Synthesis, crystal structure, EPR and magnetic properties of a cyano-bridged Cu II –Ni II heterobimetallic complex: an unusual structure with long-range ferromagnetic exchange through hydrogen bonding Mahammad Ali,* a Ambarish Ray, a William S. Sheldrick, b H. Mayer-Figge, b Song Gao c and Alexander I. Sahmes d a Department of Chemistry, Jadavpur University, Kolkata 700 032, India. E-mail: m_ali2062@yahoo.com b Lehrstuhl fur Analytischie Chemie, Ruhr-Universitat Bochum, D-44780, Bochum, Germany c College of Chemistry and Molecular Engineering, State Key Laboratory of Rare Earth Materials Chemistry and Applications, Peking University, Beijing 100871, P.R. China d Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel Received (in Montpellier, France) 13th June 2003, Accepted 30th October 2003 First published as an Advance Article on the web 13th February 2004 A cyano-bridged Cu II –Ni II dimeric complex [Cu(Me 6 Cy)][Ni(CN) 4 ] has been synthesized and characterized by its single crystal X-ray structure determination. The square planar [Cu(Me 6 Cy)] 2þ cation is converted to a distorted trigonal bipyramidal (TBP) geometry through ligation to one of the cyano groups of [Ni(CN) 4 ] 2 in the equatorial plane, keeping the other three as terminal. Inspection of the X-ray data reveals that the Cu–N(6)–C(6) angle of the bridging cyano group is perfectly linear (180  ). The room temperature (RT) EPR spectrum of polycrystalline [Cu(Me 6 Cy)][Ni(CN) 4 ] is typical for mononuclear copper(II) complexes of axial symmetry, where the flattened out symmetry axis is characterized by g ? ¼ 2.143  0.005 and g k ¼ 2.002  0.005. No half field (DM ¼ 2) signals were observed. RT EPR spectrum of polycrystalline [Cu II (Me 6 Cy)](ClO 4 ) 2 yields an EPR signal with g k ¼ 2.394  0.005 and g ? ¼ 2.045  0.005, indicating that this parent compound has a different geometry than [Cu(Me 6 Cy)][Ni(CN) 4 ]. Variable temperature magnetic moment studies on [Cu(Me 6 Cy)][Ni(CN) 4 ] indicate a very weak long-range ferromagnetic exchange through hydrogen bonding between copper(II) ions (S ¼ 1 2 ). The present investigation provides a unique example where the original square planar [Cu(Me 6 Cy)] 2þ moiety rearranges itself to a trigonal bipyramidal geometry under the influence of [Ni(CN) 4 ] 2 . This is probably only the second, rare example, and perhaps the first, for a macrocyclic precursor using only one cyano group of [Ni(CN) 4 ] 2 for bridging, leading to a discrete dinuclear complex. Introduction Self-assembly by H-bonding, p-p stacking and van der Waals interactions are all very important processes in the formation of biological architectures. 1 These mechanisms are being deve- loped as efficient design tools in material sciences for organizing individual molecular motifs into highly ordered supramole- cules. Transition-metal-directed self-assembly is also a power- ful approach for the construction of different supramolecular architectures with unusual and interesting properties. 2 A pop- ular approach for such constructions is to employ cyano com- plexes 3 like [Ag(CN) 2 ]  , [Cu(CN) 3 ] 2 , [M(CN) 4 ] 2 (M ¼ Cd, Ni, Pd, Pt, etc.) and [M(CN) 6 ] 3 (M ¼ Cr, Mn, Fe ,etc.), which act as the bridging moiety to build multidimensional structures where s ! p backbonding stabilizes the resulting complexes. Such cyanometallates with various dimensionalities and con- taining paramagnetic central atoms often show interesting magnetic properties where the bridging cyano group forms an exchange path mediating the interaction between spins localized on paramagnetic centers. 4 Tetracyanometallate anions [M(CN) 4 ] n (M ¼ Ni, Pd, Pt, Cu, Cd), 3c,4b,5–11 exhibit bridging character involving either one, two, three or four of the cyano groups and all four pos- sibilities have been found. In [{Cu 2 (medpt) 2 Ni(CN) 4 }(ClO 4 ) 2  2.5H 2 O] n 6 [medpt ¼ bis(3-aminopropyl)methylamine] all four cyano groups have been found to be involved in bridging. Recently, it has been observed that [Ni(CN) 4 ] 2 uses three out of four cyano groups to bridge to three Eu II 7 atoms in [(DMF) 4 EuNi(CN) 4 ] 8 (DMF ¼ N,N-dimethylformamide) or three Cu II atoms in [Cu(tn)Ni(CN) 4 ] (tn ¼ 1,3-propane- diamine), 8 respectively. In trans-[{Cd(en) 2 } 2 Ni(CN) 4 ], cis-[{Ni(dien)}2(m-ox){m-Ni(CN) 4 }] (ox ¼ oxalate) and cis-[{Cd- (en) 2 } 2 Ni(CN) 4 ] 9,10 two of the four cyano groups are involved in bridging, in both cis and trans fashions. On the contrary, there is only one previous report of a complex manifesting monodentate ligation, namely in [Cu(dien)(mea)]- [Ni(CN) 4 ]2H 2 O [dien ¼ N-(2-aminoethyl)-1,2-ethanediamine, mea ¼ 2-aminoethanol]. 11 In this article we report the synthesis and structural characteri- zation of Me 6 Cy2HClO 4 H 2 O and of the cyano-bridged Cu II – Ni II dinuclear complex, [Cu(Me 6 Cy)][Ni(CN) 4 ]. Here, only one cyano group of [Ni(CN) 4 ] 2 is involved in bridging in a perfectly linear fashion. It is noteworthy that under the influence of [Ni(CN) 4 ] 2 , the [Cu(Me 6 Cy)] 2þ moiety reshuffled itself from its original stable square-planar (SP) arrangement to a trigonal bipyramidal (TBP) geometry, but the nickel atom retains its ori- ginal SP geometry. To the best of our knowledge, it is only the second, rare example, 11 and probably the first for a macrocyclic precursor, in which only one cyano group of [Ni(CN) 4 ] 2 is involved in bridging, leading to a discrete dinuclear complex. NJC www.rsc.org/njc PAPER 412 New. J. Chem. , 2004, 28, 412–417 This journal is Q The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2004 DOI: 10.1039/b306866h Downloaded on 08 January 2011 Published on http://pubs.rsc.org | doi:10.1039/B306866H View Online