the structure is a mer-isomer (meridional). If the three X ligands are all
on one face of the octahedron and
the three Y ligands are on an opposite face, then it is a fac-isomer (facial). See also ambidentate; e–z
convention.
isomers See isomerism.
isometric 1. (in crystallography)
Denoting a system in which the axes
are perpendicular to each other, as in
cubic crystals. 2. Denoting a line on
a graph illustrating the way in which
temperature and pressure are interrelated at constant volume.
isomorphism The existence of two
or more substances (isomorphs) that
have the same crystal structure, so
that they are able to form *solid solutions.
isonitrile (isocyanide; carbylamine)
An organic compound containing the
group –NC, in which the bonding is
to the nitrogen atom.
297
isopolymorphism
i
trans-isomer
cis-isomer
X
Y
Y
M
Y
Y
X
mer-isomer
fac-isomer
Y
X
Y
X
M
Y
Y
X
X
Y
Y
M
Y
X
X
X
Y
Y
M
X
Y
Isomerism
A
• Information about IUPAC nomenclature
iso-octane See octane; octane
number.
isopleth A vertical line in a liquid–vapour phase diagram consisting
of a line of constant composition of
the whole system as the pressure is
changed. The word isopleth comes
from the Greek for ‘equal abundance’. See also tie line.
isopoly compound See cluster
compound.
isopolymorphism The property of
a substance with more than one crystalline structure that is isomorphous
with the crystalline structures of another substance (see polymorphism).
For example, antimony(III) oxide,
Sb 2 O 3 , has both rhombic and octahedral structures and these are isomorphous with the similar structures of
arsenic(III) oxide, As 2 O 3 ; both oxides
therefore exhibit isopolymorphism.
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