Abstract
Reactions of N,N’-bis(pyridine-4-yl)formamidine (4-Hpyf) with HgX2 (X = Cl, Br, and I) afforded the formamidinate complex {[Hg(4-pyf)2]·(THF)}n, 1, and the formamidine complexes {[HgX2(4-Hpyf)]·(MeCN)}n (X = Br, 2; I, 3), which have been structurally characterized by X-ray crystallography. Complex 1 is a 2D layer with the {44·62}-sql topology and complexes 2 and 3 are helical chains. While the helical chains of 2 are linked through N–H···Br hydrogen bonds, those of 3 are linked through self-complementary double N–H···N hydrogen bonds, resulting in 2D supramolecular structures. The 4-pyf- ligands of 1 coordinate to the Hg(II) ions through one pyridyl and one adjacent amine nitrogen atoms and the 4-Hpyf ligands of 2 and 3 coordinate to the Hg(II) ions through two pyridyl nitrogen atoms, resulting in new bidentate binding modes. Complexes 1–3 provide a unique opportunity to envisage the effect of the halide anions of the starting Hg(II) salts on folding and unfolding the Hg(II) coordination polymers. Density function theory (DFT) calculation indicates that the emission of 1 is due to intraligand π→π * charge transfer between two different 4-pyf- ligands, whereas those of 2 and 3 can be ascribed to the charge transfer from non-bonding p-type orbitals of the halide anions to π * orbitals of the 4-pyf- ligands (n→π *). The gas sorption properties of the desolvated product of 1 are compared with the Cu analogues to show that the nature of the counteranion and the solvent-accessible volume are important in determining their adsorption capability.
Highlights
Functional coordination polymers have been a research focus in recent years due to their potential applications in separation, ion exchange, catalysis, and adsorption [1,2,3,4,5]
Mononuclear and polynuclear complexes have been reported [10,11,12,13]. These types of ligands could be improved by having different directions of donor sites to construct coordination polymers with higher dimensionality [14,15]
The density functional theory (DFT) calculations were performed for complexes 1–3 at the rb3lyp/lanl2dz level [18], which was implemented using the Gaussain 09 software package [19]
Summary
Functional coordination polymers have been a research focus in recent years due to their potential applications in separation, ion exchange, catalysis, and adsorption [1,2,3,4,5]. Mononuclear and polynuclear complexes have been reported [10,11,12,13] These types of ligands could be improved by having different directions of donor sites to construct coordination polymers with higher dimensionality [14,15]. In this regard, we have designed and synthesized the dimolybdenum paddlewheel complex [Mo2(4-pyf)4][4-Hpyf = N,N’-bis(pyridine-4-yl)formamidine] (Figure 1a), which
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