Divalent rare earth metals (Sc, Y, and the lanthanides) are known in halides almost throughout the whole series. Two classes may be distinguished: RX
2
= (R
2+
)(X
−
)
2
type dihalides, in which R
2+
has the electronic configuration [Xe]6s
0
5d
0
4f
n
. Their structural behavior parallels that of the heavier alkaline‐earth metal halides; for example, EuBr
2
and SrBr
2
are isostructural. All of these class I compounds are insulators. In the second class, R
2+
has the electronic configuration [Xe]6s
0
5d
1
4f
n
−1
; the occupation of a 5d state leads to (semi)metallic behavior. Their crystal structures resemble those of intermetallic phases, for example, LaI
2
crystallizes with the CuTi
2
type of structure. This class of dihalides RX
2
is often written as (R
3+
)(e
−
)(X
−
)
2
. Except for the binary dihalides, there are a number of ternary halides, for example, CsTmCl
3
and the mixed‐valent K
5
Dy
3
I
12
(class I), as well as BaLaI
4
(class II). Oxide‐halides with divalent lanthanides are also known, for example, {OSm
4
}I
6
or the mixed‐valent Eu
2
O
2
Br.