(III) complex with unusual changes of color and magneto-structural properties with temperature: synthesis, structure, magnetization, multi-frequency ESR and DFT study.

From the reaction of 2-hydroxy-6-methylpyridine (L) with iron(II) tetrafluoroborate, a new mononuclear iron(III) octahedral complex [FeL6](BF4)3 has been isolated. The color of the complex reversibly changed from red at room temperature to yellow-orange at the liquid nitrogen temperature. Magnetization measurements indicate that iron(III) in [FeL6](BF4)3 is in a high-spin state S = 5/2, from room temperature to 1.8 K. The high-spin ground state of iron(III) is also confirmed by DFT calculations. Although the spin-crossover of the complex is not observed, X-band and multifrequency high-field/high-frequency electron spin resonance (ESR) spectroscopy shows rather uncommon iron(III) spectra at room temperature and an unusual change with cooling. Spectral simulations reveal that the S = 5/2 ground state multiplet of the complex can be characterized by the temperature independent axial zero-field splitting parameter of |D| = +2 GHz (0.067 cm-1) while the value of the rhombic parameter E of the order of some tenths MHz increases on lowering the temperature. Single crystal X-ray diffraction (SCXRD) shows that the iron(III) coordination geometry does not change with temperature while supramolecular interactions are temperature dependent, influencing the iron(III) rhombicity. Additionally, the DFT calculations show temperature variation of the HOMO-LUMO gap, in agreement with the changes of color and ESR-spectra of the iron(III) complex with temperature.

Charge Carrier Mobility Improvement in Diketopyrrolopyrrole Block-Copolymers by Shear Coating.

Shear coating is a promising deposition method for upscaling device fabrication and enabling high throughput, and is furthermore suitable for translating to roll-to-roll processing. Although common polymer semiconductors (PSCs) are solution processible, they are still prone to mechanical failure upon stretching, limiting applications in e.g., electronic skin and health monitoring. Progress made towards mechanically compliant PSCs, e.g., the incorporation of soft segments into the polymer backbone, could not only allow such applications, but also benefit advanced fabrication methods, like roll-to-roll printing on flexible substrates, to produce the targeted devices. Tri-block copolymers (TBCs), consisting of an inner rigid semiconducting poly-diketo-pyrrolopyrrole-thienothiophene (PDPP-TT) block flanked by two soft elastomeric poly(dimethylsiloxane) (PDMS) chains, maintain good charge transport properties, while being mechanically soft and flexible. Potentially aiming at the fabrication of TBC-based wearable electronics by means of cost-efficient and scalable deposition methods (e.g., blade-coating), a tolerance of the electrical performance of the TBCs to the shear speed was investigated. Herein, we demonstrate that such TBCs can be deposited at high shear speeds (film formation up to a speed of 10 mm s-1). While such high speeds result in increased film thickness, no degradation of the electrical performance was observed, as was frequently reported for polymer-based OFETs. Instead, high shear speeds even led to a small improvement in the electrical performance: mobility increased from 0.06 cm2 V-1 s-1 at 0.5 mm s-1 to 0.16 cm2 V-1 s-1 at 7 mm s-1 for the TBC with 24 wt% PDMS, and for the TBC containing 37 wt% PDMS from 0.05 cm2 V-1 s-1 at 0.5 mm s-1 to 0.13 cm2 V-1 s-1 at 7 mm s-1. Interestingly, the improvement of mobility is not accompanied by any significant changes in morphology.

Terahertz Magneto-Optical Excitations of the sd-Hybrid States of Lithium Nitridocobaltate Li2(Li1-xCox)N.

We report the results of the experimental and theoretical study of the magnetic anisotropy of single crystals of the Co-doped lithium nitride Li2(Li1-xCox)N with x = 0.005, 0.01, and 0.02. It was shown recently that doping of the Li3N crystalline matrix with 3d transition metal (TM) ions yields superior magnetic properties comparable with the strongly anisotropic single-molecule magnetism of rare-earth complexes. Our combined electron spin resonance (ESR) and THz spectroscopic investigations of Li2(Li1-xCox)N in a very broad frequency range up to 1.7 THz and in magnetic fields up to 16 T enable an accurate determination of the energies of the spin levels of the ground state multiplet Ŝ = 1 of the paramagnetic Co(I) ion. In particular, we find a very large zero field splitting (ZFS) of almost 1 THz (∼4 meV or 33 cm-1) between the ground-state singlet and the first excited doublet state. On the computational side, ab initio many-body quantum chemistry calculations reveal a ZFS gap consistent with the experimental value. Such a large ZFS energy yields a very strong single-ion magnetic anisotropy of easy-plane type resembling that of rare-earth ions. Its microscopic origin is the unusual linear coordination of the Co(I) ions in Li2(Li1-xCox)N with two nitrogen ligands. Our calculations also evidence a strong 3d-4s hybridization of the electronic shells resulting in significant electron spin density at the 59Co nuclei, which may be responsible for the experimentally observed extraordinary large hyperfine structure of the ESR signals. Altogether, our experimental spectroscopic and computational results enable comprehensive insights into the remarkable properties of the Li2[Li1-x(TM)x]N magnets on the microscopic level.

An unusual donor-acceptor system MnIIPc-TCNQ/F4-TCNQ and the properties of the mixed single crystals of metal phthalocyanines with organic acceptor molecules.

The interaction of manganese(ii) phthalocyanine with 7,7,8,8-tetracyanoquinodimethane and its perfluoro derivative proceeds with the oxidation of Mn and the reduction of the acceptor molecules to give the first mixed single crystals of manganese(iii) phthalocyanine with TCNQ/F4-TCNQ radical anions. The crystals have unusual structures with C-Hπ interactions between the ions and their orthogonal arrangement, as well as remarkable redox properties. The charge transfer was proved by spectroscopic and magnetic studies.

A Phthalocyanine-Based Layered Two-Dimensional Conjugated Metal-Organic Framework as a Highly Efficient Electrocatalyst for the Oxygen Reduction Reaction.

Layered two-dimensional (2D) conjugated metal-organic frameworks (MOFs) represent a family of rising electrocatalysts for the oxygen reduction reaction (ORR), due to the controllable architectures, excellent electrical conductivity, and highly exposed well-defined molecular active sites. Herein, we report a copper phthalocyanine based 2D conjugated MOF with square-planar cobalt bis(dihydroxy) complexes (Co-O4 ) as linkages (PcCu-O8 -Co) and layer-stacked structures prepared via solvothermal synthesis. PcCu-O8 -Co 2D MOF mixed with carbon nanotubes exhibits excellent electrocatalytic ORR activity (E1/2 =0.83 V vs. RHE, n=3.93, and jL =5.3 mA cm-2 ) in alkaline media, which is the record value among the reported intrinsic MOF electrocatalysts. Supported by in situ Raman spectro-electrochemistry and theoretical modeling as well as contrast catalytic tests, we identified the cobalt nodes as ORR active sites. Furthermore, when employed as a cathode electrocatalyst for zinc-air batteries, PcCu-O8 -Co delivers a maximum power density of 94 mW cm-2 , outperforming the state-of-the-art Pt/C electrocatalysts (78.3 mW cm-2 ).

Zn and Co redox active coordination polymers as efficient electrocatalysts.

New redox active 1D helical coordination polymers M(fcdHp) (M(ii) = Zn(1), Co(2)) have been obtained by utilizing the 1,1'-ferrocenylenbis(H-phosphinic) acid (H2fcdHp) ligand and Zn or Co nitrate salts. Complexes 1 and 2 are isomorphic, crystallizing in the chiral space groups P4122 and P4322, respectively. Their redox, electrocatalytic and other properties are described. These compounds incorporated into carbon paste electrodes and exhibited reversible redox reactions, arising from the ferrocenyl moiety. These coordination polymers are efficient as electrocatalysts for the reduction of protons to hydrogen. Using N,N-dimethylformamidium ([DMF(H)+]) as the acid in the acetonitrile solution, Co CP (2) displays a turnover frequency of 300 s-1, which is among the fastest rates reported for any CP electrocatalyst in CH3CN. This high rate of catalytic reaction comes at the cost of the 820-840 mV overpotential at the potential of catalysis. As the hydrogen evolution reaction (HER) catalysts, the CPs exhibited in 0.5 M H2SO4 the overpotential η10 of 340 or 450 mV, onset overpotential of 220 or 300 mV (vs. RHE), Tafel slope of 110 or 120 mV dec-1, correspondingly for 1 and 2, and considerable long-term stability for the HER.

Static and dynamic magnetic properties of the ferromagnetic coordination polymer [Co(NCS)2(py)2]n.

[Co(NCS)2(py)2]n (py = pyridine) is composed of ferromagnetic chains of Co(ii) cations connected by double NCS bridges. The chains are irregular because of two crystallographically inequivalent Co(ii) cations. The coordination polyhedron of the Co(ii) cations is a distorted octahedron built from two N and two S atoms of four equatorial NCS anions and two apical N atoms of the pyridine ligands. Magnetic and specific heat studies show that the compound undergoes a phase transition at 3.7 K to a ferromagnetic state. The determined magnetic interactions, intrachain (J/kB = 28 K) and interchain (zJ'/kB = 0.5 K), confirm the quasi 1D Ising magnetic character of [Co(NCS)2(py)2]n. Using AC magnetic susceptibility measurements the energy barriers for magnetization reversal of different relaxation processes were determined including those of the individual chains. By means of high field-high frequency ESR study the magnetic excitations were observed and explained in the frame of the Ising model in agreement with the results of the magnetic study. Ab initio calculations confirm the high magnetic anisotropy of the system and allow determination of the direction of the easy-axis. The broken symmetry DFT calculations support the ferromagnetic intrachain interactions. The energetic relations relevant for relaxations are discussed. It is concluded that the magnetic model of [Co(NCS)2(py)2]n is not a pure Ising but the transversal exchange plays a role.

Synthesis and magnetic properties of manganese carbonyl complexes with different coordination modes of 3,4,5-triaryl-1,2-diphospholide ligands.

The set of complexes bis-(µ:η(1),η(1)-3,4,5-triaryl-1,2-diphosphacyclopentadienyl)-bis-(tetracarbonyl manganese(i)) (aryl = C6H5 (), p-FC6H4 (), p-ClC6H4 ()) undergo an irreversible rearrangement to mononuclear 3,4,5-triaryl-1,2-diphosphacymantrenes (). According to quantum-chemical calculations binuclear complexes can be considered to be products of kinetic control and mononuclear species are thermodynamically favorable compounds. The antiferromagnetic intramolecular interaction observed for complexes can be effectively tuned by using substituents in the para-position of the arene ring, whereas mononuclear 1,2-diphosphacymantrenes are diamagnetic.

Magnetic superexchange interactions: trinuclear bis(oxamidato) versus bis(oxamato) type complexes.

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.

Band-like electron transport with record-high mobility in the TCNQ family.

The occurrence of extremely pronounced band-like transport with very high electron mobility in fluorinated tetracyanoquinodimethane (F2 -TCNQ) single-crystal field-effect transistors is discovered. This finding identifies the Fx -TCNQ family as a paradigm to investigate the fundamental aspects of electronic transport in organic crystals.

Synthesis and toxicity characterization of carbon coated iron oxide nanoparticles with highly defined size distributions.

BACKGROUND: Iron oxide nanoparticles hold great promise for future biomedical applications. To this end numerous studies on iron oxide nanoparticles have been conducted. One aspect these studies reveal is that nanoparticle size and shape can trigger different cellular responses through endocytic pathways, cell viability and early apoptosis. However, systematic studies investigating the size dependence of iron oxide nanoparticles with highly defined diameters across multiple cells lines are not available yet. METHODS: Iron oxide nanoparticles with well-defined size distributions were prepared. All samples were thoroughly characterized and the cytotoxicity for four standard cell lines (HeLa Kyoto, human osteosarcoma (U2OS), mouse fibroblasts (NIH 3T3) and mouse macrophages (J7442)) where investigated. RESULTS: Our findings show that small differences in size distribution (ca. 10nm) of iron oxide nanoparticles do not influence cytotoxicity, while uptake is size dependent. Cytotoxicity is dose-dependent. Broad distributions of nanoparticles are more easily internalized as compared to the narrow distributions for two of the cell lines tested (HeLa Kyoto and mouse macrophages (J7442)). CONCLUSION: The data indicate that it is not feasible to probe changes in cytotoxicity within a small size range (10nm). However, TEM investigations of the nanoparticles indicate that cellular uptake is size dependent. GENERAL SIGNIFICANCE: The present work compares narrow and broad distributions for various samples of carbon-coated iron oxide nanoparticles. The data highlights that cells differentiate between nanoparticle sizes as indicated by differences in cellular uptake. This information provides valuable knowledge to better understand the interaction of nanoparticles and cells.

Chemisorption of exchange-coupled [Ni2L(dppba)]+ complexes on gold by using ambidentate 4-(diphenylphosphino)benzoate co-ligands.

A new strategy for the fixation of redox-active dinickel(II) complexes with high-spin ground states to gold surfaces was developed. The dinickel(II) complex [Ni2L(Cl)]ClO4 (1ClO4), in which L(2-) represents a 24-membered macrocyclic hexaaza-dithiophenolate ligand, reacts with ambidentate 4-(diphenylphosphino)benzoate (dppba) to form the carboxylato-bridged complex [Ni2L(dppba)](+), which can be isolated as an air-stable perchlorate [Ni2L(dppba)]ClO4 (2ClO4) or tetraphenylborate [Ni2L(dppba)]BPh4 (2BPh4) salt. The auration of 2ClO4 was probed on a molecular level, by reaction with AuCl, which leads to the monoaurated Ni(II)2Au(I) complex [Ni(II)2L(dppba)Au(I)Cl]ClO4 (3ClO4). Metathesis of 3ClO4 with NaBPh4 produces [Ni(II)2L(dppba)Au(I)Ph]BPh4 (4BPh4), in which the Cl(-) is replaced by a Ph(-) group. The complexes were fully characterized by ESI mass spectrometry, IR and UV/Vis spectroscopy, X-ray crystallography (2BPh4 and 4BPh4), cyclic voltammetry, SQUID magnetometry and HF-ESR spectroscopy. Temperature-dependent magnetic susceptibility measurements reveal a ferromagnetic coupling J = +15.9 and +17.9 cm(-1) between the two Ni(II) ions in 2ClO4 and 4BPh4 (H = -2 JS1S2). HF-ESR measurements yield a negative axial magnetic anisotropy (D<0), which implies a bistable (easy axis) magnetic ground state. The binding of the [Ni2L(dppba)]ClO4 complex to gold was ascertained by four complementary surface analytical methods: contact angle measurements, atomic-force microscopy, X-ray photoelectron spectroscopy, and spectroscopic ellipsometry. The results indicate that the complexes are attached to the Au surface through coordinative Au-P bonds in a monolayer.

An interplay between the spin density distribution and magnetic superexchange interactions: a case study of mononuclear [(n)Bu4N]2[Cu(opooMe)] and novel asymmetric trinuclear [Cu3(opooMe)(pmdta)2](NO3)2·3MeCN.

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.

New dinuclear nickel(II) complexes: synthesis, structure, electrochemical, and magnetic properties.

The reaction of [NiBr(2)(bpy)(2)] (bpy = 2,2'-bipyridine) with organic phosphinic acids ArP(O)(OH)H [Ar = Ph, 2,4,6-trimethylphenyl (Mes), 9-anthryl (Ant)] leads to the formation of binuclear nickel(II) complexes with bridging ArP(H)O(2)(-) ligands. Crystal structures of the binuclear complexes [Ni(2)(µ-O(2)P(H)Ar)(2)(bpy)(4)]Br(2) (Ar = Ph, Mes, Ant) have been determined. In each structure, the metal ions have distorted octahedral coordination and are doubly bridged by two arylphosphinato ligands. Magnetic susceptibility measurements have shown that these complexes display strong antiferromagnetic coupling between the two nickel atoms at low temperatures, apparently similar to binuclear nickel(II) complexes with bridging carboxylato ligands. Cyclic voltammetry and in situ EPR spectroelectrochemistry show that these complexes can be electrochemically reduced and oxidized with the formation of Ni(I),Ni(0)/Ni(III) derivatives.