A mononuclear complex [Fe(tBu 2 qsal) 2 ] has been obtained by a reaction between an Fe(II) precursor salt and a tridentate ligand 2,4-di(tert-butyl)-6-((quinoline-8-ylimino)methyl)phenol (tBu 2 qsalH) in the presence of triethylamine. The complex exhibits a hysteretic spin transition at 117 K upon cooling and 129 K upon warming, as well as light-induced excited spinstate trapping at lower temperatures. Although the strongly cooperative spin transition suggests substantial intermolecular interactions, the complex is readily sublimable, as evidenced by the growth of its single crystals by sublimation at 573 → 373 K and ∼10 −3 mbar. This seemingly antagonistic behavior is explained by the asymmetric coordination environment, in which the tBu substituents and quinoline moieties appear on opposite sides of the complex. As a result, the structure is partitioned in well-defined layers separated by van der Waals interactions between the tBu groups, while the efficient cooperative interactions within the layer are provided by the quinoline-based moieties. The abrupt spin transition is preserved in a 20 nm thin film prepared by sublimation, as evidenced by abrupt and hysteretic changes in the dielectric properties in the temperature range comparable to the one around which the spin transition is observed for the bulk material. The changes in the dielectric response are in excellent agreement with differences in the dielectric tensor of the low-spin and high-spin crystal structures evaluated by density functional theory calculations. The substantially higher volatility of [Fe(tBu 2 qsal) 2 ], as compared to a similar complex without tBu substituents, suggests that asymmetric molecular shapes offer an efficient design strategy to achieve sublimable complexes with strongly cooperative spin transitions.

The advent of two-dimensional (2D) crystals has led to numerous scientific breakthroughs. Conventional 2D systems have in-plane covalent bonds and a weak out-of-plane van-der-Waals bond. Here we report a new type of 2D material composed of discrete magnetic molecules, where anisotropic van-der-Waals interactions bond the molecules into a 2D packing. Through mechanical exfoliation, we can obtain single-crystalline molecular monolayers, which can be readily integrated into other 2D systems. Optical spectroscopy suggests the few-layered molecules preserve the temperature-induced spin-crossover switching observed in the bulk form but show a drastic increase in thermal hysteresis unique to these thin 2D molecule assemblies. The trapping of spin bistability with decreasing layer number can arise from domain wall dynamics in reduced dimensions. Our results establish molecular solids with strong anisotropy of intermolecular interactions as precursors to a new class of 2D materials, affording possibilities to control molecular functionalities through substrate and interlayer interactions.

We report a series of heteroleptic cobalt complexes of the general formula [Co( t Bu 2 sq) 2 (L) 2 ], where t Bu 2 sq = 3,5-di(tert-butyl)-o-semiquinonato ligand and L represents pyridines functionalized with sulfur-containing substituents. The octahedral coordination of the Co metal center in these mononuclear complexes is formed by two chelating t Bu 2 sq ligands in the equatorial plane and two axial pyridines in the axial positions. All complexes exhibit layered crystal packings, with Scontaining substituents providing cohesion within the layers and the t Bu substituents of dioxolenes protruding into the interlayer space, where disordered solvent molecules are located. The presence of thienyl substituents in the para position of the pyridine ring leads to the formation of molecular chains within the layers, due to efficient π−π interactions between the L ligands. Even more efficient packing with two-dimensional intermolecular π−π interactions is achieved when two thienyl substituents are present in the meta positions of the pyridine ring. Introduction of a terminal cyano or 1,3-dithiole-2-one substituent on the opposite end of the pyridyl-bound thienyl group leads to the disruption of the π−π interactions, thus decreasing the crystal packing efficiency. Such disruption, however, is not observed when the thienyl group is terminated with methyl-carboxylate. Magnetic measurements reveal an onset of valence-tautomeric spin-crossover (VT-SCO) from the [LS-Co III ( t Bu 2 sq • )( t Bu 2 cat)(L) 2 ] state (low-spin, S = 1/2) to the [HS-Co II ( t Bu 2 sq • ) 2 (L) 2 ] state (high-spin, S = 5/2) above 300 K for the complexes with para-thienyl-substituted pyridines, while the complexes with a bithienyl substituent in the para position or two thienyl substituents in the meta positions exhibit only LS state up to 400 K. Adding a terminal group to the para-thienyl substituent lowers the VT-SCO temperature, leading to two-step spin-state conversion.

This paper describes a novel approach to the assessment of spatial cognition in children. In particular we present a wireless instrumented toy embedding magneto-inertial sensors for orientation tracking, specifically developed to assess the ability to insert objects into holes. To be used in naturalistic environments (e.g. daycares), we also describe an in-field calibration procedure based on a sequence of manual rotations, not relying on accurate motions or sophisticated equipment.The final accuracy of the proposed system, after the mentioned calibration procedure, is derived by direct comparison with a gold-standard motion tracking device. In particular, both systems are subjected to a sequence of ten single-axis rotations (approximately 90 deg, back and forth), about three different axes. The root-mean-square of the angular error between the two measurements (gold-standard vs. proposed systems) was evaluated for each trial. In particular, the average rms error is under 2 deg.This study indicates that a technological approach to ecological assessment of spatial cognition in infants is indeed feasible. As a consequence, prevention through screening of large number of infants is at reach.

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A heteroleptic spin-crossover (SCO) complex, [Fe(tpma)(xnap-bim)](ClO 4 ) 2 (1; tpma = tris(2-pyridylmethyl)amine, xnap-bim = 8,15-dihydrodiimidazo[1,2-, has been obtained by reacting a Fe(II) precursor salt with tetradentate tpma and bidentate xnap-bim ligands. Depending on crystallization conditions, two different solvates have been obtained, 1•2.25py•0.5H 2 O and 1•py. The former readily loses the interstitial solvent to produce either a powder sample of 1 upon filtration or crystals of 1 if the solvent loss is slowed by placing the crystals of 1•2.25py•0.5H 2 O in diethyl ether. In contrast, 1•py exhibits higher stability toward solvent loss. The crystal packing of both solvates and of the solvent-free structure features double columns of [Fe(tpma)(xnap-bim)] 2+ cations formed by efficient π−π interactions between the pyridyl groups of tpma ligands, as well as by stacks supported by π−π interactions between interdigitated naphthalene fragments of xnap-bim ligands. While both solvates show a gradual SCO between the high-spin (HS) and low-spin (LS) states of the Fe(II) ion, solvent-free complex 1 exhibits an abrupt spin transition centered at 127 K, with a narrow 2 K thermal hysteresis. Complex 1 also shows a light-induced excited spin state trapping effect, manifested as LS → HS conversion upon irradiation with white light at 5 K. The metastable HS state relaxes to the ground LS state when heated above 65 K.

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