Crystal and molecular structure of a potential DNA groove-spanning chelate: [MV][Pt-2(hdta)Cl-2]center dot 4H(2)O (MV2+=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) (MV2+ = 1,1'-dime thyl-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 s hown to have space group C2/c, having unit cell dimensions of a = 22.757(5) Angstrom, b = 13.566(3) Angstrom, and c = 12.120(2) Angstrom 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 NO2Cl square-planar mer coordination. The P t-N(1) distance (N(1) is the N donor of the hdta(4-) ligand) is 2.001(9) An gstrom, only slightly shorter than typical Pt-N distances (2.04-2.09 Angstr om) for sp(3) donors. The Pt-O distances to the coordinated glycinato donor s in 1 are 2.012(7) and 2.000(8) Angstrom, values very similar to those of trans-[Pt(gly)(2)] (gly = glycinate). The Pt-Cl distance of 2.310(3) Angstr om is in the range of 2.27-2.32 Angstrom observed for other Pt(II)-Cl- bond s. The bond angles are close to the ideal 90 degrees or 180 degrees value: angle N-Pt-O = 85.4(3)degrees and 83.2(4)degrees; angle N-Pt-Cl = 176.6(2)d egrees. 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 pr ovides square-planar to square-planar stacking of the headgroups. H-1 and C -13 NMR data are presented which show that the [Pt-2(hdta)Cl-2](2-) coordin ation of the solid state is maintained in solution. The coordinated glycina to arms of [Pt-2(hdta)Cl-2](2-) are equivalent, exhibiting only one AB patt ern in the H-1 NMR (H-a, 4.31 ppm; H-b, 3.89 ppm; J(ab) = 16.1 Hz) and one type of coordinated carboxylate (C-13 NMR resonance at 189.7 ppm). Time-dep endent H-1 and C-13 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 o f the glycinato arms, detectable at 175.0 ppm by C-13 NMR. The sequential n ature 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 D NA in the manner of the Farrell-type binuclear platinum(Il) amine complexes .