[CrF(O₂C^tBu)₂]₉: Synthesis and Characterization of a Regular Homometallic Ring with an Odd Number of Metal Centers and Electrons

Abstract

The first regular homometallic ring containing an odd number of metal centers is reported. The ring was synthesized by means of amine-templated self-assembly. Extensive physical characterization studies,including magnetic measurements,p owder inelastic neutron scattering (INS), and DFT calculations,s how that the molecule has an ear perfect matchtothe expected behavior for afrustrated system with the lowest energy pair of S = 1/2 spin states separated by only 0.1 meV (0.8 cm À1).The literature on polymetallic compounds with cyclic metal cores has certain unusual gaps.S ince the publication in 1990 of both {Fe 10 } [1] by Lippard and Taft and {Cr 8 } [2] by Timco and co-workers,awide range of sizes have been reported for homometallic rings,i ncluding {Fe 18 }/{Ga 18 } [3] rings (currently the largest reported regular wheels,that is,where every edge and every vertex is chemically equivalent) to the more complex {Mn 32 }d ouble decker structure.[4] "Magic number" rings of {Mn 84 } [5] and {Pd 84 } [6] have also been reported. The largest cyclic metal structures remain the extraordinary molybdate wheels from Müller and co-workers.[7] However, rings with odd numbers of metal centers (termed herein oddnumbered rings), particularly those larger than triangles,a re conspicuous by their near absence.There are afew reported heterometallic nine-metal rings, including {Cr 7 V 2 }a nd a{ Cr 8 M} family.[8] However,r egular homometallic rings containing odd numbers of metal centers are restricted to metal triangles,asmall number of pentagons, [9,10] and as ingle heptametallic {V 7 }ring made by Oshio and co-workers with the vanadium sites bridged by ac yclodextrin ligand. [11] Large regular odd-numbered rings would show interesting physics associated with spin frustration, [12,13] which occurs when the classical magnetic energy cannot be simultaneously minimized for all individual two-spin interaction terms. Theoretical studies to classify the degree of frustration in such systems have been recently reported. [14] In 2002 the structures of two toroidal thiolate-bridged nickel structures, {Ni 9 }and {Ni 11 }, were published by Dahl and co-workers,both of which showed considerable geometric irregularity;h owever,n oc haracterization beyond crystallography was reported.[15] In 2004, Mezei et al. reported an onametallic copper ring {Cu 9 }that was not isolated but co-crystallized with arange of other copper rings. [16] We previously reported two nonametallic rings {Cr 9 F 10 } and {Cr 9 F 11 }( see below), each of which contained one edge with adefect breaking the regularity of the ring.[17] Herein, we report the synthesis of the first regular nine-metal homometallic ring, [CrF(O 2 C t Bu) 2 ] 9 1,a long with characterization of the ring by magnetometry and inelastic neutron scattering (INS) to explore the extent of spin frustration.Thes ynthesis of 1 is based on ap rocedure we previously developed for synthesizing hexametallic and heptametallic chromium horseshoes [18] -addition of at emplating amine to ar eaction that...

Unravelling the Spin Dynamics of Molecular Nanomagnets with Four‐Dimensional Inelastic Neutron Scattering

“…Thus, after selecting incident neutrons with the desired 𝐸 𝑖 and 𝐤 𝐢 , equation (10) gives us the accessible values of the transferred energy 𝐸 and momentum 𝐐 for every scattering angle 𝜑. The accessible ranges in both 𝐸 and 𝐐 increase if 𝐸 𝑖 is increased.…”

“…Thus, the crystals behave like an ensemble of non-interacting identical molecules, enabling single-molecule properties to be accessed by bulk measurements. MNMs represent therefore ideal test beds for fundamental concepts in quantum mechanics such as quantum-tunnelling of the magnetization, [3,4] Berry-phase interference, [5] frustration, [6][7][8][9][10][11][12] finite-size effects in open or closed rings, [13][14][15] Néel-vector tunnelling, [16,17] entanglement [18][19][20][21] or coherence. [22][23][24] Moreover they are also promising building blocks for technological applications ranging from high-density data storage [25][26][27] to magnetocaloric refrigeration, [28][29][30][31] spintronics [32][33][34] and quantum information processing.…”

“…[51,52] For instance, antiferromagnetic (AF) rings have been fully characterised by this technique, [13,22,28,53,54] together with many other MNMs. [55][56][57][58][59][60][61] Moreover, the rich physics displayed by MNMs can be probed by INS, unravelling some of the above mentioned peculiar quantum phenomena, such as Néel-vector tunnelling, [16,17] frustration, [8,10,11,[62][63][64][65] and finite-size effects. [14,66] Finally, INS has been employed to evidence the effect of pressure on the Mn12 anisotropy barrier [67] and to monitor its relaxation dynamics.…”

The Lagrange variety approach applied to frustrated classical wheels

“…Ring-shaped magnetic molecules play an important role due to possible realization of single molecule magnets or molecular qubits [1][2][3][4][5][6]. Moreover, these, with an odd number of spins and dominant antiferromagnetic couplings, are interesting subjects in the study of the spin frustration [7][8][9][10][11][12][13][14].…”

Magnetic properties of transition metal dimers probed by inelastic neutron scattering

“…Thanks to their relatively small size and their zero-dimensional characteristics, they offer a remarkable opportunity to study fundamental physical phenomena of both quantum and classical nature. [1][2][3][4][5][6][7][8] Moreover, the high degree of achieved chemical control makes them promising systems for many different applications, such as quantum-information processing [9][10][11][12][13][14] , high-density data storage [15][16][17] and low-temperature magnetic refrigeration 18,19 .…”