A new quaternary layered transition-metal oxide, Na
2Cu
2TeO
6, has been synthesized under air using stoichiometric(with respect to the cationic elements) mixtures of Na
2CO
3, CuO, and TeO
2. Na
2Cu
2TeO
6 crystallizes in the monoclinicspace group
C2
/m with
a = 5.7059(6) Å,
b = 8.6751(9) Å,
c = 5.9380(6) Å,
![](/images/gifchars/beta2.gif)
= 113.740(2)
![](/images/entities/deg.gif)
,
V = 269.05(5) Å
3,and
Z = 2, as determined by single-crystal X-ray diffraction. The structure is composed of
![](/isubscribe/journals/inocaj/44/i14/eqn/ic0502832e10001.gif)
[Cu
2TeO
6] layers withthe Na atoms located in the octahedral voids between the layers. Na
2Cu
2TeO
6 is a green nonmetallic compound,in agreement with the electronic structure calculation and electrical resistance measurement. The magneticsusceptibility shows Curie-Weiss behavior between 300 and 600 K with an effective moment of 1.85(2)
B/Cu
IIand
c = -87(6) K. A broad maximum at 160 K is interpreted as arising from short-range one-dimensionalantiferromagnetic correlations. With the aid of the technique of magnetic dimers, the short-range order was analyzedin terms of an alternating chain model, with the surprising result that the stronger intrachain coupling involves asuper-superexchange pathway with a Cu-Cu separation of >5 Å. The
J2/
J1 ratio within the alternating chain refinedto 0.10(1), and the spin gap is estimated to be 127 K.