Homochiral self-assembly of biocoordination polymers: anion-triggered helicity and absolute configuration inversion

The templating roles of ClO4 – and CF3SO3 – allow control and reversible inversion of the chirality of nucleotide-based copper(ii) helices. These results hold great potential for developing responsive materials.

Refinement details for 1 P : All non-hydrogen atoms were refined anisotropically. The hydrogen atoms of the bipy and CMP ligands were set in calculated positions and refined using a riding model, except those on the N(4) atom of the cytosine nucleobases, which were located on the ΔF map and refined with distance restraints instead. The hydrogen atom on the hydroxo group in the tetranuclear core and those on the water molecules (both coordinated and not-coordinated) were located on the ΔF map and refined with distance restraints, with thermal factors fixed to 1.5 times the U value of the oxygen atom they are linked to. The perchlorate ions were refined with the aid of similarity restraints on 1,2-and 1,3-distances and rigid-bond restraints. 6 Refinement details for 2 M : All non-hydrogen atoms were refined anisotropically, except the O(18w)-O(22w) oxygen atoms, belonging to disordered water molecules of crystallization. The bipy ligands were refined using geometrical constraints to help improving the data to parameter ratio. The hydrogen atoms of the bipy and CMP ligands were set in calculated positions and refined using a riding model, except those on the N(4) atom of the cytosine nucleobases, which were located on the ΔF map and refined with distance restraints instead. The hydrogen atom on the bridging hydroxo group and those on the coordinated water molecules O(1w)-O(6w) in the three tetranuclear cores of 2 M were at first placed in calculated positions following the direction of plausible hydrogen bonds, then shortly refined with distance restraints and thermal factors fixed to 1.5 times the U value of the oxygen atom they are linked to, then fixed. The hydrogen atoms on the water molecules of crystallization were not placed. The large amount of free triflate counterions was found affected by some disorder. The disordered triflate ions were refined with the aid of similarity restraints on 1,2and 1,3-distances and rigid-bond restraints. One of such disorder was found to affect the tetranuclear core indicated as cluster III (see Figure S4). In our best model for 2 M , in fact, a water molecule competes against a triflate anion for the coordination to the Cu(11) atom. This particular triflate anion appears thus statistically disordered; we modeled it over two sites [S(15s), O(43s), O(44s), S4 O(45s), C(15s), F(43s), F(44s), F(45s) and S(16s), O(46s), O(47s), O(48s), C(16s), F(46s), F(47s), F(48s) sets of atoms], one in the Cu(11) coordination sphere and one out: the relative occupancy of each disorder component was refined freely while constraining the sum of the occupancies to unity. 6 The competing water molecule [O(7w)], included in the disorder model, was refined freely while constraining the sum of its own occupancy and that of the coordinated triflate ion to unity. This model provided atom Cu(11) in cluster III being coordinated either to a water molecule or a triflate ion with a statistics of about 70% vs. 30%, respectively.

Further structural details
Hereunder have been reported details concerning the butterfly tetranuclear cores of copper ions for 1 P and 2 M .
Within the tetranuclear cores in 1 P three of the four copper ions exhibit a slightly distorted square pyramidal environment the fourth being six-coordinated in an elongated distorted octahedral environment (Fig. S1). In 2 M there are three crystallographically not equivalent tetranuclear cores (I-III), one consisting of all four Cu II ions in a slightly distorted square pyramidal environment, and two with one of the four copper atoms six-coordinated, being further linked to a triflate [Cu (2)] or a water molecule [Cu(11)] (Figs. S2-S47). In both compounds each copper atom is coordinated by a bpy ligand and linked by two µ4-phosphate groups. A hydroxide group furnishes further bridging between Cu (1) and Cu (2) in 1 P and Cu (1) and Cu (2), Cu (6) and Cu (7) and Cu (11) and Cu (12) (1), Cu (6), Cu (7) and Cu(12) in 2 M ] are comprised of two bpy nitrogen donors, a phosphate oxygen atom, with corner shared µ2-OHoxygen atom completing the basal plane. Apical coordination is provided by the two bridging phosphate oxygen atoms, respectively. For Cu (1) in 1 P a further coordination of a perchlorate anion in a monodentate fashion complete the coordination sphere. In 2 M the coordination sphere around Cu (2) and Cu (11) is completed by a a further coordination of a triflate and a water molecule, respectively (see experimental structural section for details). The N2O3 coordination chromophore about Cu (3) and Cu (4) (3) and Cu (4), Cu(8) and Cu (9), Cu(13) and Cu(14) in 2 M ] is provided by two bpy nitrogen donors and two phosphate oxygen atoms, which form the basal plane of the squarepyramid, with a coordinated water molecule occupying the apex of the pyramid.
Bonding about each copper centre is as expected for square pyramidal geometry [or octahedral for Cu (1) (1 P ) and Cu (2) and Cu(11) (2 M )] and it varies with donor type and position with apical bond lengths significantly longer than the basal-plane/equatorial ones, as might be anticipated by the Jahn-Teller theorem (Table S2- (1)···Cu (2), Cu (6)···Cu (7) and Cu(11)···Cu(12). These bridging interactions dispose the four copper atoms of each core in an irregular trapezoidal arrangement. The bpy ligands of the cores participate in intramolecular offset π-π interactions and a separation at closest contact of 3.30 and 3.45 Å.
In the crystal lattice of 1 P and 2 M , there is a columnar staggered alignment of the cationic chains developing along the crystallographic a (1 P ) and b axis (2 M ) ( Figure S5). The cohesion of adjacent chains is ensured by an extended network of H-bonds involving coordinated and non-coordinated anions and water molecules (see Table S2H for 1 P ) together with intermolecular π-π interactions that occur among the bpy ligands from the connectors and their related neighbors of the tetranuclear cores, giving closest contact separations varying in the ranges of 3.25-3.36 (1 P ) and 3.36-3.48 Å (2 M ).