A robust microporous 3D cobalt(II) coordination polymer with new magnetically frustrated 2D lattices: single-crystal transformation and guest modulation of cooperative magnetic properties

摘要

A microporous 3D cobalt( II) coordination polymer featuring pillared layers [ Co-2( ma)( ina)] (n) . 2nH(2)O ( 1 . 2H(2)O) ( ma = malate, ina = isonicotinate) was generated by hydrothermal treatment with a void volume of 25.8%, in which the in- situ generated ma ligands connect the Co-II ions into a 2D lattice with mixed and multiple exchange- bridges, affording a new geometrical topology different from the Kagome lattice and leading to spin frustration. The rigid ina- pillared metallic- layered structure could retain 3D structural ordering upon guest removal and exchange. By soaking guest- free host ( 1) in MeOH and methanamide ( HCONH2) solutions, single crystals of dehydrated 1 were transformed into single crystals of 1.MeOH and 1.HCONH2, respectively, without apparent host- structural changes. 1 can also be rehydrated into 1.2H(2)O . The guest- inclusion crystals have been characterized by X- ray single- crystal diffraction at 293 K and 93 K, confirming the single- crystal- to- single- crystal transformations and providing detailed information of the guest molecules confined in the subnanospace and host - guest and/ or guest - guest hydrogen- bonding interactions. The magnetic behaviours of this family of porous magnetic materials are complex due to the influences of multiple metal sites, intra- and inter- layer exchanges, spin - orbit coupling, as well as geometrical frustration, which show magnetic ordering at < 2 K, 3.5 K, 3.5 K, and 8 K for 1, 1. MeOH, 1 . HCONH2, and 1 . 2H(2)O, respectively, due to the different size of guest molecules along with the different host - guest interaction, which may slightly modify the path of magnetic exchange, decrease the intensity of the spin- frustration in the 2D lattice, and cooperatively enhance the magnetic ordering temperature.