Spin switching via targeted structural distortion

The deliberate stepwise structural distortion of the [(Mn6O2)-O-III(sao)(6)(O2CR)(2)L-4] (S = 4, U-eff = 28 K) family of SMMs (where sao(2-) is the dianion of salicylaldoxime or 2-hydroxybenzaldeyhyde oxime and L = MeOH, EtOH) via the use of derivatized oxime ligands and bulky carboxylates leads to a family of single-molecule magnets with larger spin ground states and enhanced blocking temperatures. Replacing sao(2-) and HCO2- in the molecule [(Mn6O2)-O-III(sao)(6)(O2CH)(2)(MeOH)(4)] (1), with Et-sao(2-) (Et-saoH(2) = 2-hydroxypropiophenone oxime) and Me3CCO2- (pivalate), produces the complex [(Mn6O2)-O-III(Et-sao)(6)(O2CCMe3)(2)(EtOH)(5)] (2) that displays an S = 7 ground state with U-eff = 30 K. Replacing Me3CCO2- with PhCO2- produces the complex [(Mn6O2)-O-III(Et-sao)(6)(O2CPh)(2)(EtOH)(4)(H2O)(2)] (3) that displays an S = 12 ground state with U-eff = 53 K. The ligand substitution invokes a subtle structural distortion to the core of the molecule evidenced by an increased twisting of the oxime moiety (Mn-N-O-Mn) and a change in carboxylate ligation, which, in turn, invokes a dramatic change in the observed magnetic properties by switching weak antiferromagnetic exchange to weak ferromagnetic exchange.