High Nuclearity (Octa-, Dodeca-, and Pentadecanuclear) Metal (M = Co^II, Ni^II) Phosphonate Cages: Synthesis, Structure, and Magnetic Behavior

Abstract

The synthesis, structural characterization, and magnetic property studies of five new transition metal (M = Co, Ni) phosphonate-based cages are reported. Three substituted phenyl and benzyl phosphonate ligands [RPO3H2; R1 = p-tert-butylbenzyl, R2 = p-tert-butylphenyl, R3 = 3-chlorobenzyl] were synthesized and employed to seek out high-nuclearity cages. Complexes 1-3 are quasi-isostructural and feature a dodecanuclear metal-oxo core having the general molecular formula of [M12(μ3-OH)4 (O3PR)4(O2C(t)Bu)6 (HO2C(t)Bu)6(HCO3)6] {M = Co, Ni and R = R1 for 1 (Co12), R2 for 2, 3 (Co12, Ni12)}. The twelve metal centers are arranged at the vertices of a truncated tetrahedron in a manner similar to Keggin ion. Complex 4 is an octanuclear nickel phosphonate cage [Ni8(μ3-OH)4 (OMe)2(O3PR1)2 (O2C(t)Bu)6(HO2C(t)Bu)8], and complex 5 represents a pentadecanuclear cobalt phosphonate cage, [Co15(chp)8(chpH) (O3PR3)8(O2C(t)Bu)6], where chpH = 6-chloro-2-hydroxypyridine. Structural investigation reveals some interesting geometrical features in the molecular cores, which may provide new models in single molecular magnetic materials. Magnetic property measurements of compounds 1-5 indicate the coexistence of both antiferromagnetic and ferromagnetic interactions between magnetic centers for all cages.

Magnetic and thermodynamic properties of the octanuclear nickel phosphonate-based cage

“…One can see from this figure that, not only ED and QMC results are in accordance with each other, but also they are in a good agreement with the experimental results reported in Ref. [18,19]. To understand the spin exchange anisotropy effects on the magnetization process of the octanuclear nickel phosphonate cage, we plot in Fig.…”

“…Single-molecule magnets have also attracted increased interest owing to the fact that they can possibly be characterized by Heisenberg models [18,19,20,21,22,24,25,26,27,28,29,30]. Polynuclear complexes involving transition-metal and lanthanide-metal ions, synthesized from either identical or different metal ions, are amongst the themes of increasing interest in the study of molecular magnetism.…”

“…These can be properly introduced in terms of Heisenberg models such as: Fe III 6 (µ 3 − O) 2 (µ−OH) 2 {µ−(C 6 H 11 ) 2 PO 2 } 6 (µ−tBuCO 2 ) 6 (η 1 −OH 2 ) 2 ]·2CH 3 CN·CH 2 Cl 2 (for more details see Ref. [22]), and nickel containing complex Ni 8 (µ 3 − OH) 4 (OMe) 2 (O 3 PR 1 ) 2 (O 2 C t Bu) 6 (HO 2 C t Bu) 8 [18,19,20] [23].…”

“…(for more details see Ref. [22]), and nickel containing complex Ni 8 (µ 3 − OH) 4 (OMe) 2 (O 3 PR 1 ) 2 (O 2 C t Bu) 6 (HO 2 C t Bu) 8 [18,19,20] [23].…”

Synthesis and structural characterization of a dumbbell-like phenylphosphonate-stabilized Ti7–oxide cluster

“…Multidentate phosphonate ligands have a strong coordination ability and multiple coordination sites, which contribute to the formation of higher nuclearity coordination clusters (Pineda et al, 2014;Sheikh et al, 2014;Smith et al, 2014;Packiam & Vidyasagar, 2017). In the course of our research of polyoxotitanium clusters (PTCs) (Liu et al, 2016;Narayanam et al, 2016;Fang et al, 2017;Gao et al, 2017), we noticed that PTCs stabilized by phenylphosphonate ligands are relatively less frequently reported, with some typical examples being from Schubert and co-workers (Czakler et al, 2013(Czakler et al, , 2014(Czakler et al, , 2015.…”