Chemical tuning of [Ni(hmp)(ROH)Cl]4 single molecule magnets and their self assembly onto gold

Author(s): Ma, James Minh | Abstract: A series of tetra-nuclear cubane single molecule magnet (SMM) complexes were synthesized with the general formula [Ni(hmp)(ROH)Cl]₄ where ROH is an alcohol group or water. The following alcohol groups were explored to examine to effect of chemical modification on the magnetic characteristics of the compound and open the possibility of new chemistries: propyl alcohol, isobutyl alcohol, propargyl alcohol, water, benzyl alcohol, 2- thiophenemethanol, and 2-(methylthio)ethanol. Chemical modification of the compound varies the level of interaction between neighboring molecules and introducing other functional groups allow for post-modification of the complex. The analysis of both of molar paramagnetic susceptibility [chi]MT versus temperature data and reduced magnetization measurements confirm the ferromagnetic coupling in the Ni₄ cubane molecule to give an S=4 ground state. AC susceptibility measurements were done to observe the kinetic effects of the barrier for reversal of magnetization. Synthesis of self assembled monolayers (SAMs) of SMMs on gold surfaces and gold nanoparticles was explored. [Ni(hmp-Cl)(MeOH)Cl]₄, [MnII₂MnIII₂(mdea)₂(Hmdea)₂(O₂CPhBr)₂Cl₂], and [MnII₂MnIII₂(mdea)₂(Hmdea)₂ (O₂CPhN₃)₄] were synthesized and possesses the functionality to undergo Suzuki or Click coupling reactions. The magnetic properties of the compounds were characterized and indicated ferromagnetic coupling to form S=4 and S=9 compounds, respectively. Suzuki coupling was carried out on the Ni₄ compound with gold surfaces and gold nanoparticles functionalized with 4 -mercaptophenylboronic acid. XPS and IRRAS were used to monitor reaction progress and to verify the presence of the Ni₄ but results are inconclusive. Magnetic measurements were conducted on the functionalized AuNP and indicated a significant change in the magnetic susceptibility