Influence of a counteranion on the zero-field splitting of tetrahedral cobalt(ii) thiourea complexes

• Verfasst von: Tripathi, Shalini [VerfasserIn]
• Verfasst von: Vaidya, Shefali [VerfasserIn]
• Verfasst von: Ansari, Kamal Uddin [VerfasserIn]
• Verfasst von: Ahmed, Naushad [VerfasserIn]
• Verfasst von: Rivière, Eric [VerfasserIn]
• Verfasst von: Spillecke, Lena [VerfasserIn]
• Verfasst von: Koo, Changhyun [VerfasserIn]
• Verfasst von: Klingeler, Rüdiger [VerfasserIn]
• Verfasst von: Mallah, Talal [VerfasserIn]
• Verfasst von: Rajaraman, Gopalan [VerfasserIn]
• Verfasst von: Shanmugam, Maheswaran [VerfasserIn]
• Titel: Influence of a counteranion on the zero-field splitting of tetrahedral cobalt(ii) thiourea complexes
• Verf.angabe: Shalini Tripathi, Shefali Vaidya, Kamal Uddin Ansari, Naushad Ahmed, Eric Rivière, Lena Spillecke, Changhyun Koo, Rüdiger Klingeler, Talal Mallah, Gopalan Rajaraman, Maheswaran Shanmugam
• E-Jahr: 2019
• Jahr: June 27, 2019
• Umfang: 16 S.
• Fussnoten: Gesehen am 25.05.2020
• Titel Quelle: Enthalten in: Inorganic chemistry
• Ort Quelle: Washington, DC : American Chemical Society, 1962
• Jahr Quelle: 2019
• Band/Heft Quelle: 58(2019), 14, Seite 9085-9100
• ISSN Quelle: 1520-510X
• DOI: doi:10.1021/acs.inorgchem.9b00632
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 169872635X

Abstract

Four mononuclear cobalt(II) complexes with pseudo tetrahedral geometry were isolated with different counteranions; their structure solution reveals the molecular formula as [Co(L1)4]X2 [where L1 = thiourea (NH2CSNH2) and X = NO3 (1), Br (2), and I (3)] and [Co(L1)4](SiF6) (4). The detailed analysis of direct-current (dc) magnetic data reveals a zero-field splitting (ZFS; D) with mS = ±3/2 as the ground levels (D < 0) for the four complexes. The magnitude of the ZFS parameter is larger, in absolute value, for 1 (D = −61.7 cm-1) than the other three complexes (−5.4, −5.1, and −12.2 cm-1 for 2-4, respectively). The sign of D for 1, 2, and 4 was unambiguously determined by X-band electron paramagnetic resonance (EPR) spectroscopy of the diluted samples (10%) at 5 K. For 3, the sign of D was naturally endorsed from the frequency-dependent out-of-phase signal (χM″) observed in the absence of an external dc magnetic field and confirmed by high-frequency EPR (70-600 GHz) experiments performed on a representative pure polycrystalline 3, which gave a quantitative D value of −5.10(7) cm-1. Further, the drastic changes in the spin Hamiltonian parameters and their related relaxation dynamics phenomena (of 2-4 compared to 1) were rationalized using ab initio complete-active-space self-consistent field/n-electron valence perturbation theory calculations. Calculations disclose that the anion-induced structural distortion observed in 2-4 leads to a nonfavorable overlap between the π orbital of cobalt(II) and the π* orbital of the sulfur atom that reduces the overall |D| value in these complexes compared to 1. The present study demonstrates that not only the first but also the second coordination sphere significantly influences the magnitude of the ZFS parameters. Particularly, a reduction of D of up to ∼90% occurs (in 2-4 compared to 1) upon a simple variation of the counteranions and offers a viable approach to modulate ZFS in transition-metal-containing single-molecule magnets.