화학공학소재연구정보센터
Inorganic Chemistry, Vol.33, No.22, 4840-4849, 1994
Copper(II) 12-Metallacrown-4 - Synthesis, Structure, Ligand Variability, and Solution Dynamics in the 12-MC-4 Structural Motif
An important goal for generalizing the metallacrown analogy was to prepare metallacrowns with divalent ring metals using di- and trianionic supporting organic ligands that retain a high yield synthesis for a predicted metallacrown structural motif. This goal has been achieved with Cu(II) using anthranilic hydroxamic acid, 2-pyridylacetohydroxamic acid, 3-hydroxy-2-naphthohydroxamic acid, salicylhydroxamic acid, 5-deuterio- and 3,5 dideuterio-salicylhydroxamic acid, 4-hydroxysalicylhydroxamic acid, 4-methylsalicylhydroxamic acid, 5-hydroxysalicylhydroxamic acid, 5-methoxysalicylhydroxamic acid and 5-butylsalicylhydroxamic acid. These organic ligands vary not only the organic periphery but also the metal coordination donor set. Each farms the generalized [Cu-II(12-MC(Cu(II)N(ligand,)-4)] structure in one-step, high yield syntheses. The dianionic ligands (e.g. anthranilic hydroxamic acid) demonstrate that neutral metallacrown rings with divalent ring metals may be synthesized. The trianionic ligands (e.g. salicylhydroxamic acid) provide the first formally charged metallacrown rings demonstrating that the accumulation of charge does not hinder metallacrown formation. Appending hydroxy, alkyl, and alkyloxy functional groups to the [Cu-II(12-MC-4)]’s demonstrate in principle that incorporation of functionalities potentially capable of forming mesogenic phases or binding to clean metal surfaces can be accomplished. A variety of analytical techniques, i.e. UV-vis, ESI-MS, FAB-MS, and solution magnetic susceptibility measurements, were employed to probe the solution integrity and dynamics of the [Cu-II(12-MC-4)]’s. These studies allow us to conclude that all of the copper metallacrowns presented retain their structure in solution. Additionally, UV-vis titrations demonstrate the [Cu-II(12-MC-4)]’s are stable in DMF even in the presence of excess acetate ion or ligand. The solution dynamics of the [Cu-II(12-MC-4)] system was probed using electrospray ionization mass spectrometry and H-1 NMR. These studies revealed that the copper(II) 12-metallacrown-4’s are inert to ligand exchange. Variable temperature magnetic susceptibility measurements show weak antiferromagnetic coupling between the copper(II) ions in the metallacrown which results in an S = 1/2 ground state, i.e. mu(eff) approximate to 1.73 mu(B) per metallacrown at 4 K. The solution and solid state magnetic susceptibilities at 300 K are comparable, thus providing additional evidence for metallacrown solution integrity. The totality of evidence from W-vis, ESI-MS and FAB-MS, H-1 NMR, solution magnetic susceptibility measurements, and EPR support the conclusion that copper(II) metallacrowns retain their structure in solution.