Covalent to ionic bond

[sonial]

Hi,

Thanks for developing this pipeline and making it available, it is really useful!

I noticed that the standardizer fixes covalent bonds to ionic in alkaline oxides, and it might be worth extending this to alkaline-earth oxides and metal halides.

See the example below for calcium chloride with covalent bonds (wrong SMILES created on purpose), as well as the ChEMBL entry for Calcium oxide erroneously represented with a covalent double bond.

from chembl_structure_pipeline import standardizer
from rdkit import Chem

smiles = "[Ca](Cl)Cl"
mol = Chem.MolFromSmiles(smiles)
mol

mol_stand = standardizer.standardize_molblock(Chem.MolToMolBlock(mol))
Chem.MolFromMolBlock(mol_stand)

Cheers, Sonia