Inelastic Neutron Scattering Measurement of the Ground State Tunneling Gap in Tb and Ho Analogues of a Dy Field-Induced Single-Molecule Magnet

Abstract

Recent advances in single-molecule magnet (SMM) research have placed great value on interpretation of inelastic neutron scattering (INS) data for rare earth (RE)-containing SMMs. Here, we present the synthesis of several rare earth complexes where combined magnetic and INS studies have been performed, supported by ab initio calculations. The reaction of rare earth nitrate salts with 2,2′-bipyridine (2,2′-bpy) and tetrahalocatecholate (X 4 Cat 2− , X = Br, Cl) ligands in methanol (MeOH) afforded two new families of compounds [RE(2,2′-bpy) 2 (X 4 Cat)(X 4 CatH)-(MeOH)] (X = Br and RE = Y, Eu, Gd, Tb, Dy, Ho, Yb for 1-RE; X = Cl and RE = Y, Tb, Dy, Ho, and Yb for 2-RE). Addition of triethylamine (Et 3 N) to the reaction mixture delivered Et 3 NH[RE-(2,2′-bpy) 2 (Br 4 Cat) 2 ] (3-RE, RE = Er and Yb).Interestingly, cerium behaves differently to the rest of the series, generating (2,2'-bpyH) 2 [Ce(Br 4 Cat) 3 (2,2′-bpy)] (4-Ce) with tetravalent Ce(IV) in contrast to the trivalent metal ions in 1−3. The static magnetic properties of 1-RE (RE = Gd, Tb, Dy and Ho) were investigated in conjunction with INS measurements on 1-Y, 1-Tb, and 1-Ho to probe their ground state properties and any crystal field excitations. To facilitate interpretation of the INS spectra and provide insight into the magnetic behavior, ab initio calculations were performed using the single-crystal X-ray diffraction structural data of 1-RE (RE = Tb, Dy and Ho). The ab initio calculations indicate ground doublets dominated by the maximal angular momentum projection states of Kramers type for 1-Dy and Ising type for 1-Tb and 1-Ho. Dynamic magnetic susceptibility measurements indicate that 1-Dy exhibits slow magnetic relaxation in the presence of a small applied magnetic field mainly through Raman pathways. Inelastic neutron scattering spectra exhibit distinct transitions corresponding to crystal field-induced tunneling gaps between the pseudo-doublet ground state components for 1-Tb and 1-Ho, which is one of the first direct experimental measurements with INS of such tunneling transitions in a molecular nanomagnet. The power of high-resolution INS is demonstrated with evidence of two distinct tunneling gaps measurable for the two crystallographically unique Tb coordination environments observed in the single crystal X-ray structure.

Synthesis, crystal structure and magnetic properties of octanuclear Ni4Ln4 complexes constructed using a Schiff base ligand and di-2-pyridyl ketone

“…Obviously, the continuous increase for the ln(t) values of 2 implies that the relaxation time cannot be fitted by only considering the above three processes. To fit the ln(t) vs. T À1 plot of 2, the equation of t À1 = AT + CT n + t 0 À1 exp(ÀU eff /k B T) + t QTM À1 was employed, 69,70 in which the four terms on the right side of equation represent the direct process, Raman process, Orbach process and QTM process, respectively. The obtained parameters are A = 369.1(2) K À1 s À1 , C = 5.1(6) Â 10 À6 s À1 K Àn , n = 9.6(7), t 0 = 1.6 Â 10 À4 s, U eff = 4.8(5) K and t QTM = 2.4(3) Â 10 À3 s. As we know, some 3d single ion magnets (SIMs) undergo a direct process.…”

Ab initio-based determination of lanthanoid–radical exchange as visualised by inelastic neutron scattering

“…13,[20][21][22][23] Spectroscopic techniques to measure the lowest lying electronic energy levels in Ln(III) compounds with large spin-orbit coupling include EPR, [24][25][26] luminescence, [27][28][29][30][31] far infrared, 24,32,33 and inelastic neutron scattering spectroscopies. [34][35][36][37][38] Inelastic neutron scattering (INS) offers unique advantagesit requires no applied magnetic eld to identify magnetic transitions and doesn't rely on the oen weak luminescence of Ln(III) ions. 39 By combining INS measurements with ab initio electronic structure calculations, the CF splitting in Ln(III) systems can be accurately determined.…”

Dinuclear ytterbium(iii) benzamidinate complexes with bridging S32−, Se22− and Te22− ligands: synthesis, structure and magnetic properties

“…However, a recent surge in lanthanide chemistry with heavy chalcogens has not yet been exploited in molecular magnetism, although the intrinsically large magnetic anisotropy of Ln makes them enormously popular. 3,5 Among lanthanide ions, Tb( iii ), 6 Dy( iii ), 7 Ho( iii ), 8 Er( iii ), 9 Tm( iii ) 10 and Yb( iii ) 11 are known to form single-molecule magnets (SMMs). Although dysprosium complexes dominate since the ground state of Dy( iii ) is bistable irrespective of the ligand field symmetry, 7 another key component in the design of molecular magnets is often ignored which is the exchange interaction between paramagnetic centres.…”