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The molecular tetravalent oxidation state for praseodymium is observed in solution via oxidation of the anionic trivalent precursor [K][Pr 3+ (NP(1,2-bis- t Bu-diamidoethane)(NEt 2 )) 4 ] (1-Pr(NP*)) with AgI at −35 °C. The Pr 4+ complex is characterized in solution via cyclic voltammetry, UV-vis-NIR electronic absorption spectroscopy, and EPR spectroscopy. Electrochemical analyses of [K][Ln 3+ (NP(1,2-bis- t Bu-diamidoethane)(NEt 2 )) 4 ] (Ln = Nd and Dy) by cyclic voltammetry are reported and, in conjunction with theoretical modeling of electronic structure and oxidation potential, are indicative of principal ligand oxidations in contrast to the metal-centered oxidation observed for 1-Pr(NP*). The identification of a tetravalent praseodymium complex in in situ UV-vis and EPR experiments is further validated by theoretical modeling of the redox chemistry and the UV-vis spectrum. The latter study was performed by extended multistate pair-density functional theory (XMS-PDFT) and implicates a multiconfigurational ground state for the tetravalent praseodymium complex. 

Mononuclear heteroleptic complexes [Fe(tpma)(bimz)](ClO4)2 (1a), [Fe(tpma)(bimz)](BF4)2 (1b), [Fe(bpte)(bimz)](ClO4)2 (2a), and [Fe(bpte)(bimz)](BF4)2 (2b) (tpma = tris(2-pyridylmethyl)amine, bpte = S,S′-bis(2-pyridylmethyl)-1,2-thioethane, bimz = 2,2′-biimidazoline) were prepared by reacting the corresponding Fe(II) salts with stoichiometric amounts of the ligands. All complexes exhibit temperature-induced spin crossover (SCO), but the SCO temperature is substantially lower for complexes 1a and 1b as compared to 2a and 2b, indicating the stronger ligand field afforded by the N2S2-coordinating bpte ligand relative to the N4-coordinating tpma. Our findings suggest that ligands with mixed N/S coordination can be employed to discover new SCO complexes and to tune the transition temperature of known SCO compounds by substituting for purely N-coordinating ligands. 

We report two anionic diphosphametallocenates, [K(2.2.2-crypt)][M(PC 4 Me 4 ) 2 ] (M = Cr, 2-Cr ; Fe, 2-Fe ). Both are low-spin ( S = ½) by EPR spectroscopy and SQUID magnetometry. This contrasts the high-spin ( S = ) ferrocenate, [K(2.2.2-crypt)][Fe(C 5 H 2 -1,2,4- t Bu) 2 ] ( 4-Fe ). Quantum chemical calculations suggest this is due to significant differences in ligand field splitting of the d-orbitals which also explain structural features in the 2-M complexes. 

Abstract A number of technologies would benefit from developing inorganic compounds and materials with specific electronic and magnetic exchange properties. Unfortunately, designing compounds with these properties is difficult because metal⋅⋅⋅metal coupling schemes are hard to predict and control. Fully characterizing communication between metals in existing compounds that exhibit interesting properties could provide valuable insight and advance those predictive capabilities. One such class of molecules are the series of Lindqvist iron‐functionalized and hexavanadium polyoxovanadate‐alkoxide clusters, which we characterized here using V K‐edge X‐ray absorption spectroscopy. Substantial changes in the pre‐edge peak intensities were observed that tracked with the V 3d‐electron count. The data also suggested substantial delocalization between the vanadium cations. Meanwhile, the Fe^IIIcations were electronically isolated from the polyoxovanadate core. 

Abstract Large separation of magnetic levels and slow relaxation in metal complexes are desirable properties of single‐molecule magnets (SMMs). Spin‐phonon coupling (interactions of magnetic levels with phonons) is ubiquitous, leading to magnetic relaxation and loss of memory in SMMs and quantum coherence in qubits. Direct observation of magnetic transitions and spin‐phonon coupling in molecules is challenging. We have found that far‐IR magnetic spectra (FIRMS) of Co(PPh₃)₂X₂(Co‐X; X=Cl, Br, I) reveal rarely observed spin‐phonon coupling as avoided crossings between magnetic andu‐symmetry phonon transitions. Inelastic neutron scattering (INS) gives phonon spectra. Calculations using VASP and phonopy programs gave phonon symmetries and movies. Magnetic transitions among zero‐field split (ZFS) levels of theS=3/2 electronic ground state were probed by INS, high‐frequency and ‐field EPR (HFEPR), FIRMS, and frequency‐domain FT terahertz EPR (FD‐FT THz‐EPR), giving magnetic excitation spectra and determining ZFS parameters (D, E) andgvalues. Ligand‐field theory (LFT) was used to analyze earlier electronic absorption spectra and give calculated ZFS parameters matching those from the experiments. DFT calculations also gave spin densities inCo‐X, showing that the larger Co(II) spin density in a molecule, the larger its ZFS magnitude. The current work reveals dynamics of magnetic and phonon excitations in SMMs. Studies of such couplings in the future would help to understand how spin‐phonon coupling may lead to magnetic relaxation and develop guidance to control such coupling.