Diamondoid Structure in a Metal–Organic Framework of Fe₄ Single‐Molecule Magnets

Abstract

A 3D metal-organic framework (MOF) having single-molecule magnet (SMM) linkers was prepared in crystalline form by using a tetrairon(III) complex functionalised with two divergent pyridyl groups, namely [Fe4 (pPy)2 (dpm)6 ] (1; H3 pPy=2-(hydroxymethyl)-2-(pyridin-4-yl)propane-1,3-diol, Hdpm=dipivaloylmethane). Reaction of 1 with silver(I) perchlorate afforded {[Fe4 (pPy)2 (dpm)6 ]2 Ag}ClO4 (2), which crystallises in a cubic face-centred lattice and exhibits two interlocked diamondoid networks. In 2, the SMMs act as linear ditopic synthons, and silver(I) ions as tetrahedral nodes coordinated by four pyridyl nitrogen atoms. The magnetic properties of 1 (S=5 and D≈-0.4 cm(-1) in the ground spin state) are largely preserved in 2, which shows slow magnetic relaxation with an anisotropy barrier of Ueff /kB =11.46(10) K in zero field and 14.25(8) K in an applied field of 1 kOe. However, crystal symmetry triggers highly noncollinear magnetic anisotropy contributions oriented at 109.47° from each other along the threefold axes of AgN4 tetrahedra, a unique scenario fully confirmed by a single-crystal cantilever torque magnetometry investigation. Magnetisation curves down to 0.03 K demonstrated the occurrence of a wide hysteresis loop when the magnetic field was swept along one of the four Ag-N bonds. By symmetry, the crystalline compound can then be persistently magnetised parallel or antiparallel to the four main diagonals of the unit cell, although the crystals have no overall second-order anisotropy.

New Silver(I) Coordination Polymer with Fe4 Single-Molecule Magnets as Long Spacer

“…The infrared spectrum of Fe 4 Ag fully resembles the one of Fe 4 ( Figure S5 in Supplementary Materials), which proves the intactness of the starting tetrairon(III) cluster. The presence of AgClO 4 is confirmed by the appearance of a unique perchlorate stretching band at 1122 cm −1 , distinctive of an anion in tetrahedral symmetry and purely ionic character [35], as previously observed for B [14]. It is also possible to detect a weak band at 479 cm −1 tentatively ascribable to the Ag-N bond stretching [36], confirming the coordination of silver(I) by the nitrogen atoms of the pyridyl rings.…”

“…By modulating the redox state of the Ru 2 units (II,II vs. II,III), we could introduce a significant exchange bias with intra-chain coupling, and concomitant enhancement of the remnant magnetization. The ability of A as building block of supramolecular structures has been further confirmed by reaction with silver(I) perchlorate yielding {[Fe 4 (pPy) 2 (dpm) 6 ] 2 Ag}(ClO 4 ) (B), a tridimensional metal-organic framework (3D-MOF) [14]. In this compound, Ag + ions behave as tetrahedral nodes coordinated by four pyridyl nitrogen atoms of Fe 4 units, and the cubic crystals, although with no overall second-order anisotropy, can be persistently magnetized parallel or antiparallel to the four main diagonals of the unit cell.…”

“…Complexes of the family of tetrairon(III) SMMs with general formula [Fe 4 (L) 2 (dpm) 6 ] [12][13][14] (H 3 L = tripodal ligand, Hdpm = dipivaloylmethane) include four coplanar high spin iron(III) ions (s = 5/2) forming a centered triangular geometry. The central metal atom (Fe c ) is antiferromagnetically coupled to the three peripheral ones (Fe p ) so as to give an S = 5 spin ground state.…”

“…Compound B also possesses accessible voids (14.3% of unit cell volume) able to trap small solvent molecules, which can be exploited as a means for modulating the magnetic properties. However, due to the presence of two interlocked dia networks (according to IUPAC nomenclature [27]), the space left inside the 3D-MOF is not available for bigger molecules [14]. In the attempt to build-up a new polymeric structure with larger cavities by elongating the SMM spacer, in this work we synthesized the new tripodal ligand H 3 PhpPy, 2-(hydroxymethyl)-2-(4-(pyridine-4-yl)phenyl) propane-1,3-diol (Scheme 1), where we added a phenyl ring between the triol unit and the pyridyl terminal fragment with respect to H 3 pPy.…”

Propeller‐Shaped Fe4 and Fe3M Molecular Nanomagnets: A Journey from Crystals to Addressable Single Molecules

“…These substituents lie in axial positions at opposite sides of the molecular plane and can be chosen at will to add various functionalities . Complex 3 4 ‐ Py , for instance, acts as a rigid 180°‐ditopic linker that can be assembled into a 3D MOF and chain‐like structures (Figure ) by reaction with Ag + ions and diruthenium paddlewheels [Ru 2 (OAc) 4 ] 0,+1 , respectively. Especially relevant to the present Microreview are R groups that allow to promote and control chemisorption on metals, , , , or carbon substrates, from solution.…”