AtomAccess: A predictive tool for molecular design and its application to the targeted synthesis of dysprosium single-molecule magnets

Abstract

Isolated dysprosocenium cations, [Dy(CpR)2]+ (CpR = substituted cyclopentadienyl), have recently been shown to exhibit superior single-molecule magnet (SMM) properties over closely related complexes with equatorially-bound ligands. However, gauging the crossover point at which the CpR substituents are large enough to prevent equatorial ligand binding, but small enough to approach the metal closely and generate strong crystal field splitting, has required laborious synthetic optimization. We therefore created the computer program, AtomAccess, to predict the accessibility of a metal binding site and its ability to accommodate additional ligands. Here we apply AtomAccess to rapidly screen a series of derivatized dysprosium metallocene fragments of varying steric bulk in silico, allowing us to identify the crossover point for equatorial coordination in [Dy(CpR)2]+ cations, and hence predict a cation that is at the cusp of stability without equatorial interactions, viz. [Dy(Cpttt)(Cp*)]+ (Cpttt = C5H2tBu3-1,2,4, Cp* = C5Me5). Upon synthesizing this cation we found it crystallizes as either a contact ion-pair, [Dy(Cpttt)(Cp*){Al[OC(CF3)3]4-k-F}], or separated ion-pair polymorph, [Dy(Cpttt)(Cp*)][Al{OC(CF3)3}4]C6H6. These complexes, together with their precursors and yttrium analogs, have been characterized by NMR and ATR-IR spectroscopy, elemental analysis, powder and single crystal X-ray diffraction, SQUID magnetometry and ab initio calculations. We find that the contact ion-pair shows inferior SMM properties to the separated ion-pair, as expected, due to faster Raman and quantum tunneling of magnetization relaxation processes. The experimental verification of the predicted crossover point for equatorial coordination in this work indicates that programs like AtomAccess have significant potential to boost efficiency in exploratory synthetic chemistry.

Halobenzene Adducts of a Dysprosocenium Single-Molecule Magnet

“…56 Variations in Dy•••Cp R centroid distances for the halobenzenebound complexes are insignificant (e.g., for 2-Dy, Dy••• Cp ttt centroid : 2.307(2) Å; Dy•••Cp* centroid : 2.315(2) Å) and are in accord with the corresponding distances for the SIP and CIP. 15 The Dy−X−C ipso angles of 2-Dy, 3-Dy, and 4-Dy decrease with increasing halogen size (2-Dy: 153.20(9)°; 3-Dy: 126.74(3)°; 4-Dy: 117.1(4)°). The bidentate o-C 6 H 4 F 2 ligand in 5-Dy requires a larger equatorial binding site than PhX (Table 1).…”

Isolation of a Bent Dysprosium Bis(amide) Single-Molecule Magnet

“…28 The Dy atom is sterically protected by this extremely bulky ligand system, with all visible access channels restricted to <3.4% of the solid angle at Dy (Figure S71). 41 Powder XRD was performed on a sample of S4), confirming that the single-crystal structure obtained is representative of the bulk crystalline material used for magnetic characterization. Magnetic Measurements.…”

Catalytic exploration of NHC–Ag(i)HMDS complexes for the hydroboration and hydrosilylation of carbonyl compounds

“…More recently, AtomAccess 39,40 an online tool for calculating the accessibility of an atom in a molecule has been developed. It produces a 3D map of ray clusters 39 in which the size of the cluster can be used to determine the steric hinderance at a metal centre in a complex.…”

“…More recently, AtomAccess 39,40 an online tool for calculating the accessibility of an atom in a molecule has been developed. It produces a 3D map of ray clusters 39 in which the size of the cluster can be used to determine the steric hinderance at a metal centre in a complex. 39 In this regard, we used AtomAccess on both 3 and 4 to more accurately determine the size of the clefts ( ‘holes’ ) seen in the 2D % V Bur topographical maps.…”

“…34 Encouraged by these studies and seeking to improve upon our previously reported silver(I)amide pre-catalyst 34 we now report the synthesis and characterisation of two light stable monomeric NHC silver(I) amide complexes and their application in the catalytic hydroboration and hydrosilylation of a range of aldehydes and ketones (Scheme 1d). Complementary calculations on the steric bulk of the Lewis donor ligands via %V Bur , [35][36][37][38][39][40] Solid-G 41 and AtomAccess 39,40 programs help to rationalise the different catalytic efficiencies observed of the two NHC silver(I) amide complexes.…”