High spin cycles: topping the spin record for a single molecule verging on quantum criticality

Abstract

The cyclisation of a short chain into a ring provides fascinating scenarios in terms of transforming a finite array of spins into a quasiinfinite structure. If frustration is present, theory predicts interesting quantum critical points, where the ground state and thus lowtemperature properties of a material change drastically upon even a small variation of appropriate external parameters. This can be visualised as achieving a very high and pointed summit where the way down has an infinity of possibilities, which by any parameter change will be rapidly chosen, in order to reach the final ground state. Here we report a mixed 3d/4f cyclic coordination cluster that turns out to be very near or even at such a quantum critical point. It has a ground state spin of S = 60, the largest ever observed for a molecule (120 times that of a single electron). [Fe 10 Gd 10 (Me-tea) 10 (Me-teaH) 10 (NO 3 ) 10 ]·20MeCN forms a nano-torus with alternating gadolinium and iron ions with a nearest neighbour Fe-Gd coupling and a frustrating next-nearest neighbour Fe-Fe coupling. Such a spin arrangement corresponds to a cyclic delta or saw-tooth chain, which can exhibit unusual frustration effects. In the present case, the quantum critical point bears a 'flatland' of tens of thousands of energetically degenerate states between which transitions are possible at no energy costs with profound caloric consequences. Entropy-wise the energy flatland translates into the pointed summit overlooking the entropy landscape. Going downhill several target states can be reached depending on the applied physical procedure which offers new prospects for addressability.

Isolation and Characterization of Different Homometallic and Heterobimetallic Complexes of Nickel and Zinc Ions by Controlling Molar Ratios and Solvents

“…Interestingly, SMMs possess significant energy barriers caused by a combination of a large spin value for the ground state and a negative axial magnetic anisotropy . Due to this energy barrier, slow magnetic relaxation of magnetization and magnetic hysteresis loops are observed . The specific µ 3 ‐O bridges present in the complex core play an important role in facilitating magnetic exchange interactions between the paramagnetic metal ions in such complexes …”

Quantum Monte Carlo simulations of a giant {Ni21Gd20} cage with a S = 91 spin ground state

“…To date, the highest ground spin states reported are S  =  83 / 2 for a {Mn 19 } cage 7 , S  =  61 / 2 for a {Mn 49 } cage 2 , S  = 45 for an {Fe 42 } cage 8 , and S  = 60 for a {Fe 10 Gd 10 } nano-torus 9 . The accurate magnetic analysis of such giant species is challenging because the number of energy levels increases exponentially with the magnitude and number of spins.…”

Bis-tris propane as a flexible ligand for high-nuclearity complexes

“…The use of two, or more, different metal ions to assemble large heterometallic complexes is a considerable synthetic challenge [19,40,41]. However, the potential rewards are significant, as there is a real possibility of control/design over the individual parameters that contribute to the overall molecular properties.…”

“…Current areas of interest relate to single-molecule magnets (SMMs) [4,5]; magnetic refrigerants [6]; qubits [7]; complexes with toroidal moments [8]; the magnetic behavior of high symmetry systems [9][10][11]; magnetic bistability on surfaces [12]; mimics of the oxygen evolution center in photosystem II [13], and water oxidation electrocatalysis [14]; MRI contrast agents [15] and as precursors for magnetic nanoparticles [16], or lithographic resists [17]. However, the synthetic challenges involved in isolating such systems [18] and the search for emergent properties in larger and larger systems is also a major driving force [19][20][21][22][23]. We have a long-standing interest in the use of polydentate ligands [24] to direct the assembly of homo-and heterometallic complexes and in particular a series of structurally related ligands containing the Tris unit {(Tris = 2-amino-2-(hydroxymethyl) propane-1,3-diol} [25,26] such as Bis-tris {2-[bis(2-hydroxyethyl) amino]-2-(hydroxymethyl) propane-1,3-diol} [27][28][29].…”

“…Our approach to Co/ Gd systems for MCE used {Co II (H 6 L)} precursors which undergo facile oxidation to diamagnetic Co(III) [57]. 10 Yb 10 } which are all more puckered than 23 [19,58,59,60].…”