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In the present report, homochiral hydrogen-bonded assemblies of heavily N-doped (C9H6N6) heterocyclic triimidazole (TT) molecules on an Ag(111) substrate were investigated using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) techniques. The planar and prochiral TT molecules, which exhibit a threefold rotation symmetry and lack mirror symmetry when assembled on the substrate, carry multiple hydrogen-bonding donor and acceptor functionalities, inevitably leading to the formation of hexameric two-dimensionally extended assemblies that can be either homo- (RR/SS) or heterochiral (RS). Experimental STM data showing well-ordered homochiral domains and experimental LEED data are consistent with simulations assuming the 21×21R19.1° overlayer on the Ag(111) lattice. Importantly, we report the unexpected coincidence of spontaneous resolution with the condensation of neighboring islands in adjacent “Janus pairs”. The islands are connected by a characteristic fault zone, an observation that we discuss in the context of the fairly symmetric molecule and its propensity to compromise and benefit from interisland bonding at the expense of lattice mismatches and strain in the defect zone. We relate this to the close to triangular shape and the substantial but weak bonding scheme beyond van der Waals (vdW) of the TT molecules, which is due to the three N-containing five-membered imidazole rings. Density functional theory (DFT) calculations show clear energetic differences between homochiral and heterochiral pairwise interactions, clearly supporting the experimental results.

A new mixed-valence heterometallic nonanuclear cluster [Mn7Dy2(μ4-O)2(μ3-O)4(μ3-OMe)2(μ2-OH)(piv)8(dea)2(MeOH)2(H2O)2](NO3)·H2O (1) (where Hpiv = pivalic acid) was prepared from the reaction of Mn(piv)2with Dy(NO3)3·6H2O and diethanolamine (H2dea) in a MeOH/CH2Cl2mixture. The C2-symmetric cluster comprises an unprecedented {Mn6IIIMnIVDy2III}28+core consisting of two distorted {Mn2IIIMnIVDyIIIO4} cubane moieties sharing a common MnIVvertex and decorated with two additional MnIIIatoms. Hirshfeld surface analysis and fingerprint plots are used for decoding the intermolecular interactions in 1. Magnetic studies indicate that 1exhibits a slow relaxation behavior with an effective energy barrier of 15.2 K and τ0= 1.4 × 10–7s.

Crystalline nanoporous molecular networks are assembled on the Ag(111) surface, where the pores confine electrons originating from the surface state of the metal. Depending on the pore sizes and their coupling, an antibonding level is shifted upward by 0.1–0.3 eV as measured by scanning tunneling microscopy. On molecular sites, a downshifted bonding state is observed, which is occupied under equilibrium conditions. Low-temperature force spectroscopy reveals energy dissipation peaks and jumps of frequency shifts at bias voltages, which are related to the confined states. The dissipation maps show delocalization on the supramolecular assembly and a weak distance dependence of the dissipation peaks. These observations indicate that two-dimensional arrays of coupled quantum dots are formed, which are quantitatively characterized by their quantum capacitances and resonant tunneling rates. Our work provides a method for studying the capacitive and dissipative response of quantum materials with nanomechanical oscillators.

Although methods for a periodic perforation and heteroatom doping of graphene sheets have been developed, patterning closely spaced holes on the nanoscale in graphene nanoribbons is still a challenging task. In this work, nitrogen-doped porous graphene nanoribbons (N-GNRs) were synthesized on Ag(111) using a silver-assisted Ullmann polymerization of brominated tetrabenzophenazine. Insights into the hierarchical reaction pathways from single molecules toward the formation of one-dimensional organometallic complexes and N-GNRs are gained by a combination of scanning tunneling microscopy (STM), atomic force microscopy (AFM) with CO-tip, scanning tunneling spectroscopy (STS), and density functional theory (DFT).

Bending and twisting around carbon–carbon single bonds are ubiquitous in natural and synthetic polymers. Force-induced changes were so far not measured at the single-monomer level, owing to limited ways to apply local forces. We quantified down to the submolecular level the mechanical response within individual poly-pyrenylene chains upon their detachment from a gold surface with an atomic force microscope at 5 K. Computer simulations based on a dedicated force field reproduce the experimental traces and reveal symmetry-broken bent and rotated conformations of the sliding physisorbed segment besides steric hindrance of the just lifted monomer. Our study also shows that the tip–molecule bond remains intact but remarkably soft and links force variations to complex but well-defined conformational changes.

Starting from a well-known hexanuclear mixed-valent manganese cluster, we report a synthetic protocol for its extension toward very large 3d-4f clusters. The exemplary case study demonstrates that a combination of such {Mn6} clusters with a DyIIIsalt and an auxiliary triazine-type ligand yields a large bean-like, heterometallic dotriacontanuclear mixed-valent nanocluster [Mn26Dy6O16(OH)12(O2CCHMe2)42]. This compound, which possesses a molecular C2symmetry and crystallizes in a dense packing arrangement without inclusion of solvents, comprises 16 MnIII, 10 MnII, and 6 DyIIIions, thus leading to a plurality of intracluster magnetic exchange interactions. Interestingly, this results in the highest-nuclearity Mn–Dy cluster that shows a single-molecule magnetic (SMM) behavior.

We investigated the coordination ability of the bis(1,2,4-triazolyl) module, tr2pr = 1,3-bis(1,2,4-triazol-4-yl)propane, toward the engineering of solid-state structures of copper polyoxomolybdates utilizing a composition space diagram approach. Different binding modes of the ligand including [N–N]-bridging and N-terminal coordination and the existence of favorable conformation forms (anti/anti, gauche/anti, and gauche/gauche) resulted in varieties of mixed metal CuI/MoVIand CuII/MoVIcoordination polymers prepared under hydrothermal conditions. The composition space analysis employed was aimed at both the development of new coordination solids and their crystallization fields through systematic changes of the reagent ratios [copper(II) and molybdenum(VI) oxide precursors and the tr2pr ligand]. Nine coordination compounds were synthesized and structurally characterized. The diverse coordination architectures of the compounds are composed of cationic fragments such as [CuII3(μ2-OH)2(μ2-tr)2]4+, [CuII3(μ2-tr)6]6+, [CuII2(μ2-tr)3]4+, etc., connected to polymeric arrays by anionic species (molybdate MoO42–, isomeric α-, δ-, and β-octamolybdates {Mo8O26}4–or {Mo8O28H2}6–). The inorganic copper(I,II)/molybdenum(VI) oxide matrix itself forms discrete or low-dimensional subtopological motifs (0D, 1D, or 2D), while the organic spacers interconnect them into higher-dimensional networks. The 3D coordination hybrids show moderate thermal stability up to 230–250 °C, while for the 2D compounds, the stability of the framework is distinctly lower (∼190 °C). The magnetic properties of the most representative samples were investigated. The magnetic interactions were rationalized in terms of analyzing the planes of the magnetic orbitals.

One of the main challenges to upscale the fabrication of molecular devices is to achieve a mechanically stable device with reproducible and controllable electronic features that operates at room temperature1,2. This is crucial because structural and electronic fluctuations can lead to significant changes in the transport characteristics at the electrode–molecule interface3,4. In this study, we report on the realization of a mechanically and electronically robust graphene-based molecular junction. Robustness was achieved by separating the requirements for mechanical and electronic stability at the molecular level. Mechanical stability was obtained by anchoring molecules directly to the substrate, rather than to graphene electrodes, using a silanization reaction. Electronic stability was achieved by adjusting the p–porbitals overlap of the conjugated head groups between neighbouring molecules. The molecular devices exhibited stable current–voltage (I–V) characteristics up to bias voltages of 2.0?V with reproducible transport features in the temperature range from 20 to 300?K.

The planar heterocyclic molecules 1,6,7,12-tetraazaperylene on a Ag(111) metal substrate show different charging characteristics depending on their local environment: next to vacancies in self-assembled islands, molecules can be charged by local electric fields, whereas their charge state is fixed otherwise. This enables the activation of selected molecules inside islands by vacancy creation from scanning-probe-based manipulation. This concept allows for combining the precise mutual atomic-scale alignment of molecules by self-assembly, on one hand, and the implementation of specific functionality into otherwise homogeneous monolayers, on the other. Activated molecules in the direct neighborhood influence each other in their charging characteristics, suggesting their use as molecular quantum cellular automata. Surprisingly, only very few interacting molecules exhibit a rich spectroscopic signature, which offers the prospect of implementing complex functionality in such structures in the future.

We report ultrafast transient UV–vis absorption and electrochemical spectroscopies on the photoinduced charge separation dynamics in a recently synthesized family of metal-free donor–acceptor systems, where two redox-active molecules are fused into a compact and planar structure upon annulation of a tetrathiafulvalene and a benzothiadiazole as electron donor and acceptor, respectively. We found extraordinary tunability of the lifetime of the photoinduced charge separation by more than 2 orders of magnitude (from 6 to 900 ps) upon small changes of the peripheral residues on the acceptor and the polarity of the environment. Contrary to expectations, the lifetime of the charge separation state decreases in more polar environments and with more electronegative acceptors. This study proves that such fused donor–acceptor systems give rise to a new class of electronically versatile materials whose physicochemical properties can be tuned via a targeted substitution or a suitable choice of local electrostatics.

In the presence of dicyanamide and N-butyldiethanolamine (bdeaH2), Fe(III) and Dy(III) precursors self-assemble into the charge-neutral coordination cluster [Fe6Dy3(ib)9(bdea)6(MeO)6]·MeOH (1) (ib: isobutyrate) featuring an approximately C3-symmetric wheel of edge-sharing FeO6and DyO6N2polyhedra. This is followed by a remarkable self-induced conversion of this cluster into the highly condensed globe-shaped coordination cluster [Fe7Dy4O4(OH)3(ib)9.25(bdea)6(NO3)0.75(H2O)] (2) in methanolic solution under ambient conditions. The transition from {Fe6Dy3} to {Fe7Dy4} coincides with a slowdown of the clusters’ magnetization dynamics, as evident from a shift of the onset of significant out-of-phase components of their magnetic ac susceptibility from 3.6 K up to 12 K (1000 Hz) in the absence of a static bias field.

A pentanuclear CuII5-hydroxo cluster possessing an unusual linear-shaped configuration was formed and crystallized under hydrothermal conditions as a result of the unique cooperation of bridging 1,2,4-triazole ligand (trans-1,4-cyclohexanediyl-4,4′-bi(1,2,4-triazole) (tr2cy)), MoVI-oxide, and CuSO4. This structural motif can be rationalized by assuming in situgeneration of {Cu2Mo6O22}4–anions, which represent heteroleptic derivatives of γ-type [Mo8O26]4–further interlinked by [Cu3(OH)2]4+cations through [N−N] bridges. The framework structure of the resulting compound [Cu5(OH)2(tr2cy)2Mo6O22]·6H2O (1) is thus built up from neutral heterometallic {Cu5(OH)2Mo6O22}nlayers pillared with tetradentate tr2cy. Quantum-chemical calculations demonstrate that the exclusive site of the parent γ-[Mo8O26]4–cluster into which CuIIinserts corresponds with the site that has the lowest defect (“MoO2vacancy”) formation energy, demonstrating how the local metal-polyoxomolybdate chemistry can express itself in the final crystal structure. Magnetic susceptibility measurements of 1show strong antiferromagnetic coupling within the Cu5chain with exchange parameters J1= −500(40) K (−348(28) cm–1), J2= −350(10) K (−243(7) cm–1) and g= 2.32(2), χ2= 6.5 × 10–4. Periodic quantum-chemical calculations reproduce the antiferromagnetic character of 1and connect it with an effective ligand-mediated spin coupling mechanism that comes about from the favorable structural arrangement between the Cu centers and the OH–, O2–, and tr2cybridging ligands.

The annulation of two redox-active molecules into a compact and planar structure paves the way toward a new class of electronically versatile materials whose physical properties can be tuned via a substitution of one of the constituting moieties. Specifically, we present tetrathiafulvalene–benzothiadiazole donor–acceptor molecules. The critical role played by the dielectric properties of these molecules is evident by the large spectral shifts of the ground-state absorption spectra in a range of solvents. Stark spectroscopy is performed to determine experimentally dipole and polarizability change over transitions in the visible range with particular attention to the transition from the highest-occupied molecular orbital (HOMO) to the lowest-unoccupied molecular orbital (LUMO). The experimental results are compared to the results of time-dependent density functional theory calculations, and we reciprocally validate results from calculation and experiment. This allows us to filter out effective models and reveal important insights. The calculations are initially performed in the gas phase and subsequently a polarizable continuum model is adopted to probe the influence of the solvent on the molecular dielectric properties. The results show a large charge displacement from the HOMO to the LUMO and confirm the intramolecular charge transfer nature of the lowest-energy transition. Substitution of the acceptor moiety with electron-withdrawing groups results in changes to the experimentally determined molecular properties consistent with the effects predicted by computational results. The dominant contribution to the electroabsorption signal is due to the change in dipole moment, which is measured to be roughly 20 D for all samples and forms a small angle with the transition dipole moment in a toluene solvent environment.

We have studied thin films of Fe(II) spin crossover complexes deposited on differently poled ferroelectric PMN-PT ([Pb(Mg1/3Nb2/3)O3]1–x[PbTiO3]x, x= 0.32) substrates by X-ray absorption spectroscopy. The X-ray spectra reveal the temperature-driven conversion between high-spin and low-spin states without any observable effect of the ferroelectric polarization on the spin state of the molecules down to 100 K. In the soft X-ray-induced excited spin-state trapping (SOXIESST) regime at 3 K, large differences occur between the two ferroelectric polarizations. The efficiency of X-rays in exciting the molecules to the high-spin state is more than an order of magnitude larger when the ferroelectric dipoles of the substrate are pointing toward the surface compared to the opposite polarization. We explain our findings by a modulation of the polarization-dependent efficiency of the scattering of X-ray-generated secondary electrons at the molecules. Our results provide a deep insight into the SOXIESST mechanism and suggest that such molecules could be used as detectors for electrons traveling in the substrate at energies lower than the substrate electron affinity.

Electron donor–acceptor molecules are of outstanding interest in molecular electronics and organic solar cells for their intramolecular charge transfer controlled viaelectrical or optical excitation. The preservation of their electronic character in the ground state upon adsorption on a surface is cardinal for their implementation in such single-molecule devices. Here, we investigate by atomic force microscopy and scanning tunneling microscopy a prototypical system consisting of a π-conjugated tetrathiafulvalene-fused dipyridophenazine molecule adsorbed on thin NaCl films on Cu(111). Depending on the adsorption site, the molecule is found either in a nearly undisturbed free state or in a bound state. In the latter case, the molecule adopts a specific adsorption site, leading to the formation of a chelate complex with a single Na+alkali cation pulled out from the insulating film. Although expected to be electronically decoupled, the charge distribution of the complex is drastically modified, leading to the loss of the intrinsic donor–acceptor character. The chelate complex formation is reversible with respect to lateral manipulations, enabling tunable donor–acceptor molecular switches activated by on-surface coordination.

New tetranuclear and octanuclear mixed-valent cobalt(II/III) pivalate clusters, namely, [NaCo4(O2CCMe3)6(HO2CCMe3)2(teaH)2(N3)]·2H2O (in two polymorphic modifications, 1and 1a) and [Co8(O2CCMe3)10(teaH)4(N3)](Me3CCO2)·MeCN·H2O (2) have been synthesized by ultrasonic treatment of a dinuclear cobalt(II) pivalate precursor with sodium azide and triethanolamine (teaH3) ligand in acetonitrile. The use of Dy(NO3)3·6H2O in a similar reaction led to the precipitation of a tetranuclear [NaCo4(O2CCMe3)4(teaH)2(N3)(NO3)2(H2O)2]·H2O (3) cluster and a heterometallic hexanuclear [Co3Dy3(OH)4(O2CCMe3)6(teaH)3(H2O)3](NO3)2·H2O (4) cluster. Single-crystal X-ray analysis showed that 1(1a) and 3consist of a tetranuclear pivalate/teaH3mixed-ligand cluster [CoII2CoIII2(O2CCMe3)4(teaH)2(N3)]+decorated with sodium pivalates [Na(O2CCMe3)2(HO2CCMe3)2]−(1or 1a) or sodium nitrates [Na(NO3)2]−(3) to form a square-pyramidal assembly. In 2, the cationic [Co8(O2CCMe3)10(teaH)4(N3)]+cluster comprises a mixed-valent {CoII4CoIII4} core encapsulated by an azide, 4 teaH2–alcoholamine ligands, and 10 bridging pivalates. Remarkably, in this core, the μ4-N3–ligand joins all four CoIIatoms. The heterometallic hexanuclear compound 4consists of a cationic [CoIII3DyIII3(OH)4(O2CCMe3)6(teaH)3(H2O)3]2+cluster, two NO3–anions, and a crystallization water molecule. The arrangement of metal atoms in 4can be approximated as the assembly of a smaller equilateral triangle defined by three Dy sites with a Dy···Dy distance of 3.9 Å and a larger triangle formed by Co sites [Co···Co, 6.1–6.2 Å]. The interpretation of the magnetic properties of clusters 2–4was performed in the framework of theoretical models, taking into account the structural peculiarities of clusters and their energy spectra. The behavior of clusters 2and 3containing CoIIions with orbitally nondegenerate ground states is determined by the zero-field splitting of these states and Heisenberg exchange interaction between the ions. To get a good understanding of the observed magnetic behavior of cluster 4, we take into consideration the crystal fields acting on the DyIIIions, the ferromagnetic coupling of neighboring DyIIIions, and the intercluster antiferromagnetic exchange. For all examined clusters, the developed models describe well the observed temperature dependence of the magnetic susceptibility and the field dependence of magnetization. The computational results apparently show that in cluster 4two DyIIIions with similar nearest surroundings demonstrate single-molecule-magnet (SMM) behavior, while the strong rhombicity of the ligand surrounding hinders the SMM behavior of the third DyIIIion.

A new microscopic approach to the problem of cooperative spin crossover in molecular crystals containing binuclear complexes as structural units has been developed. The cooperative interaction arising from the coupling of the molecular mode to the acoustic phonons represents the cornerstone of the approach. Another important ingredient of the model is the Coulomb interaction between the spin crossover ions in the binuclear cluster that is different in the ls–ls, hs–ls, and hs–hs states (ls, low spin; hs, high spin). The suggested approach makes it possible to reproduce all types of transitions observed in binuclear compounds including two-step transitions. The applicability of the developed approach is illustrated by the interpretation of the experimental data on spin transitions for the binuclear [{Fe(bpym)(NCSe)2}2bpym] and [{Fe(bt)(NCS)2}2bpym] cluster compounds.

Organic–organic heterojunctions are nowadays highly regarded materials for light-emitting diodes, field-effect transistors, and photovoltaic cells with the prospect of designing low-cost, flexible, and efficient electronic devices.1−3 However, the key parameter of optimized heterojunctions relies on the choice of the molecular compounds as well as on the morphology of the organic–organic interface,4 which thus requires fundamental studies. In this work, we investigated the deposition of C60molecules at room temperature on an organic layer compound, the salt bis(benzylammonium)bis(oxalato)cupurate(II), by means of noncontact atomic force microscopy. Three-dimensional molecular islands of C60having either triangular or hexagonal shapes are formed on the substrate following a “Volmer–Weber” type of growth. We demonstrate the dynamical reshaping of those C60nanostructures under the local action of the AFM tip at room temperature. The dissipated energy is about 75 meV and can be interpreted as the activation energy required for this migration process.

A heterometallic hexanuclear mixed-valence Co–Dy cluster [Co4Dy2(OH)2(O2CCMe3)8(HO2CCMe3)2(teaH)2(N3)2]·2(EtOH) (1) has been prepared from the reaction of dinuclear Co(II) pivalate with triethanolamine and azide ligands and characterized by elemental analysis, IR spectroscopy, and X-ray crystallography. The metal atoms in the {CoII2CoIII2DyIII2} cluster core are bridged by two μ3-hydroxy groups, two azide N3–anions, six pivalate residues, and two doubly deprotonated teaH2–ligands. A theoretical model has been developed to explain the magnetic behavior of 1. The model takes into account the crystal fields acting on the DyIIIions and the anti- and ferromagnetic exchange interactions in the pairs Co–Dy and Co–Co, respectively. The Stark structure for the DyIIIions is calculated with due account of the covalence effects within the frames of the exchange charge model of the crystal field. It is demonstrated that at low temperatures the magnetic properties of the cluster are determined by the interaction of the ground state Kramers doublet of the CoIIion with those Stark levels of the DyIIIions, for which the energies are smaller than the spin–orbital coupling parameter. At higher temperatures, the population of the CoIIion multiplets with the angular momentum values 3/2 and 5/2 leads to the increase of the magnetic susceptibility. The observed temperature dependence of the χMTproduct and field dependence of the magnetization are satisfactorily explained within the framework of the suggested model.

An efficient synthetic approach to a symmetrically functionalized tetrathiafulvalene (TTF) derivative with two diamine moieties, 2‐[5,6‐diamino‐4,7‐bis(4‐pentylphenoxy)‐1,3‐benzodithiol‐2‐ylidene]‐4,7‐bis(4‐pentylphenoxy)‐1,3‐benzodithiole‐5,6‐diamine (2), is reported. The subsequent Schiff‐base reactions of 2afford large π‐conjugated multiple donor–acceptor (D–A) arrays, for example, the triad 2‐[4,9‐bis(4‐pentylphenoxy)‐1,3‐dithiolo[4,5‐g]quinoxalin‐2‐ylidene]‐4,9‐bis(4‐pentylphenoxy)‐1,3‐dithiolo[4,5‐g]quinoxaline (8) and the corresponding tetrabenz[bc,ef,hi,uv]ovalene‐fused pentad 1, in good yields and high purity. The novel redox‐active nanographene 1is so far the largest known TTF‐functionalized polycyclic aromatic hydrocarbon (PAH) with a well‐resolved 1H NMR spectrum. The electrochemically highly amphoteric pentad 1and triad 8exhibit various electronically excited charge‐transfer states in different oxidation states, thus leading to intense optical intramolecular charge‐transfer (ICT) absorbances over a wide spectral range. The chemical and electrochemical oxidations of 1result in an unprecedented TTF⋅+radical cation dimerization, thereby leading to the formation of [1⋅+]2at room temperature in solution due to the stabilizing effect, which arises from strong π–π interactions. Moreover, ICT fluorescence is observed with large solvent‐dependent Stokes shifts and quantum efficiencies of 0.05 for 1and 0.035 for 8in dichloromethane.

A tetrathiafulvalene donor has been annulated to the bay region of perylenediimide through a 1H-benzo[d]pyrrolo[1,2-a]imidazol-1-one spacer affording an extended π-conjugated molecular dyad (TTF−PDI). To gain insight into its ground- and excited-state electronic properties, the reference compound Ph-PDI has been prepared via a direct Schiff-base condensation of N,N′-bis(1-octylnonyl)benzoperylene-1′,2′:3,4:9,10-hexacarboxylic-1′,2′-anhydride-3,4:9,10-bis(imide) with benzene-1,2-diamine. Both the experimental and the computational (DFT) results indicate that TTF−PDI exhibits significant intramolecular electronic interactions giving rise to an efficient photoinduced charge-separation process. Free-energy calculations verify that the light-induced process from TTF to the singlet-excited state of PDI is exothermic in both polar and nonpolar solvents. Fast adiabatic electron-transfer processes of a compactly fused, π-conjugated TTF−PDI dyad in benzonitrile, 2-methyltetrahydrofuran, anisole and toluene were observed by femtosecond transient absorption spectral measurements. The lifetimes of radical-ion pairs slightly increase with decreasing the solvent polarities, suggesting that the charge-recombination occurs in the Marcus inverted region. By utilizing the nanosecond transient absorption technique, the intermolecular electron-transfer process in a mixture of TTF-diamine/Ph-PDI has been observed via the triplet excited PDI for the first time.

Different synthetic routes have been used for the preparation of a new tetranuclear [Fe4O2(O2CCMe3)8(bpm)] cluster (1) and a one‐dimensional coordination polymer [Fe4O2(O2CCMe3)8(hmta)]n(2) (bpm = 2,2′‐bipyrimidine and hmta = hexamethylenetetramine). For cluster 1, two structural isomers, 1aand 1b·3MeCN, have been found. X‐ray crystallographic analysis showed that all complexes consist of a central {Fe4(μ3‐O)2}8+core. In 1a, metal ions in the core are additionally linked by six bridging pivalates as two other pivalates and a bpm ligand are chelated to FeIIIions, whereas in cluster 1b, metal ions in the {Fe4(μ3‐O)2}8+core are linked by seven bridging pivalates and only one carboxylate as well as bpm are chelated to the iron centers. In coordination polymer 2, [Fe4O2(O2CCMe3)8] clusters are bridged by hmta ligands to form zigzag chains. Magnetic measurements have been carried out to characterize these complexes and revealed antiferromagnetic interactions between FeIIIions with best‐fit parameters of Jwb= –72.2 (1a) and –88.7 cm–1(1b) for wing···body interactions.

Overruled!The self‐assembly of a novel group of fused donor–acceptor molecules (1) comprising hexaazatriphenylene and tetrathiafulvalene branches was studied by STM at the liquid/solid interface. A 2D assembled chiral porous network with C3symmetry was found, which is dictated by strong interactions of the extended π‐conjugated cores of the fused units with the HOPG substrate overruling the directional forces of alkyl chains.

In the search for transformations of quinone moieties into the corresponding tetracyanopquinodimethane TCNQ systems, Knoevenageltype condensations of 2thioxo1,3dithiolepbenzoquinone systems, TTFpbenzoquinone dyads and a pbenzoquinoneTTFpbenzoquinone triad with malononitrile under different experimental conditions were investigated. In order to avoid the wellknown Michael 1,4addition onto the quinone moiety, cyclopentadiene or cyclohexadiene units were incorporated as protecting groups through [4+2] Diels–Alder cycloadditions. On the one hand, aromatization leading to fused 2thioxo1,3dithiolehydroquinones was observed in the presence of acetic acid and pyridine. With use, on the other hand, of the nucleophilic malononitrile anion, an unprecedented ringopening process of the 1,3dithiole moiety occurred, affording stable ketene imines. Finally, successful conversion of 1,3dithiolepbenzoquinones into the corresponding TCNQ systems was achived by treatment with malononitrile in the presence of titaniumIV chloride and pyridine as Lehnerts reagents. All new TCNQ derivatives were unambiguously characterized. So far, the application of such experimental conditions to protected TTFpbenzoquinone dyads and a pbenzoquinoneTTFpbenzoquinone triad has been unsuccessful, maybe due to the high reactivity of the TTF moiety. © WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009

CT or not CT: Three imidazole‐annulated TTF derivatives 1–3have been prepared and fully characterized. The influence of the TTF unit on the pKavalues of the acceptor units as determined by photometric titration has been discussed. The results reported here are part of an initial exploratory study to generate a range of well‐defined coordination networks.

Stacking interactions are of significant importance in the fields of chemistry, biology, and material optoelectronics because they determine the efficiency of charge transfer between molecules and their quantum states. Previous studies have proven that when two monomers are π-stacked in series to form a dimer, the electrical conductance of the dimer is significantly lower than that of the monomer. Here, we present a strong opposite case that when two anthanthrene monomers are π-stacked to form a dimer in a scanning tunneling microscopic break junction, the conductance increases by as much as 25 in comparison with a monomer, which originates from a room-temperature quantum interference. Remarkably, both theory and experiment consistently reveal that this effect can be reversed by changing the connectivity of external electrodes to the monomer core. These results demonstrate that synthetic control of connectivity to molecular cores can be combined with stacking interactions between their π systems to modify and optimize charge transfer between molecules, opening up a wide variety of potential applications ranging from organic optoelectronics and photovoltaics to nanoelectronics and single-molecule electronics.

Narrowing the gap: A compactly fused π‐conjugated molecule combines a high‐lying HOMO with a low‐lying LUMO (Eox−Ered=0.52 eV) and a fairly low‐lying LUMO+1 on the bridging unit, giving rise to strong optical charge‐transfer transitions. A facile electron transfer has been observed by EPR and NMR spectroscopies.

Highly organized: Tetrathiafulvalene(TTF)‐modified oligonucleotides form stable double strands (see graphic). Exciton coupling reveals a high degree of structural organization in the modified region of a hetero‐duplex formed by TTF and perylene diimide‐containing strands. Fluorescence quenching in TTF/pyrene‐modified hetero‐hybrids is demonstrated. The results presented are important for the development of redox‐active, oligonucleotide‐based diagnostics or optical sensors.

Symmetrically substituted phthalocyanines (Pcs) with eight peripheral di-(tert-butyl)phenoxy (DTPO) groups self-organize on Ag(111) and Au(111) substrates into various assembly structures. These different structural phases were studied by scanning tunneling microscopy (STM). On the basis of high-resolution STM images, molecular models are provided for each phase that account for the observed unequal surface densities. Notably, the specificity of the studied Pc derivative featuring the peripheral phenoxy groups remarkably increases its conformational possibilities. Particularly, the rotational degrees of freedom allow all the DTPO substituents to be arranged above the plane of the Pc core, forming a bowl-like structure, which in turn enables the interaction of the Pc core with the metal substrate. The proximity of the Pc core to the metal substrate together with the steric entanglement between neighboring DTPO substituents causes significant retardation of the thermodynamic optimization of the conformations.

We have synthesized a new one-dimensional coordination polymer, [CuII(HL)2(4,4′-bpy)]n·2nH2O (1), (HL– = monodeprotonated 3-nitrophthalic acid, 4,4′-bpy = 4,4′-bipyridine) consisting of infinite chains of [CuII(HL)2(4,4′-bpy)]n and have investigated its structure and magnetic properties. Compound 1 crystallizes in the monoclinic C2/c space group with the [CuII(HL)2(4,4′-bpy)]n chains running parallel to the b axis. The chains are linked together by hydrogen bonding between the HL– groups and water molecules to form the three-dimensional crystal structure. The magnetic susceptibility of 1 can be well described using an antiferromagnetic S = 1/2 chain model with g = 2.11(1) and 2J = –0.61(1) cm–1. Several techniques for describing the susceptibility of S =1/2 chains are examined to compare their validity at lowvalues of kT/|2J|, including exact numerical full-matrix diagonalization techniques, from which the magnetization curve of 1 could be calculated. The calculation fits well with the measured magnetization data. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

To study the electronic interactions in donor–acceptor (D–A) ensembles, D and A fragments are coupled in a single molecule. Specifically, a tetrathiafulvalene (TTF)‐fused dipyrido[3,2‐a:2′,3′‐c]phenazine (dppz) compound having inherent redox centers has been synthesized and structurally characterized. Its electronic absorption, fluorescence emission, photoinduced intramolecular charge transfer, and electrochemical behavior have been investigated. The observed electronic properties are explained on the basis of density functional theory.

A phthalonitrile derivative 1, functionalized with two pyridyl groups, undergoes a cyclotetramerization reaction to afford the symmetric metal-free phthalocyanine 2 with peripheral metal-binding sites. In view of its insufficient solubility in organic solvents, a synthetic route to asymmetric peripherally octasubstituted Pcs, which contain a combination of 2,3-di(2-pyridyl)pyrazino and p-pentylphenoxy or p-(tert-butyl)phenoxy substituent groups, has been developed. The compounds 5–9 were synthesized by a statistical condensation reaction between two different phthalonitriles, and remarkably, all of them have been isolated and characterized as single compounds. For structural characterization, an X-ray study of the asymmetric Zn phthalocyanine 11 is given. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The synthesis of the new ligand, BEDT-TTF-bipy [4,5-ethylenedithio-4′,5′-(4′-methyl-2,2′-dipyrid-4-ylethylenedithio)tetrathiafulvalene] is reported. The first FeII coordination complex, namely [Fe(NCS)2(BEDT-TTF-bipy)2]·CHCl3, with this redox-active ligand is obtained. Magnetic measurements and Mössbauer spectroscopy revealed the coexistence of high-spin and low-spin FeII species with a ratio of 40:60 in this compound. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The reaction of o-phthalic acid (H2Pht) and 2,2'-bipyridine (bpy) with cobalt(II) carbonate at different temperatures results in the isolation of three types of new cobalt(II) and cobalt(III) compounds. The mononuclear cobalt(III) complex [Co(CO3)(bpy)2]2(Pht)·16H2O (1) is obtained when the reaction is run at 60 °C. Crystallographic analysis revealed that 1 contains two crystallographically independent [Co(CO3)(bpy)2]+ cations, a Pht2– anion, and sixteen solvate water molecules. The latter form a wall of channels with the oxygen atoms of the carboxylate groups of the Pht2– anions, which are occupied by pairs of cations. Increasing the temperature of the reaction to 80 °C leads to the formation of the open dinuclear cobalt(II) complex [(bpy)2Co(Pht)H(Pht)Co(bpy)2](HPht)(H2Pht)·2H2O (2), which crystallizes in two polymorphic modifications 2a and 2b. Compound 2a consists of a centrosymmetric dinuclear [(bpy)2Co(Pht)H(Pht)Co(bpy)2]+ cation, an HPht– anion, an H2Pht molecule, and two solvate H2O molecules. In 2b, a small alteration in the crystal structure leads to an increase of the unit-cell volume. The asymmetric unit of 2b contains six crystallographically independent CoII complexes, which combine into four [(bpy)2Co(Pht)H(Pht)Co(bpy)2]+ units. The main structural unit of the cyclic dinuclear complex [Co(Pht)(bpy)(H2O)]2·2H2O (4) is neutral and cenrosymmetric, with the two CoII atoms linked by two phthalate ligands to form a 14-membered cycle. A further temperature increase results in the isolation of both the mononuclear complex [Co(Pht)(bpy)(H2O)3]·3H2O (3) and the polynuclear helical coordination polymer [Co(Pht)(bpy)(H2O)]n (5). Extended hydrogen bonding networks as well as aromatic π–π stacking interactions stabilize multidimensional supramolecular architectures in all compounds. Magneticsusceptibility measurements have been performed for complexes 1, 2, 3, and 5. Simulations gave the following parameter sets: for complex 2 |D| = 70 cm–1, g = 2.55 and J =–0.1 cm–1; for complex 3 |D| = 80 cm–1, g = 2.6, and for complex 5 |D| = 65 cm–1, g = 2.45. Complex 1 is diamagnetic. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

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Ferromagnetic or antiferromagneticcoupling? A theoretical study of complexes containing MoV–CN–MnIIbridges reveals that a combination of local symmetry and molecular pseudosymmetry leads to a fascinating electronic structure that imposes antiferromagnetic interactions and results in a ferrimagnetic arrangement. The picture shows the spin density of the Mn9Mo6complex studied.

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Summary.:  We report major results concerning polyfunctional two- (2D) and three- (3D) dimensional oxalate bridged bimetallic magnets. As a consequence of their specific organisation they are composed of an anionic sub-lattice and a cationic counter-part. These bimetallic polymers can accommodate various counter-cations possessing specific physical properties in addition to the magnetic ones resulting from the interactions between the metallic ions in the anionic sub-lattice. Thus, molecular magnets possessing paramagnetic, conductive and optical properties are presented in this review.

The ligand 1,2-bis(1H-benzimidazol-2-yl)-1,2-ethanediol, 1, and its methylated derivative 2 are readily synthesized from tartaric acid, and act as chiral, facially coordinating tridentate ligands, forming complexes of composition ML₂ with octahedral transition metals. The copper(ii) complexes show distorted 4 + 2 coordination with benzimidazoles occupying the equatorial sites and alcohol functions weakly binding in the axial sites. Nickel(ii) complexes in three different states of protonation show regular octahedral geometry with the alcohols mutually cis. Deprotonation of the coordinated alcohol produces little structural change but the monodeprotonated complex forms a hydrogen bonded dimer. Magnetic measurements show the hydrogen bonded bridge to offer a pathway for weak antiferromagnetic coupling. UV-Visible spectroscopy shows the ligand to have a field intermediate between water and pyridine. The diastereoselectivity of complexation depends on the geometry: nickel(ii) shows a weak preference for the homochiral complex, whereas copper(ii) forms almost exclusively homochiral complexes.

The syntheses and X‐ray crystal structures of [([18]crown‐6)2Cs]+[Cp3Mn]−(1), [([18]crown‐6)2Cs]+[Cp′3Mn]−(2), [CsCp′] (3), [(CsCp′)2([18]crown‐6)] (4), and Cs[MnCp3] (5), and the synthesis of Cs[MnCp′3] (6) are reported (Cp′=C5H4Me). The anions [Cp3Mn]−(1−) and [Cp′3Mn]−(2−) are characterized by η2coordination of all three Cp or Cp′ rings. Measurements of the magnetic susceptibilities χMresulted in values of μeff=6.20μB(300 K), μeff=6.33μB(301 K), and μeff=5.83 μB(300 K) for 1, 2, and 5, respectively, which are indicative of high‐spin d5‐Mn2+centers. Density functional calculations illustrate that the coordination mode of 1−is characteristic for its sextet electronic ground state. Compound 3forms infinite chains of cesocene‐type sandwiches in the solid state, which are broken up into small subunits by the addition of crown ether to form 4. Compound 5is a rare example of a (10,3)‐a racemic interpenetrating network that crystallizes in the orthorhombic space group Pbca.

This paper describes the syntheses and characterization of two new copper(Ii) diphosphonates: [NH₃(CH₂)₂NH₃]₂[Cu₂(hedp)₂]·H₂O (1) and [NH₃CH(CH₃)CH₂NH₃]₂[Cu₂(hedp)₂] (2) (hedp = 1-hydroxyethylidenediphosphonate). Both compounds exhibit similar one-dimensional linear chain structures. The symmetrical {Cu₂(hedp)₂} dimers are connected by edge-shared {CuO₅} square pyramids and form infinite chains. The Cu(ii) ions are alternately bridged by O–P–O groups and O atoms. The Cu–O–Cu angles are 95.8(1) and 96.1(1)° for 1 and 2, respectively. Their magnetic properties show moderately strong antiferromagnetic interactions in both compounds.

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Incorporation of [Co(bpy)3]2+into the cavities of the three‐dimensional oxalate network structurein [Co(bpy)3][LiCr(ox)3] (see picture) produces chemical pressure that destabilises the normal high‐spin ground state 4T1to such an extent that the [Co(bpy)3]2+complex becomes a spin‐crossover complex. It shows a temperature‐dependent equilibrium between the 2E low‐spin and the 4T1high‐spin states.

AbstractCleverly designed molecular building blocks provide chemists with the tools of a powerful molecular-scale construction set. They enable them to engineer materials having a predictable order and useful solid-state properties. Hence, it is in the realm of supramolecular chemistry to follow a strategy for synthesizing materials which combine a selected set of properties, for instance from the areas of magnetism, photophysics and electronics. As a successful approach, host/guest solids which are based on extended anionic, homo- and bimetallic oxalato-bridged transition-metal compounds with two-and three-dimensional connectivities have been investigated. In this report, a brief review is given on the structural aspects of this class of compounds followed by a presentation of a thermal and magnetic study for two distinct, heterometallic oxalato-bridged layer compounds.

Based on a synthetic strategy, extended anionic, homo- and bimetallic oxalato-bridged transition-metal compounds with two- (2D) and three-dimensional (3D) connectivities can be synthesized and crystallized. Thereby, the choice of the templating counter ions will determine the crystal chemistry. The aim of this synthetic, supramolecular approach is to exploit host-guest solids, where each component contributes its own physical characteristics. The two entities could behave independently, resulting in composite properties, or they may interact in a synergistic way, potentially leading to new physical phenomena. Complexes de me′taux de transition comportant des systèmes du type ‘host-guest’. A l'aide d'une strate′gie de synthèse, il est possible d'obtenir et de faire cristalliser des compose′s comportant un re′seau anionique homo- et bi-me′tallique à ponts oxalates, pre′sentant des structures bi- (2D) ou tri-dimensionnelles (3D). Ainsi, le choix des contreanions jouant un effet template, de′termine-t-il la structure obtenue. Cette approche synthe′tique et supramole′culaire permet l'e′tude des compose′s ‘host-guest’, où tous les composants apportent au solide leurs propres caracte′ristiques physiques. Les deux entite′s peuvent se comporter de manière inde′pendante d'un point de vue des proprie′te′s physiques du solide, ou bien interagir et cre′er une synergie qui donne lieu à de nouveaux phe′nomènes physiques.

AbstractPolymeric two- and three-dimensional, homo- and heterometallic oxalatebridged coordination compounds offer exciting opportunities, mainly in the fields of molecular magnetism and photophysics. Given that a large variety of magnetic phenomena have been reported so far from these molecular magnets, very limited experience is gained from elastic neutron scattering experiments. Therefore, with two examples, we will address the topic of the elucidation of magnetic structures by means of the neutron scattering technique. In addition, due to the possibility of the variation of different metal ions in varying oxidation states, interesting photophysical processes can be observed within the extended three-dimensional host/guest systems.

Chemical variation and combination of metal ions of different valencies in the oxalate backbone as well as in the tris-bpy cation of the three-dimensional network structures of the type [MII2(ox)3][MII(bpy)3] (bpy = 2,2'-bipyridine, ox = C2O42-), [MIMIII(ox)3][MII(bpy)3] and [MIMIII(ox)3][MIII(bpy)3]ClO4 offer unique opportunities for studying a large variety of photophysical processes. Depending upon the relative energies of the excited states of the chromophores, excitation energy transfer either from the tris-bipyridine cation to the oxalate backbone or vice versa is observed, as for instance from [Ru(bpy)3]2+ as photo-sensitiser to [Cr(ox)3]3- as energy acceptor in the combination [NaCr(ox)3][Ru(bpy)3], or from [Cr(ox)3]3- to [Cr(bpy)3]3+ in [NaCr(ox)3][Cr(bpy)3]ClO4. In addition efficient energy migration within the oxalate backbone is observed. Furthermore, depending upon the excited state redox potentials, light-induced electron transfer processes may be envisaged.

A strategy for the design of molecule-based magnets consists of assembling transition-metal ions in two-dimensional (2D) or three-dimensional (3D) networks in order to maximize the interactions between the magnetic centers. While increasing the dimensionality of the compounds, an increase in Tc, the critical temperature of spontaneous magnetization should, in principal, be favoured.We are currently studying materials that are formed by the interaction of transition-metal ions with the oxalate ligand, C2O42-, and will present a straightforward concept for building up achiral 2D and chiral 3D homo- and bimetallic networks. Whereas a variety of metal ions can be incorporated, a correlation of the magnetic behavior and the relationship to the special topology of e.g. the chiral, cubic 3-connected 10-gon net (10,3) is not yet fully understood.