Development of new technologies for solid‐state polymerization. A conceptual and experimental approach

Abstract

A review of an extensive study on the preparation and solid‐state reactivity of squareplanar NiX2L2 complexes is presented, where X = Cl, Br, I, or NCS and L = P(CH2CH2CN)3. Physical, chemical, and crystallographic criteria have been evaluated for such complexes, from the viewpoints of the properties and reactivity of the squareplanar monomer and the analogous octahedral polymer. Factors such as nearest‐neighbor interactions, nucleation, temperature, doping, polymorphism, and crystal symmetry greatly influence the course of the thermal solid‐state reactions. The reactions per se are characterized by chemical and crystallographic specificity, stereodirectionality, highly anisotropic front motion in single crystals, and reversibility. In a series of preliminary, related experiments, the radiation‐induced polymerization of salts and complexes of β‐acryloxypropionic acid and propiolic acid has been studied; there is a great variation in reactivity among these species. Many of the reactive phases have short contacts between neighboring molecules which would appear to satisfy topochemical criteria for reaction in the solid state.

Experimental Establishment of Mother–Daughter Orientation Relationships and Twinning Effects in Phase Transitions: A Great Legacy from Jack Gougoutas and Peggy Etter

“…The geometrical relationship necessarily would be a point-group symmetry operation of the reactant lattice . Gougoutas terms this phenomenon conservative twinning , and we have found his concept to be extremely useful, both in our earlier studies of solid-state reactivity, , as well as in recent studies of twins produced during a phase transition.…”

“…In the 1970s the alignment of mother and daughter phases in molecular crystals was established through examination of aligned Weissenberg or precession photographs. − The analysis led to the following interlattice relationship, which is important in interpreting the topotaxy observed in the experiment (symbols from the 1976 article are used here): where φ ij is the topotactic transformation matrix, while b i and a j are the direct basis set vectors for the product and reactant lattices, respectively. We refer the interested reader to Etter’s paper for other elements of the theory and an interesting historical account of how φ ij was derived from observations on X-ray photographs …”

“…In 1978, I (BF) met Peggy at ICCOSS V, held here at Brandeis, and we began a friendship and a set of inspiring scientific dialogues that lasted until her untimely passing in 1992. After some initial success in topotactic thermal reactions, , we turned our attention to γ-ray-induced radical reactions in solids. The bulk of the transformations involved solid-state oligomerization reactions that led to amorphous materials. , However, most recently, we explored γ-ray induced, stereospecific oligomerizations of crotonate salts and established that the geometric course of hydrogen atom transfer in the solid state is topochemical , stereospecific , and not the result of a random process.…”

Use of Topotactic Phase Transformations To Obtain Solutions of the Crystal Structures of Highly Disordered Materials

“…The present contribution reports a different approach to the use of phase transitions: to predict , in optimal cases, the structure of a material which has remained elusive at the atomic coordinate level. Topotactic crystal-to-crystal phase transformations, including those processes involving either molecular reorientation or a chemical reaction, have been an important focus of our research for over four decades. − “In topotaxy, a single crystal of a starting material is converted into a pseudomorph containing one or more products in a definite crystallographic orientation; the conversion takes place throughout the entire volume of the crystal.” The topotactic solid-state reaction of bis­( p- methoxy)- trans -stilbene, first described in a 1984 paper by Theocharis, Jones and Rao, served as an opportunity for B.M.F. to write to Professor Bill Jones with some questions about the paper .…”