actually, I'll have to amend that:
> Dear Bernhard (and others),
> I was looking for catchy combinations of "chiral" or "enantio" and
> Latin or Greek words for "support" or "allow" -- until I realized there
> is already a name for this very concept, used widely in chemistry:
> I think the precise and correct term applicable to the "65" should be
"the 22 chiral (aka 11 enantiomorphic paris) and the 43
> pro-chiral spacegroups". They are not chiral by themselves, but addition
> of "something" /allows/ for the creation of a chiral object (i.e. the
> crystal).
>
> Cheers,
>
> Jens
>
> On Tue, 2014-04-29 at 16:12 +0200, Bernhard Rupp wrote:
> > Response to off-board mail:
> >
> > >How about [calling them] non-centro-symmetric space groups, as I often
> > >tell my students?
> >
> > Almost, but not exact enough.....
> >
> > The 65 are only a subset of non-centrosymmetric space groups:
> >
> > Not all enantiogenic (not elements of the 65-set) space groups are
> > centrosymmetric. Simplest example Pm.
> > According to above definition Pm (and many more lacking a center of
> > inversion) would be a ok space group for chiral motifs.
> >
> > (when a space group has the 'center at ....' annotation in the Tables, it
> > has a coi and is a centrosymmetric space group).
> >
> > This implies that there are actually three types of crystal structures (cf.
> > Flack):
> >
> > (a) chiral (non-centrosymmetric) crystal structures
> > (b) centrosymmetric crystal structures
> > (c) achiral non-centrosymmetric crystal structures
> >
> > And just as a reminder, the substructure inversion for 3 members of the 65
> > is not about the origin (0,0,0): I41, I4122, F4132
> > are their own enantiomorph, so for them there is no enantiomorphic pair
> > (eg. I41 and I43), in fact no separate space
> > group I43 is even necessary - look at the SG diagram #80 - both, 41 and 43
> > axes appear in the same SG. (2005 Erice paper of George explains more)
> >
> > Enough yet?
> >
> > Cheers, BR
>
