Crystal and Molecular Structure of a Potential DNA Groove-Spanning Chelate: [MV][Pt(2)(hdta)Cl(2)].4H(2)O (MV(2+) = 1,1'-Dimethyl-4,4'-bipyridinium, hdta(4)(-) = 1,6-Hexanediamine-N,N,N',N'-tetraacetate).
Light yellow crystals of [MV][Pt(2)(hdta)Cl(2)].4H(2)O (1) (MV(2+) = 1,1'-dimethyl-4,4'-bipyridinium, hdta(4)(-) = 1,6-hexanediamine-N,N,N',N'-tetraacetate) were examined by X-ray diffraction. A 0.08 x 0.24 x 0.24 nm crystal was shown to have space group C2/c, having unit cell dimensions of a = 22.757(5) Å, b = 13.566(3) Å, and c = 12.120(2) Å and unit cell angles of alpha = gamma = 90 degrees and beta = 109.07(3) degrees with Z = 4. A total of 3195 independent reflections were refined to R = 0.0454. Each Pt(II) site has the anticipated NO(2)Cl square-planar mer coordination. The Pt-N(1) distance (N(1) is the N donor of the hdta(4)(-) ligand) is 2.001(9) Å, only slightly shorter than typical Pt-N distances (2.04-2.09 Å) for sp(3) donors. The Pt-O distances to the coordinated glycinato donors in 1 are 2.012(7) and 2.000(8) Å, values very similar to those of trans-[Pt(gly)(2)] (gly = glycinate). The Pt-Cl distance of 2.310(3) Å is in the range of 2.27-2.32 Å observed for other Pt(II)-Cl(-) bonds. The bond angles are close to the ideal 90 degrees or 180 degrees value: angleN-Pt-O = 85.4(3) degrees and 83.2(4) degrees; angleN-Pt-Cl = 176.6(2) degrees. The [Pt(2)(hdta)Cl(2)](2)(-) units are packed in an end-to-end fashion such that the [Pt(II)(iminodiacetate)Cl] headgroups are overlapping. This provides square-planar to square-planar stacking of the headgroups. (1)H and (13)C NMR data are presented which show that the [Pt(2)(hdta)Cl(2)](2)(-) coordination of the solid state is maintained in solution. The coordinated glycinato arms of [Pt(2)(hdta)Cl(2)](2)(-) are equivalent, exhibiting only one AB pattern in the (1)H NMR (H(a), 4.31 ppm; H(b), 3.89 ppm; J(ab) = 16.1 Hz) and one type of coordinated carboxylate ((13)C NMR resonance at 189.7 ppm). Time-dependent (1)H and (13)C NMR spectra show that inosine first displaces only Cl(-) in [Pt(2)(hdta)Cl(2)](2)(-) in solutions up to one inosine per Pt(II) center. A higher concentration of inosines (Ino) results in the displacement of one of the glycinato arms, detectable at 175.0 ppm by (13)C NMR. The sequential nature and binding of two Ino ligands, necessarily cis in [Pt(2)(hdta)(Ino)(4)], mimics the steps necessary to allow major groove-spanning ligation of DNA in the manner of the Farrell-type binuclear platinum(II) amine complexes.
Kortes
Richard A.
RA
Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260.
Geib
Steven J.
SJ
Lin
Fu-Tyan
FT
Shepherd
Rex E.
RE