Modulating the structural topologies from star-shape to cross-shape for Co-Dy heterometallic complexes with slow magnetic relaxation behavior

• Published in: CrystEngComm Vol. 25; no. 5; pp. 726 - 737
• Main Authors: Wang, Hui-Sheng, Yu, Chun-Fang, Ye, Si-Qi, Chen, Yong, Liu, Xueru, Wu, Yanfang, Zhou, Pengfei, Zhang, Yi-Quan
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 30.01.2023
• Subjects: Diamagnetism; Ketones; Magnetic induction; Magnetic relaxation; Mathematical analysis; Structural analysis; Topology; Triethylamine
• ISSN: 1466-8033; 1466-8033
• DOI: 10.1039/d2ce01381a

Two novel Co-Dy heterometallic complexes, namely, [Co III 2 Dy III 2 (HL)L{(py) 2 CO 2 }{(py) 2 C(OCH 3 )O}(NO 3 ) 4 CH 3 OH]·2CH 3 CN·2.5H 2 O ( 1 , H 3 L = 2-((2-hydroxy-benzylidene)amino)propane-1,3-diol, (py) 2 C(OH) 2 = the gem -diol form of di-2-pyridyl ketone (dpk) and (py) 2 C(OCH 3 )OH = the hemiacetal form of dpk) and [Co III {(py) 2 C(OH)O} 2 ][Co II 2 Dy III 4 Dy III (HL) 4 (L) 4 ]·3CH 3 CN·15H 2 O ( 2 ), have been obtained by employing H 3 L, dpk and Dy(NO 3 ) 3 ·5H 2 O reacting with Co(NO 3 ) 2 ·6H 2 O or anhydrous Co(CH 3 CO 2 ) 2 in the solutions of CH 3 OH and CH 3 CN ( V / V = 1/20) containing N(Me) 4 OH·5H 2 O or triethylamine. Structural analysis indicated that two Dy III and two Co III in 1 formed a star-like topology, while the metal ions in [Co II 2 Dy III 4 Dy III (HL) 4 (L) 4 ] − of 2 formed a cross-shaped topology, in which one Dy III and two Co II formed a linear Co II 2 Dy III paramagnetic unit. Interestingly, the paramagnetic Co II 2 Dy III units in 2 were isolated not only by four diamagnetic Co III in the [Co II 2 Dy III 4 Dy III (HL) 4 (L) 4 ] − , but also by the diamagnetic [Co III {(py) 2 C(OH)O} 2 ] + . More interestingly, the distortion of the square antiprism (SAP-8) coordination geometry of Dy III in 2 can be ascribed to the presence of four long Dy-O bonds and four short Dy-O bonds, which could result from the discrepancies of the polarization of Co II and Co III . Magnetic studies indicated that 1 exhibit two types of magnetic relaxation behavior, in which the magnetic relaxation of the fast relaxation (FR) phase is mainly governed by QTM, while that of the slow relaxation (SR) phase is mainly governed by Orbach and Raman processes with an effective energy barrier ( U eff ) value of 59.4(9) K. To our knowledge, the U eff value is relatively high among the reported Co III -Dy III heterometallic complexes. For 2 , it only shows slow relaxation behavior with a U eff of 6.43 K. Ab initio calculations revealed that the SR phase and FR phase are governed by the magnetic relaxation of Dy2 and Dy1, respectively, though the axial symmetry of Dy2 (muffin, C s ) is lower than that of Dy1 (triangular dodecahedron, D 2d ). However, for 2 , the theoretical calculations indicated that the severely compressed SAP-8 geometry of Dy III leads to a relatively low U eff value. A star-like Co III 2 Dy III 2 complex ( 1 ) and a cross-shaped Co II/III -Dy complex ( 2 ) have been obtained, in which 1 exhibits double magnetic relaxation behavior, while 2 only shows slow magnetic relaxation signals.