Modulating the Framework Negative Charge Density in the System [BDT−TTP^•+]/[Re₆S₅Cl₉^1-]/[Re₆(S/Se)₆Cl₈^2-]/[Re₆S₇Cl₇^3-]:  Templating by Isosteric Cluster Anions of Identical Symmetry and Shape, Variations of Incommensurate Band Filling, and Electronic Structure in 2D Metals

A series of 2D metals, β-(BDT-TTP)₆[Re₆Se₆Cl₈]·(CHCl₂−CHCl₂)₂, 2; β-(ST-TTP)₆[Re₆S₆Cl₈]·(CH₂Cl−CHCl₂)₂, 3; β-(BDT-TTP)₇[Re₆S₆Cl₈]_0.5[Re₆S₇Cl₇]_0.5·(CH₂Cl₂), 4; β-(BDT-TTP)₇[Re₆Se₆Cl₈]_0.5[Re₆S₇Cl₇]_0.5·(CH₂Cl₂), 5; β-(BDT-TTP)₈[Re₆S₇Cl₇]·(CH₂Cl₂)₄, 6 (BDT-TTP and ST-TTP are 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene and 2-(1,3-diselenol-2-ylidene)-5(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene, respectively) is reported to have one single β-slab layered topology despite successive increases of the cluster anion negative charge. The charge density within the templating composite inorganic−neutral molecule slab is shown to remain above a threshold of ca. one negative charge per square nanometer, that is, for cluster anions with two negative charges and higher. Conversely, discrete stacks are shown to be stabilized instead in the semiconducting salts (BDT-TTP)₂[Re₆S₅Cl₉], 1 where the cluster anion bears one negative charge only. The electronic structure of salts 2−6 is shown to be very stable and kept almost intact across the series. The templating strategy is shown to fulfill its anticipated potential for deliberate installment of incommensurate band fillings in molecular metals. The deliberate admixture of the 6:1 and 8:1 structures yields novel phases with a 7:1 stoichiometry with the anticipated crystal and electronic structures. The action at the organic−inorganic interface triggered by changing the anion charge yet keeping its shape and volume identical, which ultimately governs the shape of the unit cell, is of paramount importance in defining the Fermi surface of these metallic salts. The present BDT-TTP salts thus provide a series of materials with strongly related but subtly different Fermi surfaces worthy of many physical studies. Shubnikov−de Haas measurements are expected to be particularly interesting since they are especially sensitive to the details of the Fermi surface.