Syntheses, crystal structures, and magnetic properties of three new molecular solids based on bis(maleonitriledithiolate)Ni(III) monoanion and substituted chlorobenzyl-4-dimethylaminopyridinium
Abstract
Three new molecular solids, [nClBzPyN(CH3)2][Ni(mnt)2]([BzPyN(CH3)2]+ = benzyl-4-dimethylaminopyridinium; mnt2− = maleonitriledithiolate; n = 2(1), 3(2), 4(3)), have been prepared and characterized. The [Ni(mnt)2]− anions of 1 and 2 form a 1D column in which the former is non-uniform one with the Ni⋯Ni distances of 4.412 and 6.072 Å, and the latter is uniform one with the distance of 7.352 Å, while the ones of 3 show a stepwise structure through Ni⋯S, Ni⋯C, π⋯π, or C⋯N short interactions. The [2ClBzPyN(CH3)2]+ cations(C) and [Ni(mnt)2]− anions (A) of 1 stack into a 1D column with a ⋯A
CCACCA⋯ sequence, while the cations stake into a 1D column via N⋯π and Cl⋯Cl short interactions for 2. The change of the chlorine position on the benzyl ring from ortho, meta to para-position results in the significant differences in stacking modes of these molecular solids. Magnetic susceptibility measurements in the temperature range 2–300 K show that 1, 2 and 3 exhibit a spin gap transition around 172, 150 and 92 K.
Introduction
As early as 1996, A.T. Coomber and co-workers discovered a new molecular magnet, NH4·Ni(mnt)2·H2O(mnt2− = maleonitriledithiolate), which consists of stacked planar metal ligands separated by ammonium cations and exhibits long-range ferromagnetic order below 4.5 K [1]. From then on, the [M(mnt)2]− (where M = Ni, Pt, or Pd) monoanion have been widely used for synthesis of molecular solids with unusual magnetic properties such as magnetic transition, meta-magnetism, spin-Peierls-like transitions, ferromagnetic ordering at low temperature, and spin gap transitions [1], [2], [3], [4] because such [M(mnt)2]− possess a planar configuration with an extended electronic structure, and favors one-dimensional columnar molecular arrangements [1], [5], [6], [7], [8]. For molecular solids containing [M(mnt)2]− anion, the unusual magnetic behavior is totally attributed to the anionic part, and the magnetic coupling is highly sensitive to the interaction contacts and the overlapping patterns of [M(mnt)2]− anions. In addition, the shape, size and configuration of counter-cation may influence the crystal packing. The focus of study in these series of molecular solids is to search for some excellent multifunctional organic cations that can effectively mediate the magnetic coupling between the spin carriers [Ni(mnt)2]− anions, and establish a relationship between the magnetic interactions and the stacking pattern of anions or cations [6], [7], [8], [9], [10], [11], [12]. In previous papers we have described the [Ni(mnt)2]-based solids formed by substituted benzyl 4-dimethylaminopyridinium ([RBzPyN(CH3)2]+, R = H, F, CN, or NO2) cation, and found that [BzPyN(CH3)2][Ni(mnt)2] shows an antiferromagnetic behavior [13], whereas [4FBzPyN(CH3)2][Ni(mnt)2] [14], [4CNBzPyN(CH3)2][Ni(mnt)2] [14] and [4NO2BzPyN(CH3)2][Ni(mnt)2] [13] exhibit spin gap transitions upon the temperature is lowering [16], [17], [18]. In this study, in order to widen our research, we have obtained single crystal of three molecular solids, [nClBzPyN(CH3)2][Ni(mnt)2] (n = 2(1), 3(2) and 4(3)), and investigated the effect on the crystal structures, weak interaction, overlapping mode between the anions, and magnetic properties when the substitution position of chlorine atom from ortho- to meso- and para-position on benzyl ring of the cation.
Section snippets
General materials
2-Chlorobenzyl bromide, 3-chlorobenzyl bromide, 4-chlorobenzyl bromide and 4-dimethylaminopyridine were purchased from Aldrich and were used without further purification. 1-(2′-Chlorobenzyl)-4-dimethylaminopyridinium bromide ([2ClBzPyN(CH3)2]Br), 1-(3′-chlorobenzyl)-4-dimethylaminopyridinium bromide ([3ClBzPyN(CH3)2]Br), 1-(4′-chlorobenzyl)-4-dimethylaminopyridinium bromide ([4ClBzPyN(CH3)2]Br) and disodium maleonitriledithiolate (Na2mnt) and were synthesized following the literature procedures
Descriptions of crystal structures
Compounds 1–3 are isostructural, and crystallize in triclinic system with space group P−1. The anionic [Ni(mnt)2]− entities for both compounds are completely planar. As shown in Fig. 1a, there are two planar [Ni(mnt)2]− anions and two curving [2ClBzPyN(CH3)2]+ cations in an asymmetric unit of 1. Selected bond distances and bond angles are summarized in Table 2, and these values are in the expected range for those [Ni(mnt)2]− compounds [13], [14]. In [2ClBzDMAP]+ moiety containing N(9) atom, the
Conclusion
Three new molecular solids, [2ClBzPyN(CH3)2][Ni(mnt)2] (1), [3ClBzPyN(CH3)2][Ni(mnt)2] (2) and [4ClBzPyN(CH3)2][Ni(mnt)2] (3) with unusual magnetic properties have been prepared and characterized. The [Ni(mnt)2]− anions of both 1 and 2 form a 1D column, while the ones of 2 show a stepwise structure through Ni⋯S, Ni⋯C, π⋯π, or C⋯N short interactions. The [2ClBzPyN(CH3)2]+ cations (C) and [Ni(mnt)2]− anions (A) of 1 stack into a 1D column with a ACCACCA sequence, while the cations stake into a 1D
Supplementary data
The detail crystallographic data of 1, 2 and 3 have been deposited at the Cambridge Crystallographic Data Center as supplementary publication No. CCDC-852953, No. CCDC-852954 and No. CCDC-852955. Copies of the data may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44 1223 336033; [email protected] or www: http://www.ccdc.cam.ac.uk).
Acknowledgments
This work has been supported by the Science and Technology Project (No. 2012B010200041) from Guangdong Science and Technology Department, the key Academic Program of the 3rd phase “211 Project” (No. 2009B010100001) of South China Agricultural University and the university students’ innovative experimental project (No. 1056411137) from Education Department of Guangdong Province.
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Effects of different dithiolate ligands on electrocatalytic hydrogen production of nickel complexes in acetic acid or water
2023, Journal of Molecular StructureThe effect of oxidation state of metal on hydrogen production electro-catalyzed by nickel complexes supported by maleonitriledithiolate ligand
2017, Journal of Electroanalytical ChemistryCitation Excerpt :With the acetic acid concentration increased from 0.0 to 5.0 × 10− 3 mol L− 1, the onset of the catalytic wave moves positive ca. 0.17 V from − 1.51 to − 1.34 V versus Ag/AgNO3. On the basis of the above observations, analyses and literature precedents [21,22], a possible catalytic cycle for the generation of hydrogen from acid mediated by 1 is depicted in Scheme 2. One-electron reduction of [NiII(mnt)2]2 − 1 produces a putative [NiI(mnt)2]3 − species.