Weak Interactions and Hydrogen Bonding

Weak Interactions and Hydrogen Bonding

The Hydrogen Bond
- A Flexible Tool in Supramolecular Chemistry
(Ch. 2.6-7, p. 92 – 102, Concepts and Models of Inorganic
Chemistry : Douglas et al, 3rd Edition, Wiley, 1994 )

Latimer and Rodebush in 1920 introduced the term
“Hydrogen bond” to describe the nature of
association in the liquid state of water, hydrogen
fluoride, & so on.
(1) D:H:A (responsible for m.p. & b.p.)
(2) D-H (O, F, N) … A
~ 4 - 50 kJ/mol for neutral molecules
(~ 100 - 400 kJ/mol for typical covalent bonds)

Evidence for Hydrogen Bonding

Intermolecular hydrogen bonding in pure substances
increases the heat of vaporization in two ways :
(1) By increasing the attraction between molecules.
(b.p.)
(2) By restricting rotation of the molecules in the
liquid. (∆S

Consequences of Hydrogen Bonding
Also apply for some nonaqueous solutions.

Hydrogen Bonding Involving Charged Species
Anion-Molecule Interactions
(1) NaF (s) + (HF) x(g) ↔ NaHF 2(s) ∆H = -69 kJ/mol
(LiF : -43kJ/mol, KF : -88kJ/mol, RbF : -93kJ/mol,
CsF : -98kJ/mol, TMAF : -155kJ/mol)

KHF 2 : K + (FHF) - ; F … F in (FHF) - = 225 pm
(r F - = 119 pm)
mp : KF – 846 °C, KHF 2 –239 °C
(Production of F 2 by electrolysis of fused KF-HF
baths at LT)

Summary :
1. Loss in lattice energy (old & new)
2. Gain in hydrogn-bonding energy

Strong acid of liquid HF, but weak acid in water,
indicating that ∆ solv of the fluoride ion is much
more negative in HF than in water. HCl & HBr
are strong acids in water.

(2) KOH (s) + H 2 O (g) → KOH . H 2 O (s)
∆H = -84 kJ/mol
(especially where it is also desirable simultaneously
to remove CO 2 )

Cation-Molecule Interactions
(3) Solids may contain the hydrated hydrogen ion
in species varying from H 3 O + up to H 9 O 4+ .
HBr (mp = -86 °C)
HBr . H 2 O (mp = -4 °C), HBr . 4H 2 O (mp = -56.8 °C)
Same for HI (x = 4), but not for HCl (x < 4).

4 x C (4-coordinate)
6 x N (6-coordinate)
Clathrated benzene
[Co(NCS) 4 ] 2- , [Hg(SCN) 4 ] 2-
[Pd(NCS) 4 ] 2- at RT (solid)
[Pd(SCN) 4 ] 2- at HT (solid) or in solution

(S 2 )
(S 1 )

2.7.4 van der Waals Radii
The internuclear separation between nonbonded
atoms that are in contact is determined by their
van der Waals Radii (For both atoms are identical
– then, the van der Waals Radius is simply half
of the nonbonding separation).

If two atoms are found to be closer than the sum
of their van der Waals Radii in a crystal, a
hydrogen bond between them usually supplies the
explanation (shortening distance : O … O / O … N ~
30 pm).

M = Au, Ag

Stavropoulos et al, JACS, 1997, 119, 2942.

Cu…Cu intra = 3.52(5) Å
Cu…Cu inter = 2.905(3) Å

Ag(1)…Ag(3) = 3.835(5)Å
Ag…Ag inter = 3.227(2) Å

Linear-Chain Pt Materials
(I) Interesting structural properties
(II) Intriguing spectroscopic properties
(III) Conductivity

Electrical Conductivity :
1. Free-electron model versus energy-band model
2. Electrical conductivities:
Metals – σ > 10 3 S/cm (or Ω -1 /cm)
Semiconductor (0.7-1 eV)
Insulators - σ < 10 -9 S/cm ( > 6 eV)

One-Dimensional Conductors :
(1) Salts of partially oxidized tetracyanoplatinate
complexes
Anion-deficient salts :
(cation) 2 [Pt(CN) 4 ]X x. yH 2 O (x < 0.4)
- KCP(X), K 2 [Pt(CN) 4 ]X 0.3. 3H 2 O, X=Cl, Br

(2) Salts of partially reduced tetracyanoplatinate
complexes
Cation-deficient salts :
(cation) x [Pt(CN) 4 ] . yH 2 O (1 < x < 2)
Rb 2 [Pt(CN) 4 ] . (FHF) 0.4 – metallic luster & large
electrical conductivity (2,300 S/cm)

[Pt(CN) 4 ] z- : Pt-Pt = 2.86 – 2.97 Å
(2.775 Å in metallic Pt)
metallic behavior : Pt considered as equivalents
and electron delocalization along a delocalized
partially filled electron-energy band comprised
of overlapped platinum 5d z2 orbitals.
(10 5 for parallel to the Pt-Pt chain compare to
the perpendicular one).

(i) Intramolecular interactions (i.e., S … S)
(ii) Strained chelates
NH
NH

The most favorable cases for trigonal prismatic
coordination are d 0 , d 1 , d 5 , d 10 , & high-spin d 7 .
These are cases that do not involve strong preference
for octahedral coordination because of ligandfield
stabilization (LFSE).