TY - JOUR

T1 - MCD spectroscopy of hexanuclear Mn(III) salicylaldoxime single-molecule magnets

AU - Bradley, Justin M

AU - Thomson, Andrew J

AU - Inglis, Ross

AU - Milios, Constantinos J

AU - Brechin, Euan K

AU - Piligkos, Stergios

PY - 2010

Y1 - 2010

N2 - The hexanuclear cages [Mn(6)O(2)(R-sao)(6)L(2)(EtOH)(x)(H(2)O)(y)] "Mn(6)" behave as single-molecule magnets (SMMs) below a characteristic blocking temperature. As with [Mn(12)O(12)(O(2)CR)(16)(H(2)O)(4)] "Mn(12)" the electronic absorption spectra are rather featureless, yielding little information on the electronic structure of the magnetic ions. Low temperature Magnetic Circular Dichroism (MCD) spectra afford greater resolution of the optical transitions and also probe the magnetic properties of the system. Both the ground state spin and blocking temperature of the Mn(6) cages are determined by subtle structural perturbations of a generic Mn(6)O(2) core. Absorbance and MCD spectra are reported for [Mn(6)O(2)(Et-sao)(6){O(2)CPh(Me)(2)}(2)(EtOH)(6)] (1), [Mn(6)O(2)(Et-sao)(6){O(2)CPh}(2)(EtOH)(4)(H(2)O)(2)] (2), [Mn(6)O(2)(sao)(6){O(2)CPh}(2)(EtOH)(4)]·EtOH (3) and the trinuclear precursor [Mn(3)O(Et-sao)(3)(MeOH)(3)](ClO(4)) (4) cast into polymer film. SMM behaviour has previously been observed using magnetic susceptibility measurements on powder and single-crystal samples. The ligand field environment of the magnetic ions is assumed to be similar in (1) and (2) and their different blocking temperatures are attributed to the magnitude of the effective exchange constant. The MCD spectra of (1) and (2), in which the ground state spin S = 12, show that the ligand field environments of the Mn ions are almost identical and that magnetic hysteresis persists for isolated molecules when crystal packing forces are removed. The subtle structural differences between (1) and (2) are manifested in the field dependence of the MCD response at different wavelengths that reflect changes in band polarisation. The MCD spectrum of (3) contains features not apparent in those of (1) and (2). These are attributed to 5-coordinate Mn(iii), which is unique to (3) among the compounds studied. (3) has ground state spin S = 4, a lower blocking temperature and consequently no observable hysteresis in the MCD down to 1.7 K. Comparison of the MCD spectra of (1)-(3) to that of (4) confirms the integrity of the Mn(6)O(2) core when these materials are cast into polymer film.

AB - The hexanuclear cages [Mn(6)O(2)(R-sao)(6)L(2)(EtOH)(x)(H(2)O)(y)] "Mn(6)" behave as single-molecule magnets (SMMs) below a characteristic blocking temperature. As with [Mn(12)O(12)(O(2)CR)(16)(H(2)O)(4)] "Mn(12)" the electronic absorption spectra are rather featureless, yielding little information on the electronic structure of the magnetic ions. Low temperature Magnetic Circular Dichroism (MCD) spectra afford greater resolution of the optical transitions and also probe the magnetic properties of the system. Both the ground state spin and blocking temperature of the Mn(6) cages are determined by subtle structural perturbations of a generic Mn(6)O(2) core. Absorbance and MCD spectra are reported for [Mn(6)O(2)(Et-sao)(6){O(2)CPh(Me)(2)}(2)(EtOH)(6)] (1), [Mn(6)O(2)(Et-sao)(6){O(2)CPh}(2)(EtOH)(4)(H(2)O)(2)] (2), [Mn(6)O(2)(sao)(6){O(2)CPh}(2)(EtOH)(4)]·EtOH (3) and the trinuclear precursor [Mn(3)O(Et-sao)(3)(MeOH)(3)](ClO(4)) (4) cast into polymer film. SMM behaviour has previously been observed using magnetic susceptibility measurements on powder and single-crystal samples. The ligand field environment of the magnetic ions is assumed to be similar in (1) and (2) and their different blocking temperatures are attributed to the magnitude of the effective exchange constant. The MCD spectra of (1) and (2), in which the ground state spin S = 12, show that the ligand field environments of the Mn ions are almost identical and that magnetic hysteresis persists for isolated molecules when crystal packing forces are removed. The subtle structural differences between (1) and (2) are manifested in the field dependence of the MCD response at different wavelengths that reflect changes in band polarisation. The MCD spectrum of (3) contains features not apparent in those of (1) and (2). These are attributed to 5-coordinate Mn(iii), which is unique to (3) among the compounds studied. (3) has ground state spin S = 4, a lower blocking temperature and consequently no observable hysteresis in the MCD down to 1.7 K. Comparison of the MCD spectra of (1)-(3) to that of (4) confirms the integrity of the Mn(6)O(2) core when these materials are cast into polymer film.

KW - TARGETED STRUCTURAL DISTORTION

KW - HIGH-SPIN MOLECULES

KW - INELASTIC NEUTRON-SCATTERING

KW - OXIDATION-STATE

KW - GROUND-STATE

KW - CLUSTER CHEMISTRY

KW - MN-12 COMPLEXES

KW - MAGNETIZATION

KW - ANISOTROPY

KW - RELAXATION

U2 - 10.1039/c0dt00634c

DO - 10.1039/c0dt00634c

M3 - Journal article

C2 - 20721404

VL - 39

SP - 9904

EP - 9911

JO - Acta chemica Scandinavica. Series A: Physical and inorganic chemistry

JF - Acta chemica Scandinavica. Series A: Physical and inorganic chemistry

SN - 1477-9226

IS - 41

ER -