Tuneable solvent adsorption and exchange by 1D bispidine-based Mn(II) coordination polymers via ligand design.

Here we report novel bispidine-based coordination polymers (CPs) 2·TCM, 3·TCM, 3·NB, 5·TCM and 5·TCM·NB, of compostition [Mn(Cl)2(L2)2·(TCM)2], [Mn(Cl)2(L3)2·(TCM)5], [Mn(Cl)2(L3)2·(NB)8], [Mn(Cl)2(L5)2·(TCM)4], [Mn(Cl)2(L5)2·(TCM)2·(NB)2], respectively (NB = nitrobenzene; TCM = chloroform). They were obtained starting from novel bispidine ligands L2 (dimethyl 7-isopropyl-3-methyl-9-oxo-2,4-di(pyridin-4-yl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylate), L3 (dimethyl 7-(cyclohexylmethyl)-3-methyl-9-oxo-2,4-di(pyridin-4-yl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylate) and L5 (dimethyl 7-(4-(dimethylamino)benzyl)-3-methyl-9-oxo-2,4-di(pyridin-4-yl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylate), The novel CPs were characterized by single crystal X-ray diffraction (SC-XRD), powder X-ray diffraction (PXRD) and thermal analyses (TGA). We describe their structural and dynamic properties in terms of solvent exchange and adsorption processes, and we outline the general trends observed on the basis of a total of 16 X-ray structures (4 new) and 21 microcrystalline powder phases (10 new), which have been obtained so far for CPs by coordination of ligands L1-L5, having different substitution at the N7 position. This large set of CPs comprises monosolvated, bisolvated and desolvated species, and it shows a good demonstration of how small differences in the functionalization of the organic ligand can have a strong impact on the resulting structural and dynamic properties of this class of 1D CPs.

Combined structural and theoretical investigation on differently substituted bispidine ligands: predicting the properties of their corresponding coordination polymers.

Pyridine-based bispidine ligands L1-L7, which differ in the substituent at the N7 position of the bispidine scaffold, have been studied by single crystal X-ray diffraction and density functional theory (DFT) calculations, also including solid-state algorithms. Qualitative description of the packing interactions and quantitative data on the stability of each ligand in the solid-state have been employed to draw reasonable predictions on the ligand potential for the formation of linear 1D coordination polymers (CPs) with Mn(ii)Cl2 and on their resulting dynamic properties, in terms of adsorption and solvent exchange capabilities. The basic assumption lies in the fact that volume and polarizability of the ligands would similarly affect packing energies in both molecular solids and CP materials. The results here obtained confirm the data previously reported on CPs (those made from L4 are less dynamic than the ones with L1), but they also allow the prediction that CPs made with L2 and L5 should be more dynamic than expected, while CPs with L6 and L7 should not form altogether. This latter prediction was derived from the analysis of the steric and electronic factors of the ligand substituents on the N7 position and it is further substantiated by the obtainment of a 2 : 1 molecular complex, and not a CP, by crystallization of L6 with MnCl2.