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Over the past few decades, the scenario of luminescent transition metal complexes has experienced a great blossom. In this context, the spotlight of the research program that I have carried out in my PhD studies has been dealing with the design, the preparation and the study of the photophysical properties of a new series of luminescent metal complexes containing anionic ligands such as 5-aryl tetrazolates [R-CN4]-. The choice of this specific class of nitrogen rich derivatives stemmed from the observation of how these ligands can effectively rule the luminescent output of the corresponding Ru (II) polypyridyls, Ir(III) bis-cyclometalates and tris carbonyl Re(I)-diimine complexes. In particular, the synthetic versatility of tetrazolate derivatives combined with the peculiar sensitivity to electrophilic additions – both permanent and reversible - that is displayed by the coordinated tetrazolate ring constitute the background for the further exploitment of their coordination chemistry and their applicative panorama. On these basis, we have recently prepared the first examples of anionic Ir(III) tetrazolate complexes and new Re(I)-based species containing ditopic tetrazolate ligands, with particular attention dedicated to their use as components for white light emitting Ir(III)-based ion pairs (“soft salts”), for covalently linked Ir(III)-Re(I) dyads, and for the investigation of Re(I) tetrazolate complexes as luminescent chemosensors. Moreover, studies which have dealt with Ru(II) tetrazolate complexes, pointed the way for the preparation of tetrazole –based Dye Sensitized Solar Cells.

Objective: To provide the first Italian data on pathogens causing early-onset sepsis (EOS) and their antimicrobial susceptibility, after the successfully prevention of Group B streptococcus (GBS) EOS. Methods: Retrospective area-based cohort study from Emilia-Romagna (Italy). Cases of EOS registered (from 2009 to 2012) in all gestational age neonates were reviewed. Results: Live births (LB) numbered 146 682. Ninety neonates had EOS and 12 died (incidence rates of 0.61 and 0.08/1000 LB, respectively). EOS and mortality were the highest among neonates with a birth weight n = 27, 0.18/1000 LB) and Escherichia coli (n = 19, 0.13/1000 LB). Most infants affected by E. coli EOS were born preterm (n = 13), had complications (n = 4) or died (n = 7). Among 90 isolates tested, only 3 were resistant to both first line empirical antibiotics. Multivariate logistic regression analysis showed that low gestational age, caesarean section and low platelet count at presentation were significantly associated with death or brain lesions (area under ROC curve = 0.939, H-L = 0.944, sensitivity 76.0%, specificity 90.7%). Conclusions: GBS slightly exceeds E. coli as a cause of EOS. However, E. coli is the prominent cause of death, complications and in most cases affects preterm neonates. Empirical antimicrobial therapy of EOS seems appropriate.

Herein we report the easy incorporation of brightly phosphorescent cationic iridium(III) tetrazole complexes into a silica based matrix via an easily scalable colloidal process. For this purpose, two cationic Ir(III) emitters bearing 5-aryl tetrazole ligands (R-CN4) were selected: blue [F2IrPTZ-Me]+ (C^N = F2ppy; N^N = PTZ-Me – 2-(2-methyl-2H-tetrazol-5-yl)pyridine) and red [IrQTZ-Me]+ (C^N = ppy; N^N = QTZ-Me – 2-(2-methyl-2H-tetrazol-5-yl)quinoline). The cationic complexes were readily adsorbed to negatively charged silica nanoparticles and trapped in the sol–gel matrix. The sol-to-solid phase transfer was performed by using an innovative spray-freeze-drying technique, leading to the formation of phosphorescent solid micro-granules. The structural and optical characterisation of the Ir(III) complexes together with SiO2 nanoparticles, nanosols (Ir@SiO2) and powders (Ir@SiO2 powders), revealed how the presence of the Ir(III)-based complexes did not alter the morphology of the colloidal silica or granulated phases. Moreover, the silica matrix did not interfere with the optical properties of the embedded complexes. The distribution of [F2IrPTZ-Me]+ and [IrQTZ-Me]+ in the spray-freeze-dried powders was qualitatively evaluated by fluorescence microscopy, revealing how the luminescent particles were homogeneously dispersed all over the silica matrix. Interestingly, in aqueous solution the release of complex [F2IrPTZ-Me]+ from the corresponding Ir@SiO2 powder is almost negligible, therefore suggesting that a strong interaction occurs between the host–silica matrix and the Ir(III) guest complex., This project has benefited from the EU-H2020 research program under grant agreement no. 654360 and has benefited from the access provided by the Fundacio Institut Català de Nanociència y Nanotecnologia – ICN2 – Barcelona (Spain) and the Foundation for Research and Technology Hellas – FORTH – Heraklion (Greece) within the framework of the NFFA-Europe Transnational Access Activity. The ICN2 is funded by the CERCA programme (Generalitat de Catalunya) and is supported by the Severo Ochoa programme of the Spanish Ministry of Economy, Industry and Competitiveness (MINECO, grant no. SEV-2013-0295). The authors wish to thank the Italian Ministry of Education, University and Research (MIUR) for their financial support (PRIN project: Towards a Sustainable Chemistry: Design of Innovative Metal–Ligand Systems for Catalysis and Energy Applications).

The stereodynamic properties of amino bis-mesityl-boranes bearing carbazole and benzocarbazole as donor heterocycles have been investigated by dynamic NMR analysis and simulated by DFT calculations. The π-contribution to the B–N bond has been estimated to be 24 kcal mol−1 when carbazole is the donor heterocycle, while a value of 21.7 kcal mol−1 has been found for the benzocarbazole series. Two rotational barriers were determined for the B–N bond, the lower one (11.1–16.9 kcal mol−1) leading to conformational enantiomers, and the higher one (21.0–24.0 kcal mol−1) likely being responsible for the E-Z isomerization in compounds bearing different aryl rings bound to the boron atom. It has been shown that both kinds of dynamic rearrangements involve a correlated motion of all the three rings. The difference in the ground state geometries and the different π-contributions led to pronounced variations in the fluorescence spectra, due to different geometric rearrangements in the TICT excited state. Stokes shifts larger than 10 000 cm−1 were observed in the carbazole series, with quantum yields up to 50%. It has been found that the π-contribution to the B–N bond in the excited state is still significant, with B–N isomerism likely not taking place on the ns scale.

The versatile rhenium complex [ReCl(CO)3(bpyC[triple bond, length as m-dash]CH)] (HC[triple bond, length as m-dash]Cbpy = 5-ethynyl-2,2'-bipyridine) is used to generate a series of bimetallic complexes through the hydrometallation of [MHCl(CO)(BTD)(PPh3)2] (M = Ru, Os; BTD = 2,1,3-benzothiadiazole). The ruthenium complex [Ru{CH[double bond, length as m-dash]CH-bpyReCl(CO)3}Cl(BTD)(CO)(PPh3)2] was characterised structurally. Ligand exchange reactions with bifunctional linkers bearing oxygen and sulfur donors provide access to tetra- and pentametallic complexes such as [{M{CH[double bond, length as m-dash]CH-bpyReCl(CO)3}(CO)(PPh3)2}2(S2CNC4H8NCS2)] and Fe[C5H4CO2M{CH[double bond, length as m-dash]CH-bpyReCl(CO)3}(CO)(PPh3)2]2. The effect of the group 8 metal on the photophysical properties of the rhenium centre was investigated using the complexes [Ru{CH[double bond, length as m-dash]CH-bpyReCl(CO)3}Cl(BTD)(CO)(PPh3)2] and [M{CH[double bond, length as m-dash]CH-bpyReCl(CO)3}{S2P(OEt)2}(CO)(PPh3)2] (M = Ru, Os). This revealed the quenching of the rhenium-based emission in favour of weak radiative processes based on the Ru and Os centres. The potential for exploiting this effect is illustrated by the reaction of [Ru{CH[double bond, length as m-dash]CH-bpyReCl(CO)3}Cl(CO)(BTD)(PPh3)2] with carbon monoxide, which results in a 5-fold fluorescence enhancement in the dicarbonyl product, [Ru{CH[double bond, length as m-dash]CH-bpyReCl(CO)3}Cl(CO)2(PPh3)2], as the quenching effect is disrupted.

The bis-tetrazolate dianion [1,2 BTB](2-), which is the deprotonated form of 1,2 bis-(1H-tetrazol-5-yl)benzene [1,2-H2BTB], is for the first time exploited as an ancillary N^N ligand for negatively charged [Ir(C^N)2(N^N)](-)-type complexes, where C^N is represented by cyclometalated 2-phenylpyridine (ppy) or 2-(2,4-difluorophenyl)pyridine (F2ppy). The new Ir(iii) complexes [Ir(ppy)2(1,2 BTB)]- and [Ir(F2ppy)2(1,2 BTB)]- have been fully characterised and the analysis of the X-ray structure of [Ir(ppy)2(1,2 BTB)]- confirmed the coordination of the [1,2 BTB](2-) dianion in a bis chelated fashion through the N-atoms adjacent to each of the tetrazolic carbons. Both of the new anionic Ir(iii) complexes displayed phosphorescence in the visible region, with intense sky-blue (λmax = 460-490 nm) or aqua (λmax = 490-520 nm) emissions originating from [Ir(F2ppy)2(1,2 BTB)]- and [Ir(ppy)2(1,2 BTB)]-, respectively. In comparison with our very recent examples of anionic Ir(iii)tetrazolate cyclometalates, the new Ir(iii) tris chelate complexes [Ir(F2ppy)2(1,2 BTB)]- and [Ir(ppy)2(1,2 BTB)]-, display an improved robustness, allowing the study of their reactivity toward the addition of electrophiles such as H(+) and CH3(+). In all cases, the electrophilic attacks occurred at the coordinated tetrazolate rings, involving the reversible - by a protonation deprotonation mechanism - or permanent - upon addition of a methyl moiety - switching of their global net charge from negative to positive and, in particular, the concomitant variation of their photoluminescence output. The combination of the anionic complexes [Ir(F2ppy)2(1,2 BTB)]- or [Ir(ppy)2(1,2 BTB)]- with a deep red emitting (λmax = 686 nm) cationic Ir(iii) tetrazole complex such as [IrTPYZ-Me]+, where TPYZ-Me is 2-(2-methyl-2H-tetrazol-5-yl)pyrazine, gave rise to two fully Ir(iii)-based soft salts capable of displaying additive and O2-sensitive emission colours, with an almost pure white light obtained by the appropriate choice of the ionic components.

Within the general framework of our past and current studies dealing with the investigation of the photophysical properties and the biological behavior of the family of tetrazolato and tetrazole Re(i) complexes, we have endeavored to investigate their potential in the luminescent staining of proteins purified by acrylamide gel electrophoresis. With the aim to provide the first examples of luminescent Re(i) complexes to be exploited for this specific purpose, we have designed and prepared four new Re(i)-based species with the general formula fac-[Re(CO)₃(N^N)(Tph)]²⁻/⁰, where Tph is the 5-(phenyl)tetrazolato anion and N^N is in turn represented by bathophenanthroline disulfonate (BPS), bathocuproine disulfonate (BCS) or by the SO₃-free bathocuproine (BC). In this latter case, the neutral complex fac-[Re(CO)₃(BC)(Tph)] served as a model species for the characterization of the former disulfonate complexes. Its cationic analogue fac-[Re(CO)₃(BC)(Tph-Me)]+was also prepared by a straightforward methylation reaction. All complexes displayed bright phosphorescence in organic media and, relative to their water solubility, the dianionic species fac-[Re(CO)₃(BPS)(Tph)]²⁻and fac-[Re(CO)₃(BCS)(Tph)]²⁻were also highly emissive in aqueous solution. The sulfonate groups played a key role in promoting and significantly enhancing the luminescent staining performances of both the Re(i) complexes fac-[Re(CO)₃(BPS)(Tph)]²⁻and fac-[Re(CO)₃(BCS)(Tph)]²⁻for proteins. Highlighting a response superior to that of Coomassie Blue and comparable to the one obtained by the well-known silver staining method, these dianionic Re(i)-complexes could efficiently detect up to 50 ng of pure Bovine Serum Albumin (BSA), as well as all proteins found in a Standard Protein Marker mix and from a total protein extract. A lower but still good response for luminescent protein staining was surprisingly obtained by employing the-SO₃-free neutral and cationic complexes fac-[Re(CO)₃(BC)(Tph)] and fac-[Re(CO)₃(BC)(Tph-Me)]+, respectively. These preliminary results open up new possibilities for the further widening of the use of Re(i)-based complexes as luminescent protein staining agents. Refereed/Peer-reviewed

Two neutral cyclometalated Ir(III)-tetrazolato complexes that differ by variations of the substituents on either the phenylpyridine or the tetrazolate ligand have been converted into the corresponding methylated and cationic analogues. NMR (1H and 13C) characterization of the Ir(III) complexes provided the results in agreement with the chemo- and regioselective character of methylation at the N-3 position of the Ir(III)-coordinated tetrazolato ring. This evidence was further corroborated by the analysis of the molecular structures of the cationic complexes obtained by X-ray diffraction. In view of the photophysical properties, the addition of a methyl moiety to neutral Ir(III) tetrazolates, which behave as sky-blue or orange phosphors, caused a systematic red shift of their phosphorescence output. The transformation of neutral Ir(III) tetrazolates into cationic Ir(III)-tetrazole complexes was screened for any eventual antimicrobial activity in vitro against Gram negative (E. coli) and Gram positive (D. radiodurans) microorganisms. While both kinds of complexes were not active against E. coli, the conversion of the neutral Ir(III) tetrazolates into the corresponding methylated and cationic Ir(III)tetrazole derivatives determined the turn-on of a good to excellent antimicrobial activity toward Gram positive Deinococcus radiodurans, a non-pathogenic bacterium that is listed as one of the toughest microorganisms in light of its outstanding resistance to radiation and oxidative stress.

The first examples of anionic Ir(iii) bis-tetrazolate complexes and their combination with a cationic Ir(iii)tetrazole derivative forming “fully tetrazolate” Ir(iii) based soft salts as O2-sensitive white emitters are described herein.