Bulky ligands shape the separation between the large spin carriers to condition field-induced slow magnetic relaxation

• Published in: Dalton transactions : an international journal of inorganic chemistry 2020-01, Vol.49 (2), p.3-311
• Main Authors: Kobylarczyk, Jedrzej, Liberka, Michal, Konieczny, Piotr, Baran, Stanis aw, Kubicki, Maciej, Korzeniak, Tomasz, Podgajny, Robert
• Format: Article
• Language: English
• Subjects: Bonding strength; Chains; Clusters; Crystallography; Hydrogen bonds; Ligands; Low temperature; Magnetic induction; Magnetic permeability; Magnetic relaxation; Relaxation time; Separation; Temperature dependence; Time dependence
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c9dt03903a

Crystal engineering of magnetic relaxation in supramolecular networks based on almost isotropic cyanido-bridged {Mn 9 [W(CN) 8 ] 6 L 8 (solv) 8 } clusters decorated by bulky 4,4′-di- tert -butyl-2,2′-bipyridine (Bu t 2 bpy) and 4,7-diphenyl-1,10-phenanthroline (Ph 2 phen) ligands is presented. The three new compounds {Mn II 9 [W V (CN) 8 ] 6 (Bu t 2 bpy) 8 (MeOH) 8 }·Pr i 2 O·13MeOH ( 1 ), {Mn II 9 [W V (CN) 8 ] 6 (Bu t 2 bpy) 8 (MeOH) 6 (H 2 O) 2 }·4Pr i 2 O·2H 2 O ( 1a ), and {Mn II 9 [W V (CN) 8 ] 6 (Ph 2 phen) 8 (MeOH) 8 }·29MeOH·6H 2 O ( 2 ) were characterized structurally and magnetically. Compound 1 exhibits unequivocal domination of repulsive intercluster contacts operating between the side Bu t groups leading to intercluster distances exceeding 10 Å in all three dimensions. Compound 1a reveals a 1-dimensional (1D) supramolecular chain structure with very close intercluster distances of 6.7 Å realized through the direct W-CN HO-Mn hydrogen bonds along the chain, further isolated by the above repulsive Bu t Bu t synthons. Compound 2 shows significant separation in all three directions with the intercluster distances close to 10, 12 and 13.5 Å. However, in contrast to 1 , these separations are accompanied by indirect hydrogen bond arrays and local π-π interactions of potential to assist in the transfer of weak magnetic interactions. The dc magnetic data show the signature of S = 39/2 in the ground state, which is typical in this group of compounds. The high-spin clusters are accompanied by different intercluster interactions, illustrated by the effective zJ ′ values of +0.010 cm −1 ( 1 ), +0.008 cm −1 ( 1a ) and +0.001 cm −1 ( 2 ). The low temperature ac susceptibility measurements revealed a temperature- and field-dependent magnetic relaxation time for all 1 , 1a and 2 compounds ( τ 1 , τ 1a -fast , and τ 2 -fast in the range 10 −3 -10 −4 s). In contrast and only in the case of 1a and 2 , an additional temperature independent slow process was detected ( τ 1a -slow and τ 2 -slow located between 0.1 s and 1 s). The magnetic relaxations were correlated with the obtained supramolecular networks, indicating the significant role of dipolar fields, weak non-covalent interactions, hydrogen bonds and π-π interactions. Magnetic relaxations in isotropic high spin S = 39/2 cyanido-bridged {Mn 9 [W(CN) 8 ] 6 L 8 (solv) 8 } clusters tuned by crystal engineering.