Two new transition-metal tellurium oxy-chlorides of the general formula Ni
5(TeO
3)
4X
2 (X= Cl, Br) have been isolated during the investigation of the ternary phase diagram NiO-NiCl
2-TeO
2. They crystallize in the monoclinic system, space group
C2/
c, and for the caseof Ni
5(TeO
3)
4Cl
2 the unit cell is
a = 19.5674(2) Å,
b = 5.2457(1) Å, and
c = 16.3084(1) Å,with
= 125.289(1)
. The structure is layered and built up of corner-connected [Ni
5O
17X
2]entities, made of five nickel(II) octahedra associated by edge and face sharing. The tellurium(IV) atoms are fixed upon the nickel layers. Their lone pairs
E and the halogen atoms arepacked in a double layer perpendicular to the [010] direction. From the magnetic point ofview, this system provides a new 2D
S = 1 quantum spin system with antiferromagneticsuperexchange interaction. The magnetic susceptibility shows anomalies pointing to magneticordering phenomena. The observed transition temperatures vary with the interlayerseparation.