Ultrafast Wiggling and Jiggling: Ir_2(1,8-diisocyanomenthane)_4^(2+)

Binuclear complexes of d^8 metals (Pt^(II), Ir^I, Rh^I,) exhibit diverse photonic behavior, including dual emission from relatively long-lived singlet and triplet excited states, as well as photochemical energy, electron, and atom transfer. Time-resolved optical spectroscopic and X-ray studies have revealed the behavior of the dimetallic core, confirming that M–M bonding is strengthened upon dσ* → pσ excitation. We report the bridging ligand dynamics of Ir2(1,8-diisocyanomenthane)_4^(2+)(Ir(dimen)), investigated by fs–ns time-resolved IR spectroscopy (TRIR) in the region of C≡N stretching vibrations, ν(C≡N), 2000–2300 cm^(–1). The ν(C≡N) IR band of the singlet and triplet dσ*pσ excited states is shifted by −22 and −16 cm^(–1) relative to the ground state due to delocalization of the pσ LUMO over the bridging ligands. Ultrafast relaxation dynamics of the ^1dσ*pσ state depend on the initially excited Franck–Condon molecular geometry, whereby the same relaxed singlet excited state is populated by two different pathways depending on the starting point at the excited-state potential energy surface. Exciting the long/eclipsed isomer triggers two-stage structural relaxation: 0.5 ps large-scale Ir–Ir contraction and 5 ps Ir–Ir contraction/intramolecular rotation. Exciting the short/twisted isomer induces a ∼5 ps bond shortening combined with vibrational cooling. Intersystem crossing (70 ps) follows, populating a ^3dσ*pσ state that lives for hundreds of nanoseconds. During the first 2 ps, the ν(C≡N) IR bandwidth oscillates with the frequency of the ν(Ir–Ir) wave packet, ca. 80 cm^(–1), indicating that the dephasing time of the high-frequency (16 fs)^(−1) C≡N stretch responds to much slower (∼400 fs)^(−1)Ir–Ir coherent oscillations. We conclude that the bonding and dynamics of bridging di-isocyanide ligands are coupled to the dynamics of the metal–metal unit and that the coherent Ir–Ir motion induced by ultrafast excitation drives vibrational dephasing processes over the entire binuclear cation

A cryptic record of Burgess Shale-type diversity from the early Cambrian of Baltica

Exceptionally preserved ‘Burgess Shale-type’ fossil assemblages from the Cambrian of Laurentia, South China and Australia record a diverse array of non-biomineralizing organisms. During this time, the palaeocontinent Baltica was geographically isolated from these regions, and is conspicuously lacking in terms of comparable accessible early Cambrian Lagerstätten. Here we report a diverse assemblage of small carbonaceous fossils (SCFs) from the early Cambrian (Stage 4) File Haidar Formation of southeast Sweden and surrounding areas of the Baltoscandian Basin, including exceptionally preserved remains of Burgess Shale-type metazoans and other organisms. Recovered SCFs include taxonomically resolvable ecdysozoan elements (priapulid and palaeoscolecid worms), lophotrochozoan elements (annelid chaetae and wiwaxiid sclerites), as well as ‘protoconodonts’, denticulate feeding structures, and a background of filamentous and spheroidal microbes. The annelids, wiwaxiids and priapulids are the first recorded from the Cambrian of Baltica. The File Haidar SCF assemblage is broadly comparable to those recovered from Cambrian basins in Laurentia and South China, though differences at lower taxonomic levels point to possible environmental or palaeogeographical controls on taxon ranges. These data reveal a fundamentally expanded picture of early Cambrian diversity on Baltica, and provide key insights into high-latitude Cambrian faunas and patterns of SCF preservation. We establish three new taxa based on large populations of distinctive SCFs: Baltiscalida njorda gen. et sp. nov. (a priapulid), Baltichaeta jormunganda gen. et sp. nov. (an annelid) and Baltinema rana gen. et sp. nov. (a filamentous problematicum)

Ultrafast Wiggling and Jiggling: Ir_2(1,8-diisocyanomenthane)_4^(2+)

Binuclear complexes of d^8 metals (Pt^(II), Ir^I, Rh^I,) exhibit diverse photonic behavior, including dual emission from relatively long-lived singlet and triplet excited states, as well as photochemical energy, electron, and atom transfer. Time-resolved optical spectroscopic and X-ray studies have revealed the behavior of the dimetallic core, confirming that M–M bonding is strengthened upon dσ* → pσ excitation. We report the bridging ligand dynamics of Ir2(1,8-diisocyanomenthane)_4^(2+)(Ir(dimen)), investigated by fs–ns time-resolved IR spectroscopy (TRIR) in the region of C≡N stretching vibrations, ν(C≡N), 2000–2300 cm^(–1). The ν(C≡N) IR band of the singlet and triplet dσ*pσ excited states is shifted by −22 and −16 cm^(–1) relative to the ground state due to delocalization of the pσ LUMO over the bridging ligands. Ultrafast relaxation dynamics of the ^1dσ*pσ state depend on the initially excited Franck–Condon molecular geometry, whereby the same relaxed singlet excited state is populated by two different pathways depending on the starting point at the excited-state potential energy surface. Exciting the long/eclipsed isomer triggers two-stage structural relaxation: 0.5 ps large-scale Ir–Ir contraction and 5 ps Ir–Ir contraction/intramolecular rotation. Exciting the short/twisted isomer induces a ∼5 ps bond shortening combined with vibrational cooling. Intersystem crossing (70 ps) follows, populating a ^3dσ*pσ state that lives for hundreds of nanoseconds. During the first 2 ps, the ν(C≡N) IR bandwidth oscillates with the frequency of the ν(Ir–Ir) wave packet, ca. 80 cm^(–1), indicating that the dephasing time of the high-frequency (16 fs)^(−1) C≡N stretch responds to much slower (∼400 fs)^(−1)Ir–Ir coherent oscillations. We conclude that the bonding and dynamics of bridging di-isocyanide ligands are coupled to the dynamics of the metal–metal unit and that the coherent Ir–Ir motion induced by ultrafast excitation drives vibrational dephasing processes over the entire binuclear cation

Redox-innocent scandium(III) as the sole catalyst in visible light photooxidations

In recent years, the catalytic activity of scandium triflate Sc(OTf)3 has attracted significant attention due to its robust Lewis acidity and the oxophilicity of Sc3+. These features have led to impressive progress in developing diverse organic reactions, including C-C bond formation. The Sc3+ also facilitates single electron transfer in photoinduced reactions either by coordination to an organophotoredox catalyst, which modifies its redox reactivity, or by the formation of a scandium–superoxide anion complex after electron transfer from a light-absorbing redox-active compound. The prior consideration of Sc3+ as a redox-inactive/innocent metal ion initially hampered the investigation of the possibility of using Sc(OTf)3 as a sole visible light photoredox catalyst. This work demonstrates the use of Sc(OTf)3 as a visible light photocatalyst capable of direct and mild aerobic oxidative C-H functionalisation of aromatic substrates by oxidation of the benzylic position and direct cyanation of the aromatic ring

Soil biota in boreal urban greenspace : Responses to plant type and age

Plant functional type influences the abundance and distribution of soil biota. With time, as root systems develop, such effects become more apparent. The relationship of plant type and time with the structure and abundance of soil microbial and invertebrate communities has been widely investigated in a variety of systems. However, much less is known about long-term soil community dynamics within the context of urban environments. In this study, we investigated how soil microbes, nematodes and earthworms respond to different plant functional types (lawns only and lawns with deciduous or evergreen trees) and park age in 41 urban parks in southern Finland. As non-urban controls we included deciduous and evergreen trees in 5 forest sites. We expected that microbial biomass and the relative abundance of fungi over bacteria would increase with time. We also expected major differences in soil microbial and nematode communities depending on vegetation: we hypothesized that i) the presence of trees, and evergreens in particular, would support a greater abundance of fungi and fungal-feeding nematodes over bacteria and bacterial-feeding nematodes and ii) the fungi to bacteria ratio would be lowest in lawns, with deciduous trees showing intermediate values. In contrast to our predictions, we showed that old deciduous trees, rather than evergreens, supported the highest fungal abundances and fungal-feeding nematodes in the soil. Consistent with our predictions, microbial biomass in urban park soils tended to increase with time, whereas - in contrast to our hypotheses - fungal-feeding nematode abundance declined. Even in the oldest parks included in the current study, microbial biomass estimates never approximated those in the minimally managed natural forests, where biomass estimates were three times higher. Anecic earthworm abundance also increased with time in urban parks, whereas abundances of fungal-feeding, plant-feeding and omnivorous nematodes, as well as those of epigeic and endogeic earthworms remained constant with time and without any distinct differences between urban parks and the control forests. Our findings highlight that although urban park soils harbor diverse soil communities and considerable microbial biomass, they are distinct from adjacent natural sites in community composition and biomass.Peer reviewe

A cryptic record of Burgess Shale-type diversity from the early Cambrian of Baltica

Palaeontology published by John Wiley & Sons Ltd on behalf of The Palaeontological Association.Exceptionally preserved ‘Burgess Shale-type’ fossil assemblages from the Cambrian of Laurentia, South China and Australia record a diverse array of non-biomineralizing organisms. During this time, the palaeocontinent Baltica was geographically isolated from these regions, and is conspicuously lacking in terms of comparable accessible early Cambrian Lagerstätten. Here we report a diverse assemblage of small carbonaceous fossils (SCFs) from the early Cambrian (Stage 4) File Haidar Formation of southeast Sweden and surrounding areas of the Baltoscandian Basin, including exceptionally preserved remains of Burgess Shale-type metazoans and other organisms. Recovered SCFs include taxonomically resolvable ecdysozoan elements (priapulid and palaeoscolecid worms), lophotrochozoan elements (annelid chaetae and wiwaxiid sclerites), as well as ‘protoconodonts’, denticulate feeding structures, and a background of filamentous and spheroidal microbes. The annelids, wiwaxiids and priapulids are the first recorded from the Cambrian of Baltica. The File Haidar SCF assemblage is broadly comparable to those recovered from Cambrian basins in Laurentia and South China, though differences at lower taxonomic levels point to possible environmental or palaeogeographical controls on taxon ranges. These data reveal a fundamentally expanded picture of early Cambrian diversity on Baltica, and provide key insights into high-latitude Cambrian faunas and patterns of SCF preservation. We establish three new taxa based on large populations of distinctive SCFs: $\textit{Baltiscalida njorda}$ gen. et sp. nov. (a priapulid), $\textit{Baltichaeta jormunganda}$ gen. et sp. nov. (an annelid) and $\textit{Baltinema rana}$ gen. et sp. nov. (a filamentous problematicum).We acknowledge the support of Churchill College, Cambridge (BJS) and Clare Hall College, Cambridge (RG). This research was funded by the Natural Environmental Research Council, UK, grant NE/K005251/1 (BJS, THPH, RG, NJB)