Heterometallic
Coordination Polymers Assembled from
Trigonal Trinuclear Fe<sub>2</sub>Ni-Pivalate Blocks and Polypyridine
Spacers: Topological Diversity, Sorption, and Catalytic Properties
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Abstract
Linkage of the trigonal complex [Fe<sub>2</sub>NiO(Piv)<sub>6</sub>] (where Piv<sup>–</sup> = pivalate)
by a series of polypyridine ligands, namely, tris(4-pyridyl)triazine
(L<sup>2</sup>), 2,6-bis(3-pyridyl)-4-(4-pyridyl)pyridine (L<sup>3</sup>), <i>N</i>-(bis-2,2-(4-pyridyloxymethyl)-3-(4-pyridyloxy)propyl))pyridone-4
(L<sup>4</sup>), and 4-(<i>N</i>,<i>N</i>-diethylamino)phenyl-bis-2,6-(4-pyridyl)pyridine
(L<sup>5</sup>) resulted in the formation of novel coordination polymers
[Fe<sub>2</sub>NiO(Piv)<sub>6</sub>(L<sup>2</sup>)]<sub><i>n</i></sub> (<b>2</b>), [Fe<sub>2</sub>NiO(Piv)<sub>6</sub>(L<sup>3</sup>)]<sub><i>n</i></sub> (<b>3</b>), [Fe<sub>2</sub>NiO(Piv)<sub>6</sub>(L<sup>4</sup>)]<sub><i>n</i></sub>·<i>n</i>HPiv (<b>4</b>), and [{Fe<sub>2</sub>NiO(Piv)<sub>6</sub>}<sub>4</sub>{L<sup>5</sup>}<sub>6</sub>]<i><sub>n</sub></i>·3<i>n</i>DEF (<b>5</b>, where DEF is <i>N</i>,<i>N</i>-diethylformamide),
which were crystallographically characterized. The topological analysis
of <b>3</b>, <b>4</b>, and <b>5</b> disclosed the
3,3,4,4-connected 2D (<b>3</b>, <b>4</b>) or 3,4,4-connected
1D (<b>5</b>) underlying networks which, upon further simplification,
gave rise to the uninodal 3-connected nets with the respective fes
(<b>3</b>, <b>4</b>) or SP 1-periodic net (4,4)(0,2) (<b>5</b>) topologies, driven by the cluster [Fe<sub>2</sub>Ni(μ<sub>3</sub>-O)(μ-Piv)<sub>6</sub>] nodes and the polypyridine μ<sub>3</sub>-L<sup>3,4</sup> or μ<sub>2</sub>-L<sup>5</sup> blocks.
The obtained topologies were compared with those identified in other
closely related derivatives [Fe<sub>2</sub>NiO(Piv)<sub>6</sub>(L<sup>1</sup>)]<sub><i>n</i></sub> (<b>1</b>) and {Fe<sub>2</sub>NiO(Piv)<sub>6</sub>}<sub>8</sub>{L<sup>6</sup>}<sub>12</sub> (<b>6</b>), where L<sup>1</sup> and L<sup>6</sup> are tris(4-pyridyl)pyridine
and 4-(<i>N</i>,<i>N</i>-dimethylamino)phenyl-bis-2,6-(4-pyridyl)pyridine,
respectively. It was shown that a key structure-driven role in defining
the dimensionality and topology of the resulting coordination network
is played by the type of polypyridine spacer. Compounds <b>2</b> and <b>3</b> possess a porous structure, as confirmed by the
N<sub>2</sub> and H<sub>2</sub> sorption data at 78 K. Methanol and
ethanol sorption by <b>2</b> was also studied indicating that
the pores filled by these substrates did not induce any structural
rearrangement of this sorbent. Additionally, porous coordination polymer <b>2</b> was also applied as a heterogeneous catalyst for the condensation
of salicylaldehyde or 9-anthracenecarbaldehyde with malononitrile.
The best activity of <b>2</b> was observed in the case of salicylaldehyde
substrate, resulting in up to 88% conversion into 2-imino-2<i>H</i>-chromen-3-carbonitrile