Abstract
The assembly of [Co2III(μ-2,5-dpp)(CN)8]2− anions and [MII(CH3OH)2(DMSO)2]2+ cations resulted into the formation of two heterobimetallic 1D coordination polymers of formula [MII(CH3OH)2(DMSO)2(μ-NC)2Co2III(μ-2,5-dpp)(CN)6]n·4nCH3OH [M = CoII (1)/FeII (2) and 2,5-dpp = 2,5-bis(2-pyridyl)pyrazine. The [Co2III(μ-2,5-dpp)(CN)8]2− metalloligand coordinates the paramagnetic [MII(CH3OH)2(DMSO)2]2+ complex cations, in a bis-monodentate fashion, to give rise to neutral heterobimetallic chains. Cryomagnetic dc (1.9–300 K) and ac (2.0–13 K) magnetic measurements for 1 and 2 show the presence of Co(II)HS (1) and Fe(II)HS (2) ions (HS – high-spin), respectively, with D values of +53.7(5) (1) and −5.1(3) cm−1 (2) and slow magnetic relaxation for 1, this compound being a new example of SIM with transversal magnetic anisotropy. Low-temperature Q-band EPR study of 1 confirms that D value is positive, which reveals the occurrence of a strong asymmetry in the g-tensors and allows a rough estimation of the E/D ratio, whereas 2 is EPR silent. Theoretical calculations by CASSCF/NEVPT2 on 1 and 2 support the results from magnetometry and EPR. The analysis of the ac magnetic measurements of 1 shows that the relaxation of M takes place in the ground state under external magnetic dc fields through dominant Raman and direct spin-phonon processes.
Highlights
The design of heterometallic coordination polymers (CPs) is of high interest due to their potential applications as molecular magnets and luminescent or multifunctional materials [1–13]
We have shown that the use as a metalloligand of the [Co2III(μ-2,5-dpp)(CN)8]2− complex anion towards the preformed complex of formula [MnII(MAC)(H2O)2]Cl2 · 4H2O (MAC = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo-[12.3.1]-octadeca-(18),2,12,14,16-pentaene] afforded a neutral {CoIII2MnII} chain exhibiting a Curie law behavior because of the occurrence of intrachain magnetically isolated {MnII(MAC)} units whose trans-positioned coordinated water molecules were replaced by two cyanide groups from two 2,5-dpp-bridged dicobalt(III)
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Summary
The design of heterometallic coordination polymers (CPs) is of high interest due to their potential applications as molecular magnets and luminescent or multifunctional materials [1–13]. In comparison with the homoleptic analogues, the capping ligands reduce the number of potential bridges, favoring the achievement of low-dimensional CPs. Single-ion and single-molecule magnets (SIMs and SMMs) are highly anisotropic discrete motifs showing slow relaxation of the magnetization [40–44]. Coordinative and supramolecular architectures enclosing magnetically isolated SIMs and SMMs moieties are very appealing considering their potential use in molecular electronics [66,67]. These networks consist of organic diamagnetic spacers that connect the spin centers [68–81]. Diamagnetic cyanido-bearing building blocks such as the homo- [CoIII(CN)6]3− and [MIV(CN)8]4− (MIV = Mo and W) or the heteroleptic [WIV(bipy)(CN)6]2− complex anions were less employed as metalloligands to prepare extended structures of molecule-based nanomagnets [86–90]. Their synthesis, X-ray structure and cryomagnetic investigation are discussed
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