Deciphering the role of anions and secondary coordination sphere in tuning anisotropy in Dy(III) air-stable D5h SIMs

Precise control of the crystal field and symmetry around the paramagnetic spin centre has recently facilitated the engineering of high-temperature single-ion magnets (SIMs), the smallest possible units for future spin-based devices. In the present work, we report a series of air-stable seven coordinate Dy(III) SIMs {[L2Dy(H2O)5][X]3·L2·n(H2O), n = 0, X = Cl (1), n = 1, X = Br (2), I (3)} possessing pseudo-D5h symmetry or pentagonal bipyramidal coordination geometry with high anisotropy energy barrier (Ueff) and blocking temperature (TB). While the strong axial coordination from the sterically encumbered phosphonamide, tBuPO(NHiPr)2 (L), increases the overall anisotropy of the system, the presence of high symmetry significantly quenches quantum tunnelling of magnetization, which is the prominent deactivating factor encountered in SIMs. Although the local coordination geometry and the symmetry around the Dy(III) in all the three complexes are similar and display only slight deviations, the variation of halide anions in the secondary coordination sphere which is hydrogen-bonded to the coordinated equatorial water molecules, show subtle alteration in the magnetic properties. The energy barrier (Ueff) and the blocking temperature (TB) decrease in the order 3 > 2 > 1 with the change of anions from larger iodide to smaller strongly hydrogen-bonded chloride in the secondary coordination sphere. Ab initio CASSCF/RASSI-SO/SINGLE_ANISO calculations further provide deeper insights into the dynamics of magnetic relaxation in addition to the role of the secondary coordination sphere in modulating the anisotropy of the D5h systems, using diverse models. Thus, in addition to the importance of the crystal field and the symmetry to obtain high-temperature SIMs, this study also probes the significance of the secondary coordination sphere that can be tailored to accomplish novel SIMs.

Effect of the proximal secondary sphere on the self-assembly of tetrahedral zinc-oxo clusters

Metal-oxo clusters can serve as directional and rigid building units of coordination and noncovalent supramolecular assemblies. Therefore, an in-depth understanding of their multi-faceted chemistry is vital for the development of self-assembled solid-state structures of desired properties. Here we present a comprehensive comparative structural analysis of isostructural benzoate, benzamidate, and new benzamidinate zinc-oxo clusters incorporating the [O,O]-, [O,NH]- and [NH,NH]-anchoring donor centers, respectively. We demonstrated that the NH groups in the proximal secondary coordination sphere are prone to the formation of intermolecular hydrogen bonds, which affects the packing of clusters in the crystal structure. Coordination sphere engineering can lead to the rational design of new catalytic sites and novel molecular building units of supramolecular assemblies.

Access to Monomeric Hydridoplumbate(II) Anions with Remarkable Thermostability

We report on the remarkable stability of synthesized monomeric hydridoplumbates M+[LPb(II)H]− (M[1-H]) where L = 2,6-bis(3,5-diphenylpyrrolyl)pyridine and M = (18-crown-6)potassium or ([2.2.2]-cryptand)potassium. The half-life of [K18c6][1-H] is approximately 2 days in tetrahydrofuran at ambient temperature. The presence of a Pb–H bond in the hydridoplumbates was unambiguously identified by performing 1H, 2H (with a lead(II) deuteride analogue), 207Pb{1H}, proton-coupled 207Pb, and 1H-207Pb 2D nuclear magnetic resonance spectroscopy. The experimental observations and theoretical calculations indicated the presence of dihydrogen bonding as a secondary coordination sphere interaction between the protons of the ligand backbone and the hydride ligand that helps stabilize Pb–H bonding. The Pb–H bond readily adds to the C = O bond of benzaldehyde to form a benzyloxy compound. The regeneration of Pb(II)–H moieties was observed by treating pinacolborane with lead(II) benzyloxy compounds, which indicated that lead(II) hydrides can be used as catalysts for hydroelementation reactions involving unsaturated molecules.

Iron(II) Complexes Featuring a Redox-Active Dihydrazonopyrrole Ligand

<div>Nature uses control of the secondary coordination sphere</div><div>to facilitate an astounding variety of transformations. Similarly, synthetic chemists have found metal-ligand cooperativity to be a powerful strategy for designing complexes that can mediate challenging reactivity. In particular, this strategy has been used to facilitate two electron reactions with first row transition metals that</div><div>more typically engage in one electron redox processes. While NNN pincer ligands feature prominently in this area, examples which can potentially engage in both proton and electron transfer are less common. Dihydrazonopyrrole (DHP) ligands have been isolated in a variety of redox and protonation states when complexed to Ni. However, the redox-state of this ligand scaffold is less obvious when</div><div>complexed to metal centers with more accessible redox couples. Here, we synthesize a new series of Fe-DHP complexes in two distinct oxidation states. Detailed characterization supports that the redox chemistry</div><div>in this set is still primarily ligand based. Finally, these</div><div>complexes exist as 5-coordinate species with an open coordination site offering the possibility of enhanced reactivity.</div>