Above: I'm an American. Of course it's in the middle (and apologies if I, er, cut you off). Light pollution map as of the data available on 8 March 2025. See the excellent/astronomically depressing details at lightpollutionmap.info.
The most recent issue of Free Astronomy Magazine (March-April 2025) is available for your reading and downloading pleasure in English, Italian, Spanish, French, and Arabic at www.astropublishing.com (and facebook).
The March-April 2025 cover. Click to go to the issue.
Two very young children, COVID, and life in general kept me indoors most evenings (and away from observing) for much of 2020-2021. What I do vividly remember around mid-March 2021 was taking out the garbage a little bit earlier in the morning than usual and seeing a massive celestial caravan moving from west-to-east through a crystal-clear sky. At that moment, I was astounded at the progress SpaceX had made with Starlink, as I'd never seen anything that massive and coordinated and that fast in the sky before (and that includes seeing a space shuttle undock from the ISS over the course of two full orbits, which itself I won't soon forget).
I personally do not know any amateur astronomer who considers that caravan "progress" (feel free to correct me). The good fight from darksky.org, the now-defunct SELENE-NY, whose web presence ended around 2019 (last snap – web.archive.org/web/20190101182128/http://selene-ny.org/; skipping what might be a hacked site, a link and mention is, for instance, skykeepers.org/activism.html), and other local, national, and international organizations seems most up-the-hill as we progress upwards. If it were easy for astrophotographers to plant their gear just past the edge of GEO, it would likely be a different situation. But that's a long time in waiting (because they spent all their money on gear and can't affords rockets and space platforms).
In the defense of progress, very little in the nighttime sky will get a crowd of 200 people looking at the exact same location faster than a pinpoint of light hauling in front of a field of stars. I have no doubt that the sight of a satellite can be a gateway for someone into the hobby (or into one of the many associated professions).
The problem remains far worse here on the ground, as even the darkest of dark skies are seeing light pollution either slowly or rapidly advance (see the cover article above). The tension continues.
Above: the largest dication in the study (barium) produces the most asymmetric coordination complex in the crystal phase (and retains a THF to boot).
Published in the Journal of Coordination Chemistry (article link) and "…dedicated to Professor Jim Atwood to honor his many years as Editor-in-Chief of the Journal or Coordination Chemistry [huzzah!]." I most definitely still have my copy of Inorganic and Organometallic Reaction Mechanisms; that cover stared back at me for six months in one of my grad school offices. The raw data for this paper goes back several years and has finally been put into form – "several years" being long enough that the theory work for this one didn't overlap with the method work that went into the Azobenzene as an Effective Ligand in Europium Chemistry article I posted several days back (as to whether the predictions would have been different or not, we may never know).
We've solved the protein folding problem (fairly well as of late) but still haven't solved the (molecular) crystal polymorphism problem. While this paper and field of work focuses on the presented alkali (Li -> Fr) and alkaline earth (Be -> Ra) metals, in these systems those metals really are just charged, spherical linkers that will preferentially stick to some organic functional groups better than others (ignoring the chemistry to get those metals there, of course). For anyone pondering the design of crystals or (macro)molecular complexes out of these spheres, the key issues are (a) dicationic radius, (b) effective charge at the metals, (c) the strength of the interaction of these spheres with the functional groups, and (d) the preferred means of these metals to interacting with varied ligands due to the varied dependencies within the other three items.
The high-symmetry (or locally so in the "Pseudo-C3" structures) molecular complexes used to study the preferences for two-fold or three-fold symmetric coordination environments for the Ca/Sr/Ba series.
These tetrahedral tetraarylborate anions are valuable molecules because their high symmetry means that many coordination modes are available that can still retain some of the symmetry elements of the isolated anion – this provides the theoretician with a healthy opportunity to speed the calculations along and impose symmetry-constrained geometries that let us explore binding preferences at higher levels of theory. In terms of developing computational models to explore preferred binding modes, these ligands are excellent test cases because they are highly symmetric molecules that, except for barium, prefer to produce highly (locally) symmetric coordination complexes. This was exploited to great extent in the Gaussian 09 (I did say this theory work was older) calculations performed to try to draw firm conclusions about the preferred binding modes across the Ca-Sr-Ba series – and the calculations well-reproduced the observed trends (so there).
Some additional work was done to model the preferred numbers of coordinated solvent molecules (THF and Et2O) down the alkali earth series, but that's an even more academic question given the known coordination energies of both molecules, and so was not included in the article.
Catherine M. Lavin, Damian G. Allis, Miriam M. Gillett-Kunnath, Ashley Clements, Alan G. Goos, Joshua J. Woods, Paul Hager, Donyell S. Logan, and Karin Ruhlandt-Senge
Abstract: The use of the weakly binding tetraarylborate ligands and the careful selection of co-ligands affords novel contact ion pairs exclusively stabilized by Ae-π (Ae = calcium, strontium and barium) interactions of the form [Ae(B{(3,5-Me2)C6H3}4)2(thf)n] (Ae = Ca, n = 0, 1; Sr, n = 0, 2), [Ba(B{(3,5-Me2)C6H3}4)2(thf)]. HN(SiMe3)2, 3 and [Ba(B{(4-tBu)C6H4}4)2].Et2O, 4. The variety of and preference for binding geometries with choice of metal is considered using theoretical calculations.
Above: Along the crystal a axis of [Eu(thf)3]2(µ-n1:n1-N2Ph2)2, the structure used in the computational analysis reported in the Molecules paper below. See text for more info. Image hastily made with Vesta.
Published somewhat recently in Molecules. And Greek letters are being difficult in WordPress at the moment – those in the know please forgive the use of "n" and "w" where inappropriate).
Left: [Eu(thf)3]2(µ-n1:n1-N2Ph2)2 (1), containing Ci symmetry. Right: [Eu(dme)2]2(µ-n2:n2N2Ph2)2, containing no symmetry (making the reported analysis easier on the Ci case given the theory levels and number of calculations performed in this study).
Reminded of a phrase often spoken by the late Marshall Nye – actor, director (one of the first shows I ever drummed for was his directing of "Grease"), thespian, all-around good guy and ninth grade math teacher.
For the record, my remembering this had to do with the modeling of europium as a theoretical chemist, not the deep dive that has been taken in terms of my inbox after having an article submitted to an Open Access journal. Maybe.
The Math
To the technical details – with a particular authorship deadline in mind for its publication, the theoretical section turned into part one of what is hoped to be an extended set of density functional theory comparisons for their assessment w.r.t. a selection of alkali and alkali earth metal coordination complexes with specific families of coordinating ligands. The extended set of the structures not reported in this first paper spans the Ca/Sr/Ba series, with Eu being a particularly similar metal in terms of ionic radius and coordination behavior (no surprise). The question to be addressed was how well/differently several recent density functionals reproduced structural parameters of the coordination complexes, this as a wide stepping stone to some rational design of ligands to alter various properties (vapor pressure, binding strengths (most easily through steric modification), intermolecular interactions for potential extended coordination networks, etc.) in these smaller model systems based on theoretical work.
As these structural details are all from crystal structures of these complexes, and because the units cells are large enough to not want to treat them by periodic methods for the time being at the employed levels of theory, there is also the obvious issue of if disagreements with the calculations are attributable to the crystal environment changing the geometries or the theory levels actually over/underestimating something (the clear concern for any coordination interactions to the europium, to the extent those differences matter to the behavior of the systems).
A few aside takeaways from the work itself:
The calculated and crystal geometries are quite close all around, indicating that these are well-defined complexes that then pack in the solid-state (my interpretation).
I tried to use the same as-large-as-possible/methodologically-appropriate basis set for single-point calculations, which then required going to the Basis Set Exchange for Def2-SVP and Def2-TZVP. Convergence of the wavefunction in Gaussian 09 was an awful fight down to default "tight" values. Part of the solution was the reuse of the checkpoint file from the previous run (guess=read – good practice for reducing the time to convergence generally), part was reducing the convergence threshold to 10^-7 (consider Q-Chem's default for single-point calcs!).
The LRC-wPBEh density functional was generally excellent for these systems. The one oddity was the way that it split select N=N stretching modes compared to CAM-B3LYP and wB97XD (as discussed in the paper).
With time constraints in mind, this work only covered the smaller of the two complexes, but some tests on the larger system play out equally well (although it is even more sensitive to crystal packing given how some of the ligands binds and are prone to local disorder, so the more rigid structure RMSD for structure 1 needs to be tempered with analyses at the bond and angle levels for 2).
All that said, Molecules is Open Access – I don't need to summarize what you can read for free. Speaking of…
The Aftermath
This was my first foray into the open access model, where you get an invite, a reduced rate for publishing, and hopefully a good set of reviewers committed to (a) the open access philosophy and (b) scientific rigor.
I have, since publication of this article, received 5x more invitations to submit my research to journals than I had prior. It is an obvious leap in invite count. Might be fine if the emails did not look like the following:
Dear Dr. Allis Damian,
Hope you are doing well!
Can you kindly let us know if you can submit any type of article towards our Journal? As we are short of one article to close the issue.
Waiting to receive your reply as early as possible.
Sincerely, Annals of Chemical Science Research ISSN: 2688-8394 | Impact Factor: 1.599
I realize it's been a long year since publishing something last, but are other folks in this same boat? Are the bots that busier? Are folks sitting on these journals waiting to scrape the pages for @ symbols?
Abstract: The preparation and characterization of two novel europium–azobenzene complexes that demonstrate the effectiveness of this ligand for stabilizing reactive, redox-active metals are reported. With the family of rare earth metals receiving attention due to their potential as catalysts, critical components in electronic devices, and, more recently, in biomedical applications, a detailed understanding of factors contributing to their coordination chemistry is of great importance for customizing their stability and reactivity. This study introduces azobenzene as an effective nonprotic ligand system that provides novel insights into rare earth metal coordination preferences, including factors contributing to the coordinative saturation of the large, divalent europium centers. The two compounds demonstrate the impact of the solvent donors (tetrahydrofuran (THF) and dimethoxyethane (DME)) on the overall coordination chemistry of the target compounds. Apart from the side-on coordination of the doubly-reduced azobenzene and the anticipated N-N bond elongation due to decreased bond order, the two compounds demonstrate the propensity of the europium centers towards limited metal-pi interactions. The target compounds are available by direct metallation in a straightforward manner with good yields and purity. The compounds demonstrate the utility of the azobenzene ligands, which may function as singly- or doubly-reduced entities in conjunction with redox-active metals. An initial exploration into the computational modeling of these and similar complexes for subsequent property prediction and optimization is performed through a methodological survey of structure reproduction using density functional theory.
