Orthophosphoric acid and orthophosphates

Discrete PO ions exist in normal orthophosphates. In dihydrogen phosphates such as KH2PO4 and (N2Hs)H2P04 P02(0H)2 units are hydrogen-bonded to form extended anions—see p. 318. Several X-ray and n.d. studies give P—0 close to 

2- 50 A. In the (layer) structure of H3P04 there are also hydrogen bonds of length 2 84 A this structure is described in Chapter 8. The P-0 bond lengths found in H3PO4 and its hemihydrate are P—0, 1-52 and 1-49 A, and P—OH, 1-57 and 1-55 A respectively. 

The structures of a number of orthophosphates are similar to those of forms of silica or of silicates. For example, AIPO4 crystallizes with all the three normal silica structures and also undergoes a transition from a low- to a high-temperature form in each case YPO4 and YASO4 crystallize with the zircon (ZrSi04) structure. 

---

C.Y. Shen and C.F. Callis, Orthophosphoric acid and orthophosphates. Prep. Inorg. Reactions, 2, 157, 1965. 

Uptake studies Small waterhyacinth plants floating in a defined medium (Hoagland s solution) were treated with known amounts of Mn(EDTA) and manganese (II)-54, or Fe(EDTA) and iron(III)-59, or phosphorus-32 as orthophosphoric acid and orthophosphate (18). Rates of radioactivity were counted appropriately using portions of roots or portions of stems at various times. By... 

---