Spin 1/2 Delafossite Honeycomb Compound Cu5SbO6

Cu5SbO6 is found to have a monoclinic, Delafossite-derived structure consisting of alternating layers of O–Cu­(I)–O sticks and magnetic layers of Jahn–Teller distorted Cu­(II)­O6 octahedra in an edge sharing honeycomb arrangement with Sb­(V)­O6 octahedra. This yields the structural formula Cu­(I)3Cu­(II)2Sb­(V)­O6. Variants with ordered and disordered layer stacking are observed, depending on the synthesis conditions. The spin 1/2 Cu2+ ions form dimers in the honeycomb layer. The magnetic susceptibility measured between 5 and 300 K is characteristic of the presence of a singlet–triplet spin gap of 189 K. High resolution synchrotron X-ray diffraction studies indicate that changes in the intra- or interdimer distances between 300 and 20 K, such as might indicate an increase in strength of the Peierls-like distortion through the spin gap temperature, if present, are very small. A comparison to the NaFeO2-type Cu2+ honeycomb compounds Na3Cu2SbO6 and Na2Cu2TeO6 is presented.