Tunable SIM properties in a family of 3D anilato-based lanthanide-MOFs

Abstract

By reacting a 3,6-ditriazolyl-2,5-dihydroxybenzoquinone (H₂trz₂An) anilato linker with Ln^III ions (Ln^III = Dy, Tb, Ho), two different series of polymorphs, formulated as [Ln₂(trz₂An)₃(H₂O)₄]_n·10H₂O (Dy^III, 1a; Tb^III, 2a, Ho^III, 3a) and [Ln₂(trz₂An)₃(H₂O)₄]_n·7H₂O (Dy^III, 1b, Tb^III, 2b, Ho^III, 3b) have been obtained. In these series the two Dy^III-coordination networks (1a and 1b) and the Tb^III-coordination polymer (2b) show a Single Ion Magnet (SIM) behavior. 1–3a MOFs show reversible structural flexibility upon removal of a coordinated water molecule from a distorted hexagonal 2D framework to a distorted 3,6-brickwall rectangular 3D structure in [Ln₂(trz₂An)₃(H₂O)₂]_n·2H₂O (Dy^III, 1a_des; Tb^III, 2a_des, Ho^III, 3a_des) involving shrinkage/expansion of the hexagonal–rectangular networks. Noteworthy, 2b represents the first example of a Tb^III–anilate-based coordination polymer showing SIM behaviour to date and the best SIM properties within the polymorphs. Theoretical investigation via ab initio CASSCF calculations supports this behavior, since 2b shows less mixing between the m_J states of the ground state among all the studied complexes.