What Controls the Magnetic Exchange and Anisotropy in a Family of Tetranuclear {Mn2IIMn2III} Single-Molecule Magnets?
Twelve heterovalent, tetranuclear manganese(II/III) planar diamond or "butterfly" complexes, 1-12, have been synthesized and structurally characterized, and their magnetic properties have been probed using experimental and theoretical techniques. The 12 structures are divided into two distinct "classes". Compounds 1-8 place the Mn(III), S = 2, ions in the body positions of the butterfly metallic core, while the Mn(II), S = 5/2, ions occupy the outer wing sites and are described as "Class 1". Compounds 9-12 display the reverse arrangement of ions and are described as "Class 2". Direct current susceptibility measurements for 1-12 reveal ground spin states ranging from S = 1 to S = 9, with each complex displaying unique magnetic exchange parameters (J). Alternating current susceptibility measurements found that that slow magnetic relaxation is observed for all complexes, except for 10 and 12, and display differing anisotropy barriers to magnetization reversal. First, we determined the magnitude of the magnetic exchange parameters for all complexes. Three exchange coupling constants (Jbb, Jwb, and Jww) were determined by DFT methods which are found to be in good agreement with the experimental fits. It was found that the orientation of the Jahn-Teller axes and the Mn-Mn distances play a pivotal role in determining the sign and strength of the Jbbparameter. Extensive magneto-structural correlations have been developed for the two classes of {MnII2MnIII2} butterfly complexes by varying the Mnb-O distance, Mnw-O distance, Mnb-O-Mnbangle (α), Mnb-O-Mnb-O dihedral angle (γ), and out-of-plane shift of the Mnwatoms (β). For the magnetic anisotropy the DFT calculations yielded larger negative D value for complexes 2, 3, 4, and 6 compared to the other complexes. This is found to be correlated to the electron-donating/withdrawing substituents attached to the ligand moiety and suggests a possible way to fine tune the magnetic anisotropy in polynuclear Mn ion complexes.
IITB-Monash Research Academy, IIT Bombay , Mumbai 400076, India.
Kuduva R
KR
Vignesh
School of Science and the Environment, Chemistry Division, Manchester Metropolitan University , Manchester, United Kingdom.
Stuart K
SK
Langley
School of Chemistry, Monash University , Clayton, Victoria 3800, Australia.
Christopher J
CJ
Gartshore
School of Chemistry, Monash University , Clayton, Victoria 3800, Australia.
Boujemaa
B
Moubaraki
School of Chemistry, Monash University , Clayton, Victoria 3800, Australia.
Keith S
KS
Murray
Department of Chemistry, Indian Institute of Technology Bombay , Mumbai 400076, India.
Gopalan
http://orcid.org/0000-0001-6133-3026
G
Rajaraman