Photochemistry of framework-supported M(diimine)(CO) 3 X complexes in three-dimensional lithium carboxylate metal–organic frameworks: monitoring the effect of framework cations

The structures and photochemical behaviour of two new metal–organic frameworks (MOFs) are reported. Reaction of Re(2,2′-bipy-5,5′-dicarboxylic acid)(CO) 3 Cl or Mn(2,2′-bipy-5,5′-dicarboxylic acid)(CO) 3 Br with LiCl or LiBr, respectively, produces single crystals of {Li 2 (DMF) 2 [(2,2′-bipy-5,5′-dicarboxylate)Re(CO) 3 Cl]} n ( ReLi ) or {Li 2 (DMF) 2 [(2,2′-bipy-5,5′-dicarboxylate)Mn(CO) 3 Br]} n ( MnLi ). The structures formed by the two MOFs comprise one-dimensional chains of carboxylate-bridged Li(I) cations that are cross-linked by units of Re(2,2′-bipy-5,5′-dicarboxylate)(CO) 3 Cl ( ReLi ) or Mn(2,2′-bipy-5,5′- dicarboxylate)(CO) 3 Br ( MnLi ). The photophysical and photochemical behaviour of both ReLi and MnLi are probed. The rhenium-containing MOF, ReLi , exhibits luminescence and the excited state behaviour, as established by time-resolved infrared measurements, is closer in behaviour to that of unsubstituted [Re(bipy)(CO) 3 Cl] rather than a related MOF where the Li(I) cations are replaced by Mn(II) cations. These observations are further supported by density functional theory calculations. Upon excitation MnLi forms a dicarbonyl species which rapidly recombines with the dissociated CO, in a fashion consistent with the majority of the photoejected CO not escaping the MOF channels. This article is part of the themed issue ‘Coordination polymers and metal–organic frameworks: materials by design’.