Photoactive complexes with earth-abundant metals have attracted increasing interest in the recent years fueled by the promise of sustainable photochemistry. However, sophisticated ligands with complicated syntheses are oftentimes required to enable photoactivity with nonprecious metals. Here, we combine a cheap metal with simple ligands to easily access a photoactive complex. Specifically, we synthesize the molybdenum(0) carbonyl complex Mo(CO)3(tpe) featuring the tripodal ligand 1,1,1-tris(pyrid-2-yl)ethane (tpe) in two steps with a high overall yield. The complex shows intense deep-red phosphorescence with excited state lifetimes of several hundred nanoseconds. Time-resolved infrared spectroscopy and laser flash photolysis reveal a triplet metal-to-ligand charge-transfer (3MLCT) state as the lowest excited state. Temperature-dependent luminescence complemented by density functional theory (DFT) calculations suggest thermal deactivation of the 3MLCT state via higher lying metal-centered states in analogy to the well-known photophysics of [Ru(bpy)3]2+. Importantly, we found that the title compound is very photostable due to the lack of labilized Mo–CO bonds (as caused by trans-coordinated CO) in the facial configuration of the ligands. Finally, we show the versatility of the molybdenum(0) complex in two applications: (1) green-to-blue photon upconversion via a triplet–triplet annihilation mechanism and (2) photoredox catalysis for a green-light-driven dehalogenation reaction. Overall, our results establish tripodal carbonyl complexes as a promising design strategy to access stable photoactive complexes of nonprecious metals avoiding tedious multistep syntheses.

The ground state of Fe2+ (S = 2) in α- and β-FeMoO4 is investigated by experiments including X-ray diffraction, Raman scattering, and 57Fe–Mössbauer spectroscopy below 300 K and evaluated by theoretical modeling. Both modifications crystallize in the space group C2/m with the same set of Wyckoff positions. The structural feature of α- and β-FeMoO4 is a tetramer of the so-called butterfly motif. Two iron-sites (Fe2) form an antiferromagnetically coupled dimer whereas two Fe1 establish an antiferromagnetic intertetramer coupling. The effective magnetic exchange of the two magnetic sublattices is based on dominating Dzyaloshinskii–Moriya interaction due to the rare situation of canceling Heisenberg exchange interactions. According to our investigations, the ground states of the two polymorphs differ in terms of their Fe-site specific electric field gradients V ii . Contrary to the α-phase, a degenerate set of V zz and V yy for both iron sites in β-FeMoO4 is extracted from density functional theory calculations. In the vicinity of the phase transition (β → α), the degeneracy of the β-phase is lifted. Correspondingly, we observe a softening of the ν­(Mo–O) phonon modes. Detailed Mössbauer spectra confirm the crosslike 90° antiferromagnetic structure for both modifications and solve the origin of the longstanding issue of disparate quadrupole splittings in α- and β-FeMoO4.

We present muon spin relaxation (μSR) measurements of the S = 3/2 undistorted triangular lattice established in RbAg 2 Cr[VO 4 ] 2. The zero-(ZF) and longitudinal-field μSR spectra evidence the absence of spin freezing and long-range magnetic ordering down to T = 25 mK, supporting the formation of a dynamic ground state. Noticeably, we observe an anomalous temperature dependence of the ZF muon spin relaxation rate λ ZF (T), featuring a decrease below T = 20 K. This suggests the alteration of the dominant relaxation mechanism by the development of short-range magnetic correlations. A subsequent leveling off of λ ZF (T) below T = 2 K indicates persistent spin dynamics and reveals the presence of exotic magnetic excitations. The field dependence of the muon spin relaxation rate at T = 25 mK is well described by a diffusive spin transport model with algebraic spin-spin correlations. The suppressed long-range order and the peculiar temperature-dependent behavior of λ ZF (T) will be discussed in terms of the exchange interaction between Cr 3+ moments via nonmagnetic [VO 4 ] 3− entities. In the title compound, the degeneracy of the t 2g-orbital set is not lifted by a space group symmetry reduction or subject to significant anisotropy resulting from spin-orbit coupling.

Photoactive complexes with earth-abundant metals have attracted increasing interest in the recent years fueled by the promise of sustainable photochemistry. However, sophisticated ligands with complicated syntheses are oftentimes required to enable photoactivity with non-precious metals. Here, we combine a cheap metal with simple ligands to easily access a photoactive complex. Specifically, we synthesize the molybdenum(0) carbonyl complex Mo(CO)3(tpe) featuring the tripodal ligand tris(pyridyl)ethane (tpe) in two steps with high overall yield. The complex shows intense deep-red phosphorescence with excited state lifetimes of several hundred nanoseconds. Time-resolved infrared spectroscopy and laser flash photolysis reveal a triplet metal-to-ligand charge-transfer (3MLCT) state as lowest excited state. Temperature-dependent luminescence complemented by density functional theory (DFT) calculations suggest thermal deactivation of the 3MLCT state via higher lying metal-centered states in analogy to the well-known photophysics of [Ru(bpy)3]2+. Importantly, we found that the title compound is very photostable due to the lack of labilized Mo–CO bonds (as caused by trans-coordinated CO) in the facial configuration of the ligands. Finally, we show the versatility of the molybdenum(0) complex in two applications: (1) green-to-blue photon upconversion via a triplet-triplet annihilation mechanism and (2) photoredox catalysis for a green-light driv-en dehalogenation reaction. Overall, our results establish tripodal carbonyl complexes as a promising design strategy to ac-cess stable photoactive complexes of non-precious metals avoiding tedious multi-step syntheses.