Coordination number incommensurate cluster formation, part 21 - Design, formation and properties of tetrahedral M4L4 and M4L6 supramolecular clusters

The rigid tris- and bis(catecholamide) ligands H(6)A, H4B and H4C form tetr ahedral clusters of the type M4L4 and M4L6 through self-assembly reactions with tri- and tetravalent metal ions such as Ga-III, Fe-III, Ti-IV and Sn-I V. General design principles for the synthesis of such clusters are present ed with an emphasis on geometric requirements and kinetic and thermodynamic considerations. The solution and solid-state characterization of these com plexes is presented, and their dynamic solution behavior is described. The tris-catecholamide H(6)A forms M4L4 tetrahedra with Ga-III, Ti-IV, and Sn-I V; (Et3N)(8)[Ti(4)A(4)] crystallizes in R(3) over bar c (No. 167), with a = 22.6143(5) Angstrom, c = 106.038(2) Angstrom. The cluster is a racemic mix ture of homoconfigurational. tetrahedra (all Delta or all A at the metal ce nters within a given cluster). Though the synthetic procedure for synthesis of the cluster is markedly metal-dependent, extensive electrospray mass sp ectrometry investigations show that the M(4)A(4) (M = Ga-III, Ti-IV, and Sn -IV) clusters are remarkably stable once formed. Two approaches are present ed for the formation Of M4L6 tetrahedral clusters. Of the bis(catecholamide ) ligands, H4B forms an M4L6 tetrahedron (M = Ga-III) based on an "edge-on" design, while H4C forms an M4L6 tetrahedron (M = Ga-III, Fe-III) based on a "face-on" strategy. K-5[Et4N](7)[Fe4C6] crystallizes in I (4) over bar 3d (No. 220) with a = 43.706(8) Angstrom. This M4L6 tetrahedral cluster is al so a racemic mixture of homoconfigurational tetrahedra and has a cavity lar ge enough to encapsulate a molecule of Et4N+. This host-guest interaction i s maintained in solution as revealed by NMR investigations of the Ga-III co mplex.