Source of materialImidazo[4,5-f]1,10-phenanthroline (ip; 0.5 mmol), 2-bromo-1,4-benzenedicarboxylic acid (0.5 mmol), Mn(OAc) 2 ·4 H 2 O( 123 mg, 0.5 mmol) and KOH (0.5 mmol) were added to water (12 ml) in aTeflon-lined stainless steel reactor. The mixture was heated at 400 Kfor 3days, and then slowly cooled down to room temperature. Yellow crystals of the title compound were obtained. Experimental deatailsThe Br atoms are disordered over two sites, viz. Br1 (bonded to atom C20) and Br2 (bonded to atom C16). The site occupancy factors of Br1 and Br2 atoms were independently refined and converged to 0.890(2) and 0.110(2), respectively [1,2]. DiscussionDesigning the solid state materials with molecules that encode welldefined non-covalent motifs has recently become ar apidly growing area of research due to the fascinating molecular and/or supramolecular structural diversity and potential applications for catalysis [3,4] and material sciences [5,6]. Asuccessful strategy in building such networks is to employ appropriate bridging ligands that can bind metal ions in different modes and provide more robust polymeric structures [7,8]. In this context, benzenedicarboxylic acid and its derivatives, such as 1,3-benzenedicarboxylic acid, 1,4-benzenedicarboxylic acid, 5-hydroxyisophthalic acid) are widely used as building blocks to link metal ions to produce metal-organic frameworks with interesting structures and properties [9]. The following reasons inspired us to investigate its analogues, 2-bromo-1,4-benzenedicarboxylic acid: (a)ithas two carboxyl groups which may be completely or partially deprotonated, inducing multiple coordination modesa nd allowing interesting structures with higher dimensions;(b)itcan act not only as hydrogen-bond acceptor but also as hydrogen-bond donor, depending upon the numbers of deprotonated carboxyl groups. In the title crystal structure, the asymmetric unit consists of one Mn 2+ cation, one imidazo[4,5-f]1,10-phenanthroline (ip) molecule, one disordered 2-bromo-1,4-benzenedicarboxylic acid ,two water molecules of crystallization. The Mn(II) ion has aslightly distorted octahedral arrangement (MnO 2 N 4 )w ith four nitrogen atoms from two ip molecules and two carboxylate oxygen atoms from two coordinated benzenedicarboxylic acid molecules. The Mn-O bond lengths are both 2.117(3) Å and the Mn-N bond lengths are in the range of 2.261(3) -2 .306(3) Å,r espectively. Noteworthy, within the asymmetric unit, uncoordinated water molecule O6 acts as hydrogen-bond donor, via H1W and H2W, respectively,t oc arboxylate atom O2 at (x+1/2,y−1/2,z)a nd imidazole atomN 3a t( x +1/2,−y+1/2,z+1/2); Simultaneity, O6 also acts as hydrogen-bond acceptor from carboxylate atom O5 at (x+1,y,z),via H5. The mononuclear units are assembled by hydrogen bonds between ip molecules, benzenedi-carboxylic acid molecules, and uncoordinated water molecules O6 to afford a3D supramolecular structure. The bond lengths and angles of the above three hydrogen bonding parametres are in the range of 2.590(4) -2.849(5) Å and 135.0°-179....