Synthesis, molecular and crystalline architectures, and properties of novel bis(bidentate) and bis(tridentate) Schiff base bridged dinuclear mercury(II)pseudohalides: Control of coordination numbers by varying denticities

A tetracoordinated [Hg2(L1)(SCN)4] (1) [L1 = N,N′-(bis-(pyridin-2-yl)benzylidene)-1,2-ethanediamine] and two pentacoordinated [Hg2(L2)(X)4] [L2 = N-((1-pyridin-2-yl)formylidene)-N′-[2-(4-{2-[((1-pyridin-2-yl)formylidene) amino]ethyl}piperazin-1-yl)ethyl]amine; X = N3-, (2) and X = NCS−, (3)] dinuclear mercury(II) compounds have been prepared and characterized using microanalytical, spectroscopic, thermal and X-ray crystallographic results. Structural analyses reveal bis(bidentate) congregation behaviour of classical tetradentate L1 and bis(tridentate) character of L2 encapsulating two metal centers. Each mercury(II) center in 1 is in a distorted tetrahedral coordination environment with HgN2S2 chromophore. Hg(1) is attached with two N atoms of L1 and two S atoms of two terminal thiocyanates whereas neighbouring Hg(1) is ligated to the other two N donor set of the same Schiff base completing its bis(bidentate) mode and two S atoms of thiocyanates. In 2 and 3 each mercury(II) center adopts a distorted square pyramidal geometry with MN5 (in 2) and MN3S2 (in 3) chromophores and two metal(II) centers are encapsulated by bis(tridentate) congregation behaviour of L2 through donation of three N donor set to each metal and the fourth and fifth positions are occupied by two N atoms of terminal azides in 2 and two S atoms of terminal thiocyanates in 3. In solid-state, dinuclear units of 1 pack through cooperative C–H⋯N and C–H⋯S hydrogen bonds and C–H⋯π interactions giving rise to a 3D network. Individual dinuclear units of 2 and 3 self-assemble through cooperative C–H⋯N hydrogen bondings and C–H⋯π interactions affording 3D network structure and 2D continuum, respectively. In DMF solutions at room temperature all the complexes display high-energy intraligand 1(π–π∗) fluorescence.

Synthesis, structures and luminescence properties of three dinuclear compounds [Hg2(L1)(SCN)4] (1), [Hg2(L2)(N3)4] (2) and [Hg2(L2)(SCN)4] (3) are described where classical tetradentate (L1) and hexadentate (L2) Schiff bases behave as bis(bidentate) and bis(tridentate) congregators encapsulating two mercury(II) centers. Variation in coordination numbers around the metal ions has been achieved through change of denticities of the Schiff bases. Different crystalline architectures are the result through different kinds of hydrogen bondings (C–H⋯N and C–H⋯S) and C–H⋯π interactions.Figure optionsDownload as PowerPoint slide