Date of Award

1-1-2010

Document Type

Campus Access Dissertation

Department

Chemistry and Biochemistry

Sub-Department

Chemistry

First Advisor

Daniel L Reger

Abstract

A new hetero-bifunctional ligand designed to form supramolecular structures with a combination of covalent and noncovalent forces has been prepared. The ligand, (1,8- naphthalimide)CH2C6H4CH2OCH2C(pz)3 (Ltris, pz = pyrazolyl ring), contains both a

tris(pyrazolyl)methane coordination unit and a 1,8-naphthalimide strong π...π stacking unit. The reactions of iron(II), copper(II) and cadmium(II) tetrafluoroborate salts with two equivalents of Ltris yield [Fe(Ltris)2](BF4)2 (1), [Cd(Ltris)2](BF4)2 (2) and [Cu(Ltris)2](BF4)2 (3), respectively. Vapor diffusion crystallization yielded two pseudopolymorphs for 1. In the solid-state structures of both forms the iron is in an octahedral environment with bond distances expected for low-spin iron(II); both tris(pyrazolyl)methane donor sets are in a κ3-coordination mode with each Ltris ligand in a U-shaped, syn arrangement. In one pseudopolymorph, the 1,8-naphthalimide side chains are on the same side of the molecule when viewed down the metal axis (syn-1), twisted only 30° with respect to each other. In the second pseudopolymorph the side chains are oriented in opposite directions at 180° (anti-1). Both structures are one-

dimensional, organized by intermolecular π...π stacking interactions of the 1,8– naphthalimide units. Each naphthalimide unit reaches past the naphthalimide unit on the

adjacent cation, leading to a π...π stack using the face of the naphthalimide unit directed toward its metal complex, interlocking the U-shaped groups.

The interaction of the two naphthalimide groups is directionally specific; they are oriented head to tail with substantial overlap of the parallel rings. The twisting of the side chains at 30° for syn-1 leads to a helical structure, whereas the 180° orientation of the side chains in anti-1 leads to a linear structure. The cadmium(II) complex is isostructural to syn-1 and the copper(II) is isostructural to anti-1. Although the supramolecular structures of these two compounds are similar to the matched iron(II) complexes because of the similar orientations of the side-chains and the consistent noncovalent interactions of the naphthalimide synthon, the larger size of cadmium(II) leads to a highly distorted

9 structure about the metal. The copper(II) structure is also distorted, as expected for a d

complex. New enantionpure trifunctional carboxylate ligands have also been built by

linking the strong π...π stacking 1,8-naphthalimide group to three naturally occurring amino acids using the azide/alkyne click reaction so as to place a flexible, enantiopure

- spacer between the donor atoms and the supramolecular synthon (glycine, Lgly ; alanine

-- Lala and serine, Lser ). These ligands were used to prepare the complexes [M(Lamino

acid)2(4,4’-bipy)(H2O)2]•xH2O (M = Fe, Co, Ni, Cu, Zn; x = 4.25 to 4.84) by layering methods. Despite the differences in the sidechains, these complexes are isostructural, with the central metal atom coordinated to two κ 1-carboxylate ligands, two water molecules, and one end each of two 4,4’-bipyridyl ligands in a distorted octahedral environment, with each ligand oriented in a trans arrangement. They all have homochiral, helical, supramolecular metal organic framework three-dimensional structures with the helix organization of the individual metallic units held together solely by strong, noncovalent π...π stacking interactions of the naphthalimide; the other two dimensions are organized by the bipyridine ligands. The helices are extremely large; one

turn of the helix travels ~60 Ǻ and has a diameter of ca. 40 Ǻ. The helices of the

complexes for the two enantiopure ligands have the P orientation. For the achiral ligand -

Lgly , the nickel complex forms two types of homochiral crystals in the same tube, one in the enantiomorphous space group P6122 and the other in P6522, a clear example of spontaneous resolution. Despite the large size, the individual helices are tightly interconnected and nestled closely together. Part of the interconnection comes from the interstitial water molecules held inside the framework of the complexes in isolated pockets by hydrogen bonding interactions. For both [Cu(Lala)2(4,4’-bipy)(H2O)2]•4.5H2O and [Co(Lala)2(4,4’-bipy)(H2O)2]•4.76 H2O, the intersitial water molecules can be removed by placing them under vacuum for several hours, a process that can be reversed by exposure to atmospheric moisture. This removal/reinterduction of the interstitial waters takes place with no loss of crystallinity, a dramatic example of a gas/solid single crystal to single crystal transformation. The crystals undergo little change other than the pockets holding the interstitial water molecules in the hydrated structures become void spaces in the dehydrated structures. It is proposed that the removal/reintroduction of the waters in these closely packed solids is facilitated by the “soft” π...π stacking interactions organizing one dimension of the structures. The observed magnetic and Mössbauer spectral properties are typical of isolated, magnetically dilute, paramgnetic pseudooctahedral divalent transition metal complexes.

Shorter, more rigid tri- and tetrafunctional enantiopure ligands have been prepared from commercially-available 1,8-naphthalic anhydride and the amino acids L- alanine, R-phenylglycine, and L-asparagine to produce (S)-2-(1,8-naphthalimido)propanoic acid (HLala), (R)-2-(1,8-naphthalimido)-2-phenylacetic acid (HLphg), and (S)-4-amino-2-(1,8 naphthalimido)-4-oxobutanoic acid (HLasn),

- respectively. Reactions of Lala with copper(II) acetate under a variety of solvent

conditions has lead to the formation and characterization by X-ray crystallography of

three similar copper(II) paddlewheel complexes with different axial ligands,

Cu2(Lala)4(THF)2] (1), [Cu2(Lala)4(HLala)] (2) and [Cu2(Lala)4(py)(THF)] (3). A similar -

reaction using THF and Lphg leads to the formation of [Cu2(Lphg)4(THF)2] (4). With the

exception of a disordered component in the structure of 4, the naphthalimide groups in all

of these compounds are arranged on the same side of the square, central paddlewheel

unit, forming what is known as the chiral crown configuration. The shape of the four

naphthalimide groups that form this chiral crown pocket on one end of the dimers varies

with the axial ligand, being fairly narrow and symmetrical when THF is the axial ligand

and expands and is more asymmetric with larger axial ligands. In the case of pyridine as

the axial ligand, C-H···π interaction from the pyridine 2- and 6-position hydrogen atoms

draw in the naphthalimide groups involved in the interaction, forcing the other two

farther apart. The 1,8-naphthalimide groups organize all of these complexes in different

types of supramolecular structures ranging from three- to two- to one-dimensional. The

- addition of the amide group functionality in the Lasn ligand leads to the formation of

tetrameric [Cu4(Lasn)8(py)(MeOH)] (5), where reciprocal axial coordination of one of the amide carbonyl oxygen atoms between two dimers leads to the tetramer. Extensive supramolecular interactions in 5, mainly caused by the 1,8-naphthalimide supramolecular synthon, support an open three-dimensional structure containing large pores filled with ordered and disordered solvent. When crystals of [Cu4(Lasn)8(py)(MeOH)] are exposed

to (S)-ethyl lactate vapor, the coordinated methanol molecule and the crystal lattice solvents are replaced by (S)-ethyl lactate, bonding through the carbonyl oxygen, yielding [Cu4(Lasn)8(py)((S)-ethyl lactate)] (6) without loss of crystallinity. With the exception of the replacement of the one axial ligand, the structures of 5 and 6 are very similar. In a similar experiment of 5 with vapors of (R)-ethyl lactate, again a change occurs without loss of crystallinity, but in this case the (R)-ethyl lactate displaces only half of the axial methanols, and coordinates through the hydroxyl group. When crystals of [Cu4(Lasn)8(py)(MeOH)] are exposed to vapors of racemic ethyl lactate, the coordinated methanol molecule is displaced without loss of crystallinity exclusively by (S)-ethyl lactate, yielding a new form of the tetramer [Cu4(Lasn)8(py)(S-EtLac)], in which the ethyl lactate in the pocket is bonding through the carbonyl oxygen as with 6, but those in the pores appear to be racemic, as apposed to only the S-form in 6. These results demonstrate an enatioselective single-crystal to single-crystal gas/solid-mediated transformation is taking place in the chiral pocket of 5. They also show the large pores in the structure of 5 allow this exchange in the gas/solid phases with the large (S)-ethyl lactate molecule. These exchanges are also supported by the “flexibility” imparted to these solid-state structures by the π...π stacking interactions of the 1,8-naphthalimide supramolecular synthon.

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