Single-molecule magnet behavior in 2,2’-bipyrimidine-bridged dilanthanide complexes

Abstract

SummaryA series of 2,2’-bipyrimidine-bridged dinuclear lanthanide complexes with the general formula [Ln(tmhd)3]2bpm (tmhd = 2,2,6,6-tetramethyl-3,5-heptanedionate, bpm = 2,2’-bipyrimidine, Ln = Gd(III), 1; Tb(III), 2; Dy(III), 3; Ho(III), 4 and Er(III), 5) has been synthesized and characterized. Sublimation of [Tb(tmhd)3]2bpm onto a Au(111) surface leads to the formation of a homogeneous film with hexagonal pattern, which was studied by scanning tunneling microscopy (STM). The bulk magnetic properties of all complexes have been studied comprehensively. The dynamic magnetic behavior of the Dy(III) and Er(III) compounds clearly exhibits single molecule magnet (SMM) characteristics with an energy barrier of 97 and 25 K, respectively. Moreover, micro-SQUID measurements on single crystals confirm their SMM behavior with the presence of hysteresis loops.

A Chiral Bipyrimidine-Bridged Dy2 SMM: A Comparative Experimental and Theoretical Study of the Correlation Between the Distortion of the DyO6N2 Coordination Sphere and the Anisotropy Barrier

“…This fact is not unexpected, as the electrostatic interactions between the Dy III ion and oxygen atoms of the tfacam − ligands are larger than those involving the nitrogen atoms of the bipym bridging ligand. Similar bond distances have been observed for the analogous achiral [(μ-bipym){(β-diketonate) 3 Dy} 2 ] complexes (Sun et al, 2016 ; Yu et al, 2016 ). The [(μ-bipym){((+)-tfacam) 3 Dy} 2 ] molecules are well-isolated in the structure because they are neither involved in hydrogen bond interactions nor in close intermolecular contacts.…”

“…The inherent chirality of the ligand may introduce additional functions to coordination compounds with interesting magnetic properties such as magnetochiral dichroism (MChD) effect (Rikken and Raupach, 1997 , 2000 ; Train et al, 2008 , 2011 ), second harmonic generation (SHG) (Bogani et al, 2006 ; Train et al, 2009 ), and ferroelectric properties (Wang et al, 2012 ; Li et al, 2017 ). It has been recently shown that mononuclear tris(β-diketonate) Dy III complexes containing a N,N-bidentate chelate aromatic ligand, such as 2,2′-bipyrimidine and 1,10-phenanthroline derivatives, as well as Dy 2 dinuclear complexes containing bis(didentate) bridging ligands connecting two tris(β-diketonate) Dy III moieties, such as 2,2'-bipyrimidine and 2,2'-bipyrimidine-N-oxide, exhibit Single-Molecule Magnet (SMM) behavior at zero field with significant thermal energy barriers ( U eff ) (Chen et al, 2011 , 2012 ; Wang et al, 2013 ; Tong et al, 2015 ; Sun et al, 2016 ; Yu et al, 2016 ; Cen et al, 2017 ; Díaz-Ortega et al, 2018 ). SMMs are nanomagnets that, in addition to the classical properties of a magnet, such as freezing of magnetization and magnetic hysteresis below the so called blocking temperature (T B ), exhibit interesting quantum properties, such as quantum tunneling of the magnetization (QTM) and quantum phase interference (Aromí and Brechin, 2006 ; Gatteschi et al, 2006 ; Andruh et al, 2009 ; Bagai and Christou, 2009 ; Sessoli and Powell, 2009 ; Brechin, 2010 ; Guo et al, 2011 ; Rinehart and Long, 2011 ; Sorace et al, 2011 ; Clemente-Juan et al, 2012 ; Luzon and Sessoli, 2012 ; Wang and Gao, 2012 ; Habib and Murugesu, 2013 ; Woodruff et al, 2013 ; Zhang et al, 2013 ; Bartolomé et al, 2014 ; Layfield, 2014 ; Sharples and Collison, 2014 ; Craig and Murrie, 2015 ; Layfield and Murugesu, 2015 ; Liddle and van Slageren, 2015 ; Rosado Piquer and Sañudo, 2015 ; Tang and Zhang, 2015 ; Frost et al, 2016 ; Harriman and Murugesu, 2016 ).…”

“…This paper reports the synthesis, crystal structure, detailed ac and dc magnetic studies and ab initio theoretical calculations of the dinuclear complexes [(μ-bipym){((+)-tfacam) 3 Dy} 2 ] (d- 1 ) and [(μ-bipym){((-)-tfacam) 3 Dy} 2 ] (l- 1 ), where (+)/(-)-Htfacam are (+)/(–)-3-(trifluoroacetyl)camphor enantiopure ligands and bipym is the bipyrimidine bridging ligand. It is worth mentioning that three achiral [(μ-bipym){(β-diketonate) 3 Dy} 2 ]complexes have been previously prepared where β-diketonate = dibenzoylmethane(HDbzm) and 2,2,6,6-tetramethyl-3,5-heptanedioneand (Htmh) (Sun et al, 2016 ; Yu et al, 2016 ). The complex [(μ-bipym){(Dbzm) 3 Dy} 2 ]·2CH 3 Cl ( 2 ) (Sun et al, 2016 ) displays two relaxation processes with U eff = 201 and 67 K at zero field, while the analogous complex with different crystal solvent molecules [(μ-bipym){(Dbzm) 3 Dy} 2 ]·MeCN ( 3 ) (Sun et al, 2016 ) and the complex [(μ-bipym){(tmh) 3 Dy} 2 ]( 4 ) (Yu et al, 2016 ) exhibit only a relaxation process with U eff = 267 and 97 K, respectively.…”

“…It is worth mentioning that three achiral [(μ-bipym){(β-diketonate) 3 Dy} 2 ]complexes have been previously prepared where β-diketonate = dibenzoylmethane(HDbzm) and 2,2,6,6-tetramethyl-3,5-heptanedioneand (Htmh) (Sun et al, 2016 ; Yu et al, 2016 ). The complex [(μ-bipym){(Dbzm) 3 Dy} 2 ]·2CH 3 Cl ( 2 ) (Sun et al, 2016 ) displays two relaxation processes with U eff = 201 and 67 K at zero field, while the analogous complex with different crystal solvent molecules [(μ-bipym){(Dbzm) 3 Dy} 2 ]·MeCN ( 3 ) (Sun et al, 2016 ) and the complex [(μ-bipym){(tmh) 3 Dy} 2 ]( 4 ) (Yu et al, 2016 ) exhibit only a relaxation process with U eff = 267 and 97 K, respectively. In view of these results, the SMM behavior of 1 appears to be guaranteed.…”

Hysteresis in a bimetallic holmium complex: A synergy between electronic and nuclear magnetic interactions

“…The study of the interplay of the SMM behavior in dinuclear complexes is quite recent and is mainly focused on Dy-containing complexes [12][13][14][15][16][17][18][19]. Magnetization hysteresis loops have been observed in a series of Ln(III) [20] and in several bimetallic Dy(III) [21][22][23][24]. However, to the best of our knowledge, no magnetic hysteresis loop was reported for binuclear Ho(III)-containing complexes [25].…”