4,4′,6,6′-Tetramethyl-2,2′-bipyrimidine hexahydrate

In the title compound, C12H14N4·6H2O, the two pyrimidine rings make a dihedral angle of 5.285 (6)°. Intermolecular O—H⋯O hydrogen bonds link the six water molecules, generating edge-fused four-, five- or six-membered ring motifs and forming two-dimensional sheets. The sheets are stabilized by the formation of O—H⋯N hydrogen bonds between the water molecules and the bipyrimidine molecules, resulting in a three-dimensional network.

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXS97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009). We are grateful to the National Natural Science Foundation of China (grant No. 20872057) and the Natural Science Foundation of Henan Province (No. 082300420040) for financial support. 4,4',6,6'-Tetramethyl-2,2'-bipyrimidine hexahydrate Y. Ma, L. Zhou, D. Deng and B. Ji Comment 2,2'-Bipyrimidine and its derivatives have been used as the ligands in inorganic and organometallic chemistry (Ji et al. 2000;Baumann et al. 1998). On the other hand, the investigations of hydrogen-bonded water clusters in compound have recently attracted a great deal of interest (Buck et al. 2000;Lakshminarayanan et al. 2006). These studies can provided clues to understand the nature of water-water interactions in bulk water or ice (Zhang et al. 2005). In view of the importance of these compound, we herein report the synthesis and crystal structure of the title compound.
The molecule of the title compound ( Fig. 1.), is built up form one pyrimidine ring connected to the other pyrimidine ring through the 2 and 2' carbon atoms, in which the bond lengths and angles are within ranges as reported by Berg et al. (2002).
In the crystal structure, the four substituent methyl groups lie in the corresponding pyrimidine ring plane, respectively. And, the dihedral angle between the two pyrimidine rings is 5.285 (6)°. It must be pointed out that the striking feature of the title compound is the interesting arrangement of the six water molecules, which connected each other by the formation of intermolecular O-H···O hydrogen bonds, generating the edge-fused four-, five-, or six-membered ring motifs, to form a two-dimensional sheet (Fig.2.). Interestingly, every water O atom in the sheet is tri-coordination, which unlike the water at the surface of ice or in liquid water shows four coordination. Furthermore, the sheets are anchored in four nitrogen atoms of the titlelte molecule by the formation of O-H···N hydrogen bonds, resulting in a three-dimensional network, in which these hydrogen bonding interactions, with O-H···O hydrogen bonds may be effective in the stabilization of the crystal packing.
Detail hydrogen bonds are given in Table 1.

Experimental
The title compound was prepared according to the reported Ullmann coupling method (Vlad & Horvath, 2002). Under nitrogen-protected, 4,6-dimethyl-2-iodopyrimidine (351 mg, 1.5 mmol), absolute DMF (2.0 ml) and activated copper powder (508 mg, 8.0 mmol) were placed in a 25 ml flask. The reaction mixture was heated to 358 K with vigorous stirring. After 4 h, 127 mg (2 mmol) of activated copper powder was added to the mixture. After another 3.5 h, the temperature was increased to 398 K and the stirring was continued for 2 h. The suspension was then cooled to 273 K, carefully drowned into a solution of 1.4 g potassium cyanide in 6 ml of 25% aqueous solution of ammonia, and filtered. The solid residue on the filter was extracted with the same amount of cyanide solution and filtered again. The combined filtrates were treated with 58 mg of potassium cyanide and extracted with chloroform (5 times 20 ml). Washed with water and dried. Recrystallization of the crude product from ethyl acetate-petroleum ether gave 81 mg. The crystalline compound was luckily obtained by the reaction of the title compound with NdCl 3 under the hydrothermal condition.

Refinement
All H atoms were positioned geometrically and treated as riding, with C-H bond lengths constrained to 0.93 Å (aromatic CH), 0.96 Å (methyl CH 3 ), and 0.83 or 0.84 Å (OH), and with U ĩso (H) = 1.2U eq (C) or 1.5U eq (methylene C or OH).  Fig. 1. View of the title molecular structure with atom numbering scheme and 30% probability displacement ellipsoids for non-hydrogen atoms.