I've always thought that a Bijvoet pair is any pair for which an
anomalous difference could be observed. This includes Friedel pairs
(h & h-bar), but it also includes pairs of the form h & h', where h'
is symmetry-related to h-bar. Thus Friedel pairs are a subset of all
possible Bijvoet pairs.
This is what Ed and I say in our book, at least (shameless plug); and
you can buy it from Amazon, so it must be right, yes?
Pat
On 26 Jun 2008, at 11:55 AM, Bernhard Rupp wrote:
Dear All,
I wonder about the conventions using Friedel vs Bijvoet pair.
a) there are no differences. As long as h = -h, it's a Friedel
or a Bijvoet pair. They are the same.
b) A Friedel pair is any reflection h = -h including hR = -h, i.e.
including centric reflections.
A Bijvoet pair is an acentric Friedel pair, it can carry
anomalous amplitude differences, whereas centric Friedel
pairs invariably cannot. Actually, Bijvoet pairs (acentric
Friedel pairs) invariably do carry anomalous amplitude differences.
There is no such thing as no anomalous scattering.
We may elect to ignore it, only.
c) of course, this all assumes absence of anisotropic AS.
def b) seems to be helpful in discussions and make sense given that
absolute
configuration that needs AS signal is somehow associated with
Bijvoet's
work.
Are any authoritative answers/conventions/opinions available on that ?
Thx, BR
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