In-depth structural analysis of lanthanoid coordination networks based on a flexible tripodal zwitterionic isonicotinate ligand

Crystallizing metal–organic frameworks (MOFs) has been studied using a tripodal pyridinecarboxylic acid derivative ligand and selected lanthanoid salts. The zwitterionic ligand, 1,1′,1′′-((2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene))tris(pyridin-1-ium-4-carboxylate) ( TTTPC ) introduced as a bromide salt, forms coordination networks in aqueous environments and under ambient conditions with neodymium bromide, trifluoromethanesulfonate (OTf) or acetate (OAc). Seven structures are elucidated in detail using single crystal X-ray crystallography. TTTPC NdBr 3 , TTTPC NdBr 2 OTf , TTTPC NdBr(OTf) 2 and TTTPC Nd(OTf) 3 are porous 3D networks with similar ligand–metal and ligand–anion interactions, but with different anion distributions, coordination modes and/or crystal systems. Freshly prepared TTTPC NdBr 2 OAc is a porous 2D network, and otherwise has the same attributes, but it transforms into a 3D network upon drying. All network solids crystallize in the space group P 1̄ (# 2), except TTTPC NdBr(OTf) 2 which crystallizes in P 2 1 / c (# 14). Compounds retain their crystallinity under vacuum, and a crystal structure for an evacuated sample of TTTPC NdBr 2 OTf is presented. Thermal analysis of network solids shows that upon heating, all solids exhibit solvent loss and withstand decomposition up to or over 300 °C. In addition to Nd networks, synthesis and crystal structures of several exactly or almost isostructural systems with other lanthanoids are presented. These include TTTPC YbBr 3 , TTTPC LnBr 2 OTf ( Ln = La , Sm , Eu , Gd and Tb ), TTTPC LnBr(OTf) 2 ( Ln = Sm , Eu , and Tb ), TTTPC Yb(OTf) 3 and TTTPC 2 Sm 2 (OTf) 6 . The synthesis and crystal structures of Ln(NO 3 ) 3 ( Ln = La , Nd , and Y ) are also briefly discussed as a separate, yet similar, system. Finally, a revised crystal structure of the protonated bromide TTTPC ligand, H 2.5 TTTPC , is suggested.