Cyanido-Bridged Fe(III)–Mn(III) Heterobimetallic Materials Built From Mn(III) Schiff Base Complexes and Di- or Tri-Cyanido Fe(III) Precursors

The reaction of [FeIIIL­(CN)3]− (L being bpca = bis­(2-pyridylcarbonyl)­amidate, pcq
= 8-(pyridine-2-carboxamido)­quinoline)
or [FeIII(bpb)­(CN)2]− (bpb
= 1,2-bis­(pyridine-2-carboxamido)­benzenate) ferric complexes with
MnIII salen type complexes afforded seven new bimetallic
cyanido-bridged Mn­(III)–Fe­(III) systems: [Fe­(pcq)­(CN)3Mn­(saltmen)­(CH3OH)]·CH3OH (1), [Fe­(bpca)­(CN)3Mn­(3-MeO-salen)­(OH2)]·CH3OH·H2O (2), [Fe­(bpca)­(CN)3Mn­(salpen)] (3),
[Fe­(bpca)­(CN)3Mn­(saltmen)] (4), [Fe­(bpca)­(CN)3Mn­(5-Me-saltmen)]·2CHCl3 (5),
[Fe­(pcq)­(CN)3Mn­(5-Me-saltmen)]·2CH3OH·0.75H2O (6), and [Fe­(bpb)­(CN)2Mn­(saltmen)]·2CH3OH (7) (with saltmen2– = N,N′-(1,1,2,2-tetramethylethylene)­bis­(salicylideneiminato)
dianion, salpen2– = N,N′-propylenebis­(salicylideneiminato)
dianion, salen2– = N,N′-ethylenebis­(salicylideneiminato)
dianion). Single crystal X-ray diffraction studies were carried out
for all these compounds indicating that compounds 1 and 2 are discrete dinuclear [Fe­(III)–CN–Mn­(III)]
complexes while systems 3–7 are heterometallic
chains with {−NC–Fe­(III)–CN–Mn­(III)} repeating
units. These chains are connected through π–π and
short contact interactions to form extended supramolecular networks.
Investigation of the magnetic properties revealed the occurrence of
antiferromagnetic Mn­(III)···Fe­(III) interactions in 1–4 while ferromagnetic Mn­(III)···Fe­(III)
interactions were detected in 5–7. The nature of these Mn­(III)···Fe­(III) magnetic interactions
mediated by a CN bridge appeared to be dependent on the Schiff base
substituent. The packing is also strongly affected by the nature of
the substituent and the presence of solvent molecules, resulting in
additional antiferromagnetic interdinuclear/interchain interactions.
Thus the crystal packing and the supramolecular interactions induce
different magnetic properties for these systems. The dinuclear complexes 1 and 2, which possess a paramagnetic ST = 3/2 ground state, interact antiferromagnetically
in their crystal packing. At high temperature, the complexes 3–7 exhibit a one-dimensional magnetic
behavior, but at low temperature their magnetic properties are modulated
by the supramolecular arrangement: a three-dimensional antiferromagnetic
order with a metamagnetic behavior is observed for 3, 4, and 7, and Single-Chain Magnet properties
are detected for 5 and 6.