Synthesis and Characterization of an Isomorphous Lanthanide-Thiophenemonocarboxylate Series (Ln = La–Lu, except Pm) Amenable to Color Tuning

A series of 14 lanthanide compounds bearing 2-thiophenecarboxylate (TC) have been prepared under aqueous conditions and structurally characterized. Single crystal X-ray diffraction studies reveal a full isomorphous series across the 4f block of the general formula [(Ln­(TC)₃(H₂O)₂)·(HPy·TC)]_n, (Ln = La (La-1) – Lu (Lu-1), excluding Pm), with observable contraction of the cell volume and average metal–oxygen bond distances occurring when moving from lanthanum to lutetium. The 8-coordinate Ln metal centers are bound to two water molecules as well as six oxygen atoms from one bidentate and four bridging TC units that link LnO₈ structural units into 1D chains. One lattice stabilizing pyridinium and one outer coordination sphere TC anion are present per formula unit. Reaction optimization provided moderate to high yields of the title products; a lanthanum byproduct [La­(TC)₃(HTC)₂]_n (La-2) was formed by performing the reaction at reduced temperature, or alternatively, successive grinding of La-1 in ethanol resulted in partial conversion to La-2. Solid-state fluorescence studies show ligand sensitized metal-based emission for Eu­(III), Tb­(III), and Dy­(III) in the visible region, and Nd­(III) and Er­(III) in the NIR. Color tuning was easily achieved by varying europium:terbium metal ratios in the reaction mixtures.