Superalkali-alkaline earthide ion pairs of δ+(AM-HMHC)-AM'δ- (AM = Li, Na and K; AM' = Be, Mg and Ca) possessing large NLO responses and excellent electronic stabilities and alkalide characteristics: a DFT study.

To identify superalkali-alkaline earthide ion pairs, it's theoretically shown that, as a novel class of excess electron superalkali compounds, both chair and boat forms of (AM-HMHC)-AM' (AM = Li, Na, and K; AM' = Be, Mg, and Ca; HMHC = 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane) are good candidates. An attractive superalkali-alkaline earthide ion pair in δ+(AM-HMHC)-AM'δ- is firstly exhibited, which possesses alkaline-earthide characteristics and nonlinear optical response superior to similar M+(calix[4]pyrrole)M'- (M = Li, Na, and K; M' = Be, Mg, and Ca) with high stability. The electronic and vibrational second order hyperpolarizabilities and the frequency-dependent first hyperpolarizabilities of δ+(AM-HMHC)-AM'δ- are presented. For each pair of (AM-HMHC)-AM', the boat conformation is preferred to its chair one in the case of Hyper-Rayleigh scattering response (ßHRS). These alkaline earthides suggest prominently high ßHRS up to 2.59 × 104 a.u. (boat forms of δ+(Na-HMHC)-Caδ-). We expect that this work will inspire the preparation and characterization of these new alkaline earthides as high-performance NLO materials.

The experiences of adolescent solid organ transplantation recipients, parents, and healthcare professionals in healthcare transition: A qualitative systematic review.

PROBLEM: The transition from paediatric-centred to adult healthcare services in adolescent solid organ transplantation recipients is a period of increased risk and vulnerability, the issues related to healthcare transition have become key concerns to the healthcare community. ELIGIBILITY CRITERIA: Qualitative studies of any design and qualitative components of mixed method studies that explored the experiences of healthcare transition among adolescent solid organ transplant recipients, parents, and healthcare professionals were included. SAMPLE: Nine articles were finalised and included in the review. METHODS: A systematic review of qualitative studies was conducted. Databases searched were Scopus, PsycINFO, EMBASE, Web of Science, PubMed, CINAHL and ProQuest Dissertations and Theses. Studies published between the inception of respective database and December 2022 inclusive were considered. A three-step inductive thematic synthesis method outlined by Thomas and Harden was used to form descriptive themes and the 10-item Joanna Briggs Institute Critical Appraisal Checklist was utilised to appraise the quality of included articles. RESULTS: Two hundred and twenty studies were screened, and 9 studies published between 2013 and 2022 were included. Five analytical themes were generated: 'the struggle of being an adolescent with a transplant'; 'perceptions of transition'; 'the role of parents'; 'lack of transition readiness' and 'the need for better support'. CONCLUSIONS: Adolescent solid organ transplant recipients, parents, and healthcare professionals faced multiple challenges in the healthcare transition. IMPLICATIONS: Future interventions and health policies should provide targeted intervention strategies that address the barriers present in the healthcare transition to facilitate the optimization of the youth healthcare transition.

Can a molecular switch exist in both superalkali electride and superalkalide forms?

To combine both electride and alkalide characteristics in one molecular switch, it is shown herein that the phenalenyl radical and the M3 ring (M3-PHY, M = Li, Na, and K) stacked with parallel and vertical geometries are good candidates. The former geometry is the superalkali electride e-⋯M3+-PHY while the latter geometry is the superalkalide Mδ--M2(1-δ)+-PHY-. The superalkalide Mδ--M2(1-δ)+-PHY- may isomerize to the superalkali electride e-⋯M3+-PHY (M = Li, Na, and K) using suitable long-wavelength irradiation, while the latter may isomerize to the former with suitable short-wavelength irradiation. Also, applying suitable oriented external electric fields can drive the superalkalide Mδ-M2(1-δ)+-PHY- to change into the superalkali electride e-⋯M3+-PHY (M = Li, Na, and K). The differences in the static and dynamic first hyperpolarizability (ß0) values between them were also studied.

Switching from an electride-like molecule to the molecular electride K-F6C6H6 driven by an oriented external electric field.

The exploration of innovative molecular switches has resulted in large developments in the field of molecular electronics. Focusing on a single molecular switch with different forms exhibiting different electride features, potassium-atom-doped all-cis 1,2,3,4,5,6-hexafluorocyclohexane K-F6C6H6 was studied theoretically. It was found that an oriented external electric field can drive excess electron transfer from the region outside of the K atom to that outside of F6C6H6. Subsequently, the electride-like molecule K-F6C6H6 (1) switches into the molecular electride K-F6C6H6e- (3) through another electride-like molecule K-F6C6H6 (2). The static first hyperpolarizabilities (ß0) are increased over 12- and 5-fold when moving from 1 to 2 and 3, respectively. The rise of each ß0 value constitutes an order of magnitude improvement. Between them, the different ß0 values suggest that K-F6C6H6 is a good candidate for use as a multiple-response nonlinear optics switch. The order of the ß0 values of 1-4 for M-F6C6H6 (M = Li and Na) coincide with that of K-F6C6H6, also exhibiting a switch effect.

Distinctive Characteristics of Al7Li: A Superatom Counterpart of Group IVA Elements.

A new superatom of dual valence states, namely Al7Li, has been proposed to further enrich the "three-dimensional periodic table". It bears great resemblance to group IVA elements in many aspects. Chief among them is that Al7Li favors both +2 and +4 oxidation states, which makes it analogous to the heavier carbon-group elements. Al7Li is capable of forming stable ionic compounds with carbon, oxygen, and fluorine and forming covalent tetrahydride with hydrogen, just as how germanium, tin, and lead atoms combine with these elements to form stable molecules. The nearest atomic counterpart of Al7Li in group IV is probably Sn or Pb since their oxides and tetrahydrides share like characteristics.

Novel inorganic aromatic mixed-valent superalkali electride CaN3Ca: an alkaline-earth-based high-sensitivity multi-state nonlinear optical molecular switch.

Focusing on innovative high-performance single-pole double-throw nonlinear optical (NLO) molecular switches, two C3v configurations (1 and 3) and one D3h configuration (2) of bipyramidal CaN3Ca have been obtained by using quantum mechanical methods. Not only are 1, 2, and 3 alkaline-earth-based aromatic superalkalis, but they are also interesting electrides. The salt-like electronic structures of e-Ca2+N33-Ca2+ (1) and Ca2+N33-Ca2+e- (3) with localized redox centres are rare inorganic Robin-Day class II-type structures, and e0.5-Ca2+N33-Ca2+e0.5- (2) with a delocalized structure is a class III-type mixed-valent superalkali electride. Under a small external electric field of ±0.0110 a.u. (0.565 V Å-1), the short-distance hopping of Ca atoms in CaN3Ca from the D3h configuration with in-plane aromaticity to each C3v configuration with out-of-plane aromaticity brings about the long-range transfer of half an electron from one Ca atom to another. And, subsequently, a large dipole moment (µ0) and remarkable static first hyperpolarizability (ß0) occur. µz and ßzzz range from 0 (D3h, off form) to -12.1 or 12.1 D (C3v, on forms) and from 0 (D3h, off form) to -19 428 or 19 428 a.u. (C3v, on forms), respectively. These extremely large differences in µz and ßzzz values between the D3h and each of the C3v configurations confirm the potential of these inorganic aromatic Robin-Day-type superalkali electrides for applications in high-sensitivity multi-state nonlinear optical switches.

Electric field induced intra-molecular self-redox: superalkali Li3N3Mg as a candidate for NLO molecular switches.

A novel intra-molecular self-redox switch, Li3N3Mg, is constructed theoretically. Our investigation showed that a suitably oriented external electric field (OEEF) can drive a long-range excess electron transfer from Mg atoms to Li3 rings. And subsequently, an interesting intra-molecular self-redox from Li32+N33-Mg+ to Li3+N33-Mg2+ accompanying the large different electronic static first hyperpolarizability (ß) is exhibited. The increase of the ß value constitutes an order of magnitude improvement from Li32+N33-Mg+ (34 986 a.u.) to Li3+N33-Mg2+ (101 225 a.u.), which indicates that Li3N3Mg is a good candidate for a self-redox NLO molecular switch.

Coinage metalides: a new class of excess electron compounds with high stability and large nonlinear optical responses.

The possibility of using coinage metal atoms as excess electron acceptors is examined for the first time by designing a new class of M+-1-M'- (M = Li, Na, and K; M' = Cu, Ag, and Au) compounds termed "coinage metalides" on the basis of an intriguing Janus-type all-cis1,2,3,4,5,6-hexafluorocyclohexane (1) molecule. Under the large facial polarization of 1, the outermost ns1 electrons of alkali metal atoms can be transferred to coinage metal atoms, forming diffuse excess electrons around them. Consequently, the resulting M+-1-Cu- and M+-1-Ag- compounds exhibit significantly large nonlinear optical (NLO) responses. In particular, these novel M+-1-M'- compounds exhibit much higher stability (larger VIEs and Ec values) than that of the corresponding M+·1·M'- (M, M' = Li, Na, and K) alkalides. We hope this work could open up new possibilities for NLO material design by using coinage metal atoms as excess electron acceptors and, on the other hand, attract more experimental interest and efforts to synthesize such stable compounds in the laboratory.

On the Possibility of Using the Jellium Model as a Guide To Design Bimetallic Superalkali Cations.

The potential application of the jellium model as guidance in the rational design of bimetallic superalkali cations is examined under gradient-corrected density functional theory for the first time. By using Li, Mg, and Al as atomic building blocks, a series of bimetallic cationic clusters with 2, 8, 20, and 40 valence electrons are obtained and investigated. As the corresponding neutral clusters tend to lose one valence electron to achieve closed-shell states in the jellium model, these studied cations exhibit much lower vertical electron affinities (EAvert , 3.42-4.95 eV) than the ionization energies (IEs) of alkali metal atoms, indicating their superalkali identities. The high stability of these cationic clusters is guaranteed by their considerable HOMO-LUMO gaps and binding energies per atom. Moreover, the feasibility of using the designed superalkalis as efficient reductants to activate CO2 and N2 molecules and as stable building blocks to assemble ionic superatom compounds is explored. Therefore, this study may provide an effective method for obtaining various metallic superatoms with extensive applications on the basis of the simple jellium rule.

Boron-Substituted Coronene: Intriguing Geometric and Electronic Properties, and Large Nonlinear Optical Response.

By substituting boron atoms for selected carbon atoms of a graphene quantum dot (GQD) model, namely a coronene molecule, the substituent effect on its geometric and electronic structure, as well as nonlinear optical response has been systemically investigated in theory. Our computations reveal that the boron substitution leads to a similar noncentrosymmetric apophysis structure for the boron-substituted coronene in singlet and triplet states. Noticeably, due to the small energy difference of 2.5 kcal mol-1 between the singlet and triplet states, the boron-substituted molecule can easily be switched between the antiferromagnetic (singlet state) and ferromagnetic (triplet state) state by slightly changing the external conditions. Notably, the boron-substituted coronene exhibits a considerably large first hyperpolarizability of 36241 au, because boron substitution yields a raised structure with an intermediate singlet diradical character. Hence, it is expected that this study not only provides new insights for the boron-substituent effect on the structure and properties of graphene but also may promote practical applications of GQDs in the fields of spintronics and nonlinear optics.

Can Coinage Metal Atoms Be Capable of Serving as an Excess Electron Source of Alkalides with Considerable Nonlinear Optical Responses?

Alkalides, as a representative kind of excess electron compounds, have been demonstrated to be potential nonlinear optical (NLO) materials with large static first hyperpolarizabilities (ß0). The possibility of utilizing coinage metal atoms as a novel excess electron source to design a series of alkalides, i.e., (M@36adz)M' (M = Cu, Ag, and Au; M' = Li, Na, and K), was examined by density functional theory calculations. The alkalide characteristics of these compounds are guaranteed by their HOMOs and VIE values as well as NBO analysis. In particular, all proposed alkalides exhibit considerable first hyperpolarizabilities (ß0) up to 61 590 au, indicating that they can be considered as novel NLO molecules of high performance. Moreover, a larger cage-complexant has been considered, and the resulting (Ag+@TriPip222)K- alkalide possesses a remarkably large ß0 value of 180 068 au. We hope that this work will provide a new recipe for designing excess electron compounds and, on the other hand, attract more research interest and efforts in exploring new, unconventional alkalides.

Can Fluorinated Molecular Cages Be Utilized as Building Blocks of Hyperhalogens?

Based on the density functional theory for exchange-correlation potential, fluorocarbon molecular cages are investigated as building blocks of hyperhalogens. By utilizing C8 F7 as a ligand, a series of hyperhalogen anions, that is, M(C8 F7 )2 (-) (M=Li, Na, and K) and M(C8 F7 )3 (-) (M=Be, Mg, and Ca), are modeled. Calculations show that all the C8 F7 moieties preserve their geometric and electronic integrity in these anions. These anionic molecules possess larger vertical electron detachment energies (5.11-6.45 eV) than that of C8 F7 (-) , verifying their hyperhalogen nature. Moreover, it is also revealed that using larger fluorinated cage C10 F9 as ligands can bring about hyperhalogen anions with larger vertical electron detachment energies. The stability of these studied anions is determined by their large HOMO-LUMO gaps and positive dissociation energies of predetermined possible fragmentation pathways. It is hoped this study will provide an approach for the construction of new types of hyperhalogens and stimulate more research in superatom chemistry.

Stability and Nonlinear Optical Response of Alkalides that Contain a Completely Encapsulated Superalkali Cluster.

Guided by density functional theory (DFT) computations, a new series of superalkali-based alkalides, namely FLi2 (+) (aza222)K(-) , OLi3 (+) (aza222)K(-) , NLi4 (+) (aza222)K(-) , and Li3 (+) (aza222)K(-) were designed with various superalkali clusters embedded into an aza222 cage-complexant. These species possess diverse isomeric structures in which the encapsulated superalkalis preserve their identities and behave as alkali metal atoms. The results show that these novel alkalides possess larger complexation energies and enhanced hyperpolarizabilities (ß0 ) compared with alkali-metal-based and previous superalkali-based clusters. Especially, a prominent structural dependence of ß0 is observed for these studied compounds. Hence, the geometric factors that affect the nonlinear optical (NLO) response of such alkalides is elucidated in detail in this work. This study not only provides novel candidates for alkalides, it also offers an effective way to enhance the NLO response and stability of alkalides.

Theoretical Study of the Substituent Effects on the Nonlinear Optical Properties of a Room-Temperature-Stable Organic Electride.

Excess-electron compounds can be considered as novel candidates for nonlinear optical (NLO) materials because of their large static first hyperpolarizabilities (ß0 ). A room-temperature-stable, excess-electron compound, that is, the organic electride Na@(TriPip222), was successfully synthesized by the Dye group (J. Am. Chem. Soc. 2005, 127, 12416). In this work, the ß0 of this electride was first evaluated to be 1.13×106  au, which revealed its potential as a high-performance NLO material. In particular, the substituent effects of different substituents on the structure, electride character, and NLO response of this electride were systemically studied for the first time by density functional theory calculations. The results revealed that the ß0 of Na@(TriPip222) could be further increased to 8.30×106  au by introducing a fluoro substituent, whereas its NLO response completely disappeared if one nitryl group was introduced because the nitro-group substitution deprived the material of its electride identity. Moreover, herein the dependence of the NLO properties on the number of substituents and their relative positions was also detected in multifluoro-substituted Na@(TriPip222) compounds.

Does Alkaline-Earth-Metal-Based Superalkali Exist?

A series of MkF2k-1+ (M = Mg, Ca; k = 2, 3) cations have been theoretically investigated to make a new attempt to design superalkali species. As expected, most of these cations were identified as pseudoalkali or even superalkali cations in view of their low electron affinities (EAs). The stability of these cationic clusters is indicated by considerable HOMO-LUMO gaps and positive dissociation energies. More intriguingly, these alkaline-earth-metal-based cations have advantages over alkali-metal-based superalkalis in two aspects: (1) they possess much larger binding energy values; (2) they can keep the chemical stability along with the increasing cluster size. Therefore, it is proposed here that the alkaline-earth-metal atoms could partner with halogens to construct stable cations of low EA value, which may add new candidates to the superalkali family.

The polar 2e/12c bond in phenalenyl-azaphenalenyl hetero-dimers: Stronger stacking interaction and fascinating interlayer charge transfer.

An increasing number of chemists have focused on the two-electron/multicenter bond (2e/mc) that was first introduced to interpret the bonding mechanism of radical dimers. Herein, we report the polar two-electron/twelve center (2e/12c) bonding character in a series of phenalenyl-azaphenalenyl radical hetero-dimers. Interestingly, the bonding energy of weaker polar hetero-dimer (P-TAP) is dominated by the overlap of the two different singly occupied molecular orbital of radicals, while that of stronger polar hetero-dimer (P-HAP) is dominated by the electrostatic attraction. Results show that the difference between the electronegativity of the monomers plays a prominent role in the essential attribution of the polar 2e/12c bond. Correspondingly, a stronger stacking interaction in the hetero-dimer could be effectively achieved by increasing the difference of nitrogen atoms number between the monomers. It is worthy of note that an interesting interlayer charge transfer character is induced in the polar hetero-dimers, which is dependent on the difference between the electronegativity of the monomers. It is our expectation that the new knowledge about the bonding nature of radical hetero-dimers might provide important information for designing radical based functional materials with various applications.

On the feasibility of designing hyperalkali cations using superalkali clusters as ligands.

The possibility of using superalkali clusters instead of alkali atoms as ligands to design a class of cationic compounds, referred to as hyperalkali cations, has been examined by using gradient-corrected density functional theory. By taking typical superalkalis (FLi2, OLi3, and NLi4) as examples, a series of hyperalkali cations ML2+ [M = (super)halogen; L = superalkali] have been constructed and investigated. Calculational results show that all the superalkali moieties preserve their geometric and electronic integrity in these proposed cations. The stability of these studied cations is guaranteed by the strong ionic bonds between superalkali ligand and (super)halogen core, as well as their large highest occupied molecular orbital-lowest unoccupied molecular orbital gaps and positive dissociation energies. In particular, all these proposed cations possess lower vertical electron affinities (2.36-3.56 eV) than those of their corresponding cationic superalkali ligands, verifying their hyperalkali nature. We, therefore, hope that this study will provide an approach to obtain new species with excellent reducing capability by utilizing various superalkalis as building blocks.

A theoretical study on novel alkaline earth-based excess electron compounds: unique alkalides with considerable nonlinear optical responses.

On the basis of stable alkaline earth metal ammines, a series of M(NH3)6NaCl and M(NH3)6Na2 (M = Mg and Ca) excess electron compounds were theoretically constructed and studied by using the density functional theory. The electride or alkalide characteristics of these compounds are verified by their electronic structures, HOMOs, and small VIE values. It is worth noting that the M(NH3)6Na2 alkalides have novel electronic structures that contain double alkali metal anions. As expected, all the noncentrosymmetric M(NH3)6NaCl and M(NH3)6Na2 compounds possess considerable first hyperpolarizabilities (ß0) up to 123 050 au, which can be attributed to low excitation energies (ΔEs) and large oscillator strength (f0) of their crucial excited states. In addition, results reveal that the Ca(NH3)6-based species with lower ΔEs and larger transition moments (Δµ) show larger ß0 values compared with the corresponding Mg(NH3)6-based ones with similar geometries. This study may be significant in terms of designing excess electron compounds of new-type, especially alkalides with multiple alkali metal anions.

Electric field effects on the intermolecular interactions in water whiskers: insight from structures, energetics, and properties.

Modulation of intermolecular interactions in response to external electric fields could be fundamental to the formation of unusual forms of water, such as water whiskers. However, a detailed understanding of the nature of intermolecular interactions in such systems is lacking. In this paper, we present novel theoretical results based on electron correlation calculations regarding the nature of H-bonds in water whiskers, which is revealed by studying their evolution under external electric fields with various field strengths. We find that the water whiskers consisting of 2-7 water molecules all have a chain-length dependent critical electric field. Under the critical electric field, the most compact chain structures are obtained, featuring very strong H-bonds, herein referred to as covalent H-bonds. In the case of a water dimer whisker, the bond length of the novel covalent H-bond shortens by 25%, the covalent bond order increases by 9 times, and accordingly the H-bond energy is strengthened by 5 times compared to the normal H-bond in a (H2O)2 cluster. Below the critical electric field, it is observed that, with increasing field strength, H-bonding orbitals display gradual evolutions in the orbital energy, orbital ordering, and orbital nature (i.e., from typical π-style orbital to unusual σ-style double H-bonding orbital). We also show that, beyond the critical electric field, a single water whisker may disintegrate to form a loosely bound zwitterionic chain due to a relay-style proton transfer, whereas two water whiskers may undergo intermolecular cross-linking to form a quasi-two-dimensional water network. Overall, these results help shed new insight on the effects of electric fields on water whisker formation.

Lower the electron affinity by halogenation: an unusual strategy to design superalkali cations.

A new kind of cationic superatom compounds (M-F)(+) (M = OLi4, NLi5, CLi6, BLi7, and Al14) with low vertical electron affinities (VEA) has been designed based on the distinctive electronic structure of superalkaline-earth atom. The stability of the studied superatom architectures is guaranteed by strong M-fluorine interactions, considerable HOMO-LUMO gaps, as well as large dissociation energies. What is extraordinary is that fluorination plays an important role in lowering the VEA value of M(+) and enables the resulting (M-F)(+) fluorides to join the superalkali family. However, the same strategy does not work as well for the alkaline-earth atoms whose valence electrons are more tightly bound. The comparative study on (OLi4-X)(+) (X = F, Cl, Br) reveals that fluorination is more effective than chlorination and bromination to reduce the VEA value of the OLi4(+) cation. As for the (Al14-X)(+) species, there is no obvious dependence of VEA values on halogen atomic number.