Dinuclear dysprosium SMMs bridged by a neutral bipyrimidine ligand: two crystal systems that depend on different lattice solvents lead to a distinct slow relaxation behaviour

Abstract

Two dinuclear dysprosium complexes with the Dy(iii) ions bridged by the neutral bipyrimidine (BPYM) ligand were synthesized and magnetically characterized. They crystallized in a monoclinic and triclinic crystal system, respectively, with almost the same structural core, only differing in the lattice solvent molecules. Alternating current (ac) susceptibility measurements revealed that they exhibit significant slow relaxation of magnetization until 25 K in the absence of a dc field. The single and double relaxation processes were assigned to one and two types of Dy(iii) environments in the two dimmers, respectively, with barriers of 266 and 345 K under zero field conditions. The magnetic hysteresis loops of 1 and 2 were both observed up to 2.5 K.

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.…”

“…al. (Sun et al, 2016 ) and the third molecule has been studied by Mario Ruben et al (Yu et al, 2016 ). The CShM values of the above three molecules along with those of d- 1 are listed in the Table 1 .…”

“…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.…”