Interplay of Halogen and Hydrogen Bonding in a Series of Heteroleptic iron(III) Complexes

Abstract

<div>The influence of the halogen substituent on crystal packing and redox properties is investigated in a series of heteroleptic complexes [Fe(qsal-X)(dipic)]MeOH (qsal-X = 4-halogen-2-[(8-quinolylimino)methyl]phenolate; dipic = 2,6-pyridinedicarboxylate; X = F 1, Cl 2, Br 3 and I 4).</div><div>Compounds 1 and 2 exhibit triclinic symmetry (P1̅), whereas 3 and 4 crystallise in monoclinic P21/n. The crystal packing shows self-sorting of the ligands with - interactions between the qsal-X ligands and overlap of the dipic ligands to form a 1D chain, that is supported by C-H···O interactions. In 1 and 2, the cross-section of the 1D chain is square, while for 3 and 4, it is rectangular. In the former, the dipic ligands interact through C=O··· interactions, while - interactions are found in 3 and 4. Neighbouring chains are connected via - interactions involving the quinoline rings, but their relative position is driven by the preference of 1 and 2, for C-H···X interactions, whereas 3 and 4 form O···X halogen bonds. The nature and topology of the electron density of these interactions have been investigated using molecular electrostatic potential (MEP) mapping, quantum theory of atoms in molecules (QTAIM) and ‘non-covalent interactions’ (NCI) analysis. UV-Visible experiments show MLCT bands associated with the qsal-X ligands, confirming the structure is stable in solution. Electrochemical studies reveal slight tuning of the Fe3+/Fe2+ redox couple showing a linear relationship between E° and the Hammett parameter σp.</div><div><br></div>

Structural and theoretical insights into solvent effects in an iron(iii) SCO complex

“…Halogen bonding also appears in [Fe(qsal-Br) 2 ]NO 3 •MeOH, 46 helping to improve cooperativity (stepped SCO), while in 1 the effect is minimal, reflecting the smaller σ hole typically found for Cl. 47 Notably, the neighboring chains for 2ns are connected by C-H⋯O interactions involving the nitrate anion (Fig. S3 †).…”

Selective Pathway toward Heteroleptic Spin-Crossover Iron(II) Complexes with Pyridine-Based N-Donor Ligands

“…■ RESULTS AND DISCUSSION Synthesis. Our failed attempts 31 to obtain a heteroleptic iron(II) complex by a simple mixing of 3-bpp and tpy ligands with an iron(II) salt, which successfully produced their cobalt(II) analogues 32 or other heteroleptic complexes after proper purification, [27][28][29][34][35][36]49,50 prompted us to devise an alternative synthetic pathway. A ligand substitution 51 is often the method of choice; 51,52 however, it is not the best one for the weak-field 3-bpp ligands.…”

“…A new synthetic procedure is devised to selectively produce previously elusive 31 heteroleptic iron(II) complexes with the Ndonor ligands from two popular families�terpyridines (tpy) and bis(pyrazol-3-yl)pyridines (3-bpp)�that stabilize the opposite spin states of the metal ion. This approach accommodates a wider scope of substrates than the simple mixing of ligands and a metal salt 31 often used for this purpose [27][28][29][34][35][36]49,50 or the ligand substitution. 95 As compared to other synthetic pathways, 53−55 the stepwise introduction of the ligands proceeds selectively because of a good solubility of the intermediate pentacoordinate complex with the triflate ligands; the latter does not have to be isolated from the reaction.…”

“…27 As previously suggested, 48 a heteroleptic complex is a kinetic product, while a homoleptic complex is thermodynamically favored. Although the former is often obtained [27][28][29][34][35][36][37]49,50 by mixing of two ligands and a metal salt followed by purification, this method can only be applied if the heteroleptic complex is the major product, and hence, there is no thermodynamic control of the reaction. Otherwise, another approach is needed that provides the kinetic control, 48 such as the ligand substitution 51,52 or a stepwise introduction of the ligands into the coordination sphere of the metal ion through the formation of an intermediate pentacoordinate complex with chloride or acetylacetonate ligands.…”

AIE in the halogenated anils and their utilization as fluorescent probes for explosive nitro-aromatics

“…[4][5][6] Understanding the weak intermolecular interactions is pivotal for the growth and development of crystal engineering and its broader domain of supramolecular chemistry. 7,8 Hydrogen bonding [9][10][11] and p-stacking 12 interactions are established intermolecular interactions that have been utilized with design for the development of smart materials with applications in pharmaceuticals, electronics, sensing, and memory-based devices. 13,14 Halogen bonding is a recent interaction of great significance, utilized for anion recognition, 15 liquid crystal displays, 16 semiconductors, 17 molecular magnets, 18 biomolecular engineering, 19 chemical separation, 20 porous materials, 21 and gelators, 22 and this lesser-explored interaction provides immense opportunities for the development of futuristic smart materials.…”