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A New Family of Trinuclear Nickel(II) Complexes as Single‐Molecule Magnets
Author(s) -
Biswas Rituparna,
Ida Yumi,
Baker Michael L.,
Biswas Saptarshi,
Kar Paramita,
Nojiri Hiroyuki,
Ishida Takayuki,
Ghosh Ashutosh
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201202795
Subject(s) - crystallography , nickel , chemistry , electron paramagnetic resonance , octahedron , magnetization , ferromagnetism , single crystal , anisotropy , magnetic anisotropy , ion , ground state , spectral line , crystal structure , nuclear magnetic resonance , magnetic field , condensed matter physics , atomic physics , physics , organic chemistry , quantum mechanics , astronomy
Three new trinuclear nickel (II) complexes with the general composition [Ni 3 L 3 (OH)(X)](ClO 4 ) have been prepared in which X=Cl − ( 1 ), OCN − ( 2 ), or N 3 − ( 3 ) and HL is the tridentate N,N,O donor Schiff base ligand 2‐[(3‐dimethylaminopropylimino)methyl]phenol. Single‐crystal structural analyses revealed that all three complexes have a similar Ni 3 core motif with three different types of bridging, namely phenoxido (μ 2 and μ 3 ), hydroxido (μ 3 ), and μ 2 ‐Cl ( 1 ), μ 1,1 ‐NCO ( 2 ), or μ 1,1 ‐N 3 ( 3 ). The nickel(II) ions adopt a compressed octahedron geometry. Single‐crystal magnetization measurements on complex 1 revealed that the pseudo‐three‐fold axis of Ni 3 corresponds to a magnetic easy axis, being consistent with the magnetic anisotropy expected from the coordination structure of each nickel ion. Temperature‐dependent magnetic measurements indicated ferromagnetic coupling leading to an S =3 ground state with 2 J / k =17, 17, and 28 K for 1 , 2 , and 3 , respectively, with the nickel atoms in an approximate equilateral triangle. The high‐frequency EPR spectra in combination with spin Hamiltonian simulations that include zero‐field splitting parameters D Ni / k =−5, −4, and −4 K for 1 , 2 , and 3 , respectively, reproduced the EPR spectra well after a anisotropic exchange term was introduced. Anisotropic exchange was identified as D i,j / k =−0.9, −0.8, and −0.8 K for 1 , 2 , and 3 , respectively, whereas no evidence of single‐ion rhombic anisotropy was observed spectroscopically. Slow relaxation of the magnetization at low temperatures is evident from the frequency‐dependence of the out‐of‐phase ac susceptibilities. Pulsed‐field magnetization recorded at 0.5 K shows clear steps in the hysteresis loop at 0.5–1 T, which has been assigned to quantum tunneling, and is characteristic of single‐molecule magnets.