CRYSTAL-CHEMISTRY OF THE COPPER BROMIDE 2-AMINOPYRIMIDINE SYSTEM

The preparation and crystal structures are reported for seven compound s obtained from the interaction of copper(II) bromide with 2-aminopyri midine. This includes four copper(II) bromide compounds and three copp er(I) bromide complexes. The L = 2-aminopyrimidine moiety can exist as neutral L species, as well as either a monoprotonated LH+ cation or a diprotonated LH22+ dication in which one or two of the ring nitrogen atoms, respectively, are protonated. The neutral ligand is found to co ordinate to one or two Cu ions through the ring nitrogen atoms, while the monocation may or may not coordinate through the unprotonated ring nitrogen atom. The crystals are stabilized by hydrogen bonding betwee n the halide ions and the -NH2 and/or > N-H+ fragments. The Cu(II) spe cies show a range of coordination geometries. L2CuBr2 contains isolate d four-coordinate species with a planar coordination geometry (Cu-N = 1.996(5) and Cu-Br = 2.401(1) Angstrom). (LH)(2)CuBr4 contains isolate d six-coordinate species with a square planar CuBr42- arrangement (Cu- Br = 2.427(1) and 2.487(1) Angstrom) augmented by two LH ligands (Cu-N = 2.787(6) Angstrom). The (LH)(2)Cu2Br6 salt contains planar bibridge d Cu2Br62- dimers (Cu-Br(av.) = 2.424 Angstrom) which aggregate into s tacks through the formation of semicoordinate Cu-Br bonds (distances = 3.067(1) and 3.335(1) Angstrom). Finally, (LH)(2)CuBr4 contains isola ted distorted tetrahedral CuBr42- anions, with Cu-Br = 2.388 Angstrom (av.) and the larger trans Br-Cu-Br angles of 135.4 degrees (av.). The Cu(I) compounds all contain a common structural element: a (CuBr)(n) chain as illustrated in I with Cu-Br similar or equal to 2.52-2.56 Ang strom and Cu-Br-Cu = 99-107 degrees. In each chain, the Cu(I) ion comp letes a tetrahedral coordination by forming bonds to Br- ions or ring N GRAPHICS atoms in the ligands, In LCuBr, the pyrimidine ligands brid ge Cu atoms on adjacent chains, forming a rectangular two dimensional network. This gives the Cu(I) ion a N2Br2 coordination environment. Fo r the LCu2Br2 compound, the (Cu-Br)(n) chains dimerize through the for mation of Cu-Br linkages between chains. The pyrimidine ligands now br idge between Cu atoms on adjacent dimerized chains. Thus the Cu(I) ion has a Br3N coordination environment. Finally, in (LH)CuBr2, each copp er ion in the chain completes its coordination sphere by coordinating to one pyrimidinium cation and to one bromide ion, to also attain a Br 3N coordination sphere.