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What are the problems of (science) education in science in US? (E. O. Wilson) It's the culture (ASU Chem: 1/3 foreign-born, mostly recent hires) The culture can be changed. Cf. Ireland. What should we do? Convince David Nelson to convince NSF to work on changing the national culture.
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What are the problems of (science) education in science in US? (E. O. Wilson) It's the culture (ASU Chem: 1/3 foreign-born, mostly recent hires) The culture can be changed. Cf. Ireland
What should we do? Convince David Nelson to convince NSF to work on changing the national culture.
Alright, what about Solid State Chemistry? First, change the name. Materials Chemistry? It's no accident we are part of DMR. Educate our colleagues. "Everyone" knows biological chemistry is a big growth area materials chemistry is the other. make peace with engineers
Why interest in nets? The Cambridge Crystal Structure database is growing exponentially (t2 = doubling time): all structures t2 = 9.3 yr extended structures based on periodic nets t2 = 5.7 yr metal-organic frameworks (MOFs) t2 = 3.9 yr Thanks to Nate Ockwig
What are the topics needed but missing in Chemistry curriculum? Mathematics of periodic structures Fourier transforms Space groups Periodic nets and surfaces (e.g. gyroid) Crystallography Diffraction methods Diffraction by point scatterers Direct methods The facts! Crystal structures: MgCu2 as well as NaCl Materials: zeolites, magnetic materials, cement, minerals
What do we know about electron density in crystals? It is always positive It is close to zero “almost” everywhere this is very non-random basis of "direct methods"
The charge-flipping algorithm (Oslányi & Süto, 2004) F(g) + random phases FT r(r) flip the sign of the electron density of the lowest fraction of all pixels. Fraction may be as much as 80% flip FT r'(r) FT-1 new phases = F'(g)/| F'(g)| notice that all we are doing is finding new phases original F(g) + new phases
How do we know what’s happening? R = S||F'(h)|-|F(h)|/S|F(h) Note that R does not measure agreement with “model” (if no pixels flipped R = 0)
First application to a real crystal C6Br6 ZC = 6, ZBr = 35 mean of six projected density after one run note that the molecules are slightly inclined (20°) to the plane of projection J. S. Wu, J. C. H. Spence, M. O'Keeffe, T. L. Groy. Acta Crystallogr. (2004), A60, 328-330.
The srs net is chiral (symmetry I4132). The dual is the enantiomorph. Here two srs nets of opposite hand are intergrown to form a centrosymmetric structure (srs-c) (symmetry Ia-3d). The surface separating the two nets is the G minimal surface (gyroid)
Alan Schoen's gyroid – periodic minimal surface G Fragments of two srs nets The same – "blown up" A "tile" of the G surface
The 5-coordinated net fcz As a 32.4.3.6 tiling of the G surface As a 2[62.103] + 3[38.42102] tiling of space (the set of all tiles fill space completely)
SU-M (ASU-17) a germanate with cubic cell 51.3 Å X. Zou, T. Conradsson, M. Klinstedt, M. S. Dadachov & M. O'Keeffe, Nature (2005)
SU-MB symmetry I4132. Chiral! one set of pores of SU-M blocked by six 7 Ge clusters. These are the clusters from ASU-16 etc. clusters in SU-MB cage one cage in SU-MB faujasite "supercage"