Contact Ion Pairs Research Articles

The Many-Body Expansion for Aqueous Systems Revisited: IV. Stabilization of Halide-Anion Pairs in Small Water Clusters.

We report the structures, energetics, many-body effects, and vibrational spectra of water clusters stabilizing pairs of halide-anions, X-(H2O)kY- (k = 2-6, X/Y = F, Cl, Br, I) as well as their stability in the gas phase relative to fragmentation. We find that these metastable cluster structures mimicking the solvent-separated ion pair (SSIP) configurations in aqueous solutions are less stable relative to fragmentation into smaller ionic aqueous clusters containing a single halide anion. The many-body expansion (MBE) at these geometries was found to converge at the 4-body term, which is, however, significant, amounting to >20% of the total binding energy in several instances. The binding motif of these ion pair aqueous clusters starts as networks in which the water molecules form a "bridge" between the two halide-anions. As the cluster grows, these structures become destabilized by a more repulsive 3-body term for distances R(O-O) < 3.45 Å with respect to networks in which water molecules move outside the bridge, solvating the other side of the anion.

Bidentate NHC‐Containing Ligands for Copper Catalysed Synthesis of Functionalised Diaryl Ethers

Diaryl and heteroaryl ethers are important and common motifs in drug discovery and agrochemicals. Here we present a catalytic system for the copper catalysed arylation of phenols with aryl halides. Bidentate N‐heterocyclic carbene ligands provide a well‐defined catalytic system that enable low loading of copper in effective coupling reactions (0.5 mol% Cu or lower). The reaction scope of aryl iodides and aryl bromides is developed, that is tolerant of functional groups and a library of biaryl ethers with lead‐like properties is prepared. The presence of excess ligand (in a 1:3 ratio) is shown to be optimal to prevent catalyst degradation, presumably by avoiding decomplexation of the ligand. This is also supported by the catalytic results obtained with pre‐formed copper complexes. The kinetics of the reaction are examined and shown to be first order in copper, supportive of a well‐defined catalyst species, first order in phenol and aryl iodide, and zero order in base under the developed conditions. Computational studies performed using Minnesota MN15‐L parametrisation method support an oxidative addition–reductive elimination pathway. Reductive elimination would be turnover limiting and occurr through an intimate ion pair intermediate.

Organic Cationic-Coordinated Perfluoropolymer Electrolytes with Strong Li+-Solvent Interaction for Solid State Li-Metal Batteries.

The practical application of solid-state polymer lithium-metal batteries (LMBs) is plagued by the inferior ionic conductivity of the applied polymer electrolytes (PEs), which is caused by the coupling of ion transport with the motion of polymer segments. Here, solvated molecules based on ionic liquid and lithium salt with strong Li+-solvent interaction are inserted into an elaborately engineered perfluoropolymer electrolyte via ionic dipole interaction, extensively facilitating Li+ transport and improving mechanical properties. The intensified formation of solvation structures of contact ion pairs and ionic aggregates, as well as the strong electron-withdrawal properties of the F atoms in perfluoropolymers, give the PE high electrochemical stability and excellent interfacial stability. As a result, Li||Li symmetric cells demonstrate a lifetime of 2500 h and an exceptionally high critical current density above 2.3 mA cm-2, Li||LiFePO4 batteries exhibit consistent cycling for 550 cycles at 10 C, and Li||uncoated LiNi0.8Co0.1Mn0.1O2 cells achieve 1000 cycles at 0.5 C with an average Coulombic efficiency of 98.45 %, one of the best results reported to date based on PEs. Our discovery sheds fresh light on the targeted synergistic regulation of the electro-chemo-mechanical properties of PEs to extend the cycle life of LMBs.

Direct observation of the complex S(IV) equilibria at the liquid-vapor interface

The multi-phase oxidation of S(IV) plays a crucial role in the atmosphere, leading to the formation of haze and severe pollution episodes. We here contribute to its understanding on a molecular level by reporting experimentally determined pKa values of the various S(IV) tautomers and reaction barriers for SO2 formation pathways. Complementary state-of-the-art molecular-dynamics simulations reveal a depletion of bisulfite at low pH at the liquid-vapor interface, resulting in a different tautomer ratio at the interface compared to the bulk. On a molecular-scale level, we explain this with the formation of a stable contact ion pair between sulfonate and hydronium ions, and with the higher energetic barrier for the dehydration of sulfonic acid at the liquid-vapor interface. Our findings highlight the contrasting physicochemical behavior of interfacial versus bulk environments, where the pH dependence of the tautomer ratio reported here has a significant impact on both SO2 uptake kinetics and reactions involving NOx and H2O2 at aqueous aerosol interfaces.

The Trifluorooxygenate Anion [OF3]-: Spectroscopic Evidence for a Binary, Hypervalent Oxygen Species.

Experimental evidence for hypervalent compounds of second-row elements is still scarce in literature. Here, we present the first report of the long-sought binary hypervalent trifluorooxygenate anion [OF3]-. It was isolated in solid Ne matrices under cryogenic conditions after reacting oxygen difluoride with free fluoride ions from laser ablation of alkali metal fluorides MF (M = Li-Cs). As predicted by VSEPR theory and calculations at the CCSD(T) level, and confirmed by FTIR spectroscopy as well as isotopic labeling, [OF3]- exhibits a C2v-symmetric T-shaped structure with one short and two long O-F bond distances. Analysis of the natural local molecular orbitals shows the presence of 2c-2e bond and one 3c-4e bond. Natural resonance theory indicates the importance of the stability of [OF2]•- for the stability of [OF3]-. Although free [OF2]•- was not detected, the species MOF2 (M = Na-Cs) could be observed in the same experiments, which are best described as contact ion pairs of M+[OF2]•-.

Ion Association and Hydration of Some Heavy-Metal Nitrate Salts in Aqueous Solution.

Aqueous solutions of four heavy-metal nitrate salts (AgNO3, TlNO3, Cd(NO3)2 and Pb(NO3)2) have been studied at 25 °C using broadband dielectric relaxation spectroscopy (DRS) at frequencies 0.27 ≤ ν/GHz ≤ 115 over the approximate concentration range 0.2 ≲ c/mol L-1 ≲ 2.0 (0.08 ≲ c/mol L-1 ≲ 0.4 for the less-soluble TlNO3). The spectra for AgNO3, TlNO3, and Pb(NO3)2 were best described by assuming the presence of three relaxation processes. These consisted of one solute-related Debye mode centered at ∼2 GHz and two higher-frequency solvent-related modes: one an intense Cole-Cole mode centered at ∼18 GHz and the other a small-amplitude Debye mode at ∼500 GHz. These modes can be assigned, respectively, to the rotational diffusion of contact ion pairs (CIPs), the cooperative relaxation of solvent water molecules, and its preceding fast H-bond flip. For Cd(NO3)2 solutions an additional solute-related Debye mode of small-amplitude, centered at ∼0.5 GHz, was required to adequately fit the spectra. This mode was consistent with the presence of small amounts of solvent-shared ion pairs. Detailed analysis of the solvent modes indicated that all the cations are strongly solvated with, at infinite dilution, effective total hydration numbers (Zt0 values) of irrotationally bound water molecules of ∼5 for both Ag+ and Tl+, ∼10 for Pb2+, and ∼20 for Cd2+. These results clearly indicate the presence of a partial second hydration shell for Pb2+(aq) and an almost complete second shell for Cd2+(aq). However, the hydration numbers decline considerably with increasing solute concentration due to ion-ion interactions. Association constants for the formation of contact ion pairs indicated weak complexation that varies in the order: Tl+ < Ag+ < Pb2+ < Cd2+, consistent with the charge/radius ratios of the cations and their Gibbs energies of hydration. Where comparisons were possible the present constants mostly agreed well with the rather uncertain literature values.

Solvation structures in weakly solvating solvents lead to hybrid vehicular/structural ion transport

Despite the reported benefits of weakly solvating electrolytes (WSEs), investigations on the solvation structures and ion transport mechanisms present in WSEs are limited. This is particularly the case for electrolytes containing the weakly solvating 1,2-diethoxyethane (DEE), which has shown great promise recently. It is for this purpose, we employ molecular dynamics simulations and quantum mechanical calculations to investigate the solvation structure and Li+ transport for lithium bis(fluorosulfonyl)imide (LiFSI) in DEE. From the results reported herein, it was found that at lower concentrations, solvent separated ion pairs are particularly stable, primarily due to the presence of FSI– in the second solvation shell of Li+. As the salt concentration increases, cation–anion complexes appear and form large aggregates. The presence of these large aggregates promotes a hybrid/structural diffusion mechanism at high concentrations, where Li+ ions readily exchange ligands with FSI– anions but remains coordinated with DEE molecules. Hence, the results reported herein investigate how the solvation structure influences transport properties in weakly solvating solvents and provides insights that can be used to optimize electrolytes for energy storage applications.

Electrolyte Solvation Engineering Stabilizing Anode-Free Sodium Metal Battery With 4.0V-Class Layered Oxide Cathode.

Anode-free sodium metal batteries (AFSMBs) are regarded as the "ceiling" for current sodium-based batteries. However, their practical application is hindered by the unstable electrolyte and interfacial chemistry at the high-voltage cathode and anode-free side, especially under extreme temperature conditions. Here, an advanced electrolyte design strategy based on electrolyte solvation engineering is presented, which shapes a weakly solvating anion-stabilized (WSAS) electrolyte by balancing the interaction between the Na+-solvent and Na+-anion. The special interaction constructs rich contact ion pairs (CIPs) /aggregates (AGGs) clusters at the electrode/electrolyte interface during the dynamic solvation process which facilitates the formation of a uniform and stable interfacial layer, enabling highly stable cycling of 4.0V-class layered oxide cathode from -40°C to 60°C and excellent reversibility of Na plating/stripping with an ultrahigh average CE of 99.89%. Ultimately, industrial multi-layer anode-free pouch cells using the WSAS electrolyte achieve 80% capacity remaining after 50 cycles and even deliver 74.3% capacity at -30°C. This work takes a pivotal step for the further development of high-energy-density Na batteries.

Facile heterolytic bond splitting of molecular chlorine upon reactions with Lewis bases: Comparison with ICl and I2

AbstractFormation of molecular complexes and subsequent heterolytic halogen‐halogen bond splitting upon reactions of molecular Cl2 with nitrogen‐containing Lewis bases (LB) are computationally studied at M06‐2X/def2‐TZVPD and for selected compounds at CCSD(T)/aug‐cc‐pvtz//CCSD/aug‐cc‐pvtz levels of theory. Obtained results are compared with data for ICl and I2 molecules. Reaction pathways indicate, that in case of Cl2∙LB complexes the activation energies for the heterolytic Cl‐Cl bond splitting are lower than the activation energies of the homolytic splitting of Cl2 molecule into chlorine radicals. The heterolytic halogen splitting of molecular complexes of X2∙Py with formation of [XPy2]+… contact ion pairs in the gas phase is slightly endothermic in case of Cl2 and I2, but slightly exothermic in the case of ICl. Formation of {[ClPy2]+…}2 dimers makes the overall process exothermic. Taking into account that polar solvents favor ionic species, generation of donor‐stabilized Cl+ in the presence of the Lewis bases is expected to be favorable. Thus, in polar solvents the oxidation pathway via donor‐stabilized Cl+ species is viable alternative to the homolytic Cl‐Cl bond breaking.

Mechanochemically accelerated deconstruction of chemically recyclable plastics.

Plastics redesign for circularity has primarily focused on monomer chemistries enabling faster deconstruction rates concomitant with high monomer yields. Yet, during deconstruction, polymer chains interact with their reaction medium, which remains underexplored in polymer reactivity. Here, we show that, when plastics are deconstructed in reaction media that promote swelling, initial rates are accelerated by over sixfold beyond those in small-molecule analogs. This unexpected acceleration is primarily tied to mechanochemical activation of strained polymer chains; however, changes in the activity of water under polymer confinement and bond activation in solvent-separated ion pairs are also important. Together, deconstruction times can be shortened by seven times by codesigning plastics and their deconstruction processes.

NMR Spectroscopy and Multiscale Modeling Shed Light on Ion-Solvent Interactions and Ion Pairing in Aqueous NaF Solutions.

The balance between ion solvation and ion pairing in aqueous solutions modulates chemical and physical processes from catalysis to protein folding. Yet, despite more than a century of investigation, experimental determination of the distribution of ion-solvation and ion-pairing states remains elusive, even for archetypal systems like aqueous alkali halides. Here, we combine nuclear magnetic resonance (NMR) spectroscopy and multiscale modeling to disentangle ion-solvent interactions from ion pairing in aqueous sodium fluoride solutions. We have developed a high-accuracy method to collect experimental NMR resonance frequencies for both ions as functions of temperature and concentration. Comparison of these data with resonance frequencies for nonassociating salts allows us to differentiate the influence of solvation and ion pairing on NMR spectra. These high-quality experimental NMR data are used to validate our modeling framework comprising polarizable force field molecular dynamics (MD) simulations and quantum chemical calculations of NMR resonance frequencies. Our experimental and theoretical resonance frequency shifts agree over a wide range of temperatures and concentrations. Structural analysis reveals how both trends are dominated by interactions with water molecules. For the more sensitive 19F nucleus, the NMR resonance frequency decreases as hydrogen bonds between fluoride and water molecules are reduced in number with increased temperature and molality. Through a detailed analysis of the theoretical NMR resonance frequencies for both ions, we show that NMR spectroscopy can distinguish both contact ion pairs and single-solvent-separated ion pairs from free ions. This quantitative framework can be applied directly to other systems.

Solvation Regulation Reinforces Anion-Derived Inorganic-Rich Interphase for High-Performance Quasi-Solid-State Li Metal Batteries.

Solid-state polymer lithium metal batteries are an important strategy for achieving high safety and high energy density. However, the issue of Li dendrites and inherent inferior interface greatly restricts practical application. Herein, this study introduces tris(2,2,2-trifluoroethyl)phosphate solvent with moderate solvation ability, which can not only complex with Li+ to promote the in-situ ring-opening polymerization of 1,3-dioxolane (DOL), but also build solvated structure models to explore the effect of different solvation structures in the polymer electrolyte. Thereinto, it is dominated by the contact ion pair solvated structure with pDOL chain segments forming less lithium bonds, exhibiting faster kinetic process and constructing a robust anion-derived inorganic-rich interphase, which significantly improves the utilization rate of active Li and the high-voltage resistance of pDOL. As a result, it exhibits stable cycling at ultra-high areal capacity of 20 mAh cm-2 in half cells, and an ultra-long lifetime of over 2000h in symmetric cells can be realized. Furthermore, matched with LiNi0.9Co0.05Mn0.05O2 cathode, the capacity retention after 60 cycles is as high as 96.8% at N/P value of 3.33. Remarkably, 0.7 Ah Li||LiNi0.9Co0.05Mn0.05O2 pouch cell with an energy density of 461Wh kg-1 can be stably cycled for five cycles at 100% depth of discharge.

Antioxidant Activity of MgSO4 Ion Pairs by Spin-Electron Stabilization of Hydroxyl Radicals through DFT Calculations: Biological Relevance.

Magnesium sulfate has been of great interest as an antioxidant for its ability to decrease the oxidizing capacity of the hydroxyl radical. Previously, it was shown that the contact ion pair of this salt could stabilize •OH by coordinating with Mg and delocalizing the unpaired electron over sulfate. The present study explores in detail the MgSO4 antioxidant properties, considering all its ion pairs with •OH in different conformations. The analyses were based on structural, spin, and energetic properties using the DFT approach. As a result, the high antioxidant potential of MgSO4 is related to the spin-electron transfer from SO4 -2 to •OH causing electron spin delocalization and electrostatic stabilization. This transfer occurs for all ion pairs when •OH approaches the Mg first solvation shell, without being coordinated to Mg. The direct Mg-•OH interaction further stabilizes the radical system. These results show that spin-electron transfers are feasible in all hydrated ion pairs MgSO4-•OH, even at a •OH-sulfate distance greater than 10 Å.

Designing ester-ether hybrid electrolytes for aldehyde-based organic anode to achieve superior K-storage

Electrolyte engineering strategy has attracted high expectations for addressing the universally existed serious dynamics and thermodynamics issues in potassium-ion batteries (PIBs), especially for the batteries adopted with organic electrode materials. Herein, a new kind of ester-ether hybrid electrolytes (EEHEs) was developed with widely manipulatable solvation structures from solvent-separated ion pair (SSIP) to aggregate (AGG)-dominated states for PIBs. The optimized EEHEs of 5 M KFSI/EC+DME enabled high Coulombic efficiency and ultra-stable K plating/stripping stability in K||Cu cells and K||K symmetric cells, respectively. When the developed novel organic anode material of 2-Bromobenzene-1,3-dialdehyde/carbon nanotube (BBD/CNT) was matched with the 5 M KFSI/EC+DME electrolyte, it delivered a reversible capacity of about 288 mAh g−1 at 50 mA g−1 and approximately 244 mAh g−1 at 200 mA g−1 with negligible capacity fade. The excellent performance should be attributed to the surface capacitive-dominated mechanism with fast K-storage kinetics guaranteed by the AGG-dominated solvation structures.

Structure and intermolecular interactions in ionic liquid 1-ethyl-3-methylimidazolium bromide and its aqueous solutions investigated by vibrational spectroscopy and quantum chemical computations.

The recently developed efficient protocol to explicit quantum mechanical modeling of structure and IR spectra of liquids and solutions (S. A. Katsyuba, S. Spicher, T. P. Gerasimova, S. Grimme, J. Phys. Chem. B 2020, 124, 6664) is applied to ionic liquid (IL) 1-ethyl-3-methylimidazolium bromide (EmimBr), its C2-deuterated analog [Emim-d]Br and its aqueous solutions. It is shown that the solvation strongly modifies frequencies and IR intensities of the CH/CD stretching vibrations (νCH/νCD) of the imidazolium ring. The main vibrational spectroscopic features of the neat IL are reproduced by the simulations for a cluster (EmimBr)9, in which all three imidazolium CH moieties of the solvated cation form short contacts with three Br- anions, and another two Br- anions are located on top and bottom of imidazolium ring. Cluster models of aqueous solutions reproduce the experimental vibrational frequencies of actual solutions, provided that the Br- anion of solvated contact ion pair (CIP) is situated on top of imidazolium ring, and CH/CD moieties of the latter participate in short contacts with surrounding water molecules. Both structural and spectroscopic analysis allow to interpret the short contacts CH/CD⋯Br- and CH/CD⋯OH2 as hydrogen bonds of approximately equal strength. Enthalpies of bonding of these liquid-state H-bonds, estimated with the use of empirical correlations, amount to ca. 1.4 kcal⋅mol-1, while the analogous estimates obtained for the gas-phase charged species [Emim]2Br+ increase to 5.6 kcal⋅mol-1. It is shown that formation of solvent-shared ion pair (SIP) in aqueous solution, where the counterions of IL are separated by two water molecules H-bonded to a Br- anion, produces frequency shifts ΔνCH/CD, strongly different from the case of CIP formation. This difference can be used for IR/Raman spectroscopic differentiation of the type of solvated ion pairs of EmimBr or other related ILs.

Computational Analysis of Ion Clustering Statistics in Liquid Battery Electrolytes

The transport properties of liquid battery electrolytes critically depend on molecular-level solvation structures of ions. In contrast to the dilute regime where the majority of counterions are sufficiently separated spatially, in global or localized high-concentrated electrolytes (HCEs) counterions tend to form superstructures such as contact-ion pairs (CIPs) or aggregates (AGGs). The presence and relative population of such superstructures can drastically change the ionic transport behavior in liquid electrolytes. We have developed a computer program [1] that can efficiently perform analysis of ion clustering statistics from molecular dynamics simulations, complementary to experimental measurements. We have successfully applied our method to various systems, including (1) a prototypical concentrated liquid electrolyte (Li:EC:DEC) [2], and (2) a series of newly developed high-entropy liquid electrolytes [3]. In both cases, we find consistent agreements between our prediction and experimentally measured nanostructures and solvation strengths. We envision that our method would be widely applicable to generic structurally disordered systems.[1] Cohen et al., Journal of Open Source Software 8, 84 (2023)[2] Xie and Wang et al., Science Advances 9, eadc9721 (2023)[3] Kim and Wang et al. Nature Energy 8, 814–826 (2023)

Designing Interphases in Zn and Al Aqueous Electrolytes

This talk will cover two recent studies led by the Army Research Laboratory investigating interphase formation and cation solvation in zinc and aluminum aqueous electrolytes, respectively. In the former, two co-cations were carefully designed to offer distinct, complementary improvements in aqueous Zn electrolytes: a partially fluorinated pyrrolidinium cation effectively suppresses parasitic reactions such as hydrogen evolution (< 6 µA cm-2), and an ether-functionalized ammonium cation inhibits dendrite formation (almost 10 Ah cm-2 cumulative capacity, > 1 year, Zn||Zn). In the later, transient electrostatic hydrolysis of Al-OH2 ligands, without Al-OTf contact ion pairs, leads to insufficient reductive stability for rechargeable metal anodes. These contrasting systems provide helpful guidance for designing aqueous electrolytes with energy-dense multivalent metal anodes.

Role of ion pairs in model glycosylation reactions of permethylated glucosyl and xylosyl triflates

Elucidating the molecular mechanisms of chemical O-glycosylation remains a significant challenge in glycochemistry. This study examines the mechanism of the nucleophilic substitution reaction between glycosyl triflates, which are extensively used in studies of glycosylation mechanisms, and several acceptor alcohols. The investigation was conducted through a comparative analysis of permethylated glucosyl triflate GTf and its xylosyl counterpart XTf. The glycosylation reactions, conducted in dichloromethane using GTf and XTf with EtOH, tBuOH, and CF3CH2OH, exhibited diverse α/β selectivities depending on the types of donor and acceptor molecules used. Identifying a unified mechanism to explain this range of selectivities proved challenging. Notably, we observed a distinct trend wherein the addition of excess triflate salt (Bu4NOTf) had a more pronounced effect on the α/β selectivity in glycosylation reactions utilizing XTf compared to those using GTf. Quantum chemical calculations performed at the SCS-MP2//DFT(M06-2X) level, with explicit inclusion of five solvent molecules, showed that contact ion pairs arising from XTf were significantly more stable than those from GTf. These experimental and computational results strongly suggest that ion pairs play a more crucial role in the glycosylation process involving XTf than GTf. Additionally, our quantum chemical analyses clarified that the enhanced stability of the ion pairs from XTf was attributed not to the strength of the C-1−OTf bond within XTf but to the flexibility in the conformational changes of XTf's pyranosyl ring.

Dynamic Ion Correlations and Ion-Pair Lifetimes in Aqueous Alkali Metal Chloride Electrolytes.

Electrolytes are central to many technological applications, as well as life itself. The behavior and properties of electrolytes are often described in terms of ion pairs, whereby ions associate as either contact ion pairs (in which ions are "touching") solvent-separated ion pairs (in which ions' solvent shells overlap) or solvent-solvent-separated ion pairs (in which ions' solvent shells are distinct). However, this paradigm is generally restricted to statistically averaged descriptions of solution structure and ignores temporal behavior. Here we elucidate the time-resolved dynamics of these ion-ion interactions in aqueous metal chloride electrolytes using the partial van Hove correlation function, based on polarizable molecular dynamics simulations. Our results show that the existence and persistence of ion pairs in aqueous metal chloride electrolytes should not be assumed a priori, but in fact are ion specific features of the solution with lifetimes on subpicosecond time scales.

Uncovering the binding nature of thiocyanate in contact ion pairs with lithium ions.

Ion pair formation is a fundamental molecular process that occurs in a wide variety of systems, including electrolytes, biological systems, and materials. In solution, the thiocyanate (SCN-) anion interacts with cations to form contact ion pairs (CIPs). Due to its ambidentate nature, thiocyanate can bind through either its sulfur or nitrogen atoms, depending on the solvent. This study focuses on the binding nature of thiocyanate with lithium ions as a function of the solvents using FTIR, 2D infrared spectroscopy (2DIR) spectroscopies, and theoretical calculations. The study reveals that the SCN- binding mode (S or N end) in CIPs can be identified through 2DIR spectroscopy but not by linear IR spectroscopy. Linear IR spectroscopy shows that the CN stretch frequencies are too close to one another to separate N- and S-bound CIPs. Moreover, the IR spectrum shows that the S-C stretch presents different frequencies for the salt in different solvents, but it is related to the anion speciation rather than to its binding mode. A similar trend is observed for the anion bend. 2DIR spectra show different dynamics for N-bound and S-bound thiocyanate. In particular, the frequency-frequency correlation function (FFCF) dynamics extracted from the 2DIR spectra have a single picosecond exponential decay for N-bound thiocyanate and a biexponential decay for S-bound thiocyanate, consistent with the binding mode of the anion. Finally, it is also observed that the binding mode also affects the line shape parameters, probably due to the different molecular mechanisms of the FFCF for N- and S-bound CIPs.