Abstract
Three new compounds have been synthesized and characterized with Fe(II), Co(II) and Mn(II), the polynitrile anionic ligand 1,1,3,3-tetracyano-2-(3-hydroxypropoxy)-propenide (tcnopr3OH−) and the co-ligand 4,4′-bipyridine (4,4′-bpy). The Fe(II) compound, formulated as [FeII(tcnoprOH)2(H2O)2(4,4′-bpy)2] (1), contains monomeric complexes where the Fe(II) ion is coordinated to two trans polynitrile ligands, two trans 4,4′-bpy ligands and two trans water molecules. Compounds [MII(H2O)4(µ-4,4′-bpy)][MII(tcnoprOH)4(µ-4,4′-bpy)].3H2O, M = Mn (2) and Co (3), are isostructural and crystallize in segregated cationic and anionic chains that can be formulated as [MII(H2O)4(µ-4,4′-bpy)]n2n+ and [MII(tcnoprOH)4(µ-4,4′-bpy)]n2n−, respectively with M = Mn (2) and Co (3). The magnetic properties of Compound 1 show the expected paramagnetic behavior for an isolated high spin S = 2 Fe(II) ion with a zero field splitting of |D| = 4.0(1) cm−1. Compound 3 presents the expected behavior for isolated Co(II) centers, whereas Compound 2 shows an unexpected partial smooth spin crossover (SCO) transition in the anionic [MnII(tcnoprOH)4(µ-4,4′-bpy)]n2n− chain together with a paramagnetic contribution of the cationic [MnII(H2O)4(µ-4,4′-bpy)]n2n+ chain. This behavior has been confirmed with DSC measurements. This is one of the very few examples of SCO transition observed in a Mn(II) complex and the first one in a Mn(II) chain.
Highlights
The synthesis of new coordination polymers (CP) with interesting properties constitutes a hot topic given the interesting properties that these materials may show
The synthesis of the three compounds was performed under similar conditions and using a method similar to that used to prepare the closely-related compounds with the ligand tcnoetOH
Mn(II) ions is in a low spin and other is in aare high spinlonger configuration, the calculated difference must be attributed to the huge steric effect of the polynitrile ligand in the anionic chain
Summary
The synthesis of new coordination polymers (CP) with interesting properties constitutes a hot topic given the interesting properties that these materials may show. Besides the aforementioned simple bridging ligands, other, more complex poly-dentate bridging ligands and co-ligands, such as polynitrile anions, have been used to prepare many different CP [20,21,22,23,24,25,26] In this context, in previous works with polynitrile anions, we have synthesized different ligands with up to four cyano groups oriented in two different directions and an additional potentially coordinating alcohol or thiol function (Scheme 1) [27]. 1,1,3,3-tetracyano-2-(3-hydroxypropoxy)-propenide (tcnopr3OH ) and 4,4 -bipyridine (4,4 -bpy) as a bipyridine (4,4′‐bpy) as a bridging co‐ligand combined withions different transition metal ionsThis as Mn(II), bridging co-ligand combined with different transition metal as Mn(II), Fe(II) and. Fe(II) and study shows additional carbon atom ligand in the and sidethe chain of the shows that Co(II) Both theThis additional carbon that atomboth in thethe side chain of the polynitrile transition polynitrile ligand transition metal ion play a key role in forms the final structure obtained.
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