Acta Chim. Slov. 2002, 49, 251-258. 251 SYNTHESIS AND CRYSTAL STRUCTURE OF THE ADDUCT: COPPER(II) FORMATE - FORMIC ACID (1:2) - A NEW POLYMORPHIC FORM (ß-form) Nina Lah, Primož Šegedin and Ivan Leban* Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, P.O. Box 537, SI-1001 Ljubljana, Slovenia † This paper is dedicated to the memory of our colleague Dr. Karel Lutar. Received 10-12-2001 Abstract A new polymorphic adduct of copper(II) formate with formic acid, catena-bis(µ2-formato-O,O’)-bis(formic acid-O)-copper(II) (ß-form) has been prepared and structurally characterised by single crystal X-ray diffraction. Compound crystallizes in the orthorhombic space group Pbca with the following cell dimensions: a = 7.8773(17), b = 8.4775(2) and c = 12.1423(3) A. The results show polymeric structure of the [Cu(HCOO)2(HCOOH)2]n composition with copper atoms being connected by formate anions in anti-anti mode into layers, parallel to ab plane with Cu-O distances 1.9453(10) and 1.9750(9) A. Formic acid molecules are coordinated to copper ions at longer distances of 2.4346(12) A as monodentate terminal ligands and are involved in a hydrogen bond connection of the neighbouring layers. Introduction Carboxylate anions are very versatile ligands in the light of the wide variety of coordination modes they exhibit in many metal coordination compounds. Among copper(II) carboxylates the nuclearity varies from monomeric to dimeric, oligomeric as well as polymeric compounds. Polymeric complexes can be formed by means of bridging carboxylate ions or by means of other ligands with the bridging ability. Carboxylate group can link two copper(II) ions as a bridging bidentate or as monoatomic bridging ligand. In the case of bridging bidentate coordination three distinctive arrangements are possible: sys-syn, syn-anti and anti-anti binding modes. Formate ion is the smallest among carboxylic ligands and has been often used in the synthesis of copper compounds. As the consequence of this fact there is a great number of published structures, which include the formate ion as the only ligand coordinated to copper or the compounds contain additional, either N- or O-donor ligands (after survey through Cambridge Structural Database).1 N. Lah, P. Šegedin, I. Leban: Structure of the adduct: Copper(II)formate - formic acid (1:2… 252 Acta Chim. Slov. 2002, 49, 251-258. This investigation is a part of our continuous endeavour to find new synthetic methods for preparation of copper carboxylates using several additional ligands.2,3,4 Here, we report the synthesis and the crystal structure of the orthorhombic form of the polymeric adduct of copper(II) formate – formic acid (1:2). A previous structure determination was reported for the similar monoclinic structure (?-form) of catena-bis(µ2-formato-O,O’)-bis(formic acid-O)-copper(II).5 The CSD refcode for this compound from reference 1 is DOKPOI from CSD release 5.2.1, April 2001. Experimental Synthesis and X-ray Crystallographic Work A small amount of copper(II) formate tetrahydrate was dissolved in the hot formic acid (98%) to achieve a saturation at approximately 80o C. The saturated solution was filtered off and slowly cooled to room temperature and then left in the refrigerator for one week. The obtained crystals were very unstable when taken from the mother liquor and were transferred immediately into the cold nitrogen stream of the diffractometer at Table 1. Crystal Data and Data Collection Summary Empirical formula [C4H6O8Cu]n Formula weight 245.63 Crystal shape, colour prismatic, sky-blue Crystal dimensions / mm 0.22, 0.20, 0.20 Radiation MoK? / A 0.71073 T / K 150 Crystal system orthorhombic Space group Pbca a / A 7.8773(2) b / A 8.4775(2) c / A 12.1423(3) V / A3 810.86(3) Z 4 Density (g.ml-1) 2.012 µ / mm1 2.708 Reflections collected 5791 (6max=27.5o) Independent reflections 916 Reflections with I>2?(I) 787 Rint 0.025 R1, wR2 (observed reflections) 0.022, 0.059 R1, wR2 (all reflections) 0.028, 0.069 N. Lah, P. Šegedin, I. Leban: Structure of the adduct: Copper(II)formate - formic acid (1:2… Acta Chim. Slov. 2002, 49, 251-258. 253 150 K. The data were collected on a KappaCCD Nonius diffractometer which is equipped with the low-temperature Oxford Cryosystem device 700 using Collect6 andprocessed with DENZO and SCALEPACK programmes7. The structure was solved by direct methods implemented in SHELXS-97 and refined by full-matrix least squares using SHELXL-97.8 All hydrogen atoms were found in the difference electron-density map and were included in the refinement with isotropic displacement parameters. The figures were prepared with the aid of ORTEP-III and PLATON programmes.9,10 Additional crystallographic data for the structure reported in this paper are available on request at the Cambridge Crystallographic Data Centre with quotation number 175622.11 Results and discussion The formal composition found in the structural work can be represented as [Cu(HCOO)2(HCOOH)2]n. ORTEP-III view of one building unit is presented in Figure 1. Copper atoms are located on an a special position (0,0,0) in a square planar coordination environment, formed by four oxygen atoms from four formate ions. Only two of the oxygen atoms are crystallographically unique and are located at the distances of 1.9453(10) and 1.9750(9) A (for geometrical details see Table 2). The most typical pseudo-octahedral 4+2 coordination is completed by formic acid molecule, coordinated to the copper ion through oxygen atom at a distance of 2.4345(12) A as a terminal ligand. The divalent copper ions are connected through the formate bridges in a typical anti-anti mode presented on Figure 1. Thus, the sheets of CuO4 units are formed, parallel to ab plane. View of one such sheet is depicted in Figure 2. Formic acid molecules protrude from these planes on both sides as shown on Figure 3. There is no covalent interaction between the sheets. However, the planes of copper(II) formate units are linked by hydrogen bonds of the type O-H...O between formic acid molecules (O4 acting as a donor) and formate oxygen atoms of a neighbouring sheet (O1 and O2 are the corresponding acceptors). The bond lengths and angles within formic acid molecules and formate moieties are normal and in agreement with the values for the related compounds. N. Lah, P. Šegedin, I. Leban: Structure of the adduct: Copper(II)formate - formic acid (1:2… 254 Acta Chim. Slov. 2002, 49, 251-258. Comparison of the two polymorphic forms It should be noted, that polymeric layered structure has been commonly observed also in other copper(II) formates.1 In all of these structures anti-anti carboxylate binding mode is predominant. The structure of monoclinic form of the title compound has already 04^OH3 H2 I c-côC2 ^Vo3 Figure 1. Ortep-III view of the coordination of formic acid molecules and formate ions around Cu2+ ion in ß-form. Only the atoms of the asymmetric unit are labelled. Displacement ellipsoids are drawn at 50% probability level. Table 2. Selected geometrical parameters (A, °) Cu-O1 Cu-O2i Cu-O3 1.9453(10) 1.9750(10) 2.4345(12) C1-O1 C1-O2 C2-O3 C2-O4 1.2521(18) 1.2651(19) 1.205(2) 1.310(3) Hydrogen bonds: D-H···A O4-H3···O2ii O4-H3···O1ii d(D-H) 0.78(3) 0.78(3) d(H···A) 1.93(3) 2.58(3) d(D···A) K •ft>..s.<, ¦•&¦ «ftsvî>- 'O- "C&> C i (a) l ( S>?.*s ..-iKy5**ri... Ns l± o ¦iC^.iS, L \ lU a ^.«^-sS. y ^ ' J^ u. M (b) Figure 3. Packing diagrams for orthorhombic (this study) (a) and monoclinic form5 (b) viewed along the CuO4 sheets. The sheets of copper ions, connected through the formate ions, are arranged in parallel planes. Molecules of formic acids, apically coordinated to copper ions, protrude from the planes on both sides of the CuO4 sheets. Hydrogens are omitted for clarity. 0 N. Lah, P. Šegedin, I. Leban: Structure of the adduct: Copper(II)formate - formic acid (1:2… Acta Chim. Slov. 2002, 49, 251-258. 257 attributed to the different orientation of the formic acid with respect to the sheet containing copper atoms (Table 2). The corresponding torsion angles Cu1-O1-C1-O2 and Cu1-O3-C2-O4 are: -179.98(9) and -175.86(16)o for this study, and -174(1) and -159(1)o for the monoclinic form, respectively. The protrusion of formic acid ligands of one sheet into the other is therefore much more pronounced in the orthorhombic than in monoclinic form and as the consequence, the orthorhombic structure is more densely packed (Dx=2.012 g cm-3) compared to the monoclinic form (Dx=1.823 g cm-3). The effective distance between the sheets of copper formates are consequently: 6.071 A for the orthorhombic and 7.778 A for the monoclinic structure, respectively. Acknowledgements We acknowledge with thanks the financial support of the Ministry of Education, Science and Sports (MŠZŠ), Republic of Slovenia, through grant PS-511-103. The purchase of the KappaCCD Nonius Diffractometer was possible through grant X-2000 of MŠZŠ and with the financial support of the Faculty of Chemistry and Chemical Technology, University of Ljubljana, Ljubljana, which is also gratefully acknowledged. References and Notes 1. Allen, F.H. and Kennard, O. Chem. Des. Autom. News. 1993, 8, 31-37. 2. Kozlevčar, B., Lah, N., Makuc, S., Šegedin, P. and Pohleven, F., Acta Chim. Slov., 2000, 47, 421-434. 3. Kozlevčar, B., Lah, N., Žlindra, D., Leban, I. and Šegedin, P., Acta Chim. Slov., 2001, 48, 363 -374. 4. Lah, N., Doctoral Dissertation, University of Ljubljana, Ljubljana, Slovenia, 2001. 5. Wang H., Zhu, N. and Fu H., Chinese J. Struc. Chem. 1985, 4, 111 - 116. 6. COLLECT, Data Collection Software, Nonius B.V., 1999. 7. Otwinowski, Z. and Minor, W., Method. Enzym., 1997, 276, 307 - 326. 8. Sheldrick, G.M., SHELX-97, Program package for crystal structure solution and refinement, University of Goettingen, 1997, Germany. 9. Farrugia, L.J., J. Appl. Cryst., 1997, 565 - 567. 10. Spek, A.L., PLATON, Utrecht University, The Netherlands. 11. Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44-1223-336-033; e-mail: deposit@ccdc.cam.ac.uk). The crystallographic data as CIF file can be obtained on request, free of charge, by quoting the publication citation and the deposition number CCDC 175622. N. Lah, P. Šegedin, I. Leban: Structure of the adduct: Copper(II)formate - formic acid (1:2… 258 Acta Chim. Slov. 2002, 49, 251-258. Povzetek Pripravili smo novo polimorfno obliko adukta bakrovega(II) formiata z mravljinčno kislino in jo strukturno okarakterizirali z metodo rentgenske difrakcije na monokristalu pri 150 K. Spojina kristalizira v ortorombski prostorski skupini Pbca z naslednjimi parametri osnovne celice: a=7.8773(17), b=8.4775(2) and c=12.1423(3) A. Spojina ima polimerno zgradbo. Bakrovi ioni so preko mostovnih formiatnih anionov povezani v plasti (anti-anti način vezave) vzporedne z ravnino ab. Molekule mravljinčne kisline so koordinirane na bakrov ion kot enovezni ligand in so vključene v tvorbo vodikovih vezi, ki bakrove formiatne plasti povezujejo med seboj v kristalno strukturo. N. Lah, P. Šegedin, I. Leban: Structure of the adduct: Copper(II)formate - formic acid (1:2…