Inside Cover: A Nanoscale Molecular Switch Triggered by Thermal,Light, and Guest Perturbation (Angew. Chem. Int. Ed. 14/2009)

Continuous switching between high‐spin and low‐spin magnetic states can be accomplished by irradiation with red and green laser light, respectively. In their Communication on page 2549 ff., S. R. Batten and co‐workers report a metallo‐supramolecule that undergoes spin crossover (SCO) switching induced by temperature change or light irradiation. The SCO behavior is also dependent on the presence and nature of intercalated solvent molecules within the porous crystal structure.

     

Understanding the two-step spin-transition phenomenon in Iron(II) 1D chain materials

Three analogous one dimensional (1D) polymeric iron(II) spin crossover (SCO) materials containing the new ligand 4,6-bis(2',2'-pyridyl)pyrazine (bdpp) have been comprehensively characterised magnetically (thermal and light-induced) and structurally. Within this series are two polymorphs of the formula [Fe(NCS)(2)(bdpp)], 1 and 2 a, which differ magnetically in that phase 1 undergoes a full two-step SCO (T(1/2(1))=135 K and T(1/2(2))=90 K) whereas phase 2 a remains high spin (HS) over all temperatures. The central distinction between these two materials lies in the presence of intermolecular pi-pi interactions generated by the crystal packing in 1, which are absent in 2 a. The isostructural selenocyanate analogue of 2 a, [Fe(NCSe)(2)(bdpp)], 2 b, undergoes a full two-step SCO (T(1/2(1))=200 K and T(1/2(2))=125 K). Structural analyses of 1 and 2 b at a range of temperatures provide deep insight into their two-step SCO nature. Structural analysis of 1 at 25 K (1(LS-LS)), 123 K (1(LS-HS)) and 250 K (1(HS-HS)) reveals two distinct iron(II) centres at each temperature, with ordered, alternating HS and LS (low spin) sites at the intermediate plateau (IP) temperatures. In contrast, structural analysis of 2 b at 90 K (2 b(LS)), 150 K (2 b(LS/HS)) and 250 K (2 b(HS)) reveals one unique iron(II) centre at each temperature with an "averaged" LS/HS character at the IP temperature. Weak planes of diffuse scattering in the single-crystal X-ray diffraction patterns were observed for this phase at 90 and 150 K, indicating that 1D long range ordering of alternating HS/LS iron(II) centres occurs along the 1D coordination chains, but that there is no correlation between chains. The lack of observable diffuse scattering at 250 K suggests that the onset of the 1D structural ordering in the chain direction corresponds to the first step of the SCO and that this structural transition is electronically driven. The photomagnetic properties of both 1 and 2 b have been investigated and show approximately 62 and 53 % photo-excitation of a HS metastable state at low temperatures and T(LIESST) values of 55 and 49 K, respectively. Relaxation studies on the HS fraction in 2 b fitted well to a stretched exponential model with kinetic parameters indicative of weak cooperativity.     

{N‐[2‐(η5‐Cyclopentadienyl)ethyl]‐4‐toluenesulfonamido‐N,O}(tetrahydrofuran‐O)bis(trifluoromethanesulfonato‐O)titanium(II)

The title compound, [Ti(CF₃O₃S)₂(C₁₄H₁₅NO₂S)(C₄H₈O)], contains a unique ligand system in which the Ti ion is bound to the N and O atoms of a 2‐p‐toluene­sulfon­amide ligand, which is linked by an ethyl group to a coordinated cyclo­penta­diene moiety. The distorted octahedral geometry about the Ti ion is completed by two tri­fluoro­methane­sulfonate ligands and a tetra­hydro­furan mol­ecule. Comparison with related compounds shows that both the Ti—N and Ti—O bonds of the sulfon­amide, although longer than normal values, indicate significant bonding interactions.     

Heterogeneous surface-to-air missile defense battery location: a game theoretic approach

In the context of an air defense missile-and-interceptor engagement, a challenge for the defender is that surface-to-air missile batteries often must be located to protect high-value targets dispersed over a vast area, subject to which an attacker may observe the disposition of batteries and subsequently develop and implement an attack plan. To model this scenario, we formulate a two-player, extensive form, three-stage, perfect information, zero-sum game that accounts for, respectively, a defender’s location of batteries, an attacker’s launch of missiles against targets, and a defender’s assignment of interceptor missiles from batteries to incoming attacker missiles. The resulting trilevel math programming formulation cannot be solved via direct optimization, and it is not suitable to solve via full enumeration for realistically-sized instances. We instead adapt the game tree search technique Double Oracle, within which we embed either of two alternative heuristics to solve an important subproblem for the attacker. We test and compare these solution methods to solve a designed set of 52 instances having parametric variations, from which we derive insights regarding the nature of the underlying problem. Enhancing the solution methods with alternative initialization strategies, our superlative methodology attains the optimal solution for over 75% of the instances tested and solutions within 3% of optimal, on average, for the remaining 25% of the instances, and it is promising for realistically-sized instances, scaling well with regard to computational effort.     

Syntheses of C2-labelled 11Z-retinals

To enable solid-state NMR investigations of the rhodopsin chromophore and its photointermediates, a series of 11Z-retinal isotopomers have been synthesised containing pairs of adjacent ¹³C labels at C9/C10, C10/C11 or C11/C12, respectively. The C9 labelled carbon atom was introduced through the Heck reaction of a ¹³C-labelled Weinreb acrylamide derivative, and the label at the C12 position derived from a ¹³C-containing ethoxy Bestmann-Ohira reagent. The ¹³C labels at C10 and C11 were introduced through the reaction of β-ionone with labelled triethyl phosphonoacetate.