Hydro-ionothermal syntheses, crystal structures, and properties of five new divalent metal iminophosphonates

Abstract

The use of a moderately hydrophobic ionic liquid, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([BdMIM][BF₄]), as a cosolvent with water, has been investigated in the synthesis of metal phosphonates. This hydro-ionothermal synthesis has been carried out through a systematic combinatorial investigation of several divalent metal chlorides and two related ligands, iminobis(methylphosphonic acid) and N-methyliminiobis(methylphosphonic acid). These reactions resulted in five new divalent metal phosphonates. We present here the synthetic techniques utilized as well as the X-ray structures and characteristic properties of each of these compounds. Co(HO₃PCH₂NH₂CH₂PO₃H)₂, (1), consists of sheets that are hydrogen bonded together by pairs of P–O⋯H groups. Co(H₂O)₂(HO₃PCH₂NH₂CH₂PO₃H)₂, (2), consists of chains that are connected through an extensive network of hydrogen bonds. Co(HO₃PCH₂NH(CH₃)CH₂PO₃H)₂, (3), is made up of sheets that are hydrogen bonded together by pairing P–O⋯H interactions. Zn₃(O₃PCH₂NH₂CH₂PO₃)₂, (4), is isostructural to a previously reported cobalt compound which is a non-porous 3-dimensional network. CuClPO₃CH₂NH₂CH₃, (5), formed as a result of an in situ N–C bond cleavage. Ladders built of Cu–O–P–O 8-membered rings are crosslinked by bridging chloride atoms to form sheets. 1, 3, 4 and 5 have been synthesized using the hydrophobic ionic liquid 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([BdMIM][BF₄]) with water as a cosolvent, while 2 has been synthesized from identical conditions in the absence of the [BdMIM][BF₄]. We also report the microwave assisted hydro-ionothermal synthesis of the known polymorph of 2, Co(H₂O)₂(HO₃PCH₂NH₂CH₂PO₃H)₂, (6), synthesized in two hours providing high quality crystals in good yield. The compounds have been characterized by thermogravimetric analysis and IR spectroscopy, and their magnetic properties have been investigated.