At room temperature, it is a stable white solid, soluble in diethyl ether, that decomposes (sometimes explosively) between 140 °C and 180 °C, and reacts slowly with water.

[1] Like the other cyclic dianions with formula (CO)2−n, the deltate anion has a pronounced aromatic character which contributes to its relative stability.

[2] Replacement of the three oxygen atoms by dicyanomethylene (=C(CN)2) provides an oxidizing species that is readily reduced to a stable radical anion and dianion.

[4] The acid can also be prepared by reaction of silver squarate and trimethylsilyl chloride.

[1][5] The deltate anion has also been obtained by direct cyclotrimerization of carbon monoxide at ambient conditions.