Temperature dependence of the spin state and geometry in tricobalt paddlewheel complexes with halide axial ligandsElectronic supplementary information (ESI) available: Thermal ellipsoid plot of 1[BF4]·4CH2Cl2, diagrams showing intramolecular interactions for 1·2CH2Cl2, 3·Et2O and 4·Et2O, crystal data and refinement and selected bond distance and angles tables for newly reported compounds, χT vs. T plots and fits for previously reported compounds. CCDC 1865577-1865593 and 1877180-1877181. For ESI

Trinuclear cobalt paddlewheel complexes, [Co 3 (dpa) 4 X 2 ] (dpa = the anion of 2,2′-dipyridylamine, X = Cl − , Br − , -NCS − , -CN − , (NC) 2 N − ), are known to demonstrate a thermally-induced spin-crossover (SCO). Despite a wealth of structural and magnetic information about such complexes, the...

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Hauptverfasser: Srinivasan, Anandi, Wang, Xiaoping, Clérac, Rodolphe, Rouzières, Mathieu, Falvello, Larry R, McGrady, John E, Hillard, Elizabeth A
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Zusammenfassung:Trinuclear cobalt paddlewheel complexes, [Co 3 (dpa) 4 X 2 ] (dpa = the anion of 2,2′-dipyridylamine, X = Cl − , Br − , -NCS − , -CN − , (NC) 2 N − ), are known to demonstrate a thermally-induced spin-crossover (SCO). Despite a wealth of structural and magnetic information about such complexes, the role of the axial ligand on the characteristic SCO temperature ( T 1/2 ) remains ambiguous. The situation is complicated by the observation that the solid state geometry of the complexes, symmetric or unsymmetric, with respect to the central cobalt ion, also appears to influence the SCO behavior. In order to seek trends in the relationship between the nature of the axial ligand, geometry and magnetic properties, we have prepared the first examples of tricobalt paddlewheel complexes with axial fluorido and iodido ligands, as well as two new chlorido and bromido solvates. Their SCO properties are discussed in the context of an examination of previously reported chlorido and bromido adducts. The main conclusions are: (1) T 1/2 values follow the trend I − < Br − Cl − < F − ; (2) while the molecular geometry is predominantly guided by crystal packing for the Cl − , Br − and I − derivatives, the presence of an axial fluoride may favor a more symmetric core; (3) the magnetic characterization of a second example of an unsymmetric complex supports the observation that they display dramatically lower T 1/2 values than their symmetric analogues; and (4) SCO in crystallographically symmetric compounds apparently occurs without loss of molecular or crystallographic symmetry, while a gradual geometric transformation linking the temperature dependence of quasi-symmetric to unsymmetric in crystallographically unconstrained compounds was found. A series of tricobalt EMACs with halide axial ligands demonstrate diverse spin-crossover behaviors as a function of the molecular geometry and the nature of the axial ligand.
ISSN:1477-9226
1477-9234
DOI:10.1039/c8dt03833c