A ferric guest inside a spin crossover ferrous helicate

A designed dimetallic Fe(II) helicate made with biphenylene-bridged bispyrazolylpyridine ligands and exhibiting a process of spin crossover at temperatures above ambient is shown to encapsulate an S = 5/2 tris-oxalato Fe(III) ion. The spin relaxation dynamics of this guest are strongly reduced upon encapsulation.This research was supported by Spanish MINECO (PGC2018-098630-B-I00, PID2020-118329RB-I00), the Aragón government (E31_20R PLATON) and the EU (FET-OPEN grant 862893 FATMOLS), and used resources of the ALBA synchrotron and of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DEAC02-05CH11231. G. A. thanks the Generalitat de Catalunya for the prize ICREA Academia 2018.Peer reviewe