Synthesis and properties of cobalt(II) coordination polymers linked by 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine

Abstract

The cationic one-dimensional coordination polymers [{Co(pyterpy)2}{M(hfac)2}] 2+ (M = Co(II) or Zn(II); pyterpy = 4'-(4-pyridyl)-2,2':6',2''-terpyridine; hfac-= hexafluoroacetyloacetonate) feature alternating {Co(pyterpy)2} and {M(hfac)2} units linked through heteroditopic pyterpy ligands. Cocrystallization with [M(hfac)3]-(M = Co(II) or Zn(II)) counteranions has afforded the compounds: [{Co(pyterpy)2}{Co(hfac)2}][Co(hfac) 3 ] 2 (1) and [{Co(pyterpy)2}{Co0.7Zn0.3(hfac)2}][Zn(hfac) 3 ] 2 (2). Variable temperature crystallographic and magnetic studies indicate low spin cobalt(II) ions in the {Co(pyterpy)2} components of the coordination polymers up to room temperature; magnetic studies suggest the onset of a thermallyinduced spin crossover at these centers above room temperature.

Hysteretic Spin Crossover with High Transition Temperatures in Two Cobalt(II) Complexes

“…However, although it is easy to form an SCO active complex of a general formula of [Co­(terpy) 2 ]­X 2 ·solvent, the observed SCO properties of these complexes are usually gradual and incomplete , except for several limited examples such as the dehydrated complex [Co­(terpy) 2 ]­(BF 4 ) 2 . Decoration of the 4′-position (and recently also the 5,5″-positions) of the terpy ligand with substituent groups, such as hydroxyl, alkyl and alkoxy chains, , phenyl rings, pyridyl rings, and others, has been proved to be very efficient to modify the ligand fields and intermolecular interactions of the Co II SCO materials. Along this line, a number of interesting Co II SCO materials with strong cooperativity have been reported. ,,,,, Representative examples are the series of compounds containing long alkyl chains reported by Hayami et al, with rich SCO properties including order–disorder phase transition induced inverse spin transitions with considerable hysteresis width, reentrant SCO transitions at low temperatures, and so on. , …”

Incorporation of Switchable Inorganic Building Blocks into Heterometallic Coordination Polymers

“…Furthermore, ditopic terpyridine-based ligands have found use in higher order supramolecular assemblies such as in grids, interlocked molecules, dendrimers, coordination polymers, metal organic frameworks, and large self-assembled architectures. , Synthesis of 4-substituted terpyridines via the Kröhnke synthesis , allows for the incorporation of a secondary binding site “out the back” of the terpyridine unit. This then opens the opportunity to make heterometallic assemblies by exploiting the denticity of the binding sites and the coordination preferences of the metal ions used. ,− …”

Slow magnetic relaxation and spin crossover behavior in two mixed-valence Co(ii)/Co(iii) complexes

“…, and n = 0-6) show various SCO behaviors generating incomplete or gradual SCO curves. [45][46][47][48][49][50] The SCO behavior can be significantly influenced by counter anions and lattice solvent. [51][52][53][54][55][56] Inspired by the above, we introduce an auxiliary ligand of 1,10-phenanthroline (phen) and 2,2 0 : 6 0 ,2 00 -terpyridine (terpy) on the basis of previous mixed-valence cobalt trinuclear complexes…”

“…44 Relevant research results show that the SCO cobalt( ii ) complexes, [Co(terpy) 2 ]X 2 ·nH 2 O (X = Br − , Cl − , I − , F − , ClO 4 − , NCS − , NO 3 − , [Co(CN) 4 ] − , SO 4 − , BPh 4 − , and n = 0–6) show various SCO behaviors generating incomplete or gradual SCO curves. 45–50 The SCO behavior can be significantly influenced by counter anions and lattice solvent. 51–56…”