Metallohydrolase biomimetics with catalytic and structural flexibilityElectronic supplementary information (ESI) available. CCDC 1495702-1495704. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6dt03200a

The structural and functional properties of zinc( ii ) complexes of two nitrogen rich polydentate ligands, HTPDP = 1,3-bis(bis-pyridin-2-ylmethylamino)propan-2-ol and HTPPNOL = N , N , N ′-tris-(2-pyridylmethyl)-1,3-diaminopropan-2-ol, are compared. HTPDP is a hepta-dentate ligand with four pyridyl groups attached to a 1,3-diaminopropan-2-ol backbone while HTPPNOL contains only three pyridyl groups. In reactions with Zn(ClO 4 ) 2 , HTPDP forms a dinuclear zinc compound [Zn 2 (TPDP)(OAc)](ClO 4 ) 2 , 1 . On the other hand, mononuclear [Zn(HTPPNOL)](ClO 4 ) 2 , 2 , and tetranuclear [Zn 4 (TPPNOL) 2 (OAc) 3 ](ClO 4 ) 3 , 3 , complexes were isolated with the ligand HTPPNOL. Kinetic measurements with the substrate bis(2,4-dinitrophenyl)phosphate (BDNPP) revealed that compound 1 ( k cat = 31.4 × 10 −3 min −1 ) is more reactive than 3 ( k cat = 7.7 × 10 −3 min −1 ) at pH = 8.5, whilst the mononuclear compound 2 is inactive. Compound 1 displays a typical steady-state kinetic behaviour, while compound 3 exhibits steady-state behaviour only ∼120 s after starting the reaction, preceded by a burst-phase. 31 P NMR studies confirm that 1 can promote the hydrolysis of both ester bonds in BDNPP, generating the monoester DNPP and inorganic phosphate in the process. In contrast, DNPP is not a substrate for 3 . The crystal structure of the complex formed by 3 and DNPP reveals the formation of a tetranuclear zinc complex [Zn 4 (TPPNOL) 2 (DNPP) 2 ](ClO 4 ) 2 , 4 , in which the phosphate moiety of DNPP adopts an unusual tridentate μ-η 1 :η 1 :η 1 coordination mode. The phosphatase activity of zinc complexes containing six- and seven-dentate ligands was evaluated through kinetic and 31 P NMR studies.