Coordination complexes and polymers from the initial application of phenyl-2-pyridyl ketone azine in mercury chemistry

Abstract

A series of new mercury(II) azine Schiff base complexes have been synthesized and characterized from the initial use of phenyl-2-pyridyl ketone azine in HgII chemistry. The synthetic/crystallization technique utilized involved the use of a branched tube, where temperature differential allowed for the slow crystallization of the products. The synthesized compounds are the mononuclear [Hg(L)Cl2] (1), [Hg(L)Br2] (2), [Hg(L)(NO2)2] (3), and the dinuclear [Hg2(μ-L)(SCN)4] (4) coordination compounds, as well as a 1D coordination polymer [Hg(L)(μ-I)2HgI2]n (5) (L=phenyl-2-pyridyl ketone azine). From the X-ray data, it is evident that this versatile ligand functions as a bi- or tridentate chelate, and is also able to bridge two HgII centers. The crystal structures of 1 and 2 are similar, both containing two crystallographically independent HgII molecules, one tetrahedrally coordinated and one exhibiting trigonal bipyramidal geometry. The heptacoordinated HgII center in 3 adopts a distorted capped trigonal prismatic coordination sphere, while in the dinuclear complex 4, the metal ions are bridged via the bis(bidentate) L and each center is also bound to two S-bonded thiocyanate units. The one-dimensional coordination polymer in 5 consists of a tetrahedral HgI4 and a trigonal bipyramidal HgN3I2 chromophore unit, bridged by μ-I− bridges. The thermal stability of the crystal lattice in 1–5 follows the pattern 3>1>2>5>4, as studied by TG/DTA, while the TG data of 1, 2, and 5 are similar, but different than the respective ones for 3 and 4, between which important similarities are observed. In the solid state, the ligand and compounds 1–5 exhibit intraligand π→π∗ fluorescence at room temperature.