Lower Positive Charge Research Articles

Characteristics of a Negative Cloud-to-Ground Lightning Discharge Based on Locations of VHF Radiation Sources

AbstractThe lightning very high frequency (VHF) radiation location system based on the short-baseline time-difference of arrival (TDOA) technique provides an effective approach to describe the temporal and spatial development of lightning discharge in two dimensions with high resolution. A negative single-stroke cloud-to-ground (CG) lightning flash was analyzed in detail using the radiation location results and synchronic fast/slow electric field changes. The long-duration preliminary breakdown process appeared to propagate with bi-directional leader channels. The two negative simultaneous discharge channels sloped down with a considerable horizontal component in the lower positive charge region at speeds of about 105 m s-1. The stepped leader was clearly converted from one channel of the preliminary breakdown process and spread downwards with branches. The speeds of the stepped leaders were about 105 m s-1. The K processes after the return stroke could either directly initiate from the start region with ...

Radar and Lightning Observations of Deep Moist Convection across Northern Alabama during DC3: 21 May 2012

Abstract The Deep Convective Clouds and Chemistry (DC3) experiment seeks to understand the kinematic and microphysical controls on the lightning behavior of deep moist convection. This study utilized multiple dual-polarization Doppler radars across northern Alabama to quantify microphysical and kinematic properties and processes that often serve as precursors to lightning, such as the graupel echo volume, graupel mass, and convective updraft volume. The focus here was on one multicellular complex that occurred on 21 May 2012 in northern Alabama during DC3. The graupel echo volume and the graupel mass in the charging region correlated well with the total lightning flash rate (FR), and even better than the updraft volumes and maximum updraft velocities. The flash length scales (LS) and flash areas were generally anticorrelated to the FR, while it was correlated to the nonprecipitation ice volume. More specifically, the presence of smaller flashes was associated with a stronger lower positive charge region caused by larger graupel volumes, stronger updraft volumes, and stronger maximum updraft velocities while larger flashes occurred during lower FRs and were associated with a weakened lower positive charge region in combination with a stronger upper positive charge region, weaker updraft velocities, a smaller graupel volume and mass, and an increase in nonprecipitation ice volume.

Electrical soundings in the decay stage of a thunderstorm in the Pingliang region

An electric field sounding system, based on corona discharge, was designed to measure the vertical component of the electric fields in a thunderstorm. The decay stage of a thunderstorm that occurred during the night of August 20, 2012, in the Pingliang region, China (35.57°N, 106.59°E, 1620m above sea level (asl)), was investigated by two balloon-borne electrical soundings. The results of the first sounding showed that the thunderstorm had a tripole charge structure: a lower positive charge region located at temperatures of 3 to 15°C (2.0–4.0kmasl); a middle negative charge region located at temperatures of −3 to 3°C (4.5–5.3kmasl); and an upper positive charge region at temperatures of −10 to −3°C (5.3–6.3kmasl). In addition, there was a negative screen layer at the bottom of the thunderstorm with a depth of about 400m. The charge density of the middle negative charge region was larger than that of the lower and upper positive charge regions. Influenced by the downdraft of precipitation, each charge region moved down to a lower altitude region. The results of the second sounding showed that the lower positive charge center totally disappeared and only the middle negative charge region (3.7–4.2kmasl) and upper positive charge region (4.2–4.7kmasl) remained. We conclude that the downdraft with precipitation caused the dissipation of the lower positive charge region. Compared with the first sounding result, we found that the charge density increased and the depth decreased for both of the charge regions.

Preliminary breakdown, following lightning discharge processes and lower positive charge region

Bipolar pulse trains in wideband electric field records are often attributed to preliminary breakdown (PB) processes (Nag and Rakov, 2009). Using electric field waveforms of lightning discharges observed in Beijing and Guangzhou, the detectable PB pulses and the following discharges are analyzed, and the role of lower positive charge region (LPCR) is investigated. Furthermore, a conceptual discharge model is tested. The detailed results are as follows. (1) The percentages of detectable PB pulses are just as a function of latitude in large range of latitude to a certain extent. But the percentages are similar in a small range of latitude. (2) Four discharge types have been identified. Type I, type II, and type III exhibit PB pulses followed by inverted intracloud (IC) discharge, hybrid flash (an IC discharge followed by a negative return stroke (RS)), and leader-RS, respectively. Type IV only exhibits a leader-RS waveform without detectable PB pulses. It is believed that the charge structures of four discharges are characterized with large LPCR, modest LPCR, small LPCR and little LPCR, respectively. (3) The discharges of type IV are about 65.4% and 63.3% in Beijing and Guangzhou. And the percentages of other discharge types are obviously different. There are higher percentages for type I and type II in Beijing, which may be attributed to larger scale of LPCR. (4) The values of pulse interval (Tpi) rank in increasing order for type I, type II and type III. Compared with type III, type II exhibits longer pulse-return stroke interval (Tp-ri). As for type II, obvious larger amplitude ratio between the maximum peak of PB pulse train and the peak of the first RS (Rp-rr) is found in Beijing. It is speculated that the parameters of different discharge types are related to the scale of LPCR. The analysis results are interpreted by a conceptual discharge model and the rationality of the model is also verified by the results to a certain extent.

Latitude dependence of narrow bipolar pulse emissions

In this paper, we present a comparative study on the occurrence of narrow bipolar pulses (NBPs) and other forms of lightning flashes across various geographical areas ranging from northern regions to the tropics. As the latitude decreased from Uppsala, Sweden (59.8°N) to South Malaysia (1.5°N), the percentage of NBP emissions relative to the total number of lightning flashes increased significantly from 0.13% to 12%. Occurrences of positive NBPs were more common than negative NBPs at all observed latitudes. However, as latitudes decreased, the negative NBP emissions increased significantly from 20% (Uppsala, Sweden) to 45% (South Malaysia). Factors involving mixed-phase region elevations and vertical extents of thundercloud tops are invoked to explain the observed results. These factors are fundamentally latitude dependent. Our results suggest that the NBP emission rate is not a useful measure to monitor thunderstorm severity because regular tropical thunderstorms, where relatively high NBP emissions occur, lack suitable conditions to become severe (i.e., there is modest convective available potential energy and a lack of baroclinity in such regions). Observations of significantly high negative NBP occurrences together with very rare occurrences of positive cloud-to-ground flashes and isolated breakdown pulses in tropical thunderstorms are indicative of a stronger negative screening layer magnitude and weaker lower positive charge region magnitude than those in northern regions.

Sensing conformational changes in DNA upon ligand binding using QCM-D. Polyamine condensation and Rad51 extension of DNA layers.

Biosensors, in which binding of ligands is detected through changes in the optical or electrochemical properties of a DNA layer confined to the sensor surface, are important tools for investigating DNA interactions. Here, we investigate if conformational changes induced in surface-attached DNA molecules upon ligand binding can be monitored by the quartz crystal microbalance with dissipation (QCM-D) technique. DNA duplexes containing 59-184 base pairs were formed on QCM-D crystals by stepwise assembly of synthetic oligonucleotides of designed base sequences. The DNA films were exposed to the cationic polyamines spermidine and spermine, known to condense DNA molecules in bulk experiments, or to the recombination protein Rad51, known to extend the DNA helix. The binding and dissociation of the ligands to the DNA films were monitored in real time by measurements of the shifts in resonance frequency (Δf) and in dissipation (ΔD). The QCM-D data were analyzed using a Voigt-based model for the viscoelastic properties of polymer films in order to evaluate how the ligands affect thickness and shear viscosity of the DNA layer. Binding of spermine shrinks all DNA layers and increases their viscosity in a reversible fashion, and so does spermidine, but to a smaller extent, in agreement with its lower positive charge. SPR was used to measure the amount of bound polyamines, and when combined with QCM-D, the data indicate that the layer condensation leads to a small release of water from the highly hydrated DNA films. The binding of Rad51 increases the effective layer thickness of a 59 bp film, more than expected from the know 50% DNA helix extension. The combined results provide guidelines for a QCM-D biosensor based on ligand-induced structural changes in DNA films. The QCM-D approach provides high discrimination between ligands affecting the thickness and the structural properties of the DNA layer differently. The reversibility of the film deformation allows comparative studies of two or more analytes using the same DNA layer as demonstrated here by spermine and spermidine.

Effective surface passivation of p-type crystalline silicon with silicon oxides formed by light-induced anodisation

Electronic surface passivation of p-type crystalline silicon by anodic silicon dioxide (SiO2) was investigated. The anodic SiO2 was grown by light-induced anodisation (LIA) in diluted sulphuric acid at room temperature, a process that is significantly less-expensive than thermal oxidation which is widely-used in silicon solar cell fabrication. After annealing in oxygen and then forming gas at 400°C for 30min, the effective minority carrier lifetime of 3–5Ωcm, boron-doped Czochralski silicon wafers with a phosphorus-doped 80Ω/□ emitter and a LIA anodic SiO2 formed on the p-type surface was increased by two orders of magnitude to 150μs. Capacitance–voltage measurements demonstrated a very low positive charge density of 3.4×1011cm−2 and a moderate density of interface states of 6×1011eV−1cm−2. This corresponded to a silicon surface recombination velocity of 62cms−1, which is comparable with values reported for other anodic SiO2 films, which required higher temperatures and longer growth times, and significantly lower than oxides grown by chemical vapour deposition techniques. Additionally, a very low leakage current density of 3.5×10−10 and 1.6×10−9Acm−2 at 1 and −1V, respectively, was measured for LIA SiO2 suggesting its potential application as insulation layer in IBC solar cells and a barrier for potential induced degradation.

Solution and solid state effects of coordinated ligands in rhenium (I) complexes

In the last few years the coordination chemistry of rhenium and technetium has gained major interest for the possible use in radiopharmacy, due to its compact size, its low positive charge, coordination properties, d6 low-spin configuration and significant stability. This interest was further fuelled when Alberto remarkably synthesized fac-[99mTc-(CO)3(H2O)3] from [99mTcO4]- in aqueous medium and under mild conditions. Several fac-[M(CO)3]+ (M = Re, 99mTc) type complexes have been synthesized to date with a large number of ligand systems.[1,2] The three labile aqua ligands on the starting synthon fac-[Re(CO)3(H2O)3]+ can easily be substituted by a variety and/or combinations of ligands producing stable compounds and potential radiopharmaceuticals with many different characteristics. Our interest focuses on the fac-[Re(CO)3]+ moiety and related compounds by adopting the [2+1] approach.[3] The solid state behaviour of the complexes are explored as well as different effects such as the charge of the complexes as well as the effect of different types of donor atoms and electron donating or withdrawing systems. The influence of coordinated bidentate ligands on the rate of substitution in solution, by a variety of entering ligands, is also investigated. Crystal structures of Re(I) tricarbonyl tropolonato complexes with various monodentate incoming ligands were obtained in the study and will form part of this presentation.

Sandwich-type Au-PEI/DNA/PEI-Dexa nanocomplex for nucleus-targeted gene delivery in vitro and in vivo.

Many synthetic Au-based cationic nanoparticles (AuNPs) for nonviral gene delivery show high efficiency in vitro, but their excessive charge density, harsh reducing conditions, and nontarget delivery prevent their application in vivo. Herein, we constructed a sandwich-type layered polyethylenimine (PEI)-coated gold nanocomposite outerlaid with a nucleus-targeted Dexamethasone (Dexa), namely, Au-PEI/DNA/PEI-Dexa nanocomplex, for DNA delivery system using a low molecular weight PEI as a mild reducing agent. The nucleus-targeting Au-PEI/DNA/PEI-Dexa nanocomplex with low positive charge and low cytotoxicity condensed DNA and protected from enzymatic degradation. In vitro transfection studies demonstrated that Au-PEI/DNA/PEI-Dexa nanocomplex exhibited much more efficient nucleus transfection than Au-PEI/DNA/PEI without nucleus-targeted residues and commercially available PEI 25 kDa due to the Dexa targeting of the nucleus. Furthermore, the nanocomplex markedly transfected pTRAIL (TRAIL = tumor-necrosis-factor-related apoptosis-inducing ligand) to tumors in vivo and subsequently inhibited the tumor growth with minimal side effects. These findings suggest that nucleus-targeting Au-PEI/DNA/PEI-Dexa ternary complexes have promising potential in gene delivery.

Numerical simulation of the effect of lower positive charge region in thunderstorms on different types of lightning

Combined with the existing stochastic lightning parameterization scheme, a classic tripole charge structure in thunderstorms is assumed in the paper, and then 2-dimensional fine-resolution lighting discharge simulations are performed to quantitatively investigate the effect of lower positive charge (LPC) on different types of lightning. The results show: (1) The LPC plays a key role in generating negative cloud-to-ground (CG) flashes and inverted intra-cloud (IC) lightning, and with the increase of charge density or distribution range of LPC region, lightning type changes from positive polarity IC lightning to negative CG flashes and then to inverted IC lightning. (2) Relative to distribution range of charge regions, the magnitude of charge density of the LPC region plays a dominant role in lightning type. Only when the maximal charge density value of LPC region is within a certain range, can negative CG flashes occur, and the occurrence probability is relatively fixed. (3) In this range, the charge density and distribution range of LPC region jointly determine the occurrence of negative CG flashes, which has a linear boundary with the trigger condition of IC lightning. (4) The common effect of charge density and distribution range of the LPC region is to change the distribution of positive potential well of bottom part of thunderstorms, and inverted IC lightning occurs when the initial reference potential is close to 0 MV, and negative CG flashes occur when the initial reference potential is far less than 0 MV. lower positive charge, charge density, distribution range, lightning type, numerical simulation

Lightning Observatory in Gainesville (LOG), Florida: A review of recent results

A review of several recent studies conducted at the Lightning Observatory in Gainesville (LOG), Florida, is given, including (a) evaluation of field-to-current conversion equations, (b) lower positive charge in the cloud and lightning type, (c) positive lightning, (d) compact intracloud lightning discharges, (e) lightning interaction with the ionosphere, and (f) X-rays produced by first and subsequent strokes in natural lightning. The results serve to improve our understanding of the physics of lightning with important implications for lightning detection and lightning protection areas.

Characteristics of a Negative Cloud-to-Ground Lightning Discharge Based on Locations of VHF Radiation Sources

The lightning very high frequency(VHF) radiation location system based on the short-baseline time-difference of arrival(TDOA) technique provides an effective approach to describe the temporal and spatial development of lightning discharge in two dimensions with high resolution.A negative single-stroke cloud-to-ground(CG) lightning flash was analyzed in detail using the radiation location results and synchronic fast/slow electric field changes.The long-duration preliminary breakdown process appeared to propagate with bi-directional leader channels.The two negative simultaneous discharge channels sloped down with a considerable horizontal component in the lower positive charge region at speeds of about 105 m s-1.The stepped leader was clearly converted from one channel of the preliminary breakdown process and spread downwards with branches.The speeds of the stepped leaders were about 105 m s-1.The K processes after the return stroke could either directly initiate from the start region with negative polarity lightning discharge,or initiate from a new region in the cloud as negative recoil streamers.All K processes propagated along the preceding electrified channel,while not all K processes initiated from the tips of positive breakdowns.The speeds of the K processes were about 106–107 m s-1.

Wavelet analysis of the first electric field pulse of lightning flashes in Sweden

In this paper, we investigate the wavelet characteristics of the first electric field pulse of four different flash types namely negative cloud-to-ground flash (−CG), positive cloud-to-ground flash (+CG), cloud flash (IC) and isolated breakdown flash (IB). A total of 110 fine waveforms out of 885 were selected which have been recorded during summer between May and August 2010 in Uppsala, Sweden. The measurement was done by using an electric field broadband antenna system with the time resolution of 20 Megasample per second. Evidence from our wavelet analysis suggests that the ionization process during the initial leader development (coincide with the detection of the first electric field pulse) of at least three flashes (−CG, IC, and IB) in Sweden was dictated directly by the existence and magnitude of localized free ions region and lower positive charge center (p region). In general, we found that both single peak and multiple peaks pulses of the negative CG and IC flashes radiated energy at higher frequencies and gain larger bandwidth when compared to positive CG and IB flashes. We suggest that the initial leader development of both IC and negative CG flashes underwent very rapid and much more extensive ionization process when compared to the positive CG and IB flashes. In specific comparison between negative CG and IC flashes, both temporal and wavelet analyses suggest that the first electric field pulses of IC flash radiated energy at higher frequency in both single spread categories and radiated energy at lower frequency in both multiple spread categories when compared to the negative CG flash. This finding may explain the observation of much slower and less bright type α leader (ionization process not so extensive) compared to much faster and very bright type β leader (ionization process very rapid and more extensive). As for positive CG and IB flashes, the single peak pulses of positive CG radiated energy at much higher frequency while the multiple peaks pulses radiated energy at much lower frequency than IB flash. We suggest that the initiation mechanism of positive CG was dictated directly by the background electric field between the main positive charge center and the ground, which is distinct from the initiation mechanism of IB flash. The presence of small magnitude of localized free ions region facilitated the rapidity of the ionization process in the initial leader development of IB flash.

Thunderstorm ground enhancements—Model and relation to lightning flashes

In the beginning of last century C.T.R. Wilson proposed that strong electric field of the thunderclouds might accelerate electrons to very high energies. However, this and many other electromagnetic processes in our atmosphere are poorly understood till now; the key questions about the thundercloud electrification and lightning initiation remain unanswered. During recent decades several observations of gamma ray, electron and neutron fluxes correlated with thunderstorms were reported. Nonetheless, the origin of these fluxes is under debate till now. The direct registration of the particle showers initiated by the runaway electrons (the most popular theory) was missing. We present the experimental evidence of the microsecond duration electron bursts originated from runaway electrons accelerated in thunderclouds. The electron acceleration downward becomes possible after creation of the Lower Positive Charged Region below the main negative charged layer in the middle of the thundercloud. Our analysis is based on the vast thunderstorm data from the Aragats Mountain in Armenia, 3200m above sea level. Varieties of particle detectors located at Aragats Space Environmental Center are registering neutral and charged particle fluxes correlated with thunderstorms, so-called Thunderstorm Ground Enhancements. Simultaneously the electric mills and lightning detectors are monitoring the near-surface electric field and lightning flashes. In the paper we present the model of TGE initiation. We demonstrate the necessity of the Lower positive charge region development for the lower dipole operation and TGE initiation. Our observations establish direct relationship of the negative electric field strength and rain rate with TGE.

Development and in vitro Evaluation of Antigen‐Loaded Poly(amidoamine) Nanoparticles for Respiratory Epithelium Applications

A poly(amidoamine) with disulfide linkages in the main chain and 4-hydroxybutyl and ω-carboxy-PEG groups (9:1 ratio) as side chains was prepared by Michael addition polymerization of cystamine bisacrylamide with 4-hydroxybutylamine and ω-carboxy-PEG-amine. To develop therapeutic protein formulations for improved delivery of antigen via the intranasal route, nanoparticles were prepared from this polymer by self-assembly with p24 or ovalbumin as the model proteins and CpG as the adjuvant. The nanoparticles incorporated the antigens and adjuvant from the feed solution with high efficiency (∼90 %) and have sizes of 112 and 169 nm, respectively, with low positive surface charge (∼+2 mV). Formulations of the nanoparticles were shown to be nontoxic and stable for at least 10 days at room temperature. Their capacity to pass through epithelial and endothelial cell layers was evaluated in vitro by using a respiratory mucosa-like barrier model in which monolayers of NCI H441 respiratory epithelial cells and ISO-HAS-1 endothelial cells were co-cultured on both sides of a transwell filter membrane. It was shown that p24 incorporated in the nanoparticles was transported with >140 % greater efficiency through the two contact-inhibited layers than p24 in its free form, whereas incorporation of ovalbumin in the nanoparticles leads to a 40 % decrease in transport efficiency relative to the free antigen.

Interfacial band configuration and electrical properties of LaAlO3/Al2O3/hydrogenated-diamond metal-oxide-semiconductor field effect transistors

In order to search a gate dielectric with high permittivity on hydrogenated-diamond (H-diamond), LaAlO3 films with thin Al2O3 buffer layers are fabricated on the H-diamond epilayers by sputtering-deposition (SD) and atomic layer deposition (ALD) techniques, respectively. Interfacial band configuration and electrical properties of the SD-LaAlO3/ALD-Al2O3/H-diamond metal-oxide-semiconductor field effect transistors (MOSFETs) with gate lengths of 10, 20, and 30 μm have been investigated. The valence and conduction band offsets of the SD-LaAlO3/ALD-Al2O3 structure are measured by X-ray photoelectron spectroscopy to be 1.1 ± 0.2 and 1.6 ± 0.2 eV, respectively. The valence band discontinuity between H-diamond and LaAlO3 is evaluated to be 4.0 ± 0.2 eV, showing that the MOS structure acts as the gate which controls a hole carrier density. The leakage current density of the SD-LaAlO3/ALD-Al2O3/H-diamond MOS diode is smaller than 10−8 A cm−2 at gate bias from −4 to 2 V. The capacitance-voltage curve in the depletion mode shows sharp dependence, small flat band voltage, and small hysteresis shift, which implies low positive and trapped charge densities. The MOSFETs show p-type channel and complete normally off characteristics with threshold voltages changing from −3.6 ± 0.1 to −5.0 ± 0.1 V dependent on the gate length. The drain current maximum and the extrinsic transconductance of the MOSFET with gate length of 10 μm are −7.5 mA mm−1 and 2.3 ± 0.1 mS mm−1, respectively. The enhancement mode SD-LaAlO3/ALD-Al2O3/H-diamond MOSFET is concluded to be suitable for the applications of high power and high frequency electrical devices.

Interaction between adjacent lightning discharges in clouds

Using a 3D lightning radiation source locating system (LLS), three pairs of associated lightning discharges (two or more adjacent lightning discharges following an arbitrary rule that their space-gap was less than 10 km and their time-gap was less than 800 ms) were observed, and the interaction between associated lightning discharges was analyzed. All these three pairs of associated lightning discharges were found to involve three or more charge regions (the ground was considered as a special charge region). Moreover, at least one charge region involved two lightning discharges per pair of associated lightning discharges. Identified from electric field changes, the subsequent lightning discharges were suppressed by the prior lightning discharges. However, it is possible that the prior lightning discharge provided a remaining discharge channel to facilitate the subsequent lightning discharge. The third case provided evidence of this possibility. Together, the results suggested that, if the charges in the main negative charge region can be consumed using artificial lightning above the main negative charge regions, lightning accidents on the ground could be greatly reduced, on the condition that the height of the main negative charge region and the charge intensity of the lower positive charge region are suitable.

The Physics of Lightning

An overview of the physics of cloud-to-ground lightning is given, including its initiation, propagation, and attachment to ground. Discharges artificially initiated (triggered) from natural thunderclouds using the rocket-and-wire technique are discussed with a view toward studying properties of natural lightning. Both conventional and runaway breakdown mechanisms of lightning initiation in thunderclouds are reviewed, as is the role of the lower positive charge region in facilitating different types of lightning. New observations of negative-leader stepping and its attachment to ground are compared to similar processes in long laboratory sparks. The mechanism and parameters of compact intracloud lightning discharges that are thought to be the most intense natural producers of HF-VHF (3–300 MHz) radiation on Earth are reviewed. The M-component mode of charge transfer to ground and its difference from the leader/return-stroke mode are discussed. Lightning interaction with the ionosphere and the production of energetic radiation (X-rays and gamma radiation) by cloud-to-ground leaders are considered.

New compounds based on polyoxometalates and transition metal complexes with a lower positive charge

Four new hybrid compounds based on Keggin polyoxometallates and transition metal complexes, [Cu(phen)2]4[GeW12O40] (1), [Cu(bpy)(phen)]2[Cu(bpy)2]3[BW12O40] (2), [Cu(bpy)(phen)][Cu(bpy)2]3[SiW12O40] (3) and [Cu(bpy)2]4[GeW12O40] (4) (phen=1,10-phenanthroline, bpy=2,2′-bipyridine), have been hydrothermally synthesized and characterized by IR spectra, UV–Vis, XPS, XRD and single crystal X-ray diffraction analyses. Compounds 1, 2, 3 and 4 are new examples of hybrids based on polyoxometallates and transition metal complexes with a lower positive charge.

Conformationally Constrained N-Heterocyclic Phosphine–Diimine with Dual Functionality

Condensation of octahydro-2,2'-bipyrimidine with P(NMe2)3 gave a 1,3,2-diazaphospholidine-4,5-diimine 4a in which the "open" (exo/exo) conformation of the diimine unit was enforced by incorporation into a tricyclic molecular backbone. The coordination behavior of this potentially ambident ligand was sampled in reactions with ([(nbd)W(CO)4] and [CpCo(CO)2]) and pnictogen halides ECl3 (E = P, As, Sb). While PCl3 reacted under ring metathesis, all other reactions gave isolable complexes of composition (4a)MLn (MLn = W(CO)5, CpCo(CO), AsCl3, SbCl3); attempted recrystallization of the As-adduct yielded a complex (4a)(AsCl3)2 which was also accessible from reaction of 4a with 2 equiv of AsCl3. Single-crystal X-ray diffraction studies revealed that the ligand in [(4a)W(CO)5] and [(4a)CpCo(CO)] binds through its phosphorus lone-pair; [(4a)SbCl3] and [(4a)(AsCl3)2] contain a T-shaped ECl3 unit which binds to the chelating diimine moiety, and associate further via chloride bridges to give centrosymmetric dimers. Reactions of 4a with excess metal substrates gave no evidence that formation of bimetallic complexes with μ-bridging 1κ(2)(N,N')-2κP-coordination is feasible; the extra AsCl3 moiety in [(4a)(AsCl3)2] avoids this coordination mode by interacting with the peripheral chlorides of the central core. The observed selectivity suggests that ligand 4a specifically addresses transition metal centers with low positive charge and some back-bonding capacity through the phosphorus lone-pair, and electrophiles that behave essentially as "pure" Lewis acids through the diimine unit. This assumption was confirmed by DFT studies which disclosed further that binding of the first metal center deactivates the opposite binding site and thus strongly inhibits the formation of dinuclear complexes.