Abstract
The syntheses and structural characterization of three new monodimensional azido-bridged manganese(ii) complexes with empirical formulae [Mn(N3)2(aminopyz)2]n (1), [Mn(N3)2(4-azpy)2]n (2) and [Mn(N3)2(4-Bzpy)2]n (3) (pyz = pyrazine (1,4-diazine)), 4-azpy = 4-azidopyridine and 4-Bzpy = 4-benzoylpyridine) are reported. 1 is a monodimensional compound with double EO azido bridges, 2 is an alternating monodimensional compound with double end-on and double end-to-end azido bridges in the sequence di-EO-di-EE and 3 is a monodimensional compound with double end-on and double end-to-end azido bridges in the sequence di-EO-di-EO-diEO-di-EO-di-EE. The magnetic properties of 1-3 are reported. Periodic DFT calculations were performed to estimate the J values and quantum Monte Carlo simulations were carried out using the calculated J values to check their accuracy in comparison with the experimental magnetic measurements. From this theoretical analysis, two appealing features of the di-EO Mn(ii) compounds can be extracted: first, the exchange coupling becomes more ferromagnetic when the Mn-N-Mn bridging angle becomes larger and the spin density of the bridging nitrogen atoms has an opposite sign to that of the Mn(II) centers.
Highlights
In the last few years a plethora of polynuclear Mn(II)-azido bridging compounds have been prepared with the aim to expand the borders of the molecular magnetism field
Taking into account that the EE coordination mode typically promotes antiferromagnetic, AF, interactions and the EO coordination mode promotes ferromagnetic, F, interactions, the great diversity of dimensionalities and topologies found in the Mn(II)-azido bridging compounds has as a consequence a great diversity in their magnetic behaviour: for example, in the 1D compound with the bulk formula [Mn(N3)2(3-Mepy)2]n (3-Mepy = 3-methylpyridine) the sequence of the azido bridges is (EE–EE–EO)n which implies an (AF–AF–F)n interaction pattern and a ferrimagnetic behaviour in a homometallic chain.[14]
The octahedron is completed by two trans coordinated N atoms provided by two aminopyrazine ligands bonded via the aromatic nitrogen in the meta position to the amino sidegroup
Summary
In the last few years a plethora of polynuclear Mn(II)-azido bridging compounds have been prepared with the aim to expand the borders of the molecular magnetism field. L are usually R-pyridine monodentate ligands or (L)[2] a bidentate aromatic N-donor ligand. These [Mn(N3)2(L)2] compounds show the entire range of dimensionalities: from molecular to 3D systems.[1,2,3,4,5,6,7,8,9,10,11,12,13] the azido bridging ligand can show several coordination modes as the μ1,3 (end-to-end, EE) or μ1,1 (end-on, EO) modes, which can be present simultaneously in the same compound, generating a great variety of topologies in 1D–3D compounds. We present in this work three monodimensional compounds which are new good examples of the wide 18632 | Dalton Trans., 2015, 44, 18632–18642
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