Naphthalene-based linkers for metal phosphonates: synthesis, structure, and interesting conformational flexibility influence on final lanthanum hybrids

Abstract

Two diphosphonic acids based on naphthalene scaffold, namely naphthalene-1,4-diphosphonic acid, C₁₀H₆(PO₃H₂)₂ [1, H₄NDP(1,4)] and 1-(phosphono)naphthalene-4-(methylphosphonic) acid, C₁₀H₆(PO₃H₂)(CH₂PO₃H₂) [2, H₄NDP(1,4C)] were obtained. Their supramolecular self-assembly were studied as well as solvent effect for the second one (2a, 2b). These potential building blocks in coordination polymer chemistry were engaged with a La³⁺ ion in a room temperature reaction to produce new single crystalline metal phosphonates: (I) [La{C₁₀H₆(PO₃H)₂}{C₁₀H₆(PO₃H)(PO₃H₂)}(H₂O)₂]_n·nH₂O (3), a 2D coordination polymer with the I¹O¹ structure and {4².6}₂{4⁴.6⁴.8²} topology of the layer, and (II) [La{C₁₀H₆(PO₃H_1.5)(CH₂PO₃H)}₂(H₂O)₇]·2H₂O (4), a discrete complex. These drastic differences in hybrid material structures can be explained by ligand structures analysis including their conformational flexibility.