The creation of new compounds and materials that facilitate efficient electronic conduction is an important and on-going challenge for the development of nanoscale technologies. We study the development of a new family of one-dimensional materials whose core consists of a one-atom wide conducting wire that is surrounding by insulating protecting groups. These wires are designed simultaneously with their insulating coating such that the wires can be packed with maximum density. The insulating groups serve to isolate each wire for ease of synthesis, promote highly one-dimensional structures, and facilitate efficient conduction along but not between the wires. The proposed materials build on established compounds from our group, proven methodologies, and are expanded with new ligands and redox reactions to achieve the desired electronic structures. Salts will be prepared in which each cation and anion contain a metal atom, M, surrounded by ligands based on L and X groups. Previous work established the use of metathesis reactions to synthesize double salts with d8 and d10 metal-containing cations and anions of the form [ML3X][MX2] and [ML2X2][MX2], where L is a neutral Lewis base donor and X is anionic group. The cations and anions stack in an infinite array forming a chain of metal atoms with infinite metal-metal contacts along the length of the chain. Extensive use has been made of Au and Pt structures to date which will be elaborated upon with Co, Ni, Cu, Rh, Ir, Pr, and Ag. Other ion motifs will be developed as well including [MX4]-and [MLX3]-, This synthetic scheme is extremely flexible and will therefore allow an essentially infinite array of different electronic occupations to be prepared.
Broader Impact: This research project into the preparation of single-atom wide wires has had extensive impact via the education and training of one URM high school student, three REU summer students, and four other undergraduates including two Independent Work for Distinction (senior honors thesis) projects. The high school student is now a chemistry major at Boston University, and several of the undergraduates are now enrolled in chemistry PhD programs including those of Columbia University, University of Michigan, and the University of Tennessee, Knoxville. Three graduate students have participated in this project as well, one of whom has received a master’s degree and the other two, including a URM student, will receive their PhD degrees sometime in 2013. One female post-doctoral researcher was also involved who is now a faculty member at Murray State, a PUI, and the other senior researcher is now on the faculty at Towson University, also a PUI. These people have contributed to nine peer-reviewed publications that are in press, one more currently under review and at least two more manuscripts in preparation. Scientific Merit. We began this project with the idea that one-dimensional materials for efficient electricity conduction could be prepared from carefully designed building blocks. When a wire conducts electricity and current flows, electrons move from one atom to another and this movement is easiest (the least energy is needed for the current to flow) when an electron moves into a so-called hole. We successfully prepared a variety of square building blocks in which each metal center was bound to four groups with neutral (L) or negative (X) charge. We prepared building blocks with mostly M2+ ions so that neutral building blocks have the form [ML2X2], positively charged blocks are [ML3X]+, and negatively charged building blocks show the [MLX3]- pattern. We also prepared a few [MX2]- building blocks from Au1+ ions, and one [AuX4]- block with Au3+. We had a lot of synthetic success when M = Pt and successfully combined positively and negatively charged building blocks into so-called double salts of the form [PtL3X][PtLX3] and [PtL3X][AuX2]. We learned from these compounds that Pt2+ and Au3+ could react together to make Pt4+ and Au1+ species, which is interesting, informative, and almost unheard of, but was not going in the right direction for our goals. The Pt2+-based building blocks were much more successful and were also informative. We learned that the [PtL3X][AuX2] compounds did not have the correct internal building-block alignment for electricity conduction, and we were able to make some correlations between the colors of the new compounds and their internal Pt-Au alignments. With the [PtL3X][PtLX3] compounds, we have found that careful choice of the L and X groups can lead to a wide range of colors, including some deep blue and purple variations which is a color associated with good interactions for electronic conductivity. Work to explain these systems in more detail is ongoing. We have also created a new family of so-called lantern or paddlewheel complexes in which a [PtL4]2+ building block (wheel) is directly bonded through the paddles to a [MX4]2- building block (wheel). In these structures the electron comes from the [PtL4]2+ block and the choice of M (from Fe, Co, or Ni) makes a hole for the electron to go to in the [MX4]2- block. We have found different ways of linking these together, and in the most exciting and unprecedented cases, two of the [PtL4][MX4], M = Co, Ni, lanterns link up through their Pt atoms. Detailed magnetic studies showed that the M-Pt-Pt-M path allows the electrons to communicate throughout the double-lantern aggregate. A picture of such an aggregate is included. Future work is focusing attention on how to increase the length of these chains and measure in detail how easy it is for electrons to move from one M to another one.
