Metal–organic frameworks (MOFs) exhibit a broad range of luminescence characteristics due to the vast array of metal ions and organic linkers available as building blocks. Systematic control over the emissive output of MOFs is highly sought after. Methods for tuning emission profiles are emerging based largely on luminescent metal ions and the encapsulation of emissive guests. Herein, we show how the functionalization of the organic linkers of a series of multicomponent MUF-77 (MUF = Massey University Framework) materials can methodically tune their spectral output. This was quantified by chromaticity diagrams. White-light emission was obtained by combining the photophysical characteristics of the three distinct organic fluorophores present in these materials. Our results also show that both (i) energy transfer interactions between the organic components and (ii) noncovalent interactions with guests can also be harnessed to tune the emission. These results establish multicomponent metal–organic frameworks as fluorescent materials with unique spectral characteristics.

Reaction of a rigid tridentate ligand o-[(1H-imidazol-2-yl)methylideneamino]phenol (2-Himap) with Co(ClO) in the presence of NaN, or Co(NO) without a base yields [Co(2-Himap)] 1 and [Co(2-Himap)]NO·MeOH 2, respectively. Both complexes exhibit a mer-octahedral geometry with the cobalt centre being distorted along an octahedral-trigonal prismatic pathway. The packing in 1 and 2 is dominated by H-bonding forming 2D sheets and 1D chains, respectively. Detailed dc and ac magnetic studies indicate that 1 is a field-induced single-ion magnet (SIM) with D = 36.7 cm and E = 2.0 cm. Extensive ab initio calculations support these conclusions and suggest that relaxation of the magnetization occurs principally through direct quantum tunnelling in the ground state, with the Raman process dominant in an applied field. This contrasts with the recently reported series of mer-[Co(L)] (L = monoanionic NNO donor ligand; Inorg. Chem., 2017, 56, 6056-6066) complexes where D is negative, as these compounds have a more ambiguous geometry, and highlights the importance of supramolecular interactions in subtly altering the coordination sphere thereby impacting the magnetic behaviour.

A series of iron(iii) complexes [Fe(naphEen)2]X·sol (naphEen = 1-{[2-(ethylamino)-ethylimino]methyl}-2-naphtholate; X = F, sol = 0.5CH2Cl2·H2O 1; sol = H2O, X = Cl, 2 and X = Br 3) and [Fe(naphEen)2]I 4 has been prepared. The UV-Vis spectra reveal clear differences for 1 which DFT/TDDFT calculations suggest are due to an equilibrium between [Fe(naphEen)2]F and [Fe(naphEen)2F], the latter having a coordinated F ligand. The X-ray crystal structures of 2-4 show LS Fe(iii) centres in all cases and extensive aryl interactions that link the Fe centres into supramolecular squares. In 3 at room temperature the compound loses half an equivalent of water resulting in a change in space group from Monoclinic P21/n to C2/c. Magnetic studies indicate that 1 is trapped in a mixed spin state being ca. 40% HS while 2-4 are effectively low spin up to 350 K. In contrast, Mössbauer spectroscopic studies of 1 indicate a gradual but incomplete spin crossover. The magnetic properties of 2-4 contrast with the related [Fe(salEen-X)2]anion derivatives which are often spin crossover active.