Substituent effects of N4 Schiff base ligands on the formation of fluoride-bridged dicobalt(ii) complexes via B–F abstraction: structures and magnetism

Abstract

We report the synthesis of two fluoride bridged cobalt(ii) dimers - [Co(μ-F)(pnN4-PhCl)2(OH2)(MeCN)](BF4)3 (1) and [Co(μ-F)2(pnN4-PhCl)2](BF4)2 (2) - and related complexes derived from propyl-bridged N4 Schiff base plus pyridine ligands. Notably, the bridging fluoride ion(s) emanate from B-F abstraction processes on the BF4 anions in the starting salt, [Co(H2O)6](BF4)2. Two types of bridging motifs are generated - mono-bridged (μ-F) or di-bridged (μ-F)2- synthetically differentiated by the absence or presence of pyridine, respectively, during metalation. The synergistic roles of pyridine and the (ClPh)N4 ligand in promoting B-F abstraction were clarified by the isolation and crystallization of the simple tetrakis-pyridine monomeric complex [Co(py)4(MeCN)2](BF4)2 (4) [no B-F abstraction]; subsequent addition of the (ClPh)N4 ligand to 4 resulted in formation of the dimeric, di-bridged complex 2. Omission of pyridine during metalation resulted in formation of the mono-bridged dimer 1. The bulky chlorophenyl substituents were obligate for B-F abstraction, as metalation of the unsubstituted N4 ligand resulted in the non-fluoride-bridged dimer, [Co(pnN4)3](BF4)4 (3). In magnetic studies, complexes 1 (μeff = 6.24μB, 298 K) and 2 (μeff = 7.70μB, 298 K) both exhibit antiferromagnetic (AFM) coupling, but to different extents. Temperature-dependent magnetic susceptibility measurements (SQUID, 2 → 300 K) reveal that the linearity of the mono-fluoride bridge in 1 [∠Co-F-Co = 159.47(11)°] results in very strong AFM coupling (J = -14.9 cm(-1)). In contrast, the more acute Co2F2 diamond core [∠Co-F-Co = 98.8(2)°, 99.1(2)°] results in a smaller extent of AFM coupling (J = -2.97 cm(-1)). Overall, the results indicate the 'non-innocence' of the BF4 counterion in cobalt(ii) chemistry, and dimers 1 and 2 affirm the effect of the geometry of the bridging fluoride ion(s) in determining the extent of AFM coupling.

Divergent Solution and Solid-State Structures of Mono- and Dinuclear Nickel(II) Pyridone Complexes

“…Cleavage of BF 4 – to form fluoride ions in the presence of transition metals has been reported, − although it is a rare observation and only occurs only in systems with strong N - heterocyclic ligands such as pyridines, pyrazoles, and imidazoles. The decomposition is thought to be the result of F coordination of BF 4 – to a coordinately unsaturated metal center (ML n ) followed by B–F bond cleavage to yield a [ML n –1 F] − complex and a L·BF 3 adduct .…”

1D Copper(II)-Aroylhydrazone Coordination Polymers: Magnetic Properties and Microwave Assisted Oxidation of a Secondary Alcohol

“…Data were collected using omega scans of 0.5 • per frame and full sphere of data were obtained. Cell parameters were retrieved using Bruker SMART (Bruker, 2012) software and refined using Bruker SAINT (Bruker, 2012) on all the observed reflections. Absorption corrections were applied using SADABS (Bruker, 2012).…”

“…Cell parameters were retrieved using Bruker SMART (Bruker, 2012) software and refined using Bruker SAINT (Bruker, 2012) on all the observed reflections. Absorption corrections were applied using SADABS (Bruker, 2012). Structures were solved by direct methods by using SHELXS (Sheldrick, 2000) and refined with SHELXL 2018 (Sheldrick, 2015).…”

“…Transition metal complexes derived from multidentate Schiff base ligands received high significance due to their wide dimension of applications in the areas of molecular magnetism (Benelli and Gatteschi, 2002;Sutradhar et al, 2012Sutradhar et al, , 2013Sutradhar et al, , 2014bSutradhar et al, , 2015aSutradhar et al, , 2018Cho et al, 2016;Andruh, 2018), crystal engineering (Dong et al, 2000;Kitaura et al, 2004;Andruh et al, 2009), supramolecular chemistry (Pradeep and Das, 2013;El-Bindary et al, 2016;Dwivedi et al, 2018), catalysis (Sutradhar et al, 2013(Sutradhar et al, , 2014b(Sutradhar et al, , 2015a(Sutradhar et al, ,b,c, 2016a(Sutradhar et al, ,b,c, 2017(Sutradhar et al, , 2018(Sutradhar et al, , 2019, etc. Molecular magnetism is one of the significant domains determining magneto-structural correlations to design magnetic materials (Benelli and Gatteschi, 2002;Sutradhar et al, 2012Sutradhar et al, , 2013Sutradhar et al, , 2014bSutradhar et al, , 2015aSutradhar et al, , 2018Cho et al, 2016;Andruh, 2018). Single molecule magnets (SMMs) (Karotsis et al, 2010;Glaser et al, 2015;Maniaki et al, 2018) exhibit a large spin ground-state (S) value and large negative magnetic anisotropy and are used in potential high-density information storage devices and GRAPHICAL ABSTRACT | Two new aroylhydrazone Cu(II) 1D coordination polymers [Cu 3 (L 1 )(NO 3 ) 4 (H 2 O) 2 ] n (1) and [Cu 2 (H 2 L 2 )(NO 3 )(H 2 O) 2 ] n •(NO 3 ) n (2) (H 2 L 1 = N' 1 ,N' 2 -bis(pyridin-2-ylmethylene)oxalohydrazide and H 4 L 2 = N' 1 ,N' 3 -bis(2-hydroxybenzylidene)malonohydrazide) have been structurally characterized.…”

“…quantum computers (Leuenberger and Loss, 2001). Therefore, many efforts have been devoted to rationally establish polynuclear metal complexes and/or clusters elucidating molecular magnetism (Benelli and Gatteschi, 2002;Karotsis et al, 2010;Sutradhar et al, 2012Sutradhar et al, , 2013Sutradhar et al, , 2014bSutradhar et al, , 2015aSutradhar et al, , 2018Glaser et al, 2015;Cho et al, 2016;Andruh, 2018;Maniaki et al, 2018). Coordination polymers and molecular clusters are particular classes of compounds that can display novel magnetic properties including high ground-state spin values and single molecule magnetism behavior (Zheng et al, 2014;Journaux et al, 2018;Yue and Gao, 2019).…”