Two polymorphs, with Z' = 1 and 2, of 2-amino-4-chloro-6-morpholinopyrimidine in P21/c, and 2-amino-4-chloro-6-piperidinopyrimidine, which is isomorphous and almost isostructural with the Z' = 2 polymorph.

Crystallization of 2-amino-4-chloro-6-morpholinopyrimidine, C(8)H(11)ClN(4)O, (I), yields two polymorphs, both with space group P2(1)/c, having Z' = 1 (from diethyl ether solution) and Z' = 2 (from dichloromethane solution), denoted (Ia) and (Ib), respectively. In polymorph (Ia), the molecules are linked by an N-H...O and an N-H...N hydrogen bond into sheets built from alternating R(2)(2)(8) and R(6)(6)(40) rings. In polymorph (Ib), one molecule acts as a triple acceptor of hydrogen bonds and the other acts as a single acceptor; one N-H...O and three N-H...N hydrogen bonds link the molecules in a complex chain containing two types of R(2)(2)(8) and one type of R(4)(4)(18) ring. 2-Amino-4-chloro-6-piperidinopyrimidine, C(9)H(13)ClN(4), (II), which is isomorphous with polymorph (Ib), also has Z' = 2 in P2(1)/c, and the molecules are linked by three N-H...N hydrogen bonds into a centrosymmetric four-molecule aggregate containing three R(2)(2)(8) rings.