Crystal structure of trihydroxydicopper formate, Cu2(OH)3(HCOO)

CH4Cu2O5, monoclinic, P1211 (no. 4), a = 5.5894(2) Å, b = 6.0558(3) Å, c = 6.9321(3) Å, * = 105.926(2)°, V = 225.6 Å, Z = 2, Rgt(F) = 0.038, wRref(F) = 0.121, T = 295 K. Source of material Indoor museum air pollution by formaldehyde and formic acid (e.g., emitted from wood) may cause the formation of formates on historic objects made for example from limestone, glass, or lead [1]. Nevertheless, similiar observations on copper alloys are limited only to cases where sodium salts are present [2]. To help with future identifications, Scott et al. [3] synthesized basic copper formates following the methods given by Fowles [4] and published their hitherto unknown powder diffraction data from DebyeScherrer films. In a project to identify joint copper-glass corrosion compounds we found a diffraction pattern matching the film 770 on three corrosion samples from the contact zone of coppercontaining alloys with sodium-containing glass: a 200 year old glass flute with silver mounting (Rijksmuseum Amsterdam), a silver-mounted ruby glass box (Green Vault Dresden), and an enamelled St. Matthew cross made from brass or bronze (MAK Frankfurt) [5]. Single crystals of this compound could be grown via Fowles method. Experimental details As a result of the crystal growth via the Fowles method, we obtained crystals of poor quality. According to the systematic extinctions 0k0, k = 2n+1, the possible space groups were P21 and P21/m. The structure could only be solved in P21. First refinements indicated inversion twinning by the ratio 0.40(6) / 0.60(6). Three of the 4 hydrogen atoms (H2, H3, H4) were found by Fourier mapping. Their coordinates as well as a common isotropic displacement parameter were refined. The position of H1 was calculated and kept fixed, contrary to its displacement parameter. The refinement converged at R1 = 0.038, Rw2 = 0.121, GOOF = 1.086, Flack parameter x = 0.00(6). Upon structure inversion, only the twin ratio inverted to 0.60(6) / 0.40(6). Thus, due to inversion twinning, the resonant scattering was not sufficient to allow for the determination of the absolute structure. Discussion The crystal structure is characterized by puckered layers, made of two different edge-sharing, Jahn-Teller distorted CuO6 octahedra d(Cu1—O) = 1.931(1) 2.408(8) Å, d(Cu2—O) = 1.970(9) 2.389(2) Å, oriented parallel to (001). The basal plane corners of the octahedron, centered by Cu1, are provided by the hydroxyl groups, whereas the apices are occupied by the single-bonded oxygen atoms of the formate groups. For the Cu2 octahedron, the apices are occupied by the oxygen atoms of the formate and hydroxyl groups. Alternating chains of Cu1 and Cu2 octahedra, running parallel [010], are connected to puckered layers by three common edges. Correspondingly, the Cu atoms of each layer form a nearly regular two-dimensional hexagonal packing as do oxygen atoms above and below each Cu layer. These most likely fairly stable O–Cu–O ‘sandwiches’ are held together by hydrogen bonds between the hydrogens of hydroxyl groups and the oxygens of the formate groups d(O7—H4) = 0.97(5) Å, d(O7···O5) = 2.690(3) Å, d(H4···O5) = 1.96(6) Å, ∠O7–H4···O5 = 130(5)°. Z. Kristallogr. NCS 224 (2009) 609-610 / DOI 10.1524/ncrs.2009. 0268 609 © by Oldenbourg Wissenschaftsverlag, München Crystal: blue prism, size 0.06 × 0.08 × 0.10 mm Wavelength: Mo K+ radiation (0.71073 Å) . : 93.39 cm−1 Diffractometer, scan mode: Bruker-AXS X8 APEXII, #/% 2,max: 71.54° N(hkl)measured, N(hkl)unique: 12403, 1570 Criterion for Iobs, N(hkl)gt: Iobs > 2 )(Iobs), 1140 N(param)refined: 85 Programs: SHELXS-97 [6], SHELXL-97 [7], DIAMOND [8] Table 1. Data collection and handling.