Trimer System Research Articles

Magnetic Excitation in Interacting Spin Trimer Systems Investigated by Extended Spin-Wave Theory

Magnetic property of interacting spin trimer systems is studied theoretically focussing on (C 5 H 11 NO 2 ) 2 ·3CuCl 2 ·2H 2 O as a typical example, where the trimer is composed of three S =1/2 spins. It is reported that (C 5 H 11 NO 2 ) 2 ·3CuCl 2 ·2H 2 O has low-field and high-field magnetically ordered phases at low temperatures, where the two phases are separated by a 1/3 magnetization plateau region. The quantum phase transition and magnetic excitation are investigated on the basis of an extended spin-wave theory which was developed in studying interacting spin dimer systems. Formulation of dynamical spin correlation function is presented by introducing form factors for trimers with which interference effects inside the trimer can be taken into account appropriately. Introducing the form factors enables us to treat a trimer as a kind of an atom and makes the formulation simple. Magnetic excitations are classified with transverse and longitudinal modes. It is found that each mode is characterized by i...

Environment-assisted excitation energy transfer in LH1-RC-type and LH2-type trimers

In this work, we study environment-assisted excitation energy transfer (EET) through calculating energy transfer efficiency (ETE) in LH1-RC-type and LH2-type trimers, which can be used to mimic energy transfer behaviors in the basic unit cells of LH1-RC and LH2 light-harvesting complexes. Quantum state evolution of the trimers is described by a non-Hermitian quantum master equation. ETE in these trimer systems is investigated by the use of numerical solutions at finite temperatures for the non-Hermitian master equation. We theoretically reveal the temperature-assisted ETE enhancement. It is found that highly efficient EET with nearly unit efficiency may occur in the nearby regime of the critical point of quantum phase transition. excitation energy transfer, LH1-RC-type and LH2-type trimers, quantum phase transition

Synthesis and Reactions of the Homoleptic Chromium(II) Bis-amide [Ph2PN(iPr)P(Ph)N(iPr)−]2Cr with Relevance to a Selective Catalytic Ethene Trimerization System to 1-Hexene

New organometallic compounds were obtained on the basis of the aminodiphosphinoamine ligand Ph2PN(iPr)P(Ph)N(iPr)-H (1), which is relevant for the selective ethene trimerization system consisting of ligand 1, CrCl3(THF)3, and Et3Al. This catalytic system produces 1-hexene in more than 90% yield and high purity. Here, we report a more efficient, high-yield synthesis of the recently published homoleptic magnesium complex [Ph2PN(iPr)P(Ph)N(iPr)−]2Mg (2) by reaction of n-butylethylmagnesium and 1 in Et2O. Compound 2 can be used as a reagent to transfer the amide moiety [Ph2PN(iPr)P(Ph)N(iPr)−] effectively to a chromium or aluminum center. In situ synthesis of the magnesium amide 2 followed by addition of CrCl2(THF)2 results in the formation of the homoleptic chromium(II)bis-amide [Ph2PN(iPr)P(Ph)N(iPr)−]2Cr (3) by transmetalation. The structure of chromium compound 3 is in some aspects similar to that of the corresponding homoleptic magnesium complex 2. Reacting 2 with ethylaluminum dichloride results in the ...

A Highly Selective Ethylene Tetramerization Catalyst

Small change, big difference: The introduction of an additional CH2 group into the bridge of ligands with two P/N units leads to a different selectivity of the corresponding chromium-based catalysts. Whereas 1 produces an ethylene trimerization system, 2 provides an unprecedented ethylene tetramerization system that produces 1-octene with high purity and little or no polymer side products (see scheme; DMAO=Me3Al-depleted methylaluminoxane). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Bis- and trisporphyrin bio-inspired models for bacterial antennas and photosystems

This review presents the synthetic aspects and photophysical properties of trimeric systems constructed with a first unit consisting of a cofacial porphyrin and then of another porphyrin attached as a side arm. Two scenarios are dealt with. The first one is the case where the three chromophores are different, called donor 1–donor 2–acceptor, specifically where the cofacial fragment is composed of donor 1 and donor 2, and the side arm is the acceptor. They are considered as models for the apo-proteins used in the LH II (light harvesting device) in the purple photosynthetic bacteria. The second one is the case where the chromophores of the cofacial bisporphyrin residue are identical and are closely placed to each other for inter-ring π-interactions. The side arm is simply a mono-porphyrin, and therefore it is different. The cofacial bisporphyrin unit exhibits then similar characteristics to the special pairs located within the reaction center protein, and are designated as artificial special pairs. On the synthetic standpoint, the various pathways to access such models are presented fully exploiting the Suzuki methodology. On the photophysical side, a large emphasis will be placed on the singlet energy transfers. Cascade processes in the trimers donor 1–donor 2–acceptor are presented and each individual contributions donor 1 → donor 2; donor 2 → acceptor; donor → acceptor are addressed qualitatively and quantitatively. For the artificial special pairs flanked with an antenna, the effect of the spacer between the artificial special pair and the antenna will be discussed as well as the choice of substituents and metal demonstrating that one can reverse the orientation of the singlet energy transfer: artificial special pair → side arm or side arm → artificial special pair. Finally, the antenna effect are presented for one example of artificial special pair equipped with 6 semi-flexible dendritic antennas.

Spin Surface Crossing between Chromium(I)/Sextet and Chromium(III)/Quartet without Deprotonation in SNS-Cr Mediated Ethylene Trimerization

Experimentally unsolved problems, including the oxidation states of active species and the occurrence of ligand deprotonation in the SNS-Cr ethylene trimerization system, were studied using the density functional theory (DFT) method. The full catalytic cycle was calculated on the basis of the metallacycle mechanism, and Gibbs free energy surfaces of the trimerization reaction were completely located. A detailed spin state analysis revealed that the ground states of intermediates change along the redox cycle and the spin surface crossing occurring at the minimum energy crossing point (MECP) before metallacyclopentane formation was found to open up a much lower energy pathway by spin acceleration. Formation of metallacycloheptane was identified as the rate-determining step in this system. By comparison of the activation energies of the rate-determining step, Cr(I)/Cr(III) active species bearing nondeprotonated ligands were proposed to be most plausibly responsible for ethylene trimerization. Frontier orbitals and natural population analysis were also determined to further elucidate the reason for high 1-hexene selectivity in this system.

Controlling the Interplay of Electric and Magnetic Modes via Fano-like Plasmon Resonances

Assemblies of strongly coupled plasmonic nanoparticles can support highly tunable electric and magnetic resonances in the visible spectrum. In this Letter, we theoretically demonstrate Fano-like interference effects between the fields radiated by the electric and magnetic modes of symmetric nanoparticle trimers. Breaking the symmetry of the trimer system leads to a strong interaction between the modes. The near and far-field electromagnetic properties of the broken symmetry trimer are tunable across a large spectral range. We exploit this Fano-like effect to demonstrate spatial and temporal control of the localized electromagnetic hotspots in the plasmonic trimer.

Porphyrin Dimers and Arrays

AbstractCurrent applications of porphyrins in medicine and optics, such as photodynamic therapy or nonlinear absorbers, increasingly require the use of far‐red absorbing dyes. Modifications of the porphyrin structure to accommodate these conditions can be achieved by extending the conjugation of the porphyrin π‐system, which causes a bathochromic shift in the absorption spectrum. Thus, conjugated porphyrin oligomers have found widespread use. However, past synthetic strategies have mainly targeted symmetric porphyrin dimers, trimers, and oligomers, which limit the practical use of such chromophores. Here, a series of symmetric and unsymmetric dimeric and trimeric porphyrin systems, which are connected by conjugated linkers, namely alkyne and phenylacetylene, were synthesized by palladium‐catalyzed C–C coupling reactions. Adopting two approaches, firstly, a series of new unsymmetric dimers was synthesized by the incorporation of all substituents on the monomeric components prior to coupling. The second was the synthesis of new symmetric dimers and trimers with free meso positions enabling further chemistry to be carried out. The majority of these conjugated arrays exhibited a bathochromic shift in their UV/Vis absorption, in particular the alkyne‐linked arrays showed absorption greater than 720 nm. The mass spectra of phenylacetylene‐ and diphenylbutadiene‐linked zinc arrays exhibited detachment of zinc from the porphyrin core. These unusual results are both linker and metal dependent, usually only seen for more labile metals.

Weakly bonded cluster structures of N,N′-dimethylethyleneurea and water

Intermolecular interactions between a single water and two N,N′-dimethylethyleneurea (DMEU) molecules have been investigated using ab initio quantum chemistry method. The local and density-fitting approximations of the standard Møller–Plesset perturbation theory (DF-LMP2) have been employed together with the aug-cc-pVTZ basis set. Several trimeric systems were built where the water molecule, through the O–H⋯N hydrogen bond interactions, played the role of the bridge between the two DMEU molecules. The results show that the presence of the water molecule does not increase the stability of the trimeric systems. In the first three configurations the water molecule intercalates between two DMEU molecules, forming stable clusters. In the next three configurations, the water molecule is attached to a plane-parallel stacked DMEU dimer through the C=O⋯H–O hydrogen bond, and these structures are more stable than the first three. Small-angle neutron scattering data show clustering of DMEU molecules in their dilute aqueous solutions, and the ab initio results suggest that DMEU molecules could form contact pairs in dilute aqueous solutions.

Membrane Diffusion of Tethered Dimer and Trimer Systems

We have used molecular dynamics simulations to investigate the diffusion of tethered dimer and trimer systems in lipid bilayers. Coarse-grained (CG) models of DPPC dimers were simulated in a DPPC bilayer with the MARTINI model, and single-lipid diffusion constants compared to those obtained for dimmers and trimers at various tether lengths. The ratio of diffusion constants matches well with theoretical predictions of a simple bead model. A full theoretical model of the translational and rotational diffusion of tethered dimers and trimers was developed at the Saffman-Delbruck level, and results were compared to the simple bead model. The ratios of diffusion constants from the theoretical and CG models were then compared to experimental diffusion constants of pleckstrin homology (PH) domains bound to lipids with a PIP3 (phosphatidylinositol (3,4,5)-trisphosphate) head group. Excellent agreement between all systems was found, indicating that the frictional contributions of multiple, coupled but well-separated lipids are additive, analogous to the free-draining limit for isotropic fluids.

Synthesis and ligand binding properties of triptycene-linked porphyrin arrays

Multiporphyrin arrays are a complex class of molecules with numerous potential applications in energy transfer, photomedicine, and light harvesting. We have developed a facile/versatile route to a class of triptycene-linked porphyrin arrays via both Suzuki and Sonogashira cross-coupling methods, which makes use of the rigid three-pronged orientation of triptycene to construct trimeric porphyrin arrays linked either in the meso or β-position with various linker groups. In order to understand the properties of these potential antenna systems and probe their potential applications, the coordination behavior of zinc(II) derivatives with mono- and bidentate N-donor ligands was investigated. Depending on ligand concentration, both one- and two-point binding was observed with a bidentate ligand. Also/in addition, different cavity sizes, obtained by the use of different linker groups, resulted in differences in the binding properties of each trimeric system.

Helium trimer in the framework of Faddeev approach

Differential Faddeev equations in total angular momentum representation are used for the calculations of Helium trimer system. Numerical results on binding energies of the 4He3 and ultra-cold collisions of 4He atom on 4He dimer are reviewed.

Generation of Endosomolytic Reagents by Branching of Cell-Penetrating Peptides: Tools for the Delivery of Bioactive Compounds to Live Cells in Cis or Trans

We describe the synthesis and cellular delivery properties of multivalent and branched delivery systems consisting of cell-penetrating peptides assembled onto a peptide scaffold using native chemical ligation. A trimeric delivery system presenting three copies of the prototypical cell-penetrating peptide TAT shows an endosomolytic activity much higher than its monomeric and dimeric counterparts. This novel reagent promotes the endosomal release of macromolecules internalized into cells by endocytosis, and as a result, it can be used to achieve cytosolic delivery of bioactive but cell-impermeable macromolecules in either cis (covalent conjugation) or trans (simple coincubation).

Activation and Deactivation by Temperature: Behavior of Ph2PN(iPr)P(Ph)N(iPr)H in the Presence of Alkylaluminum Compounds Relevant to Catalytic Selective Ethene Trimerization

Coordination, deprotonation, rearrangement, and cleavage of Ph(2)PN(iPr)P(Ph)N(iPr)H (1) by trialkylaluminum compounds R(3)Al (R=Me, Et) are reported that are relevant to the selective ethene trimerization system consisting of the ligand 1, CrCl(3)(THF)(3) and Et(3)Al that produces 1-hexene in more than 90% yield and highest purity. With increasing temperature and residence time first the formation of an adduct [Ph(2)PN(iPr)P(Ph)N(iPr)H][AlR(3)] (2), second the aluminum amide [Ph(2)PN(iPr)P(Ph)(AlR(3))N(iPr)][AlR(2)] (3) and third its rearrangement to the cyclic compound [N(iPr)P(Ph)P(Ph(2))N(iPr)][AlR(2)] (4) were observed. The cleavage of 3 by an excess of R(3)Al into an amidophosphane and an iminophosphane could be the reason for its rearrangement to complex 4, as well as to the cyclic dimer [R(2)AlN(iPr)P(Ph)(2)](2) (5). The chemistry of ligand 1 in the presence of alkylaluminum compounds gives hints on possible activation and deactivation mechanisms of 1 in trimerization catalysis.

Finite Magnetization Plateau from a Two-Dimensional Antiferromagnet: Density Functional Analysis of the Magnetic Structure of Cu3(P2O6OH)2

We evaluated the intrachain and interchain spin exchanges of Cu(3)(P(2)O(6)OH) consisting of (Cu2-Cu2-Cu1)(∞) chains by density functional calculations to find that the magnetic properties of Cu(3)(P(2)O(6)OH)(2) are not governed by the J(1)-J(2)-J(2) trimer chain along the c-direction, but by a two-dimensional (2D) antiferromagnetic lattice in which J(1)-J(3)-J(3) trimer chains along the (a-c/2)-direction are interconnected by J(6) monomer chains along the a-direction. Despite its 2D character, Cu(3)(P(2)O(6)OH)(2) shows a 1/3 magnetization plateau because it is a spin-1/2 trimer system with one dominant antiferromagnetic dimer exchange.

Metalation and Transmetalation Studies on Ph2PN(iPr)P(Ph)N(iPr)H for Selective Ethene Trimerization to 1-Hexene

Different organometallic compounds of the new aminodiphosphinoamine ligand Ph2PN(iPr)P(Ph)N(iPr)-H (1) are reported that are relevant model complexes for the selective ethene trimerization system consisting of ligand 1, CrCl3(THF)3, and Et3Al that produces 1-hexene in more than 90% yield and high purity. The lithiation of 1 by n-BuLi in the presence of tetramethylethylenediamine (tmeda) yields the mononuclear compound Ph2PN(iPr)P(Ph)N(iPr)-][Li(tmeda)] (2). Without using tmeda the dinuclear species [Ph2N(iPr)P(Ph)N(iPr)-Li]2 (3) was obtained. By addition of a Grignard reagent to the ligand solution the bis(aminodiphosphinoamide)magnesium complex [Ph2PN(iPr)P(Ph)N(iPr)-]2Mg (4) could be isolated. Reaction of Li[CpCrCl3] with 3 leads to the formation of the model compound CpCrCl[-N(iPr)P(Ph)N(iPr)PPh2] (5), which can be alkylated with Na[Et4Al] to form the corresponding ethyl compound CpCrEt[-N(iPr)P(Ph)N(iPr)PPh2] (7). In THF the formation of EtCrCl2(THF)3 (8) directly from the reaction of CrCl3[Ph2PN(iPr)...

Magnetic properties of the spin trimer compoundCa3Cu2Mg(PO4)4from susceptibility measurements

The effect of the substitution of one ${\text{Cu}}^{2+}$ ion $(S=1/2)$ by ${\text{Mg}}^{2+}$ ion $(S=0)$ on the magnetic property of the linear-chain spin trimer compound ${\text{Ca}}_{3}{\text{Cu}}_{3}{({\text{PO}}_{4})}_{4}$ was studied using dc magnetic susceptibility in ${\text{Ca}}_{3}{\text{Cu}}_{2}\text{Mg}{({\text{PO}}_{4})}_{4}$ together with those in ${\text{Ca}}_{3}{\text{Cu}}_{3}{({\text{PO}}_{4})}_{4}$ and ${\text{Ca}}_{3}{\text{Cu}}_{2}\text{Ni}{({\text{PO}}_{4})}_{4}$ for comparison. A remarkable difference is observed among the results obtained in the Mg and the Ni substituted compounds. A clear signature of the reduction in the net spin of the trimers in ${\text{Ca}}_{3}{\text{Cu}}_{2}\text{Mg}{({\text{PO}}_{4})}_{4}$ was found below 65 K, which is compatible with the presence of the Cu2-Cu1-Mg trimers in the singlet ground state, together with those of the type Cu2-Cu1-Cu2 and Mg-Cu1-Mg in the doublet state. However, no signature of the reduction in the net spin of the trimers was observed in ${\text{Ca}}_{3}{\text{Cu}}_{2}\text{Ni}{({\text{PO}}_{4})}_{4}$. This finding suggests that the type of trimers present in ${\text{Ca}}_{3}{\text{Cu}}_{2}\text{Mg}{({\text{PO}}_{4})}_{4}$ and ${\text{Ca}}_{3}{\text{Cu}}_{2}\text{Ni}{({\text{PO}}_{4})}_{4}$ are different. Furthermore, a singlet ground state is partially realized in a quantum spin trimer system ${\text{Ca}}_{3}{\text{Cu}}_{2}\text{Mg}{({\text{PO}}_{4})}_{4}$.

A Selective Chromium Catalyst System for the Trimerization of Ethene and Its Coordination Chemistry

AbstractIn this paper a novel ligand of the type [PNPNH] is presented for the application in a new homogeneous highly selective ethene trimerization system for the formation of 1‐hexene, which consists of the chromium source CrCl3(thf)3, the ligand Ph2PN(iPr)P(Ph)N(iPr)H (1), and Et3Al as an activator in toluene. The excellent characteristics of this new system, e.g. very high selectivity to C6 with highest purity of the C6 fraction (>99 % 1‐hexene), activity on a constant level on a long timescale, use of small amounts of Et3Al as a cheap activator, and only very low production of PE, make it to a hot candidate for industrial application. Its organometallic background gives an indication of the nature of the active catalyst species.

Core repulsion effects in alkali trimers

AbstractThe present article is related to a talk presented during the Symposium on Coherent Control and Ultracold Chemistry held during the Sixth Congress of the International Society for Theoretical Chemical Physics (ISTCP‐VI, July 2008). The talk was entitled “Electronic structure properties of alkali dimers and trimers. Prospects for alignment of ultracold molecules.” Here we report on the electrostatic repulsion forces of the ionic cores at short separation, involved when the potential energy surfaces of alkali trimers are calculated with a quantum chemistry approach based on effective large‐core potentials for ionic core description. We demonstrate that such forces in the triatomic molecule can be obtained as the sum of three pairwise terms. We illustrate our results on the lowest electronic states of Cs3, which are computed for the first time within a full configuration interaction based on a large Gaussian basis set. As a preliminary section, we also propose a brief introduction about the importance of alkali trimer systems in the context of cold and ultracold molecules. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

Magnetic properties of a novel quasi-2D Cu(II)-trimer system

We present structural and magnetic data of a newCu2+(S = 1/2)-containing magnetictrimer system 2b·3CuCl2·2H2O (b = betaine,C5H11NO2). The trimers form a quasi-2D quantum spin system with an unusualintra-layer exchange coupling topology, which, in principle, supports diagonalfour-spin exchange. To describe the magnetic properties, a 2D effectiveinteracting-trimer model has been developed including an intra-trimer couplingJ and two inter-trimercouplings Ja and Jb. The low-energy description and effective parameters are obtained from numericalcalculations based on four coupled trimers (with periodic boundary conditions). Fits tothe experimental data using this model yield the magnetic coupling constantsJ/kB = −15 Kand Ja/kB = Jb/kB = −4 K. These parameters describe the susceptibility and magnetization data verywell over the whole temperature and field range investigated. Moreover,the model calculations indicate that, for certain ranges of the ratioJb/Ja, whichmight be accessible by either chemical substitution and/or hydrostatic pressure, the low-energy propertiesof 2b·3CuCl2·2H2O will be dominated by non-trivial four-spin exchange processes.