Cobalt Complexes with “Click”-Derived Functional Tripodal Ligands: Spin Crossover and Coordination Ambivalence

Abstract

We demonstrate the use of a Cu(I) catalyzed "Click" reaction in the synthesis of novel ligands for spin crossover complexes. The reaction between azides and alkynes was used to synthesize the reported tripodal ligand tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine, TBTA, and the new ligands tris[(1-cyclohexyl-1H-1,2,3-triazol-4-yl)methyl]amine, TCTA, and tris[(1-n-butyl-1H-1,2,3-triazol-4-yl)methyl]amine, TBuTA. Reactions of TBTA with Co(ClO(4))(2) lead to complexes of the form [Co(TBTA)(CH(3)CN)(3)](ClO(4))(2), 1, and [Co(TBTA)(2)](ClO(4))(2), 2, where complex formation can be controlled by the metal/ligand ratio and the complexes 1 and 2 can be chemically and reversibly switched from one form to another in solution resulting in coordination ambivalence. The benzyl substituents of TBTA in 2 show intramolecular C-H-π T-stacking that generates a chemical pressure to stabilize the low spin (LS) state at lower temperatures. The structural parameters of 2 are consistent with a Jahn-Teller active LS Co(II) (elongation) ion showing four short and two long bonds. 2 shows spin-crossover (SCO) behavior in the solid state and in solution with a high T(0) close to room temperature which is driven by the T-stacking. 1 remains high spin (HS) between 2 and 400 K. Reversible chemical switching is observed between 1 and 2 at room temperature, with an accompanying change in the spin state from HS to LS. The importance of the intramolecular T-stacking in driving the SCO behavior is proven by comparison with two analogous compounds that lack an aromatic substituent and remain HS down to very low temperatures.

How to Switch Spin‐Crossover Metal Complexes at Constant Room Temperature

“…Bogani, Sarkar, and co‐workers reported two closely related cobalt complexes: a heteroleptic [Co II ( 19 )(MeCN) 3 ](ClO 4 ) 2 and a homoleptic [Co II ( 19 ) 2 ](ClO 4 ) 2 (Scheme ) . In the solid state at room temperature, the former adopts a HS state (d 7 electronic configuration, S =3/2), whereas the later shows a gradual S =1/2→ S =3/2 thermally induced SCO at nearly room temperature.…”

FeII and CoII Complexes with Click‐Derived Tripodal Ligands: Influence of the Peripheral Substituents on Geometric Structures and Magnetic Properties

“…Bidentate and tridentate ligands based on 1,2,3‐triazoles have been popular for close to a decade now . Another class of 1,2,3‐triazole ligands that have found use in recent years are tripodal ligands of the form shown in Figure , where a central amine donor is flanked by three additional heterocyclic rings . The most popular ligands of this class are the C 3 symmetric ligands where all three triazole arms are the same.…”

“…However, in recent years related tripodal ligands with two or three different heterocyclic arms based on an amine anchor have also been developed. [4g], [4h], [4l], [4m], [4o]…”

“…Schematic representation (N 3 signifies donating triazole N atom of tbta) of weak intramolecular interactions observed in the complexes [M(tbta) 2 ] 2+ (M = Fe or Co, bottom). [1d], [4a], [4e]…”

Photoswitchable stable charge-distributed states in a new cobalt complex exhibiting photo-induced valence tautomerism

“…Modern chemistry and new physical investigation methods have allowed the clear evidence of phenomena, where the magnetization state can be tuned forth and back by external stimulus, such as light, as well as temperature, pressure, current or chemical doping [3][4][5][6][7][8][9][10][11][12][13][14] . For the development of new nanodevices, the individual building blocks need to be reduced down to the molecular level and need to be addressed with high precision.…”