[Big-Daddy]

How does an ion like F-H-F, with a charge of -1, form, when the only location possible for the formal charge of -1 is the H atom (each F atom has 6 lone electrons and thus has formal charge 0 but hydrogen has 2 bonds and thus formal charge -1)? Shouldn't it be energetically preferable for H not to be in the middle, thus the formal charge -1 would rest on one of the atoms that prefer a formal charge of -1 (one of the F atoms), and structure would be F-F-H (first F has 6 lone electrons, second F has 6 lone electrons and the formal charge of -1, H has one bond and thus formal charge 0) rather than F-H-F? Yet Wikipedia confirms the existence of FHF...

[Hunter2]

Hydrogenflourid also do hydrogenbridge bonds like water it does.

HF is able to bridge to a flouride anion.  Example NaF + HF => NaHF₂ is equal to Na⁺ + HF₂^-

Compare H₂O + HF => H₃O⁺ + F^-

[magician4]

in addition:

the bond situation in [FHF]^- can not be explained in the classical way easily  ( you would have to write a resonance hybrid like FH...F^{-  -}F...HF to describe the situation: this is a hydrogen bridge bond, except that this time it's not oxygen / oxygen-H that is involved, but the fluoride /hydrogenfluoride pair instead)
Nevertheless, in my opinion this still pretty much makes clear why the hydrogen has to be in the middle, doesn't it ? : a proton "oscillation" inbetween two fluoride anions.
and for this, the "man in the middle" position would be the optimal one, the positive charge (the proton) under the influence of two negative charges (the fluorides) fighting for it, however still trying to keep away from each other as much as possible.
(pls. also note, that all the atoms involved here "keep" their most beloved oxidation states / charges .. so your original considerations kind of becomes pointless, as BOTH the fluorines would bear one negative charge here)

from an other point of view, modern bond theory would describe this as a 3 center 4 electrons bond, basically this type of overlap:

(from: link )

as you see, the lowest common MO would be bonding, but not the HOMO at the same time: the HOMO would be non - bonding (as you should expect from the overlap of -+/-+ oriented p-orbitals with the central s of whatsoever orientation)


ref. your alternative geometrical proposal:  this would look something like F⁽⁰⁾-F^(-I)-H⁽⁰⁾ or F⁽⁰⁾-F^(-II)-H^(+I) , respectively, wouldn't it?
anyway, each way you look at this , the central fluorine would have to bear 10 electrons and hence be hypervalent.
... and if there's one element in the whole of the periodic table that tries to avoid to be forced to do something like this, it's fluorine  (I'm not aware of any such case known)
the energies simply would be way too high to achieve something like this, and the alternatives would be way too attractive. My expectation is, that, should something like this occur by high-energy accident somewhere in the depth of the universe (lets say, a fluoride - ion crashes in a HF from the "wrong" side , F-  FH ) , this aggregate, if stable at all, immediately would rearrange (most probably by the proton tunneling to the middle position) to give the much more favourable situation


regards

Ingo