Crystal chemistry of the copper bromide 2-aminopyrimidine system

The preparation and crystal structures are reported for seven compounds obtained from the interaction of copper(II) bromide with 2-aminopyrimidine. This includes four copper(II) bromide compounds and three copper(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 coordinate 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 between the halide ions and the -NH2 and/or > N-H+ fragments. The Cu(II) species show a range of coordination geometries. L2CuBr2 contains isolated four-coordinate species with a planar coordination geometry (Cu-N = 1.996(5) and Cu-Br = 2.401(1) Angstrom). (LH)(2)CuBr4 contains isolated 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 bibridged Cu2Br62- dimers (Cu-Br(av.) = 2.424 Angstrom) which aggregate into stacks through the formation of semicoordinate Cu-Br bonds (distances = 3.067(1) and 3.335(1) Angstrom). Finally, (LH)(2)CuBr4 contains isolated 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 Angstrom and Cu-Br-Cu = 99-107 degrees. In each chain, the Cu(I) ion completes a tetrahedral coordination by forming bonds to Br- ions or ring N GRAPHICS atoms in the ligands, In LCuBr, the pyrimidine ligands bridge Cu atoms on adjacent chains, forming a rectangular two dimensional network. This gives the Cu(I) ion a N2Br2 coordination environment. For the LCu2Br2 compound, the (Cu-Br)(n) chains dimerize through the formation of Cu-Br linkages between chains. The pyrimidine ligands now bridge between Cu atoms on adjacent dimerized chains. Thus the Cu(I) ion has a Br3N coordination environment. Finally, in (LH)CuBr2, each copper ion in the chain completes its coordination sphere by coordinating to one pyrimidinium cation and to one bromide ion, to also attain a Br3N coordination sphere.