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C40H120.5Br3.5N12Ni6O24.5, trigonal, R3 (no. 148), a = 25.341(1) Å, 2 = 90.012(1)°, V = 16263.7 Å, Z = 6, Rgt(F) = 0.057, wRref(F ) = 0.213, T = 296 K. Source of material The title compound was prepared by adding 10 mmol of N,N,N',N'-tetramethylethylenediamine (tmen) to an aqueous ethanol solution containing 10 mmol of nickel bromide, followed by bubbling carbon dioxide into the mixture. Within two days, light blue crystals were obtained suitable for X-ray studies. Experimental details All non-hydrogen atoms have been modeled anisotropically using SHELXTL [1] using absorption corrected data [2], while the carbon hydrogen atoms were fixed at calculated positions [d(C—H) = 0.96 Å (CH3), d(C—H) = 0.97 Å (CH2) and d(O—H) = 0.96 Å] after the least squares cycles but not refined. The two respective hydroxide hydrogen atoms could not be located or calculated, and hence not included in the refined model. In regard to the charge balance, the 1 3 hexanuclear clusters refined require 5 3 anions which are made up of 4 3 Br and 3 (OH). Discussion The nickel(II)-diaqua-dibromo-N,N,N',N'-tetramethylethylenediamine (tmen), [Ni(tmen)(H2O)2Br2], in aqueous ethanol spontaneously absorbed CO2 in air and self-assembled into the hexameric cluster, [{Ni2(tmen)2(H2O)4(CO3)1.33}3][Br]3.5 [OH]0.5, where the carbonate anion derived from the carbon dioxide is in a unique triply bridging coordination mode. For this analysis, the novel nickel hexameric cluster was synthesized from the monomeric nickel complex by bubbling CO2 into the ethanol reaction mixture. One of the major interests in mixed ligand complexes of transition metals including nickel is due to their intense and variable colors depending on the ligand combinations and solvent used. Thus, exhibiting their potential as indicators in various temperatures, pH and/or pressures [3-8]. Another interest is the potential CO2 fixation by nickel complexes in basic solutions and the subsequent crystallization of the nickel carbonate complexes [9-11]. To date, only six modes of coordination by the carbonate anion have been described which involve two to three metal centers, with some of the carbonate oxygen atoms bonding to one or two metals [12-16]. Multinuclear cluster complexes having as much as 6 metal centers are small in number [17-21] and the high symmetry cluster described here is, as far as we know, not precedented, where each carbonate oxygen atom bonds to a different nickel center. Each hexamer consists of six octahedrally arranged nickel centers, [Ni(tmen)(H2O)2], linked by four tetrahedrally arranged carbonate anions. Thus, each nickel center uses two coordination sites to bond to two different carbonates, while the other coordination sites are occupied by one tmen ligand and two water molecules, respectively. The carbonate anions bridge three nickel centers via their respective Z. Kristallogr. NCS 223 (2008) 523-528 / DOI 10.1524/ncrs.2008.0230 523 © by Oldenbourg Wissenschaftsverlag, München

zeitschrift für kristallographie. new crystal structures/zeitschrift für kristallographie. new crystal structures

Crystal structure of dodecaaqua-tetra-μ 3 -carbonato-hexa(N,N,N',N'- tetramethylethylenediamine)hexanickel(II) hemiheptabromide hemihydroxide, [{Ni 2 (C 6 H 16 N 2 ) 2 (H 2 O) 4 (CO 3 ) 1.33 } 3 ][Br] 3.5 [OH] 0.5