**Appendix A**

MnCl2·4H2O (99 mg, 0.5 mmol, Sigma Aldrich, UK), H4TBC[4] (97 mg, 0.15 mmol, Sigma Aldrich, UK) and NH4ClO4 (140 mg, 1.2 mmol, Sigma Aldrich, UK) were dissolved in a mixture of dmf (10 mL, Fisher Scientific, UK) and CH3CN (10 mL, Fisher Scientific, UK). 1,4 butanediol (90 mg, 1 mmol, Sigma Aldrich, UK) was then added with stirring. After five minutes, NEt3 (0.42 mL, 3 mmol, Sigma Aldrich, UK) was added dropwise and the reaction mixture stirred for two hours. X-ray quality crystals were obtained after 3 days in ~20% yield following filtration of the mother liquor with subsequent diffusion of diethyl ether (or hexane) into the resulting solution. Elemental analysis: found (calc. %) for C222H320Cl2Mn12N18O42: C 57.61 (57.43), H 6.94 (6.95), N 5.35 (5.43). Crystal Data (CCDC 1993320): C204H288Cl2Mn12N10O40 (*M* =4250.61 g/mol): triclinic, space group *P*-1 (no. 2), *a* = 16.144(16) Å, *b* = 19.437(19) Å, *c* = 22.33(2) Å, α = 110.119(15)◦, β = 104.06(2)◦, γ = 90.752(15)◦, *V* = 6347(11) Å3, *Z* = 1, *T* = 100(2) K, μ(MoKα) = 0.656 mm<sup>−</sup>1, *Dcalc* = 1.112 g/cm3, 98657 reflections measured (3.342◦ ≤ 2Θ ≤ 52.744◦), 25871 unique (*R*int = 0.0328, Rsigma = 0.0396), which were used in all calculations. The final *R*1 was 0.0564 (I > 2σ(I)) and *wR*2 was 0.1810 (all data). Magnetic properties were determined using a MPMS-XL SQUID magnetometer (Quantum Design Inc., San Diego, CA, USA) for direct current (dc) and alternating current (ac) measurements. The powdered microcrystalline sample was immobilised in eicosane. Experimental dc data were recorded at 0.1 T in the temperature range 5.0–300 K and at 2.0–7.0 K in the field range 0.5–7.0 T. Experimental ac data were collected in the temperature range 1.8–10 K and frequency range 0–1500 Hz using an amplitude of *B*ac = 3 G. All data were corrected for the sample holder contributions and intrinsic diamagnetic contributions that were determined from Pascal's constants.
