Quantifying plasmonic characteristics of pure and alkali doped aluminium clusters

Study of plasmonic response of molecules and metal nanoclusters have drawn a considerable attention during recent times due to their various practical applications. In this study, the optical properties and the plasmonic response of our recently reported Al13+ cluster [Guin et al. Journal of Molecular Graphics and Modelling, 2020, 97, 107544] and its alkali doped counterparts [Guin et al. Journal of Molecular Modeling, 2021, 27, 235] have been investigated based on Transition dipole moment (TDM), Natural Transition Orbital (NTO) and transition inverse participation ratio (TIPR) indices. Recently these indices have been utilized by various scientists to characterize plasmonic transitions of molecular systems and metal nanoclusters. In TDM analysis, the magnitude of all the contributing TDMs associated with the molecular orbital transitions have been estimated along with the angles the individual dipoles make with the resultant dipole moment vector. A transition having at least two dominating TDM contributions along with phase matching indicate a collective or plasmonic transition. The collectiveness of orbital transitions is also corroborated through NTO and TIPR analysis. The effect of solvent medium on the optical properties and plasmonic transitions have also been studied using time dependent density functional theory in the conductor like polarizable continuum model (TDDFT-CPCM). The solvent has a strong impact on the optical properties as well as the plasmonic response of the clusters. The dielectric environment of the solvent red shifts and broadens the spectra with respect to that in the gas phase. Plasmon like excitations have been found for Li doped Al13+ cluster without solvent and Na doped Al13+ cluster in ethanol and THF.

Electric field-driven up-and-down motion of the flexible tail of Al13+ cluster system-a nano-scale flipper

CONTEXT

Dynamic metal nanoclusters have become a hot area of research in the field of nanoscience and nanotechnology due to their potential applications in micro devices. One such dynamic cluster is a quasi-planar ground state (GS) Al13+ cluster which exhibits an electric field driven up and down flipping motion of the flexible tail which oscillates with respect to the mean plane. A Car-Parrinello molecular dynamics (CPMD) simulation has been carried out to understand the nature of dynamics of the cluster. CPMD simulation study reveals that the flexible tail region of the Al13+ isomeric system (two ground states M1, M2 and a transition state TS connecting them) can be engaged in a systematic up down flipping motion by the application of a transverse electric field. A saw tooth electric field of amplitude 5.19 V/nm is sufficient to induce the up-and-down flipping oscillation of the cluster, which has an average oscillation frequency of around 20 THz. AIM, NICS and AdNDP analyses also have been carried out to understand the fluxional nature of the cluster from the electronic structural perspective. Electronic structural analysis of selected optimized intermediate states in the presence of transverse electric field has also been analyzed to correlate the electronic structure with the dynamic nature of the cluster.

METHODS

Single-point energies of all intermediate states between two minima of Al13+ clusters connected through a transition state cluster. Optimized geometries of Al13+ clusters in the presence of electric field of different strengths have been carried out by using the Gaussian 03 package. 6-311 + G(d) basis set and B3LYP hybrid density functional have been utilized for these studies. To establish the flipping motion, Car-Parrinello molecular dynamics (CPMD) has been performed using the cp.x module of the Quantum ESPRESSO 6.3.0 program package using the Perdew-Burke-Ernzerhof (PBE) functional, plane-wave basis set and ultrasoft pseudopotentials. ORTEP-3 and POV ray-3.7 software packages have been used for visualization and graphics generation. Atoms in molecule (AIM), Adaptive Natural Density Partitioning (AdNDP) analysis have been carried out using Multiwfn 3.7 program package.

Effect of alkali atom doping on the electronic structure and aromatic character of planar and quasi-planar Al13+ clusters

A set of three Al₁₃⁺ clusters, one perfectly planar, and two quasi-planar structures, have been recently reported by our group (Guin et al. Journal of Molecular Graphics and Modeling, 2020, 97, 107544). All three clusters possess bilateral symmetry with identical structural features-a set of ten aluminum atoms encircle a triangular core. The symmetry axis passes through one of the Al atoms of the central triangular core and two Al atoms located on the periphery at two opposite ends of the cluster. This set of three aluminum clusters is an example of a rare metallo-aromatic system where highly anti-aromatic islands are embedded within an aromatic sea. In the present study, we have explored the effect of doping alkali atoms (Li, Na, and K) at the positions of the Al atoms that lie on the symmetry axis of the cluster intending to understand the structural stability and the effect on the aromatic character as compared to the undoped parent clusters. Besides the electronic structural analysis, NICS and ELF studies have also been carried out to characterize the aromatic nature of the doped clusters. Interestingly, it has been found that even with the incorporation of the alkali atoms, the bilateral symmetry of the clusters remains intact, but the alkali atoms are pushed out of the original location toward the edge of the cluster, whereas the aluminum atoms remain grouped. The dipole moment of the clusters systematically increases, and the overall aromaticity of the cluster systematically decreases with the increase in the atomic number of the doped alkali atoms. Effect of alkali atom doping to Al₁₃⁺ cluster.

Electrically conductive Cu(II)-based 1D coordination polymer with theoretical insight

A nitro-functionalized Cu(ii)-based one-dimensional coordination polymer (1D CP) [Cu(nip)(4-phpy)2]n (1) (H2nip = 5-nitroisophthalic acid and 4-phpy = 4-phenylpyridine) was synthesized and characterized by elemental analysis, powder X-ray diffraction (PXRD) and single crystal X-ray diffraction (SCXRD). In the solid-state self-assembly of 1, two sets of weak intermolecular forces, CHπ interaction among the axially bound 4-phpy ligands and ππ interaction among bridging nip ligands from adjacent 1D coordination polymeric chains led to 3D supramolecular packing. Interestingly compound 1 exhibited electrical conductivity in the semiconducting regime and behaved as a Schottky barrier diode.

Stabilization of cyclic water tetramers and dimers in the crystal host of 2D coordination networks: electrical conductivity and dielectric studies

Construction of Zn(ii)-based 2D coordination polymers for selective recognition of water tetramers and dimers in crystal hosts and their exploitation in electrical studies.

Metal–ligand ring aromaticity in a 2D coordination polymer used as a photosensitive electronic device

14-Membered metal–ligand ring present in a photosensitive 2D coordination polymer, [Zn₂(fum)₂(4-phpy)₄(H₂O)₂] (H₂fum = fumaric acid and 4-phpy = 4-phenyl pyridine) shows aromatic character as evident by the nucleus-independent chemical shifts (NICS) calculation.

Copper(ii) induced oxidative modification and complexation of a schiff base ligand: synthesis, crystal structure, catalytic oxidation of aromatic hydrocarbons and DFT calculation

A mononuclear square planar complex [Cu^II(L^2f)], formed from a Schiff baseH2Laand Cu²⁺with the concomitant oxidation of two –CH₂OH groups to aldehyde, displayed catalytic oxidation of aromatic hydrocarbons.

Water-chloride and water-bromide hydrogen-bonded networks: influence of the nature of the halide ions on the stability of the supramolecular assemblies

Two compounds, namely, [TTPH(2)](Cl)(2) x 4 H(2)O (1) and [TTPH(2)](Br)(2) x 4 H(2)O (2), (TTP = 4'-p-tolyl-2,2':6',2''-terpyridine) were synthesized from purely aqueous media and characterized by physical techniques. In the solid-state structures of these compounds, interesting supramolecular assemblies are observed. In 1, an unusual staircase-like architecture of the tape of edge-shared planar water hexamer is of importance, where the chloride ions are at the two edges of the tape. In 2, the polymeric nature of the water-bromide assembly is of interest, where discrete open-cube water octamers are doubly bridged by bromide ions. Semiempirical and DFT calculations confirm that the nature of the anion indeed affects the topology of the water-halide assemblies. We conclude that the protonated [TTPH(2)](2+) species can act as appropriate receptors for halide ions, which in turn act as a matrix for the formation of polymeric 1D water-halide assemblies.

Robust recognition of malonate and 2-amino-4-picolinium in conjunction with M(II) as a triad (M = Ni/Co/Mn): role of this highly stable hydrogen-bonded motif in driving supramolecular self-assembly

The crystal lattice of the three isostructural compounds , (C(6)H(8)N(2)H)(2)[M(C(3)H(2)O(4))(2)(H(2)O)(2)].4H(2)O (C(6)H(8)N(2)H = protonated 2-amino-4-picoline, M = Ni/Co/Mn, C(3)H(4)O(4) = malonate dianion; hereafter, malonate) is formed by supramolecular 2D layers. Hydrogen-bonding, pi...pi and lone pair...pi interactions play crucial role in organizing monomeric [M(II)(mal)(2)(H(2)O)(2)] units into 2D sheets along the ab plane, through the self-association between two different supramolecular building blocks, namely a tetrameric water cluster including metal-coordinated water molecules, and R(2)(2)(8) and R(2)(2)(7) hydrogen-bonded recognition synthons between 2-amino-4-picolinium and malonate. DFT calculations clearly show that the robust 2-amino-4-picolinium/malonate hydrogen-bonded motif drives the self-assembly of the supramolecular network observed.