• Correlating axial and equatorial ligand field effects to the single-molecule magnet performances of a family of dysprosium bis-methanediide complexes.

      Thomas-Hargreaves, Lewis R; orcid: 0000-0002-2895-6931; Giansiracusa, Marcus J; orcid: 0000-0002-2481-4063; Gregson, Matthew; Zanda, Emanuele; O'Donnell, Felix; Wooles, Ashley J; Chilton, Nicholas F; orcid: 0000-0002-8604-0171; Liddle, Stephen T; orcid: 0000-0001-9911-8778 (2021-03-02)
      Treatment of the new methanediide-methanide complex [Dy(SCS)(SCSH)(THF)] ( , SCS = {C(PPh S) } ) with alkali metal alkyls and auxillary ethers produces the bis-methanediide complexes [Dy(SCS) ][Dy(SCS) (K(DME) ) ] ( ), [Dy(SCS) ][Na(DME) ] ( ) and [Dy(SCS) ][K(2,2,2-cryptand)] ( ). For further comparisons, the bis-methanediide complex [Dy(NCN) ][K(DB18C6)(THF)(toluene)] ( , NCN = {C(PPh NSiMe ) } , DB18C6 = dibenzo-18-crown-6 ether) was prepared. Magnetic susceptibility experiments reveal slow relaxation of the magnetisation for , with open magnetic hysteresis up to 14, 12, 15, and 12 K, respectively (∼14 Oe s ). Fitting the alternating current magnetic susceptibility data for gives energy barriers to magnetic relaxation ( ) of 1069(129)/1160(21), 1015(32), 1109(70), and 757(39) K, respectively, thus join a privileged group of SMMs with values of ∼1000 K and greater with magnetic hysteresis at temperatures >10 K. These structurally similar Dy-components permit systematic correlation of the effects of axial and equatorial ligand fields on single-molecule magnet performance. For , the Dy-components can be grouped into / and / , where the former have almost linear C[double bond, length as m-dash]Dy[double bond, length as m-dash]C units with short average Dy[double bond, length as m-dash]C distances, and the latter have more bent C[double bond, length as m-dash]Dy[double bond, length as m-dash]C units with longer average Dy[double bond, length as m-dash]C bonds. Both and hysteresis temperature are superior for the former pair compared to the latter pair as predicted, supporting the hypothesis that a more linear axial ligand field with shorter M-L distances produces enhanced SMM properties. Comparison with demonstrates unusually clear-cut examples of: (i) weakening the equatorial ligand field results in enhancement of the SMM performance of a monometallic system; (ii) a positive correlation between barrier and axial linearity in structurally comparable systems. [Abstract copyright: This journal is © The Royal Society of Chemistry.]
    • Correlating axial and equatorial ligand field effects to the single-molecule magnet performances of a family of dysprosium bis-methanediide complexes.

      Thomas-Hargreaves, Lewis R; orcid: 0000-0002-2895-6931; Giansiracusa, Marcus J; orcid: 0000-0002-2481-4063; Gregson, Matthew; Zanda, Emanuele; O'Donnell, Felix; Wooles, Ashley J; Chilton, Nicholas F; orcid: 0000-0002-8604-0171; Liddle, Stephen T; orcid: 0000-0001-9911-8778 (2021-03-02)
      Treatment of the new methanediide-methanide complex [Dy(SCS)(SCSH)(THF)] (<b>1Dy</b>, SCS = {C(PPh<sub>2</sub>S)<sub>2</sub>}<sup>2-</sup>) with alkali metal alkyls and auxillary ethers produces the bis-methanediide complexes [Dy(SCS)<sub>2</sub>][Dy(SCS)<sub>2</sub>(K(DME)<sub>2</sub>)<sub>2</sub>] (<b>2Dy</b>), [Dy(SCS)<sub>2</sub>][Na(DME)<sub>3</sub>] (<b>3Dy</b>) and [Dy(SCS)<sub>2</sub>][K(2,2,2-cryptand)] (<b>4Dy</b>). For further comparisons, the bis-methanediide complex [Dy(NCN)<sub>2</sub>][K(DB18C6)(THF)(toluene)] (<b>5Dy</b>, NCN = {C(PPh<sub>2</sub>NSiMe<sub>3</sub>)<sub>2</sub>}<sup>2-</sup>, DB18C6 = dibenzo-18-crown-6 ether) was prepared. Magnetic susceptibility experiments reveal slow relaxation of the magnetisation for <b>2Dy-5Dy</b>, with open magnetic hysteresis up to 14, 12, 15, and 12 K, respectively (∼14 Oe s<sup>-1</sup>). Fitting the alternating current magnetic susceptibility data for <b>2Dy-5Dy</b> gives energy barriers to magnetic relaxation (<i>U</i> <sub>eff</sub>) of 1069(129)/1160(21), 1015(32), 1109(70), and 757(39) K, respectively, thus <b>2Dy-4Dy</b> join a privileged group of SMMs with <i>U</i> <sub>eff</sub> values of ∼1000 K and greater with magnetic hysteresis at temperatures >10 K. These structurally similar Dy-components permit systematic correlation of the effects of axial and equatorial ligand fields on single-molecule magnet performance. For <b>2Dy-4Dy</b>, the Dy-components can be grouped into <b>2Dy-cation</b>/<b>4Dy</b> and <b>2Dy-anion</b>/<b>3Dy</b>, where the former have almost linear C[double bond, length as m-dash]Dy[double bond, length as m-dash]C units with short average Dy[double bond, length as m-dash]C distances, and the latter have more bent C[double bond, length as m-dash]Dy[double bond, length as m-dash]C units with longer average Dy[double bond, length as m-dash]C bonds. Both <i>U</i> <sub>eff</sub> and hysteresis temperature are superior for the former pair compared to the latter pair as predicted, supporting the hypothesis that a more linear axial ligand field with shorter M-L distances produces enhanced SMM properties. Comparison with <b>5Dy</b> demonstrates unusually clear-cut examples of: (i) weakening the equatorial ligand field results in enhancement of the SMM performance of a monometallic system; (ii) a positive correlation between <i>U</i> <sub>eff</sub> barrier and axial linearity in structurally comparable systems.