Templating metallocycles with a macrocycle: synthesis, structures and magnetic studies of {Cr11M2} complexes

Abstract

Addition of 1,4,8,11-tetrazacyclotetradecane (cyclam) to a reaction that produces octametallic rings when simpler amines are used, produces {Cr₁₁M₂} "pretzels" (M = Zn^II or Cu^II) where the cyclam coordinates to the M^II ion which then sits at the centre of a twelve-metal macrocycle. Magnetic studies were fitted using the finite-temperature Lanczos method (FTLM), and the results demonstrate that exchange interactions are transferable from previous exchange-coupled Cr^III rings.

Fig. 1. The structure of 1 in the crystal. Colour scheme: Cr, green; Zn, white; F, yellow; N, blue; O, red, C, black. Methyl groups on pivalates and H-atoms excluded for clarity.

Fig. 2. The magnetic behaviour of 1 shown (a) as χT(T) and (b) M(B). Measured data as black symbols, fits as red curves.

Fig. 3. The magnetic behaviour of 2 shown (a) as χT(T) and (b) M(B). Measured data as black symbols, fits as red curves.

Fig. 4. Numbering of spin centres (Cr, green; M, yellow) and exchange interactions. In 1J₁ and J₄ are not present.

Fig. 5. The X-band EPR spectra of 1 and 2. In (a) the spectrum measured at 9.388583 GHz (black), S = 5/2 state (brown), S = 3/2 state (pink) and simulation weighted at 2 : 1 for the 3/2 : 5/2 states (red). In (b) the spectrum measured at 9.388738 GHz (black), S = 1 state (orange), S = 2 state (green), S = 1/2 (blue), and simulation with equal weights for these states in red.