Reactions of Cu(hfacac)2·H2O (hfacac = Hexafluoroacetylacetonate) with Bidentate Ligands. Preparation, Characterization, and X-ray Structures of the Molecular Complexes Cu(hfacac)2(pyrazine)2 and Cu(hfacac)2(3-cyanopyridine)2 and the One-Dimensional Coordination Polymers Cu(hfacac)2(1,2-bis(4-pyridyl)ethane) and Cu(hfacac)2(4,4‘-trimethylenebipyridine)