One-dimensional ladder like and two-dimensional polymorphs of heterometallic thiocyanate bridged copper(II) and mercury(II) coordination polymer: Syntheses, structural, vibration, luminescence and EPR studies

The 1D triclinic {CuHg(en)(μ-NCS-N,S)₄}_n (1) and 2D monoclinic {CuHg(en)(μ-NCS-N,S)₃(SCN)}_n (2) (en = ethylenediamine) heterometallic coordination polymers, as the two polymorphs of the {CuHg(en)(NCS)₄}_n, were synthesized at room temperature by the reaction of mercuric thiocyanate, potassium thiocyanate, copper(II) malonate and ethylenediamine using different reagent ratios. XRD on single crystals shows that the compound 1 consists of 1D ladder like zigzag ribbons extended along the b axis, whereas compound 2 shows a 2D wavy polymeric structure running parallel to the ab plane. In the crystal packing of the both polymorphs, the polymeric structures are further interlinked to each other via weak interactions and hydrogen bonding to afford a 3D network. Diagnostic ligand and metal-ligand bands in the IR, far-IR and Raman spectra are assigned for the studied compounds. While compound 1 shows no significant emission upon excitation at any wavelength in the UV-Vis region, compound 2 exhibits intense emission at around 410 nm. Moreover, the room temperature X-band EPR spectrum of a powdered sample of 1, shows a signal of rhombic symmetry with g₁ = 2.2637, g₂ = 2.0765 and g₃ = 2.0483. In contrast to this, 2 reveals an axial signal with g_⊥ = 2.0742; however, the g_|| is unresolved.