1-(3-Halopropyl)-1H-tetrazoles and their corresponding Fe spin-crossover complexes have been investigated in a combined experimental and theoretical study. Halogen substitution was found to positively influence the spin transition, shifting the transition temperature about 70 K towards room temperature. Halogens located at the ω position were found to be too far away from the coordinating tetrazole moiety to have an electronic impact on the spin transition. The subtle variation of the steric demand of the ligand in a highly comparable series was found to have a comparatively large impact on the spin-transition behavior, which highlights the sensitivity of the effect to subtle structural changes.

Substituted 1‐biaryl‐1H‐tetrazoles are classically obtained from the corresponding 1‐aminobiaryls, limiting the selection of substrates. The development and substrate scope of a green, ligand‐free Suzuki protocol in aqueous media under ambient atmosphere, leading to 1‐biaryl‐ and heteroaryl‐substituted 1H‐tetrazoles in very good to excellent yields is presented. The combination of PdCl2/NEt3/H2O/EtOH was found to combine high yields and high purity for all substrates investigated. Comparative experiments investigating the reaction rate showed that the tetrazole does not act as a ligand for the palladium catalyst.

No abstract

) designed using a structureproperty based concept is reported. All complexes feature abrupt SCO-behavior with T 1/2 between 170 K and 187 K. These materials demonstrate that without stabilizing the effects of incorporated solvents or a hydrogen bond-network, the observed cooperativity during high-spin-low-spin transition is anion independent and originates only from the rigidity and internal strain of the propellane-moiety in the ligand. Spectroscopy and structural investigations of these materials are supported by quantum chemical calculations.Molecular bistability will be a key feature of the next generation of miniaturized magneto-optical devices.1,2 In this context, the spin crossover (SCO) effect with its inherent change of magnetic moment, 2,3 color, 4 dielectric constant, 5,6 resistance, 7-10 conductivity 7-11 and molecular extension (bondlength) 12 upon an external stimulus such as light (LIESSTeffect), 13,14 temperature, 2,3 pressure, 2,3,15 current, 7-10 etc., allows for a multitude of attractive combinations of properties, guiding coordination and materials chemists alike. Application of such materials, however, requires different criteria to be met by a suitable material. The most important of these characteristics includes an abrupt and complete spin crossover between the high-spin (HS) and the low-spin (LS) state, preferably at or near ambient temperature. In the literature, spin-state transitions are classified according to the shape of the magnetization curve 3,16 (complete, incomplete, one-step, two-step, multi-step with or without plateau, hysteresis or not) and according to the temperature range necessary for the complete change of the spin state: a spin state transition occurring over more than 10 K is termed gradual or continuous, and over fewer than 10 K, it is termed abrupt or discontinuous. 16 Systematic design of SCO-materials has, unfortunately, to date proven to be impossible. Several influences, often difficult to identify independently overlap, resulting in the observed spin state transition behavior. Among them, cooperativity -the transfer of volume-work due to the spinstate related elongation of the Fe-N bond by a rigid ligandbetween the (inter) molecular alignment and crystal packing is commonly stated as a necessary ingredient for a complete and abrupt HS-LS spin state transition. 17 There are several ways to introduce cooperativity in SCO-materials, including guest molecules, co-crystallized solvents or the appropriate choice of the anion, whereby the density of the packing in the crystal and intermolecular interactions can be tuned. 15,18,19 Hydrogen-bonding networks have proven to be especially reliable tools sharpening the abruptness of the spin crossover behavior by enhancing cooperativity. Although, this seems to be the best prospective method for tuning SCO-behavior, relying on intermolecular interactions still requires lengthy trial and error investigations, since no unambiguous quantitative relationship between hydrogen-bonding parameters and SCO behavior is known. 20,2...

Spin crossover complexes with ligands suitable for further functionalization could allow for an easy access to multifunctional switchable materials. Within this context, we recently characterized the Fe(II) SCO complexes of propargyl-1H-tetrazole. Although the design of the ligand seems similar to the one of the well-known propyl-1H-tetrazole, the spin transition behavior is notably different. Both compounds reported herein feature a gradual spin transition with a T 1/2 shifted to lower temperatures, compared to the more flexible propyl-ligand. Due to the potential instable structure of these compounds, especially of the perchlorate complex, we also investigated our compounds with regard to their sensitivity against thermal and mechanical stress. These experiments led to the conclusion that the proper handling includes no enhanced risk of explosive decomposition.