The dimeric motif is the smallest unit for two interacting spin centers allowing for systematic investigations of cooperative interactions. As spin transition compounds, dinuclear complexes are of particular interest, since they potentially reveal a two-step spin crossover (SCO), switching between the high spin–high spin [HS-HS], the high spin–low spin [HS-LS], and the low spin–low spin [LS-LS] states. Herein, we report the synthesis and characterization of six dinuclear iron­(II) complexes [FeII 2(μ2-L 1 )2]­(BF4)4 (C1), [FeII 2(μ2-L 1 )2]­(ClO4)4 (C2), [FeII 2(μ2-L 1 )2](F3CSO3)4 (C3), [FeII 2(μ2-L 2 )2]­(BF4)4 (C4), [FeII 2(μ2-L 2 )2](BF4)4 (C5), and [FeII 2(μ2-L 2 )2]­(BF4)4 (C6), based on the 1,3,4-thiadiazole bridging motif. The two novel bis-tridentate ligands (L 1 = 2,5-bis­{[(1H-imidazol-2-ylmethyl)-amino]-methyl}-1,3,4-thiadiazole and L 2 = 2,5-bis­{[(thiazol-2-ylmethyl)-amino]-methyl}-1,3,4-thiadiazole) were employed in the presence of iron­(II) salts with the different counterions. Upon varying ligands and counterions, we were able to change the magnetic properties of the complexes from a temperature-independent [HS-HS] spin state over a one-step spin transition toward a two-step SCO. When cooled slowly from room temperature, the two-step SCO goes along with two distinct phase transitions, and in the intermediate mixed [HS-LS] state distinct HS/LS pairs can be identified unambiguously. In contrast, rapid cooling precludes a crystallographically observable phase transition. For the mixed [HS-LS] state Mössbauer spectroscopy confirms a statistical (random) orientation of adjacent [HS-LS]·[HS-LS]·[HS-LS] chains.

A metal‐free photoredox‐catalyzed α‐heteroarylation of 2‐bromophosphonoacetic esters allows the synthesis of precursors for Horner‐olefinations from indoles in a single step. Numerous functional groups are tolerated in this photoinduced radical coupling under mild conditions and the subsequent reaction with aldehydes generates 2‐(indol‐2‐yl)acrylates in high yield.

Herein we report the synthesis and characterization of a novel bis-tridentate 1,3,4-thiadiazole ligand (L = 2,5-bis[(2-pyridylmethyl)thio]methyl-1,3,4-thiadiazole). Two new mononuclear complexes of the type [MII(L)2](ClO4)2 (with M = FeII (C1) and CoII (C2)) have been synthesized, containing the new ligand (L). In both complexes the metal centers are coordinated by an N4S2-donorset and each of the two ligands is donating to the metal ion with just one of the tridentate pockets. The iron(II) complex (C1) is in the low spin [LS] state below room temperature and shows an increase in the magnetic moment only above 300 K. In contrast, the cobalt(II) complex (C2) shows a gradual spin crossover (SCO) with T1/2 = 175 K. To our knowledge, this is the first cobalt(II) SCO complex with an N4S2-coordination.

Herein we report the synthesis and characterization of three new dinuclear iron(II) complexes [FeII2(I4MTD)2](F3CSO3)4 (C1), [FeII2(I4MTD)2](ClO4)4 (C2) and [FeII2(I4MTD)2](BF4)4 (C3) based on the novel ligand (I4MTD = 2,5-bis{[(1H-imidazol-4-ylmethyl)amino]methyl}-1,3,4-thiadiazole). Magnetic susceptibility measurements and single-crystal structure analysis show that the iron(II) spin centers for all complexes are in the high spin state at high temperatures. While the magnetic data of air-dried samples confirm the [HS-HS] state for C1 and C2 down to very low temperature, for C3, a gradual spin crossover is observed below 150 K. The crystal structure of C3·THF at 100 K shows that a spin transition from [HS-HS] to an intermediate state takes place, which is a 1:1 mixture of discrete [HS-HS] and [LS-LS] molecules, as identified unambiguously by crystallography. The different SCO properties of C1–C3 can be attributed to crystal packing effects in the solid state.