Photocrystallography is a technique used to determine light-induced structural changes accompanying formation of excited-state species, or other photoreaction products, in crystals via X-ray diffraction methods. Among others, it can be employed to investigate photo-linkage isomerism in the solid state. Photoswitchable compounds of this kind contain ambidentate ligands, e.g., NO₂, SCN or NO groups, which can bind to a metal centre in several different ways. Such linkage isomers can exhibit different physical properties such as: colour, density, or conductivity, which makes them interesting materials for various applications. Photoswitchable systems can be used in data storage devices, solar panels, as biological markers, etc.

The current project is dedicated to comprehensive investigations of a series of trinitrocobalt(III) coordination compounds[1] which are potential photoswitchable systems. According to literature cobalt nitrocomplexes may exhibit thermoswitchable properties[2], but there is in general very limited information about light-induced linkage isomerism of this group of compounds. In turn, three nitro groups attached to a metal centre interact in a crystal structure in different ways, which enables analyses of the crystal packing effect on photoswitchable properties. In the course of our research conditions assuring the most effective isomerisation reaction in the examined crystal systems were determined on the basis of multi-temperature X-ray diffraction, photocrystallographic and spectroscopic measurements results. Additionally, the influence of packing and intermolecular interactions on the isomerisation reaction was examined. The experimental findings were supported by theoretical computations.

It appeared that some of the studied compounds undergo the nitro group isomerisation reaction along with temperature changes, while the metastable-state form, nitrito isomer, may exist up to a relatively high temperature (about 240 K). Nevertheless the thermo-induced conversion usually does not exceed 30%. UV-Vis-light irradiation (230-660 nm) of the crystal samples elevates the observed conversion by only several percent. It was observed that the nitro groups engaged in relatively strong hydrogen bonds with the amine fragments of adjacent molecules do not undergo any transformation. Also, the stabilisation of the potential metastable-state form in the crystal structure is of great importance.

The authors thank A. Krówczyński and W. Buchowicz (Warsaw, Poland) for assistance during the syntheses of the examined compounds. The PRELUDIUM grant (2017/25/N/ST4/02440) of the NCN (Poland) is gratefully acknowledged for financial support. The X-ray diffraction experiments were carried out at the Department of Physics, UW, on a Rigaku Oxford Diffraction SuperNova diffractometer, which was co-financed by the EU within the European Regional Development Fund (POIG.02.01.00-14-122/09).

This research work reports the crystal structure, chemical bonding, cation distribution of three series of Cr³⁺ substituted cobalt ferrite with general formula Co_1-xCr_xFe₂O₄, Co_1+xCr_xFe_2-xO₄ and Co_1-xCr_xFe_2+xO₄ for x=0.0, 0.125, 0.25, 0.375 and 0.5, where first of the three series were calculated with stoichiometric and others were calculated with non-stoichiometric ratio. All three series of samples have been synthesized by solid-state reaction technique via ball milling for 12 hours and performing the sintering temperature of 1250o C. From the analysis of crystal structure studied by powder X-ray diffraction (XRD) technique, it is confirmed that the first two series of samples formed into a single phased cubic structure with a space group of Fd3m. But for the third series despite showing the cubic structure with a space group of Fd3m some impurity peaks of α-Fe2O3 have been observed which may due to the excess Fe. The cation distribution for the three series of samples has been estimated by the Reitveld analysis. The refinement result shows the occupancy of Cr has been found in both the tetrahedral site (A-site) and octahedral site (B-site) with exact ratio. The theoretical lattice constant has been calculated from the Reitveld refined data. For the first stoichiometric series after increasing of Cr concentration the increasing trend of experimental lattice constant related to theoretical lattice have been found but for the other two non-stoichiometric series, both types of lattice constant are decrease. Chemical bonding analyses made using Raman spectroscopic studies further confirm the cubic inverse spinel phase. Specific vibrational modes from the Raman data suggest a gradual change of inversion of the ferrite lattice with the increase of Cr concentration that is also confirm from Reitveld refined data.

Since the strain/structural defects strongly influence the physical properties [1], considerable work has been devoted for revealing their effects in both planar epitaxial layers and nanostructured materials [2]. Thus, the study of the strain field in nanomaterials represents a very important topic among different fields of applications. The quantitative analysis of the structural defects, as well as a deeper understanding of their source and nature became a highly desirable task associate to the further device development [3].

For this purpose, one of the common techniques used to detect the structural defects and quantify their density is X-ray diffraction (XRD). Recently, it was shown that the standard mosaic block or diffuse scattering models fail in the quantification of the structural defects in nanowires, and thus development of a new method became necessary [4]. In this paper, varying the incidence angle of the source, we get different penetration depths of the X-rays for different Si nanowire array morphologies – Figure 1.

Figure 1. The incidence angle of the source was varied to get different penetrationdepths of the X-rays. Recording X-ray profiles along ω and φ, we obtained bendingand torsion energy profiles.

Furthermore, implementing a new formalism based on these data, we obtained the bending and torsion profiles along z-direction, as well as the bending and torsion energy profiles. Attributing the entire energy lost to the dislocations’ formation at the coalescence regions we were able to estimate the dislocation density in nanowire arrays. The obtained results clearly suggest the close relationship between array morphology and the density of the edge and screw threading dislocations. Moreover, the impact of graphene quantum dots (GQDs) in the strain relaxation processes will be discussed.

[1] Lewis, R. B., Corfdir, P., Küpers, H., Flissikowski, T., Brandt, O. & Geelhaar, L. (2018). Nano Lett. 18, 2343–2350.

[2] Kaganer, V. M., Jenichen, B. & Brandt, O. (2016) Phys. Rev. Appl. 6, 064023.

[3] Mihalache, I., Radoi, A., Pascu, R., Romanitan, C., Vasile, E., Kusko, M. (2017) Engineering graphene quantum dots for enhanced ultraviolet and visible light p-Si nanowire-based photodetector, ACS Appl. Mater. Interf. 9, 29234-29247.

[4] Romanitan, C., Kusko, M., Popescu, M., Varasteanu, P., Radoi, A., Pachiu, C. (2019) J. Appl. Crystallogr., 52, 1077-1086.

The financial support was offered by the PN-III-P4-ID-PCE-2020-1712 project within PNCDI III, and Core Program PN 1916/2019 MICRO-NANO-SIS PLUS/08.02.2019.

Resolution of ferrocene and deuterated ferrocene conformations using dynamic vibrational IR spectroscopy

N. T. T. Tran¹, R. M. Trevorah¹, C. T. Chantler¹, D. R. T. Appadoo², F. Wang³

¹ School of Physics, The University of Melbourne, Parkville, Victoria 3010, Australia, ²Australian Synchrotron, 800 Blackburn Rd, Clayton Victoria 3168, Australia, ³Department of Chemistry and Biotechnology, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia

nicholast2@student.unimelb.edu.au

The signature of molecular vibrations and distortions in dynamic molecules gives a complex fingerprint which is insightful and can substantiate chemical hypotheses regarding molecular and conformer stability. Using high-accuracy experimental data of ferrocene (Fc) and deuterated ferrocene (dFc, Fc−d¹⁰) at temperatures from 7 K through to 388 K, we obtain complex spectral profiles which require an advanced reaction coordinate model to explain [1]. We obtain compelling evidence that the single conformer model (staggered D_5d or eclipsed D_5h) used to interpret and explain many experimental results on ferrocene is invalid. We also present compelling evidence that mixed conformer models are invalid, where ferrocene is represented by an effective dihedral angle between the cyclopentadienyl (Cp) rings; or by a mixture of Boltzmann populations of the two conformers. We find no evidence for single or mixed conformer models despite covering almost all conclusions from past literature for gas, solution or solid phase Fc [1].

A new principle based on the reaction coordinate is introduced using advanced spectroscopy and modelling for hypothesis testing, to articulate the nature of the potential surface, the reaction coordinate, and subtle conformational changes in dilute systems [1]. Theoretical calculations of the infrared spectra of D_5h and D_5d with the B3LYP/m6-31G(d) functional highlights a significant difference between Fc conformations around 450 – 500 cm^-1 [2] and early investigations provided key insight into the quantum dynamics of ferrocene [3]. A new methodology for obtaining defined uncertainties with high quality Fourier Transform Infrared (FTIR) measurements allow for quantitative hypothesis testing [4] for complex structural determination. Our experimental analysis shows that the lowest energy conformer is D_5h for both Fc and dFc at low temperatures, but as temperature increases, the population of occupied vibrational modes increases towards the D_5d conformation [1]. We obtain agreement of the model with the complex spectral evolution of profiles. These new techniques are sensitive discriminants of alternate models and chemical systems, which argues for wider application to other complex or impenetrable problems across fields arising for numerous other solutions, frozen or at room temperature.

[1] Trevorah, R.M., Tran, N.T.T., Appadoo, D.R.T., Wang, F., Chantler, C.T. (2020). Inorganica Chimica Acta, 506, 119491

[2] Mohammadi, N., Ganesan, A., Chantler C.T., Wang, F. (2012). Journal of Organometallic Chemistry. 713, 51-59

[3] Best, S.P., Wang, F., Islam, M.T., Islam, S., Appadoo, D., Trevorah, R.M., Chantler, C.T. (2016). Chemistry – A European Journal. 22 (50), 18019-18026

[4] Islam, M.T., Trevorah, R.M., Appadoo, D.R.T., Best, S.P., Chantler, C.T. (2017). Spectrochimica Acta -Part A: Molecular and Biomolecular Spectroscopy, 177, 86-92

Keywords: Infrared spectroscopy; Stereochemical analysis; Ferrocene; High-resolution FTIR

This research is supported by the AINSE Honours Scholarship Program.

For the first time the growth of a single GaAs nanowire (NW) was monitored by in-situ time resolved X-ray nano-diffraction (nXRD) using focused synchrotron radiation at beamline P09 of PETRA III storage ring (Hamburg) and a portable MBE chamber [1]. A particular position for nucleation and growth was selected within an array of holes with 5 micron pitch prepared on a lithography-free pre-patterned Si(111) substrate covered by 16nm thick oxide [2]. Exploiting a photon flux of 4·10⁹ Photons·s^-1 focused in a micro-beam of 2 x 6 micon² and probing the GaAs 111 Bragg reflection the first NW signal of above the background did appear about 24 minutes after opening the Ga and As shutters, corresponding to a NW length and diameter of about 45 nm and 28 nm, respectively. The time evolution of the NW signal could be monitored for 55 minutes up to the final length and diameter of about 2000nm and 45nm, respectively. Both parameters and the NW orientation with respect to the substrate normal were evaluated from the peak intensity and peak shape and position after background correction and separation of the NW signal from that of a parasitic island growing within the same probing volume. The final NW dimensions extracted from XRD analysis are in good agreement with ex-situ SEM data taken from the same NW after growth. In the experiment reported the observed time evolution of NW growth follows two subsequent stages: 1) dominant axial growth accompanied by unstable axial orientation of the NW followed by 2) increase of radial growth at stable axial orientation. Although successful proof of principle, quantitatively the experiment suffered from tiny fluctuations of the spatial position of the micro-beam during the entire growth cycle and/or limitations in the accuracy of angle settings.

Active research in the field of condensed matter and nanotechnology not only led to significant progress in understanding the mechanisms of formation of electrical polarization and magnetoelectric phenomena, but also showed the possibilities of creating new classes of devices based on a combination of magnetoelectric and piezoelectric properties. Meanwhile, macroscopic properties, such as multiferroism and piezoelectricity, are associated with local structural changes that occur under the influence of external perturbations. In a first step chosen crystal structures are analyzed by means of density functional theory (DFT) to validate the connection of external stress and internal change of lattice symmetry as well as atomic displacements. Among them are TeO₂, Li₂B4O₇, ZnO and SrTiO₃. Also in focus is the influence of oxygen vacancies on our structures. The research is currently accompanied by experiments in which standing acoustic waves are encoupled in crystal samples to change the structure parameters and particularly the structures' symmetry locally. Because the displacements are expected to be on the picometer scale, X-ray diffraction on forbidden reflections is applied to observe the induced effects. The obtained switching results can significantly widen the range of functional materials and can be directly used in modern technological applications.

Structures and luminescent properties of KGd_1−xEu_x(MoO₄)₂ (0≤x≤1) S. Posokhova, D. Deyneko, B. Lazoryak, V. Morozov ¹Lomonosov Moscow State University, GSP-1, Leninskie Gory, Moscow, 119991, Russian Federation posohovasm@gmail.com

Mo-based compounds with rare-earth elements are investigated as luminescent materials for photonic applications, such as phosphor converted LEDs (light-emitting diodes).¹ The influence of annealing temperature and Eu³⁺ concentration on the structure and luminescent properties of the KGd_1−xEu_x(MoO₄)₂ (0≤x≤1) was studied. Three polymorphs of KGd_1−xEu_x(MoO₄)₂ were present in the 923-1223 K range of annealing temperatures under ambient pressure: a triclinic α-phase, an incommensurately modulated monoclinic b–phase and an orthorhombic γ-phase with a KY(MoO₄)₂-type structure. The number and the character of phase transitions for KGd_1−xEu_x(MoO₄)₂ depend on the elemental composition. The formation of a continuous range of solid solutions with the triclinic α-KEu(MoO₄)₂–type structure and ordering of K⁺ and Eu³⁺/Gd³⁺ cations were observed only for the α-KGd_1−xEu_x(MoO₄)₂ prepared at 923 K.

The luminescent properties of KGd_1−xEu_x(MoO₄)₂ prepared at different annealing temperature were studied and related to their different structures. All samples’ emission spectra exhibit an intense red emission originating from the Eu³⁺⁵D₀→⁷F₂ transition. The maxima of the ⁵D₀ → ⁷F₂ integral emission intensities were found under excitation at, respectively, λ_ex = 300 nm and λ_ex = 395 nm for triclinic scheelite-type α-KGd_0.6Eu_0.4(MoO₄)₂ and for monoclinic scheelite-type β-KGd_0.4Eu_0.6(MoO₄)₂ prepared at 1173 K. The latter shows the brightest red light emission among the KGd_1−xEu_x(MoO₄)₂ phosphors. The maximum and integral emission intensity of β-KGd_0.4Eu_0.6(MoO₄)₂ in the ⁵D₀→⁷F₂ transition region is by ~20% higher than that of the commercially used red phosphor of Gd₂O₂S:Eu³⁺. β-KGd_0.4Eu_0.6(MoO₄)₂ with the incommensurately modulated structure is very attractive to be applied as a near-UV convertible red-emitting phosphor for LEDs.

Figure 1. Comparative integral intensity of the ⁵D₀ → ⁷F₂ emission of different Eu³⁺ concentration for KGd_1−xEu_x(MoO₄)₂ phases prepared at different annealing temperatures and after different excitations. All intensities are normalized on the integral intensity value of α-KEu(MoO₄)₂ (I_int). [1] Li, J.; Yan, J.; Wen, D.; Khan, W.U.; Shi, J.; Wu, M.; Sua, Q.; Tanner, P.A. Advanced red phosphors for white light-emitting diodes. J. Mater. Chem. C. 2016, 4, 8611-8623

Keywords: structure; phase transitions; molybdate; luminescence; Eu³⁺; LEDs.

This research was supported by the Russian Foundation for Basic Research through grants 18-03-00611.

Schiff bases have a remarkable coordinative capability with a wide range of transition metals, making their application in various fields of chemistry of great importance as well as a key research area.¹ The ability of Schiff bases to coordinate with many different transition metals and to stabilize different oxidation states of the metals cause Schiff bases and their metal complexes to be effective catalysts.² The ease of Schiff base preparation also allows for innumerable different modifications and functionalizations to be done to promote their catalytic activity. Many Schiff base complexes are thermally and moisture-stable and are therefore useful catalysts in high-temperature reactions.³ It has also been found that these Schiff base ligands, upon complexation with transition metals, can play an important biological role in that they have anti-bacterial, anti-fungal, anti-cancer, antioxidant, anti-inflammatory and antiviral activity.⁴

Research and development in the field of fluorescence and particularly the design and synthesis of fluorescent chemosensors have grown tremendously in the last 50 years.⁵ The application of fluorescent chemosensors is important in biochemical, physiological, pharmacological and environmental studies with the scope of analytes including cations, anions, small neutral molecules and biomacromolecules. Schiff bases have found application in the field of fluorescence with numerous studies showing its efficiency, especially in the development of fluorescent chemosensors. The photoluminescence feature of Schiff base ligands also finds application in the development of radiopharmaceuticals.⁶ In this field, cellular imaging is used to identify possible compartmentalization of drugs within cells as well as the incorporation and distribution thereof within cells and the information obtained is used to elucidate the biochemical mechanism of these drugs.⁷ A recent study showed the possibility of incorporating a Schiff base into targeting radiopharmaceuticals where it acts as a linker/chelating agent to connect the biomolecule to the radionuclide. The ease of its synthesis and structure-manipulation to contain a variety of functional groups, as well as its possible cellular imaging abilities (due to its photoluminescence), made Schiff bases excellent candidates for this application.

Protein crystallography has proven vital in the field of drug design.⁸ The molecular structure of the protein can be obtained which is necessary for the design of a suitable drug. Protein crystallography further provides structural information regarding protein-ligand interactions and subsequent insight into required ligand-modifications for optimal pharmacological action on molecular targets.

For this study, the main objective is to synthesize and fully characterise various sterically and electronically modified Schiff base ligands (IR, NMR, UV/Vis and single-crystal X-ray crystallography) followed by coordination to transition metals of Rh, Re, Pt, Pd, Co and Ni. Thereafter to perform luminescent analysis and protein crystallization on these ligands and complexes to observe protein-ligand interactions. These organometallic complexes can also potentially be utilized as catalysts in homogeneous catalysis, namely carbonylation, hydroformylation and homologation.

Seven unique N,O-bidentate Schiff base ligands were synthesized and fully characterized using IR, NMR and UV/Vis. Multiple crystallization experiments were conducted. The crystal structures of four of the Schiff base ligands were obtained. Experiments to coordinate the ligands with Co(II), Ni(II), Cu(II) and Zn(II) were performed. Crystal structures of three of these organometallic complexes (two Ni-complexes and one Co-complex) were obtained using single-crystal X-ray crystallography. Luminescence studies on all ligands were conducted, four of which showed strong luminescence at 365 nm while the remaining three appeared dark at 365 nm. The results will be described in this presentation.

Since the development of the ^99mTc generator in the 1950’s and subsequent introduction of the ¹⁸⁸Re generator the development of technetium and rhenium radiopharmaceuticals has been of great interest to the scientific community.¹ Our research is focused on the development of a target specific radiopharmaceutical. [2] In particular we are interested in using chemical functionalities of biological significance as targeting vectors for model radiopharmaceuticals wherein potential theranostic applications are considered using both ^99mTc and ¹⁸⁸Re nuclides in a cluster complex. [3]

This study is focused on the fac-[Re(CO)₃]⁺ moiety [4–6] and utilizes the {2+1} mixed ligand concept, [7] which gives the freedom to coordinate a bioactive site-containing molecule as either a monodentate or bidentate ligand to the fac-[Re(CO)₃]⁺ core. Model complexes were synthesised, aimed at improving the linking between a biomolecule and the metal centre. Additionally investigations into altering the nuclearity of metal complexes for the development of theranostic radiopharmaceuticals will be discussed. In order to understand the possible pathways that a particular drug may partake in during administration, kinetic investigations were considered important. [8] For this reason we have conducted substitution kinetics to further our understanding on how these metal complexes could behave in vivo. Furthermore we will focus on exploring the weak interactions such as hydrogen bonding as observed in small molecule crystal structures and coordinate to a protein residue in an attempt to understand and predict how and where these compounds will interact in a biological setting.

[1] Jürgens, S.; Herrmann, W. A.; Kühn, F. E. (2014) J. Organomet. Chem. 751, 83–89.

[2] Top, S.; Hafa, H. El; Vessières, A.; Jaouen, G.; Quivy, J.; Vaissermann, J.; Hughes, D. W.; McGlinchey, M. J.; Mornon, J. P.; Thoreau, E. (1995) J. Am. Chem. Soc. 117, 8372–8380.

[3] Mokolokolo, P. P.; Frei, A.; Tsosane, M. S.; Kama, D. V; Schutte-smith, M.; Brink, A.; Visser, H. G.; Meola, G.; Alberto, R.; Roodt, A. (2018) Inorganica Chim. Acta 471, 249–256.

[4] Alberto, R.; Schibli, R.; Schubiger, P. A. (1996) Polyhedron 15, 1079–1089.

[5] Jacobs, F. J. F.; Brink, A. (2020) Zeitschrift für Krist. - New Cryst. Struct. 236, 253–255.

[6] Jacobs, F. J. F. FUNCTIONALISED NITROGEN BASED LIGANDS IN DINUCLEAR RHENIUM MODEL RADIOPHARMACEUTICALS, Univeristy of the Free State, 2020. (Supervisors Brink, A. & Venter, G.J.S.)

[7] Mundwiler, S.; Kundig, M.; Ortner, K.; Alberto, R. (2004) Dalton Trans. 99, 1320–1328.

[8] Tonge, P. J. (2018) ACS Chem. Neurosci. 9, 29–39.

Oxide nanophosphors are widely explored for their utility in lasing and solid-state lighting, owing to the presence of lattice defects [1-4]. SrZnO₂ nanophosphors, synthesized by combustion synthesis using monoethanolamine fuel, are found to be exhibiting energy dependent tunable luminescence. HR-TEM images indicated about presence of defects in the lattice, the effect of which was observed on local electronic structure of the material also. Experimental X-ray absorption near edge structure at Zn and Sr K-edges were studied using simulated absorption spectra for defect free structure based on full multiple scattering theory. The presence of extra feature in Zn K-edge and broadened near edge structure at Sr K-edge in experimental spectra were supposed as signature of lattice distortion due to presence of lattice defects in system. Extended X-ray absorption fine structure analysis of first coordination shell around Zn and Sr absorbers indicated oxygen vacancies in the system, accompanied by decreased Zn-O bond lengths and increased Sr-O bond lengths. The observed structure disorder was believed to be responsible for formation of band tail states with Urbach energy 247.1 meV near the edges of optical band gap of 3.95 eV. Thermoluminescence glow curve analysis obtained at varying gamma irradiation revealed presence of shallow and deep defect states in the band gap. A collective consequence of all the results were summed up in band model, shown in Fig. 1, depicting blue emission due to radiative recombination from shallow defect state to tail states above valence band and white emission due to radiative transition between shallow to deep defect states in the forbidden gap. The energy dependent dual visible emission in SrZnO₂ is expected to be utilized for various technological applications.

The importance of transition-metal switchable compounds of real-life applications is rapidly increasing, thus investigations of nickel (II) organic complexes in which metal centre is coordinated by molecular fragments that can exist in multiple isomeric forms (e.g. NO₂, SO₂ , N₂) cannot be overestimated. Hence, the current study was devoted to obtain novel promising photoswitchable materials (Fig.1a) characterized by desired reversibility, high conversion percentage and stability.

The designed model compound is shown in Figure 1. As can be seen, the nickel(II) centre is coordinated by the ambidentate nitro ligand and the (N,N,O)-donor moiety. For the purpose of thorough analysis of its photoswitchable properties and the isomerisation reaction features, IR spectroscopy, multi-temperature and photocrystallographic XRD experiments were conducted and supported by computational investigations. Optimal photoisomerisation conditions were determined on the basis of multi-temperature XRD and spectroscopic experiments.

The studied complex crystallises in the P-1 space group with one molecule in the asymmetric unit. Upon visible light irradiation the nitro isomer transforms to the endo-nitrito form reaching about 25% conversion in the form of a single crystal sample and 100% as a powder according to the IR spectroscopy results. The generated metastable state species exist up to 200 K. Intermolecular contacts, linkage isomers’ relative stability, reaction cavity volumes and crystal packing were thoroughly investigated to understand the nitro-nitrito linkage isomerisation mechanism.

The importance of transition-metal switchable compounds of real-life applications is rapidly increasing, thus investigations of nickel (II) organic complexes in which metal centre is coordinated by molecular fragments that can exist in multiple isomeric forms (e.g. NO₂, SO₂ , N₂) cannot be overestimated. Hence, the current study was devoted to obtain novel promising photoswitchable materials (Fig.1a) characterized by desired reversibility, high conversion percentage and stability.

The designed model compound is shown in Figure 1. As can be seen, the nickel(II) centre is coordinated by the ambidentate nitro ligand and the (N,N,O)-donor moiety. For the purpose of thorough analysis of its photoswitchable properties and the isomerisation reaction features, IR spectroscopy, multi-temperature and photocrystallographic XRD experiments were conducted and supported by computational investigations. Optimal photoisomerisation conditions were determined on the basis of multi-temperature XRD and spectroscopic experiments.

The studied complex crystallises in the P-1 space group with one molecule in the asymmetric unit. Upon visible light irradiation the nitro isomer transforms to the endo-nitrito form reaching about 25% conversion in the form of a single crystal sample and 100% as a powder according to the IR spectroscopy results. The generated metastable state species exist up to 200 K. Intermolecular contacts, linkage isomers’ relative stability, reaction cavity volumes and crystal packing were thoroughly investigated to understand the nitro-nitrito linkage isomerisation mechanism.

The authors thank the PRELUDIUM grant (2017/25/N/ST4/02440) of the National Science Centre in Poland and the Inter-Faculty of Individual Studies in Mathematics and Natural Sciences, University of Warsaw, for financial support. The Wrocław Centre for Networking and Supercomputing (grant No. 285) is gratefully acknowledged for providing computational facilities. The in-house X-ray diffraction experiments were carried out at the Department of Physics, University of Warsaw, on Rigaku Oxford Diffraction SuperNova diffractometer, which was co-financed by the European Union within the European Regional Development Fund (POIG.02.01.00-14.122/09)

The chemistry of hybrid halometallates attracting increasing interest of researchers. The interest is associated with a number of physical properties inherent in this class of compounds, such as semiconductivity, photochromism, luminescence, etc. One of the prominent representatives of this class are hybrid halosmuthates - promising candidates for solar energy.

The crystal engineering of halobismuthates to prepare the substances with given anion seems to be the highest priority. In this work we report the synthesis and crystal structure of organic-inorganic hybrid halobismuthates of 1,4’-bipyridine cations. The structure and optical properties of the isolated compounds were studied. The novel anion [Bi₆I₂₆]^6- was discovered in the structure [PyPy]₂[PyPyH]₂Bi₆I₂₆. The DFT calculation of this structure showed the total energy of six Bi-I interactions in BiI₆ polyhedra remains almost constant for all crystallographically independent bismuth atoms. In this case the correlation between Bi-I bond length values and interaction energy values (R² = 0.9993) was performed. Using this correlation, the statistical analysis of Bi-I bond energies in 262 iodine-bismuthate anions found in the CCDC database (ver 5.40 September 2019) was performed. The total energy of six Bi-I bonds in BiI₆ polyhedra forming various iodine-bismuthate anions does not depend on the structure of the anions was shown. The data suggest the main factor affecting the formation of the final structure of hybrid iodobismuthates is not the energy benefit of the formation of one form or another of a bismuth-containing anion, but a combination of weak intermolecular interactions. In this fact the synthesis of such compounds with a given anion is impossible.

The interaction between metals in homo- and heterometallic complexes are known as metallophilic interactions. The photoluminescent study of metal complexes with metallophilic interactions produces promising results. [1] [2] Bis(diphenylphosphine)amine (PNP) ligand systems were identified as the ligands of choice because they consist of a parameter for the measurement of its steric bulk on the nitrogen atom. The parameter is known as the Tolman based cone angle as introduced by Cloete et al. [3] The influence of the steric bulk on the catalytic activity of the ligand was investigated by Cloete et al. [3] A wide range of steric substituents are identified and a collection of dimeric metal complexes synthesised. The photoluminescent properties of these complexes were compared as a parameter for the metallophilic interactions present in the complexes. The influence of solvents is investigated and solid state luminescence is used for the luminescence study. Firstly the formation of exciplexes are possible with a semi-coordination between the solvent and the complex. [4] The solvent interaction and quenching effects correlate to photoluminescent data from other studies. [5] [6] The structural aspects are compared using single crystal X-ray diffraction analysis and DFT calculations. This makes the comparison between theoretical and experimental data possible. The manipulation of the metal to metal distance is observed and a correlation drawn between the metal to metal distance and the steric bulk of the ligand system. Figure 1 illustrates two metal complexes with metallophilic interactions.

[1] N. Kathewad, N. Kumar, R. Dasgupta, M. Ghosh, S. Pal & S. Khan. (2019), Dalton Transactions, 48, 7274.

[2] S. Pal, N. Kathewad, R. Pant & S. Khan. (2015), Inorg. Chem., 54, 10172.

[3] N. Cloete, H.G. Visser, I. Engelbrecht, M. Overett, W. Gabrielli, A. Roodt. (2013), Inorg. Chem., 52, 2268.

[4] A. Penney, V. Sizov, E. Grachova, D. Krupenya, V. Gurzhiv, G. Starova & S. Tunik. (2016), Inorg. Chem. 4720.

[5] I. Strelnik, V. Gurzhiy, V. Sizov, E. Musina, A. Tunik, E. Grachova, (2016), Cryst. Eng. Comm., 18, 7629.

[6] Z. Lei, J-Y. Zhang, Z-J. Guan, Q-M. Wang, (2017), Chem. Commun., 53, 10902.