Iron Lanthanide Phosphonate Clusters: {Fe₆Ln₆P₆} Wells—Dawson-like Structures withD_3dSymmetry

Abstract

Reaction of [Fe3(μ3-O)(O2C(t)Bu)6(HO2C(t)Bu)3](O2C(t)Bu) and [Ln2(O2C(t)Bu)6(HO2C(t)Bu)6] (Ln = lanthanide) with three different phosphonic acids produce a family of highly symmetrical {Fe6Ln6P6} clusters with general formula [Fe6Ln6(μ3-O)2(CO3)(O3PR)6(O2C(t)Bu)18], where R = methyl 1, phenyl 2, or n-hexyl 3. All the clusters present an analogous metal frame to the previously reported {Ni6Ln6P6} both being related to the well-known Wells-Dawson ion from polyoxometallate chemistry. These highly symmetrical clusters have, or approximate very closely to, D3d point symmetry. Both Fe(III) and Gd(III) ions are magnetically isotropic and could thus exhibit promising magnetocaloric properties; hence we investigated the {Fe6Gd6P6} compounds accordingly. Modeling the magnetic data of [Fe6Gd6(μ3-O)2(CO3)(O3PPh)6(O2C(t)Bu)18] by the finite-temperature Lanczos method gave a strong antiferromagnetic Fe···Fe interaction (J(Fe-Fe) = -30 cm(-1)) and very weak Gd···Gd and Gd···Fe exchange interactions (|J| < 0.1 cm(-1)). The strong antiferromagnetic Fe···Fe interaction could account for the relatively smaller -ΔSm value observed, compared against the {Ni6Gd6P6} analogues.

Molecular Metal Phosphonates

“…214−232 In addition to the homometallic compounds described above, recently Winpenny et al synthesized heterometallic dodecanuclear complexes, [Fe 6 Ln 6 (μ 3 -O) 2 (CO 3 )(O 3 PR) 6 -(O 2 CBu-t) 8 ], where R = methyl, phenyl, or n-hexyl and Ln = Gd, Tb, Dy, or Ho. 24 These complexes have been prepared by utilizing the cluster expansion strategy involving the reaction of [Fe 3 (μ 3 -O)(O 2 CBu-t) 6 (HO 2 CBu-t) 3 ]·(O 2 CBu-t) and [Ln 2 (O 2 CBu-t) 6 (HO 2 CBu-t) 6 ] (Ln = Gd, Tb, Dy, or Ho). These complexes possess the so-called Wells−Dawson type Fe 6 Ln 6 core, as shown in Figure 101.…”

“…Both the inner and the outer parts are connected to each other by bridging [RPO 3 ] 2− and [t-BuCO 2 ] − ligands 24. …”

Coordination‐Cluster‐Based Molecular Magnetic Refrigerants

“…The self‐assemblies of (μ 3 ‐O)(O 2 C t Bu) 7 (HO 2 C t Bu) 3 ] and [Gd 2 (O 2 C t Bu) 6 (HO 2 C t Bu) 6 ] with three different phosphonic ligands yielded three highly symmetrical { Gd 6 P 6 } clusters with general formula [ Gd 6 (μ 3 ‐O) 2 (CO 3 )(O 3 P R ) 6 (O 2 C t Bu) 18 ] ( R =methyl for 130a , phenyl for 130b , and n ‐hexyl for 130c ),101 which presents an analogous metal frame to the previously reported Wells–Dawson‐type { Gd 6 P 6 } 81. Considering that both Fe III and Gd III ions are magnetically isotropic and could show promising magnetocaloric properties, the authors investigated the three CPs accordingly, and the maximum –Δ S m values obtained from the magnetization data for an applied field of 70 kOe at 3.0 K are 25.4, 22.0, and 22.9 J kg −1 K −1 for 130a – c , respectively.…”

Hexanuclear iron(iii) α-aminophosphonate: synthesis, structure, and magnetic properties of a molecular wheel

“…Iron based molecules have been investigated in biological modeling studies. [16][17][18][19][20][21] Polynuclear molecular iron phosphonates with nuclearities from {Fe 4 } to {Fe 36 } were reviewed recently. [22][23][24] All these polynuclear molecular phosphonates contain Fe 3+ ions.…”