Structures and magnetic properties of copper(ii) and manganese(ii) polymers derived from pseudohalides and a flexible zwitterionic dicarboxylate ligand

Abstract

The flexible zwitterionic dicarboxylate ligand 1,4-bis(4-carboxylato-1-pyridinium)butane (bcpb) assumes different conformations to collaborate with pseudohalides in various coordination modes to produce coordination polymers in which distinct anionic motifs with mixed carboxylate and pseudohalide bridges are interlinked by the cationic butylenebis(pyridinium) tethers. The Cu(II) compound, [Cu₂(bcpb)(N₃)₄]n·nH₂O (1), is a 1D coordination polymer based on the defective dicubane-like [Cu₄(μ₃-1,1,1-N₃)₂(μ-1,1-N₃)₂(μ-1,1-OCO)₂] cluster. With Mn(II), four distinct 3D coordination polymers, [Mn₄(bcpb)₄(N₃)(H₂O)₄]_n(ClO₄)_7n·nCH₃OH·3nH₂O (2), [Mn_2.5(bcpb)(N₃)₅(H₂O)₂]_n (3), [Mn₂(bcpb)(N₃)₄]_n·nH₂O (4), and [Mn₂(bcpb)(NCO)₄]_n·nH₂O (5), were characterized. 2 is the first Mn(II) compound with the rare μ₄-1,1,3,3 azide bridge and exhibits an unusual 3D framework based on the [Mn₄(μ₄-1,1,3,3-N₃)(μ-1,3-OCO)₆] cluster. In 3, the unique undulated honeycomb-like [Mn₂(μ-1,3-N₃)₃]_n layers are interlinked into a 3D framework by disordered [Mn(μ-1,1-N₃)₄(μ-1,3-OCO)₂] and [(O_aqua–H)₂⋯OCO]₂ moieties, and the bcpb ligands serve as additional interlayer linkers to lead to the rare self-catenated 6⁶ net. 4 and 5 show 3-fold interpenetrated 3D frameworks based on the chains with (μ-1,1-N₃)₂(μ-1,3-OCO) and (μ-N,N-NCO)₂(μ-1,3-OCO) bridges, respectively. Magnetic studies indicated that 1 shows competing ferromagnetic and antiferromagnetic interactions. Compounds 2–5 all show antiferromagnetic coupling between Mn(II) ions, while 3 shows 3D ordering. Analyses of magneto-structural data suggest a general trend that the antiferromagnetic interaction through (μ-1,1-N₃)₂(μ-1,3-OCO) or (μ-N,N-NCO)₂(μ-1,3-OCO) increases with a decrease of the Mn⋯Mn distance.