New Types of Luminescent Lanthanide Squarato-Aminophosphonates

Hydrothermal reactions of lanthanide nitrates with aminodiphosphonate ligand (H2O3PCH2)2−N−CH2−C6H4−COOH, H5L1) and squaric acid afforded a series of isostructural lanthanide(III) squarato-phosphonates, namely, Ln(HL2) (Ln = La, 1; Pr, 2; Nd, 3; Eu, 4; Gd, 5; Tb, 6; Er, 7) (H4L2 = HOOC−C6H4−CH2−N(C4O3H)(CH2PO3H2)), in which a new multifunctional squarato-phosphonate ligand (H4L2) was formed by in situ condensation reaction between the two types of organic ligands. The seven-coordinated lanthanide(III) ions in these compounds are bridged by the squarato-aminophosphonate moieties of the {HL2}3− anions into a double layer. Each {HL2}3− anion acts as septadentate metal linker, bridging with seven lanthanide ions by using one carboxylate oxygen, three squarato, and three phosphonate oxygens. These double layers are further cross-linked via the coordination of the carboxylate groups into a pillared layered architecture. The Eu, Tb, and Nd compounds exhibit strong luminescence in red light, green light, and near-IR regions, respectively.

水热反应条件下，硝酸镧系金属盐与氨基二膦酸配体（aminodiphosphonate ligand）H5L1[(H2O3PCH2)2−N−CH2−C6H4−COOH]及方酸（squaric acid）发生反应，得到一系列同构的镧(III)方酸膦酸盐配合物，通式为Ln(HL2)（其中Ln=La，1；Pr，2；Nd，3；Eu，4；Gd，5；Tb，6；Er，7；H4L2=HOOC−C6H4−CH2−N(C4O3H)(CH2PO3H2)）；该系列配合物中，两种有机配体通过原位缩合反应（in situ condensation reaction）生成了一种新型多功能方酸膦酸配体H4L2。此类配合物内的七配位镧(III)离子被{HL2}3−阴离子的方酸-氨基膦酸结构单元桥联形成双层结构，每个{HL2}3−阴离子作为七齿（septadentate）金属连接体，通过1个羧酸氧原子、3个方酸基团氧原子与3个膦酸基团氧原子，与7个镧(III)离子实现配位桥联；上述双层结构单元进一步通过羧酸基团的配位作用相互交联，构筑为柱撑层状骨架结构；其中Eu、Tb和Nd对应的配合物分别在红光、绿光以及近红外（near-IR）区域展现出较强的发光性能。