title: Switching the orientation of Jahn-Teller axes in oxime-based Mn(III) dimers and its effect upon magnetic exchange: a combined experimental and theoretical study.
abstract: A family of Mn(III) dimers of general formula [Mn(R-sao)2(dpa)2](ClO4)2 (1-5) has been synthesised using derivatised phenolic oximes (R-saoH2, where R = H, Me, Et, Ph) in combination with di-(2-picolyl)-amine (dpa). Their structures reveal a double-oxime bridged [Mn(III)(NO)]2 magnetic core in which the Jahn-Teller axes lie perpendicular to the bridging plane, in contrast to two previously reported family members (6, 7). The switch in the orientation of the Jahn-Teller axes is enforced through the use of the chelating ligand which is present in 1-5 and absent in 6-7. Dc magnetic susceptibility measurements reveal that the exchange interactions between the Mn(III) metal centres in 1-5 are antiferromagnetic in contrast to that observed for 6 and 7 which are ferromagnetic. DFT calculations performed on complexes 1-6 reproduce both the sign and strength of the J values found experimentally. Molecular orbital analysis unlocks a common mechanism of magnetic coupling based upon the orientation of the Jahn-Teller axis, with the magneto-structural correlation also dependent upon the Mn-N-O-Mn angles--with ferromagnetic interactions at smaller dihedral angles.
authors.affiliation: EaStCHEM School of Chemistry, The University of Edinburgh, David Brewster Road, Edinburgh, EH9 3FJ, Scotland, UK. E.Brechin@ed.ac.uk.
authors.forename: Priyanka
authors.initials: P
authors.lastname: Comar
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay, Mumbai, 400076, India. rajaraman@chem.iitb.ac.in.
authors.forename: Thayalan
authors.initials: T
authors.lastname: Rajeshkumar
authors.affiliation: EaStCHEM School of Chemistry, The University of Edinburgh, David Brewster Road, Edinburgh, EH9 3FJ, Scotland, UK. E.Brechin@ed.ac.uk.
authors.forename: Gary S
authors.initials: GS
authors.lastname: Nichol
authors.affiliation: UK National Crystallographic Service, Chemistry, University of Southampton, Southampton, Highfield Campus, SO17 1BJ, UK.
authors.forename: Mateusz B
authors.initials: MB
authors.lastname: Pitak
authors.affiliation: UK National Crystallographic Service, Chemistry, University of Southampton, Southampton, Highfield Campus, SO17 1BJ, UK.
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Coles
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay, Mumbai, 400076, India. rajaraman@chem.iitb.ac.in.
authors.forename: Gopalan
authors.initials: G
authors.lastname: Rajaraman
authors.affiliation: EaStCHEM School of Chemistry, The University of Edinburgh, David Brewster Road, Edinburgh, EH9 3FJ, Scotland, UK. E.Brechin@ed.ac.uk.
authors.forename: Euan K
authors.initials: EK
authors.lastname: Brechin