Tri-, tetra-, and hexanuclear copper(II) phosphonates containing n-donor chelating ligands: synthesis, structure, magnetic properties, and nuclease activity

Reaction of Cu(ClO<SUB>4</SUB>)<SUB>2</SUB>&#183;6H<SUB>2</SUB>O with cyclopentyl phosphonic acid and 2,2'-bipyridine (bpy) in presence of triethylamine afforded a trinuclear compound [Cu<SUB>3</SUB>(C<SUB>5</SUB>H<SUB>9</SUB>PO<SUB>3</SUB>)<SUB>2</SUB>(bpy)<SUB>3</SUB>(MeOH)(H<SUB>2</SUB>O)](ClO<SUB>4</SUB>)<SUB>2</SUB> (2). The latter dimerizes to a hexanuclear derivative [Cu<SUB>6</SUB>(C<SUB>5</SUB>H<SUB>9</SUB>PO<SUB>3</SUB>)<SUB>4</SUB>(bpy)<SUB>6</SUB>(MeOH)<SUB>4</SUB>](ClO<SUB>4</SUB>)<SUB>4</SUB> (1) under prolonged reaction conditions. Reaction of CuCl<SUB>2</SUB> with cyclopentyl phosphonic acid and 2,2'-bipyridylamine (bpya) affords a tetranuclear derivative [Cu<SUB>4</SUB>(C<SUB>5</SUB>H<SUB>9</SUB>PO<SUB>3</SUB>)<SUB>2</SUB>(&#956; -Cl)<SUB>2</SUB>(bpya)<SUB>4</SUB>](Cl)<SUB>2</SUB>, (MeOH)<SUB>2</SUB> (3). Reaction of the latter with NaClO<SUB>4</SUB> also affords a trinuclear compound [Cu<SUB>3</SUB>(C<SUB>5</SUB>H<SUB>9</SUB>PO<SUB>3</SUB>)<SUB>2</SUB>(&#956;-Cl)(bpya)<SUB>3</SUB>(H<SUB>2</SUB>O)](ClO<SUB>4</SUB>) (4). Double and single-bridged hexanuclear species, [{Cu<SUB>3</SUB>(C<SUB>5</SUB>H<SUB>9</SUB>PO<SUB>3</SUB>)<SUB>2</SUB>(bpy)<SUB>3</SUB>(bpp)}(MeOH)<SUB>2</SUB>(H<SUB>2</SUB>O)(CH<SUB>2</SUB>Cl<SUB>2</SUB>)(ClO<SUB>4</SUB>)<SUB>2</SUB>]<SUB>2</SUB> (5), [{Cu<SUB>3</SUB>(i-PrPO<SUB>3</SUB>)<SUB>2</SUB>(bpy)<SUB>3</SUB>(4.4'-bpy)(H<SUB>2</SUB>O)}(H<SUB>2</SUB>O)<SUB>2</SUB>(ClO<SUB>4</SUB>)<SUB>2</SUB>]<SUB>2</SUB> (6), [{Cu<SUB>3</SUB>(C<SUB>5</SUB>H<SUB>9</SUB>PO<SUB>3</SUB>)<SUB>2</SUB>(bpya)<SUB>3</SUB>(4.4'-bpy)(H<SUB>2</SUB>O)}(MeOH)(H<SUB>2</SUB>O)(ClO<SUB>4</SUB>)<SUB>2</SUB>]<SUB>2</SUB> (7), and [Cu<SUB>6</SUB>(t-BuPO<SUB>3</SUB>)<SUB>4</SUB>(phen)<SUB>6</SUB>(4,4'-bpy)(MeOH)<SUB>4</SUB>](CH<SUB>2</SUB>Cl<SUB>2</SUB>)(H<SUB>2</SUB>O)(ClO<SUB>4</SUB>)<SUB>4</SUB> (8) (phen = 1,10-phenanthroline) were obtained by the reaction of an in situ generated trinuclear complex with appropriate bridging ligands 4,4'-bipyridine (4,4'-bpy) or 1,3-bis(4-pyridyl)propane (bpp). ESI-MS studies of these complexes reveal that 2-4 retain their structures in solution. Molecular structures of 2-8 were determined by X-ray crystallography. All the compounds reveal a capping coordination mode by tridentate phosphonate [RPO<SUB>3</SUB>]<SUP>2-</SUP> ligands. Detailed magnetic studies on 2 and 4-8 reveal intramolecular antiferromagnetic interactions between Cu(II) S = &#189; spins. 2 and 4 are excellent artificial nucleases and can convert supercoiled plasmid DNA (pBR322) into its nicked form without the aid of an external oxidant