IsoPat is a small Windows program to calculate isotope patterns for ions of a given elemental composition.
It resembles the online Sheffield ChemPuter
but has some additional features:

Customizable functional group abbreviations

Customizable elemental isotope ratios

Absolute charge can be specified

Approximate sub-unit mass location

Switch for mass/intensity table only

Easy copy to clipboard

Command-line options for scripting

No internet access or installation required (SFX only adds Start Menu shortcuts)

A self-extracting archive containing IsoPat v1.0.1 with a brief documentation can be downloaded here:

To unambiguously determine the mechanism of stereomutation
for five-coordinate compounds, I have developed a complete description of their geometry.
In short, the algorithm works as follows:

Given the coordinates of 6 atoms, the atom nearest their centroid is taken to be pentacoordinate;

Based on valence angles, the other five atoms are divided into an axial pair, an equatorial pair, and the pivot;

For each pair, a best-fitting plane through the pivot bond is constructed, and the bond directions are decomposed into in-plane and out-of-plane bending angles (see right);

These are transformed into 7 independent geometrical parameters.

An Excel spreadsheet for performing this analysis on single geometries can be downloaded here; it also contains brief explanations: