Encoding metal coordination pathways and nuclearity by molecular knotting.

A molecular cinquefoil knot with bidentate and tridentate chelating sites programs metal-ion coordination pathways, yielding Mn(II)5-, Fe(II)5-, Co(II)5-, and Cd(II)5-knots with a 2-to-5 nuclearity progression.

• Why it matters: Controlling metal nuclearity and spatial organization is a key coordination-chemistry goal, but knotting has rarely been used to organize inequivalent metal-binding sites within a single ligand.
• What they did: Direct metalation produced Mn(II)5-, Fe(II)5-, Co(II)5-, and Cd(II)5-knots via a dinuclear intermediate, and crystallization of a Mn(II)2- intermediate showed partial demetalation with a “3 + 3” mode.
• The result: Crystallography and simulations support a stepwise mechanism where the dinuclear “3 + 3” environment evolves into the “3 + 2” motif of the fully metalated Fe(II)5-knot, enabling pathway-controlled multi-metallic assembly.